详细解读Volley（一）—— 基本Request对象 & RequestQueue

　　Volley它非常适合去进行数据量不大，但通信频繁的网络操作，而对于大数据量的网络操作，比如说下载文件等，Volley的表现就会非常糟糕。 所以不建议用它去进行下载文件、加载大图的操作。有人可能会问，如果我服务器中的图片都挺大的，activity中listview要加载这些图片，是不 是不能用这个框架呢？其实这个问题本身就是错误的，你想如果你服务器的图片都是大图，你要在手机上用照片墙进行展示，下载图片都会慢的要死，这个本身就是 不可行的。所以在项目初期就应该建立好服务器端的小图，照片墙用加载小图，点击后再从网络上下载大图，这才是正确思路。这时你就可以用volley加载小 图了，如果是要加载大图，可以用别的算法，强烈建议手动完成大图清除的工作，否则很可能会出现OOM。Volley本身没有做什么回收算法，还是用最基本 的GC，实际使用中可以根据需要自定义一下。

零、准备工作

Git项目，添加为lib，申请权限

git clone https://android.googlesource.com/platform/frameworks/volley 

<uses-permission android:name="android.permission.INTERNET" /> 

 

一、初始化请求对象——RequestQueue

public class MyApplication extends Application {

    public static RequestQueue requestQueue;

    @Override
    public void onCreate() {
        super.onCreate();
        // 不必为每一次HTTP请求都创建一个RequestQueue对象，推荐在application中初始化
        requestQueue = Volley.newRequestQueue(this);
    }
}

既然是Http操作，自然有请求和响应，RequestQueue是一个请求队列 对象，它可以缓存所有的HTTP请求，然后按照一定的算法并发地发出这些请求。RequestQueue内部的设计就是非常合适高并发的，因此我们不必为 每一次HTTP请求都创建一个RequestQueue对象，这是非常浪费资源的。所以在这里我建立了一个application，然后用单例模式定义了 这个对象。当然，你可以选择在一个activity中定义一个RequestQueue对象，但这样可能会比较麻烦，而且还可能出现请求队列包含 activity强引用的问题，因此我还是推荐在application中定义。

 

二、使用StringRequest接收String类型的响应

前 面定义了请求对象，那么自然就有接收响应的对象了，这个框架中有多个响应对象，像StringRequest接受到的响应就是string类型 的；JsonRequest接收的响应就是Json类型对象。其实它们都是继承自Request<T>，然后根据不同的响应数据来进行特殊的 处理。

 

2.1 初始化

    /**
     * Creates a new request with the given method.
     *
     * @param method the request {@link Method} to use
     * @param url URL to fetch the string at
     * @param listener Listener to receive the String response
     * @param errorListener Error listener, or null to ignore errors
     */
    public StringRequest(int method, String url, Listener<String> listener, ErrorListener errorListener)

    /**
     * Creates a new GET request.
     *
     * @param url URL to fetch the string at
     * @param listener Listener to receive the String response
     * @param errorListener Error listener, or null to ignore errors
     */
    public StringRequest(String url, Listener<String> listener, ErrorListener errorListener) {
        this(Method.GET, url, listener, errorListener);
    }

 这就是StringRequest的两个构造函数，不同之处是一个传入了一个method的参数，一个没有。其实看上面的源码就知道，如果你不传入method，默认会调用GET方式进行请求。当你传入了Method.POST就会用post来请求。

【参数解释】

url：请求的地址

listener：响应成功的监听器

errorListener：出错时的监听器

StringRequest getStringRequest = new StringRequest("http://www.baidu.com", new ResponseListener(), new ResponseErrorListener());

StringRequest postStringRequest = new StringRequest(Method.POST, "http://www.baidu.com", new ResponseListener(),null);

 

2.2 配置监听器

/**
     * @author:Jack Tony
     * @description  :设置响应结果监听器，因为用的是StringRequest，所以这里的结果我定义为string类型
     * @date  :2015年1月24日
     */
    private class ResponseListener implements Response.Listener<String>{

        @Override
        public void onResponse(String response) {
            // TODO 自动生成的方法存根
             Log.d("TAG", "-------------\n" + response);  
        }
    }
    
    
    /**
     * @author:Jack Tony
     * @description  :访问出错时触发的监听器
     * @date  :2015年1月28日
     */
    private class ResponseErrorListener implements Response.ErrorListener{

        @Override
        public void onErrorResponse(VolleyError error) {
            // TODO 自动生成的方法存根
             Log.e("TAG", error.getMessage(), error);  
        }
        
    }

这两个监听器没啥可说的，因为是StringRequest调用的，所以成功时触发的监听器中得到的response就是String类型。如果访问出错，那么就打印出错信息。

 

2.3 执行GET请求

现在我们有了请求对象和响应对象，外加处理响应结果的监听器，那么就执行最后一步——发送请求。发送请求很简单，将响应对象添加到请求队列即可。

　　　　  mQueue.add(getStringRequest);

完整代码：

        RequestQueue mQueue = MyApplication.requestQueue;
        StringRequest getStringRequest = new StringRequest("http://www.baidu.com", new ResponseListener(), new ResponseErrorListener());
        mQueue.add(getStringRequest);

通过简单的add()方法就直接发送了请求，如果服务器响应了请求就会触发我们的结果监听器，然后被打印出啦。现在请求的是百度，所以得到了网页的源码：

 

2.4 执行POST请求

POST和GET一样，仅仅是传入的方法不同。但一般我们的post都是要带一些参数的，volley没有提供附加参数的方法，所以我们必须要在StringRequest的匿名类中重写getParams()方法：

StringRequest stringRequest = new StringRequest(Method.POST, url,  listener, errorListener) {  
    @Override  
    protected Map<String, String> getParams() throws AuthFailureError {  
        Map<String, String> map = new HashMap<String, String>();  
        map.put("params1", "value1");  
        map.put("params2", "value2");  
        return map;  
    }  
};  

这 样就传入了value1和value2两个参数了。现在可能有人会问为啥这个框架不提供这个传参的方法，还非得让我们重写。我个人觉得这个框架本身的目的 就是执行频繁的网络请求，比如下载图片，解析json数据什么的，用GET就能很好的实现了，所以就没有提供传参的POST方法。为了简单起见，我重写了 Request类中的getParams()，添加了传参的方法，以后通过setParams()就可以传参数了。

重写的代码块：

    Map<String, String> mParams = null;
    
    /**
     * Returns a Map of parameters to be used for a POST or PUT request.  Can throw
     * {@link AuthFailureError} as authentication may be required to provide these values.
     *
     * <p>Note that you can directly override {@link #getBody()} for custom data.</p>
     *
     * @throws AuthFailureError in the event of auth failure
     */
    protected Map<String, String> getParams() throws AuthFailureError {
        return mParams;
    }

    public void setParams(Map<String, String> params){
        mParams = params;
    }

完整代码：

 

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.volley;

import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.util.Collections;
import java.util.Map;

import android.net.TrafficStats;
import android.net.Uri;
import android.os.Handler;
import android.os.Looper;
import android.os.SystemClock;
import android.text.TextUtils;

import com.android.volley.VolleyLog.MarkerLog;

/**
 * Base class for all network requests.
 *
 * @param <T> The type of parsed response this request expects.
 */
public abstract class Request<T> implements Comparable<Request<T>> {

    /**
     * Default encoding for POST or PUT parameters. See {@link #getParamsEncoding()}.
     */
    private static final String DEFAULT_PARAMS_ENCODING = "UTF-8";

    /**
     * Supported request methods.
     */
    public interface Method {
        int DEPRECATED_GET_OR_POST = -1;
        int GET = 0;
        int POST = 1;
        int PUT = 2;
        int DELETE = 3;
        int HEAD = 4;
        int OPTIONS = 5;
        int TRACE = 6;
        int PATCH = 7;
    }

    /** An event log tracing the lifetime of this request; for debugging. */
    private final MarkerLog mEventLog = MarkerLog.ENABLED ? new MarkerLog() : null;

    /**
     * Request method of this request.  Currently supports GET, POST, PUT, DELETE, HEAD, OPTIONS,
     * TRACE, and PATCH.
     */
    private final int mMethod;

    /** URL of this request. */
    private final String mUrl;

    /** Default tag for {@link TrafficStats}. */
    private final int mDefaultTrafficStatsTag;

    /** Listener interface for errors. */
    private final Response.ErrorListener mErrorListener;

    /** Sequence number of this request, used to enforce FIFO ordering. */
    private Integer mSequence;

    /** The request queue this request is associated with. */
    private RequestQueue mRequestQueue;

    /** Whether or not responses to this request should be cached. */
    private boolean mShouldCache = true;

    /** Whether or not this request has been canceled. */
    private boolean mCanceled = false;

    /** Whether or not a response has been delivered for this request yet. */
    private boolean mResponseDelivered = false;

    // A cheap variant of request tracing used to dump slow requests.
    private long mRequestBirthTime = 0;

    /** Threshold at which we should log the request (even when debug logging is not enabled). */
    private static final long SLOW_REQUEST_THRESHOLD_MS = 3000;

    /** The retry policy for this request. */
    private RetryPolicy mRetryPolicy;

    /**
     * When a request can be retrieved from cache but must be refreshed from
     * the network, the cache entry will be stored here so that in the event of
     * a "Not Modified" response, we can be sure it hasn‘t been evicted from cache.
     */
    private Cache.Entry mCacheEntry = null;

    /** An opaque token tagging this request; used for bulk cancellation. */
    private Object mTag;

    /**
     * Creates a new request with the given URL and error listener.  Note that
     * the normal response listener is not provided here as delivery of responses
     * is provided by subclasses, who have a better idea of how to deliver an
     * already-parsed response.
     *
     * @deprecated Use {@link #Request(int, String, com.android.volley.Response.ErrorListener)}.
     */
    @Deprecated
    public Request(String url, Response.ErrorListener listener) {
        this(Method.DEPRECATED_GET_OR_POST, url, listener);
    }

    /**
     * Creates a new request with the given method (one of the values from {@link Method}),
     * URL, and error listener.  Note that the normal response listener is not provided here as
     * delivery of responses is provided by subclasses, who have a better idea of how to deliver
     * an already-parsed response.
     */
    public Request(int method, String url, Response.ErrorListener listener) {
        mMethod = method;
        mUrl = url;
        mErrorListener = listener;
        setRetryPolicy(new DefaultRetryPolicy());

        mDefaultTrafficStatsTag = findDefaultTrafficStatsTag(url);
    }

    /**
     * Return the method for this request.  Can be one of the values in {@link Method}.
     */
    public int getMethod() {
        return mMethod;
    }

    /**
     * Set a tag on this request. Can be used to cancel all requests with this
     * tag by {@link RequestQueue#cancelAll(Object)}.
     *
     * @return This Request object to allow for chaining.
     */
    public Request<?> setTag(Object tag) {
        mTag = tag;
        return this;
    }

    /**
     * Returns this request‘s tag.
     * @see Request#setTag(Object)
     */
    public Object getTag() {
        return mTag;
    }

    /**
     * @return this request‘s {@link com.android.volley.Response.ErrorListener}.
     */
    public Response.ErrorListener getErrorListener() {
        return mErrorListener;
    }

    /**
     * @return A tag for use with {@link TrafficStats#setThreadStatsTag(int)}
     */
    public int getTrafficStatsTag() {
        return mDefaultTrafficStatsTag;
    }

    /**
     * @return The hashcode of the URL‘s host component, or 0 if there is none.
     */
    private static int findDefaultTrafficStatsTag(String url) {
        if (!TextUtils.isEmpty(url)) {
            Uri uri = Uri.parse(url);
            if (uri != null) {
                String host = uri.getHost();
                if (host != null) {
                    return host.hashCode();
                }
            }
        }
        return 0;
    }

    /**
     * Sets the retry policy for this request.
     *
     * @return This Request object to allow for chaining.
     */
    public Request<?> setRetryPolicy(RetryPolicy retryPolicy) {
        mRetryPolicy = retryPolicy;
        return this;
    }

    /**
     * Adds an event to this request‘s event log; for debugging.
     */
    public void addMarker(String tag) {
        if (MarkerLog.ENABLED) {
            mEventLog.add(tag, Thread.currentThread().getId());
        } else if (mRequestBirthTime == 0) {
            mRequestBirthTime = SystemClock.elapsedRealtime();
        }
    }

    /**
     * Notifies the request queue that this request has finished (successfully or with error).
     *
     * <p>Also dumps all events from this request‘s event log; for debugging.</p>
     */
    void finish(final String tag) {
        if (mRequestQueue != null) {
            mRequestQueue.finish(this);
        }
        if (MarkerLog.ENABLED) {
            final long threadId = Thread.currentThread().getId();
            if (Looper.myLooper() != Looper.getMainLooper()) {
                // If we finish marking off of the main thread, we need to
                // actually do it on the main thread to ensure correct ordering.
                Handler mainThread = new Handler(Looper.getMainLooper());
                mainThread.post(new Runnable() {
                    @Override
                    public void run() {
                        mEventLog.add(tag, threadId);
                        mEventLog.finish(this.toString());
                    }
                });
                return;
            }

            mEventLog.add(tag, threadId);
            mEventLog.finish(this.toString());
        } else {
            long requestTime = SystemClock.elapsedRealtime() - mRequestBirthTime;
            if (requestTime >= SLOW_REQUEST_THRESHOLD_MS) {
                VolleyLog.d("%d ms: %s", requestTime, this.toString());
            }
        }
    }

    /**
     * Associates this request with the given queue. The request queue will be notified when this
     * request has finished.
     *
     * @return This Request object to allow for chaining.
     */
    public Request<?> setRequestQueue(RequestQueue requestQueue) {
        mRequestQueue = requestQueue;
        return this;
    }

    /**
     * Sets the sequence number of this request.  Used by {@link RequestQueue}.
     *
     * @return This Request object to allow for chaining.
     */
    public final Request<?> setSequence(int sequence) {
        mSequence = sequence;
        return this;
    }

    /**
     * Returns the sequence number of this request.
     */
    public final int getSequence() {
        if (mSequence == null) {
            throw new IllegalStateException("getSequence called before setSequence");
        }
        return mSequence;
    }

    /**
     * Returns the URL of this request.
     */
    public String getUrl() {
        return mUrl;
    }

    /**
     * Returns the cache key for this request.  By default, this is the URL.
     */
    public String getCacheKey() {
        return getUrl();
    }

    /**
     * Annotates this request with an entry retrieved for it from cache.
     * Used for cache coherency support.
     *
     * @return This Request object to allow for chaining.
     */
    public Request<?> setCacheEntry(Cache.Entry entry) {
        mCacheEntry = entry;
        return this;
    }

    /**
     * Returns the annotated cache entry, or null if there isn‘t one.
     */
    public Cache.Entry getCacheEntry() {
        return mCacheEntry;
    }

    /**
     * Mark this request as canceled.  No callback will be delivered.
     */
    public void cancel() {
        mCanceled = true;
    }

    /**
     * Returns true if this request has been canceled.
     */
    public boolean isCanceled() {
        return mCanceled;
    }

    /**
     * Returns a list of extra HTTP headers to go along with this request. Can
     * throw {@link AuthFailureError} as authentication may be required to
     * provide these values.
     * @throws AuthFailureError In the event of auth failure
     */
    public Map<String, String> getHeaders() throws AuthFailureError {
        return Collections.emptyMap();
    }

    /**
     * Returns a Map of POST parameters to be used for this request, or null if
     * a simple GET should be used.  Can throw {@link AuthFailureError} as
     * authentication may be required to provide these values.
     *
     * <p>Note that only one of getPostParams() and getPostBody() can return a non-null
     * value.</p>
     * @throws AuthFailureError In the event of auth failure
     *
     * @deprecated Use {@link #getParams()} instead.
     */
    @Deprecated
    protected Map<String, String> getPostParams() throws AuthFailureError {
        return getParams();
    }

    /**
     * Returns which encoding should be used when converting POST parameters returned by
     * {@link #getPostParams()} into a raw POST body.
     *
     * <p>This controls both encodings:
     * <ol>
     *     <li>The string encoding used when converting parameter names and values into bytes prior
     *         to URL encoding them.</li>
     *     <li>The string encoding used when converting the URL encoded parameters into a raw
     *         byte array.</li>
     * </ol>
     *
     * @deprecated Use {@link #getParamsEncoding()} instead.
     */
    @Deprecated
    protected String getPostParamsEncoding() {
        return getParamsEncoding();
    }

    /**
     * @deprecated Use {@link #getBodyContentType()} instead.
     */
    @Deprecated
    public String getPostBodyContentType() {
        return getBodyContentType();
    }

    /**
     * Returns the raw POST body to be sent.
     *
     * @throws AuthFailureError In the event of auth failure
     *
     * @deprecated Use {@link #getBody()} instead.
     */
    @Deprecated
    public byte[] getPostBody() throws AuthFailureError {
        // Note: For compatibility with legacy clients of volley, this implementation must remain
        // here instead of simply calling the getBody() function because this function must
        // call getPostParams() and getPostParamsEncoding() since legacy clients would have
        // overridden these two member functions for POST requests.
        Map<String, String> postParams = getPostParams();
        if (postParams != null && postParams.size() > 0) {
            return encodeParameters(postParams, getPostParamsEncoding());
        }
        return null;
    }
 
    Map<String, String> mParams = null;
    
    /**
     * Returns a Map of parameters to be used for a POST or PUT request.  Can throw
     * {@link AuthFailureError} as authentication may be required to provide these values.
     *
     * <p>Note that you can directly override {@link #getBody()} for custom data.</p>
     *
     * @throws AuthFailureError in the event of auth failure
     */
    protected Map<String, String> getParams() throws AuthFailureError {
        return mParams;
    }

    public void setParams(Map<String, String> params){
        mParams = params;
    }
    
    /**
     * Returns which encoding should be used when converting POST or PUT parameters returned by
     * {@link #getParams()} into a raw POST or PUT body.
     *
     * <p>This controls both encodings:
     * <ol>
     *     <li>The string encoding used when converting parameter names and values into bytes prior
     *         to URL encoding them.</li>
     *     <li>The string encoding used when converting the URL encoded parameters into a raw
     *         byte array.</li>
     * </ol>
     */
    protected String getParamsEncoding() {
        return DEFAULT_PARAMS_ENCODING;
    }

    /**
     * Returns the content type of the POST or PUT body.
     */
    public String getBodyContentType() {
        return "application/x-www-form-urlencoded; charset=" + getParamsEncoding();
    }

    /**
     * Returns the raw POST or PUT body to be sent.
     *
     * <p>By default, the body consists of the request parameters in
     * application/x-www-form-urlencoded format. When overriding this method, consider overriding
     * {@link #getBodyContentType()} as well to match the new body format.
     *
     * @throws AuthFailureError in the event of auth failure
     */
    public byte[] getBody() throws AuthFailureError {
        Map<String, String> params = getParams();
        if (params != null && params.size() > 0) {
            return encodeParameters(params, getParamsEncoding());
        }
        return null;
    }

    /**
     * Converts <code>params</code> into an application/x-www-form-urlencoded encoded string.
     */
    private byte[] encodeParameters(Map<String, String> params, String paramsEncoding) {
        StringBuilder encodedParams = new StringBuilder();
        try {
            for (Map.Entry<String, String> entry : params.entrySet()) {
                encodedParams.append(URLEncoder.encode(entry.getKey(), paramsEncoding));
                encodedParams.append(‘=‘);
                encodedParams.append(URLEncoder.encode(entry.getValue(), paramsEncoding));
                encodedParams.append(‘&‘);
            }
            return encodedParams.toString().getBytes(paramsEncoding);
        } catch (UnsupportedEncodingException uee) {
            throw new RuntimeException("Encoding not supported: " + paramsEncoding, uee);
        }
    }

    /**
     * Set whether or not responses to this request should be cached.
     *
     * @return This Request object to allow for chaining.
     */
    public final Request<?> setShouldCache(boolean shouldCache) {
        mShouldCache = shouldCache;
        return this;
    }

    /**
     * Returns true if responses to this request should be cached.
     */
    public final boolean shouldCache() {
        return mShouldCache;
    }

    /**
     * Priority values.  Requests will be processed from higher priorities to
     * lower priorities, in FIFO order.
     */
    public enum Priority {
        LOW,
        NORMAL,
        HIGH,
        IMMEDIATE
    }

    /**
     * Returns the {@link Priority} of this request; {@link Priority#NORMAL} by default.
     */
    public Priority getPriority() {
        return Priority.NORMAL;
    }

    /**
     * Returns the socket timeout in milliseconds per retry attempt. (This value can be changed
     * per retry attempt if a backoff is specified via backoffTimeout()). If there are no retry
     * attempts remaining, this will cause delivery of a {@link TimeoutError} error.
     */
    public final int getTimeoutMs() {
        return mRetryPolicy.getCurrentTimeout();
    }

    /**
     * Returns the retry policy that should be used  for this request.
     */
    public RetryPolicy getRetryPolicy() {
        return mRetryPolicy;
    }

    /**
     * Mark this request as having a response delivered on it.  This can be used
     * later in the request‘s lifetime for suppressing identical responses.
     */
    public void markDelivered() {
        mResponseDelivered = true;
    }

    /**
     * Returns true if this request has had a response delivered for it.
     */
    public boolean hasHadResponseDelivered() {
        return mResponseDelivered;
    }

    /**
     * Subclasses must implement this to parse the raw network response
     * and return an appropriate response type. This method will be
     * called from a worker thread.  The response will not be delivered
     * if you return null.
     * @param response Response from the network
     * @return The parsed response, or null in the case of an error
     */
    abstract protected Response<T> parseNetworkResponse(NetworkResponse response);

    /**
     * Subclasses can override this method to parse ‘networkError‘ and return a more specific error.
     *
     * <p>The default implementation just returns the passed ‘networkError‘.</p>
     *
     * @param volleyError the error retrieved from the network
     * @return an NetworkError augmented with additional information
     */
    protected VolleyError parseNetworkError(VolleyError volleyError) {
        return volleyError;
    }

    /**
     * Subclasses must implement this to perform delivery of the parsed
     * response to their listeners.  The given response is guaranteed to
     * be non-null; responses that fail to parse are not delivered.
     * @param response The parsed response returned by
     * {@link #parseNetworkResponse(NetworkResponse)}
     */
    abstract protected void deliverResponse(T response);

    /**
     * Delivers error message to the ErrorListener that the Request was
     * initialized with.
     *
     * @param error Error details
     */
    public void deliverError(VolleyError error) {
        if (mErrorListener != null) {
            mErrorListener.onErrorResponse(error);
        }
    }

    /**
     * Our comparator sorts from high to low priority, and secondarily by
     * sequence number to provide FIFO ordering.
     */
    @Override
    public int compareTo(Request<T> other) {
        Priority left = this.getPriority();
        Priority right = other.getPriority();

        // High-priority requests are "lesser" so they are sorted to the front.
        // Equal priorities are sorted by sequence number to provide FIFO ordering.
        return left == right ?
                this.mSequence - other.mSequence :
                right.ordinal() - left.ordinal();
    }

    @Override
    public String toString() {
        String trafficStatsTag = "0x" + Integer.toHexString(getTrafficStatsTag());
        return (mCanceled ? "[X] " : "[ ] ") + getUrl() + " " + trafficStatsTag + " "
                + getPriority() + " " + mSequence;
    }
}

 

 

 

使用示例：

        StringRequest postStringRequest = new StringRequest(Method.POST, "http://m.weather.com.cn/data/101010100.html",
                new ResponseListener(), null);
        Map<String, String> map = new HashMap<String, String>();
        map.put("params1", "value1");
        map.put("params2", "value2");
        postStringRequest.setParams(map);
        mQueue.add(postStringRequest);

结果：

 

三、使用JsonObjectRequest接收Json类型的响应

类似于StringRequest，JsonRequest也是继承自Request类的，不过由于JsonRequest是一个抽象类，因此我们无法直接创建它的实例，那么只能从它的子类入手了。JsonRequest有两个直接的子类，JsonObjectRequest和JsonArrayRequest，从名字上你应该能就看出它们的区别了吧？一个是用于请求一段JSON数据的，一个是用于请求一段JSON数组的。

 

3.1 构造函数

    /**
     * Creates a new request.
     * @param method the HTTP method to use
     * @param url URL to fetch the JSON from
     * @param jsonRequest A {@link JSONObject} to post with the request. Null is allowed and
     *   indicates no parameters will be posted along with request.
     * @param listener Listener to receive the JSON response
     * @param errorListener Error listener, or null to ignore errors.
     */
    public JsonObjectRequest(int method, String url, JSONObject jsonRequest,
　　　　 Listener<JSONObject> listener, ErrorListener errorListener) {
        super(method, url, (jsonRequest == null) ? null : jsonRequest.toString(), listener,
                    errorListener);
    }

    /**
     * Constructor which defaults to <code>GET</code> if <code>jsonRequest</code> is
     * <code>null</code>, <code>POST</code> otherwise.
     *
     * @see #JsonObjectRequest(int, String, JSONObject, Listener, ErrorListener)
     */
    public JsonObjectRequest(String url, JSONObject jsonRequest, Listener<JSONObject> listener,
            ErrorListener errorListener) {
        this(jsonRequest == null ? Method.GET : Method.POST, url, jsonRequest,
                listener, errorListener);
    }

 

3.2 发送请求

和之前讲过的StringRequest一样，可以传入请求的类型，如果没传就默认是GET请求。参数也是如出一辙，就是泛型变了下。定义和使用的方式也完全一致，初始化对象后，添加到请求队列即可。

        JsonObjectRequest request = new JsonObjectRequest("http://m.weather.com.cn/data/101010100.html",
                null, new ResponseListener(), new ResponseErrorListener());
        mQueue.add(request);

    /**
     * @author:Jack Tony
     * @description :设置响应结果监听器，这里用的是JsonObjectRequest，所以返回的结果是JSONObject
     * @date :2015年1月24日
     */
    private class ResponseListener implements Response.Listener<JSONObject> {

        @Override
        public void onResponse(JSONObject response) {
            // TODO 自动生成的方法存根
            Log.d("TAG", "-------------\n" + response.toString());
        }

    }

    /**
     * @author:Jack Tony
     * @description :访问出错时触发的监听器
     * @date :2015年1月28日
     */
    private class ResponseErrorListener implements Response.ErrorListener {

        @Override
        public void onErrorResponse(VolleyError error) {
            Log.e("TAG", error.getMessage(), error);
        }
    }

 

结果：

你怎么查看解析是否成功了呢？服务器端的数据：

{"weatherinfo":{"city":"北京","city_en":"beijing","date_y":"2014年3月4日","date":"","week":"星期二","fchh":"11","cityid":"101010100","temp1":"8℃~-3℃","temp2":"8℃~-3℃","temp3":"7℃~-3℃","temp4":"8℃~-1℃","temp5":"10℃~1℃","temp6":"10℃~2℃","tempF1":"46.4℉~26.6℉","tempF2":"46.4℉~26.6℉","tempF3":"44.6℉~26.6℉","tempF4":"46.4℉~30.2℉","tempF5":"50℉~33.8℉","tempF6":"50℉~35.6℉","weather1":"晴","weather2":"晴","weather3":"晴","weather4":"晴转多云","weather5":"多云","weather6":"多云","img1":"0","img2":"99","img3":"0","img4":"99","img5":"0","img6":"99","img7":"0","img8":"1","img9":"1","img10":"99","img11":"1","img12":"99","img_single":"0","img_title1":"晴","img_title2":"晴","img_title3":"晴","img_title4":"晴","img_title5":"晴","img_title6":"晴","img_title7":"晴","img_title8":"多云","img_title9":"多云","img_title10":"多云","img_title11":"多云","img_title12":"多云","img_title_single":"晴","wind1":"北风4-5级转微风","wind2":"微风","wind3":"微风","wind4":"微风","wind5":"微风","wind6":"微风","fx1":"北风","fx2":"微风","fl1":"4-5级转小于3级","fl2":"小于3级","fl3":"小于3级","fl4":"小于3级","fl5":"小于3级","fl6":"小于3级","index":"寒冷","index_d":"天气寒冷，建议着厚羽绒服、毛皮大衣加厚毛衣等隆冬服装。年老体弱者尤其要注意保暖防冻。","index48":"冷","index48_d":"天气冷，建议着棉服、羽绒服、皮夹克加羊毛衫等冬季服装。年老体弱者宜着厚棉衣、冬大衣或厚羽绒服。","index_uv":"中等","index48_uv":"中等","index_xc":"较适宜","index_tr":"一般","index_co":"较舒适","st1":"7","st2":"-3","st3":"8","st4":"0","st5":"7","st6":"-1","index_cl":"较不宜","index_ls":"基本适宜","index_ag":"易发"}}

如果解析错误，就会出现警告，这时错误监听器就会被触发：

如果解析成功，就不会出现错误，这就是泛型的好处，保证了程序的正确性。

最终我们就可以在Response.Listener<JSONObject>中得到JSONObject对象，通过这个对象就能进行下一步的处理了。

 

3.3 解析Json

比如要解析出上面Json数据中city的字段，就可以按照如下方式编码：

　　　　　try {
                response = response.getJSONObject("weatherinfo");
                Log.i(TAG, "City = " + response.getString("city"));
            } catch (JSONException e) {
                // TODO 自动生成的 catch 块
                e.printStackTrace();
            }

完整监听器代码：

    private class ResponseListener implements Response.Listener<JSONObject> {

        @Override
        public void onResponse(JSONObject response) {
            // TODO 自动生成的方法存根
            Log.d("TAG", "-------------\n" + response.toString());
            
            try {
                response = response.getJSONObject("weatherinfo");
                Log.i(TAG, "City = " + response.getString("city"));
            } catch (JSONException e) {
                // TODO 自动生成的 catch 块
                e.printStackTrace();
            }
        }

    }

结果：

 

四、JsonArrayRequest简介

除此之外，还有一个相关的响应对象叫做JsonArrayRequest，这个获得的就是一个Json序列，使用方式没有任何改变，这里就不做过多介绍了，因为剩下的就是Json的知识了，和Volley没有任何关系。

源码：

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.volley.toolbox;

import com.android.volley.NetworkResponse;
import com.android.volley.ParseError;
import com.android.volley.Response;
import com.android.volley.Response.ErrorListener;
import com.android.volley.Response.Listener;

import org.json.JSONArray;
import org.json.JSONException;

import java.io.UnsupportedEncodingException;

/**
 * A request for retrieving a {@link JSONArray} response body at a given URL.
 */
public class JsonArrayRequest extends JsonRequest<JSONArray> {

    /**
     * Creates a new request.
     * @param url URL to fetch the JSON from
     * @param listener Listener to receive the JSON response
     * @param errorListener Error listener, or null to ignore errors.
     */
    public JsonArrayRequest(String url, Listener<JSONArray> listener, ErrorListener errorListener) {
        super(Method.GET, url, null, listener, errorListener);
    }

    @Override
    protected Response<JSONArray> parseNetworkResponse(NetworkResponse response) {
        try {
            String jsonString =
                new String(response.data, HttpHeaderParser.parseCharset(response.headers));
            return Response.success(new JSONArray(jsonString),
                    HttpHeaderParser.parseCacheHeaders(response));
        } catch (UnsupportedEncodingException e) {
            return Response.error(new ParseError(e));
        } catch (JSONException je) {
            return Response.error(new ParseError(je));
        }
    }
}

通过源码我们知道，这个响应对象发送的请求是Get，而且它是继承自JsonRequest，如果你想用POST来做，自行添加新的构造函数即可。

 

 Volley源码下载：http://download.csdn.net/detail/shark0017/8404451

 

 

参考自：http://blog.csdn.net/guolin_blog/article/details/17482095

 

 

 

 

详细解读Volley（二）—— ImageRequest & Request简介

上篇文章我们讲 到了如何用volley进行简单的网络请求，我们可以很容易的接受到string、JsonObjec类型的返回结果，之前的例子仅仅是一次请求，这里需 要说明volley本身就是适合高并发的，所以它可以运行你用volley在短时间内进行多次请求，并且不用去手动管理线程数。仅仅是请求文字过于基础 了，本篇将讲述如何用volley从网络下载图片。

 

一、用ImageRequest来请求图片

ImageRequest是一个图片请求对象，它继承自Request<Bitmap>，所以请求得到的结果是一个bitmap。

1.1 使用步骤

ImageRequest仍旧是一个request对象，所以使用方式和StringRequest、JsonObjectRequest、JsonArrayRequest十分相似。

步骤：

1. 建立一个RequestQueue对象
2. 建立一个ImageRequest对象
3. 将ImageRequest添加到RequestQueue中

第一步、第三步我们在上篇文章中已经做好了，如果不清楚的话可以去上一篇文章查看。

 

1.2 分析构造函数

源码中的构造函数是这样定义的：

    public ImageRequest(String url, Response.Listener<Bitmap> listener, int maxWidth, int maxHeight,
            Config decodeConfig, Response.ErrorListener errorListener) {
        super(Method.GET, url, errorListener);
        setRetryPolicy(
                new DefaultRetryPolicy(IMAGE_TIMEOUT_MS, IMAGE_MAX_RETRIES, IMAGE_BACKOFF_MULT));
        mListener = listener;
        mDecodeConfig = decodeConfig;
        mMaxWidth = maxWidth;
        mMaxHeight = maxHeight;
    }

默认的请求方式是GET，初始化方法需要传入：图片的url，一个响应结果监听器，图片的最大宽度，图片的最大高度，图片的颜色属性，出错响应的监听器。

说明：图片的颜色属性，Bitmap.Config下的几个常量都可以在这里使用，其中ARGB_8888可以展示最好的颜色属性，每个图片像素占据4个字节的大小，而RGB_565则表示每个图片像素占据2个字节大小

    /** Socket timeout in milliseconds for image requests */
    private static final int IMAGE_TIMEOUT_MS = 1000;

    /** Default number of retries for image requests */
    private static final int IMAGE_MAX_RETRIES = 2;

    /** Default backoff multiplier for image requests */
    private static final float IMAGE_BACKOFF_MULT = 2f;

• 设定超时时间：1000ms；
• 最大的请求次数：2次；
• 发生冲突时的重传延迟增加数：2f（这个应该和TCP协议有关，冲突时需要退避一段时间，然后再次请求）；

 

1.3 解释maxWidth，maxHeight参数

注释中详细说明了图片宽高的意义和作用，为了便于理解我再详细说一下。

    /**
     * Creates a new image request, decoding to a maximum specified width and
     * height. If both width and height are zero, the image will be decoded to
     * its natural size. If one of the two is nonzero, that dimension will be
     * clamped and the other one will be set to preserve the image‘s aspect
     * ratio. If both width and height are nonzero, the image will be decoded to
     * be fit in the rectangle of dimensions width x height while keeping its
     * aspect ratio.
     *
     * @param url URL of the image
     * @param listener Listener to receive the decoded bitmap
     * @param maxWidth Maximum width to decode this bitmap to, or zero for none
     * @param maxHeight Maximum height to decode this bitmap to, or zero for
     *            none
     * @param decodeConfig Format to decode the bitmap to
     * @param errorListener Error listener, or null to ignore errors
     */

先来完整解释下注释的意思：

• 建立一个请求对象，按照最大宽高进行解码 。
• 如果设定的宽和高都是0，那么下载到的图片将会按照实际的大小进行解码，也就是不压缩。
• 如果宽和高中的一个或两个值不为0，那么图片的宽/高（取决于你设定了宽还是高）会压缩至设定好的值，而另一个宽/高将会按原始比例改变。
• 如果宽和高都不是0，那么得到的图片将会“按比例”解码到你设定的宽高，也就是说最终得到的图片大小不一定是你最初设定的大小。

举个例子：

我的图片原本像素是：850x1200.

当maxWidth = 0，maxHeight = 0时，最终得到的bitmap的宽高是850x1200

当maxWidth = 0，maxHeight = 600时，得到的bitmap是425x600.这就说明它会按照一个不为0的边的值，将图片进行等比缩放。

当maxWidth = 100，maxHeight = 600时，我们得到的bitmap竟然是100x141，是按照100进行等比缩小后的图片，而不是100x600.

要弄清这个问题，我们还得看源码，源码中解析响应结果的方法叫做doParse(…)

    /**
     * The real guts of parseNetworkResponse. Broken out for readability.
     */
    private Response<Bitmap> doParse(NetworkResponse response) {
        byte[] data = response.data;
        BitmapFactory.Options decodeOptions = new BitmapFactory.Options();
        Bitmap bitmap = null;
        if (mMaxWidth == 0 && mMaxHeight == 0) {
　　　　　　　// 如果宽高都是0，那么就返回原始尺寸
            decodeOptions.inPreferredConfig = mDecodeConfig;
            bitmap = BitmapFactory.decodeByteArray(data, 0, data.length, decodeOptions);
        } else {
            // If we have to resize this image, first get the natural bounds.
　　　　　　// 如果我们已经重设了image的尺寸（宽高中有一个或两个不为0），那么先得到原始的大小

            decodeOptions.inJustDecodeBounds = true; // 设置先不得到bitmap，仅仅获取bitmap的参数。
            BitmapFactory.decodeByteArray(data, 0, data.length, decodeOptions); // 第一次解码，主要获得的是bitmap的实际宽、高
            int actualWidth = decodeOptions.outWidth; // 得到bitmap的宽
            int actualHeight = decodeOptions.outHeight; // 得到bitmap的高

            // Then compute the dimensions we would ideally like to decode to.
            // 然后计算我们想要得到的最终尺寸
            int desiredWidth = getResizedDimension(mMaxWidth, mMaxHeight,
                    actualWidth, actualHeight);
            int desiredHeight = getResizedDimension(mMaxHeight, mMaxWidth,
                    actualHeight, actualWidth);

            // Decode to the nearest power of two scaling factor.
            // 把图片解码到最接近2的幂次方的大小
            decodeOptions.inJustDecodeBounds = false;
            // TODO(ficus): Do we need this or is it okay since API 8 doesn‘t support it?
            // decodeOptions.inPreferQualityOverSpeed = PREFER_QUALITY_OVER_SPEED;
            decodeOptions.inSampleSize =
                findBestSampleSize(actualWidth, actualHeight, desiredWidth, desiredHeight);
            Bitmap tempBitmap =
                BitmapFactory.decodeByteArray(data, 0, data.length, decodeOptions);

            // If necessary, scale down to the maximal acceptable size.
            // 如果有必要的话，把得到的bitmap的最大边进行压缩来适应尺寸
            if (tempBitmap != null && (tempBitmap.getWidth() > desiredWidth ||
                    tempBitmap.getHeight() > desiredHeight)) {
                // 通过createScaledBitmap来压缩到目标尺寸
                bitmap = Bitmap.createScaledBitmap(tempBitmap,
                        desiredWidth, desiredHeight, true);
                tempBitmap.recycle();
            } else {
                bitmap = tempBitmap;
            }
        }
        if (bitmap == null) {
            return Response.error(new ParseError(response));
        } else {
            return Response.success(bitmap, HttpHeaderParser.parseCacheHeaders(response));
        }
    }
    
    /**
     * Returns the largest power-of-two divisor for use in downscaling a bitmap
     * that will not result in the scaling past the desired dimensions.
     *
     * @param actualWidth Actual width of the bitmap
     * @param actualHeight Actual height of the bitmap
     * @param desiredWidth Desired width of the bitmap
     * @param desiredHeight Desired height of the bitmap
     */
    // Visible for testing.
    static int findBestSampleSize(
            int actualWidth, int actualHeight, int desiredWidth, int desiredHeight) {
                // 计算inSampleSize的方法，详细知识自行百度吧。最终原图会被压缩为inSampleSize分之一
                // inSampleSize的值计算出来都是2的幂次方
        double wr = (double) actualWidth / desiredWidth;
        double hr = (double) actualHeight / desiredHeight;
        double ratio = Math.min(wr, hr);
        float n = 1.0f;
        while ((n * 2) <= ratio) {
            n *= 2;
        }

        return (int) n;
    }

此时我们发现重要的方法是getResizedDimension，它最终确定了图片的最终尺寸。

    /**
     * Scales one side of a rectangle to fit aspect ratio.
     *
     * @param maxPrimary Maximum size of the primary dimension (i.e. width for
     *        max width), or zero to maintain aspect ratio with secondary
     *        dimension
     * @param maxSecondary Maximum size of the secondary dimension, or zero to
     *        maintain aspect ratio with primary dimension
     * @param actualPrimary Actual size of the primary dimension
     * @param actualSecondary Actual size of the secondary dimension
     */
    private static int getResizedDimension(int maxPrimary, int maxSecondary, int actualPrimary,
            int actualSecondary) {
        // If no dominant value at all, just return the actual.
        if (maxPrimary == 0 && maxSecondary == 0) {
            return actualPrimary;
        }

        // If primary is unspecified, scale primary to match secondary‘s scaling ratio.
        if (maxPrimary == 0) {
            double ratio = (double) maxSecondary / (double) actualSecondary;
            return (int) (actualPrimary * ratio);
        }

        if (maxSecondary == 0) {
            return maxPrimary;
        }

        double ratio = (double) actualSecondary / (double) actualPrimary;
        int resized = maxPrimary;
        if (resized * ratio > maxSecondary) {
            resized = (int) (maxSecondary / ratio);
        }
        return resized;
    }

在我们目标宽、高都不为0时会调用下面的代码段：

double ratio = (double) actualSecondary / (double) actualPrimary;
        int resized = maxPrimary;
        if (resized * ratio > maxSecondary) {
            resized = (int) (maxSecondary / ratio);
        }

它会计算一个ratio（比值），这就是为啥它会按比例缩小的原因。

 

1.4 初始化对象并使用

        ImageRequest imageRequest = new ImageRequest(
                "http://img5.duitang.com/uploads/item/201409/14/20140914162144_MBEmX.jpeg", 
                new ResponseListener(), 
                0, // 图片的宽度，如果是0，就不会进行压缩，否则会根据数值进行压缩
                0, // 图片的高度，如果是0，就不进行压缩，否则会压缩
                Config.ARGB_8888, // 图片的颜色属性
                new ResponseErrorListener());

监听器：

    private class ResponseListener implements Response.Listener<Bitmap> {

        @Override
        public void onResponse(Bitmap response) {
           //  Log.d("TAG", "-------------\n" + response.toString());
            iv.setImageBitmap(response);
        }
    }

    private class ResponseErrorListener implements Response.ErrorListener {

        @Override
        public void onErrorResponse(VolleyError error) {
            Log.e("TAG", error.getMessage(), error);
        }
    }

最后将其添加到请求队列即可：

 mQueue.add(imageRequest);

 

1.5   题外话

这样我们就用volley获得了网络图片，代码也十分简单。你可能会说，有没有其 他的，更好的方式来获取图片呢？当然有的，比如volley还提供了ImageLoader、NetworkImageView这样的对象，它们可以更加 方便的获取图片。值得一提的是这两个对象的内部都是使用了ImageRequest进行操作的，也就是说imageRequest是本质，这也就是为啥我 专门写一篇来分析ImageRequest的原因。

说话要言之有理，所以贴上ImageLoader、NetworkImageView源码中部分片段来证明其内部确实是用了ImageRequest。

 

ImageLoader的源码片段：

    public ImageContainer get(String requestUrl, ImageListener imageListener,
            int maxWidth, int maxHeight) {
        // ………// The request is not already in flight. Send the new request to the network and
        // track it.
        Request<Bitmap> newRequest = makeImageRequest(requestUrl, maxWidth, maxHeight, cacheKey);
        newRequest.setShouldCache(mShouldCache);
        mRequestQueue.add(newRequest);
        mInFlightRequests.put(cacheKey,
                new BatchedImageRequest(newRequest, imageContainer));
        return imageContainer;
    }

    protected Request<Bitmap> makeImageRequest(String requestUrl, int maxWidth, int maxHeight, final String cacheKey) {
        return new ImageRequest(requestUrl, new Listener<Bitmap>() {
            @Override
            public void onResponse(Bitmap response) {
                onGetImageSuccess(cacheKey, response);
            }
        }, maxWidth, maxHeight,
        Config.RGB_565, new ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                onGetImageError(cacheKey, error);
            }
        });
    }

 在 ImageLoader重要的get()方法中，建立了一个newRequest对象，并将其放入请求队列中。这里的newRequest是通过 makeImageRequest()来产生的，而makeImageRequest()实际是返回了一个ImageRequest对象。所以用到了 ImageRequest对象。

 

NetworkImageView的源码片段：

    public void setImageUrl(String url, ImageLoader imageLoader) {
        mUrl = url;
        mImageLoader = imageLoader;
        // The URL has potentially changed. See if we need to load it.
        loadImageIfNecessary(false);
    }

它本身就调用的是ImageLoader对象，所以自然也是用到了ImageRequest。

 

二、Request简介

2.1 前言

Request是Volley中最最核心的类，之前讲到的对象都是它的子类。从字面意思看，这个对象是用来执行请求的，但通过之前的使用我们发现，它还做了很多别的事情。先贴一个Request的子类。

        ImageRequest imageRequest = new ImageRequest(
                "http://img5.duitang.com/uploads/item/201409/14/20140914162144_MBEmX.jpeg", 
                new ResponseListener(), 
                0, // 图片的宽度，如果是0，就不会进行压缩，否则会根据数值进行压缩
                0, // 图片的高度，如果是0，就不进行压缩，否则会压缩
                Config.ARGB_8888, // 图片的颜色属性
                new ResponseErrorListener());

从中我们可以发现这个ImageRequest中传入了请求的url，毕竟是request嘛，请求的url是必须的，但我们还发现这个请求对象还处理了两个监听器，这就说明它不仅仅做了请求，同时对于响应的结果也做了分发处理。

 

2.2 部分API

getCacheKey()

Returns the cache key for this request. By default, this is the URL.

返回这个请求对象中缓存对象的key，默认返回的是请求的URL

 

getBodyContentType()

Returns the content type of the POST or PUT body.

返回POST或PUT请求内容的类型，我测试的结果是：application/x-www-form-urlencoded; charset=UTF-8

从源码就能看出，默认的编码方式是UTF-8：

/**
     * Default encoding for POST or PUT parameters. See {@link #getParamsEncoding()}.
     */
    private static final String DEFAULT_PARAMS_ENCODING = "UTF-8";

    /**
     * Returns the content type of the POST or PUT body.
     */
    public String getBodyContentType() {
        return "application/x-www-form-urlencoded; charset=" + getParamsEncoding();
    }

 

getSequence()

Returns the sequence number of this request.

返回请求的序列数

 

getUrl()

Returns the URL of this request.

返回请求的URL

 

setShouldCache(boolean bl)

Set whether or not responses to this request should be cached.

设 置这个请求是否有缓存，这个缓存是磁盘缓存，和内存缓存没什么事情，默认是true，也就是说如果你不设置为false，这个请求就会在磁盘中进行缓存。 其实，之前讲的的StringRequest，JsonRequest，ImageRequest得到的数据都会被缓存，无论是Json数据，还是图片都 会自动的缓存起来。然而，一旦你设置setShouldCache(false)，这些数据就不会被缓存了。

 

getBody()

Returns the raw POST or PUT body to be sent.

返回POST或PUT的请求体

 

deliverError()

分发错误信息，这个就是调用监听器的方法，贴源码就明白了。

    /**
     * Delivers error message to the ErrorListener that the Request was
     * initialized with.
     *
     * @param error Error details
     */
    public void deliverError(VolleyError error) {
        if (mErrorListener != null) {
            mErrorListener.onErrorResponse(error);
        }
    }

 

setRetryPolicy(RetryPolicy retryPolicy)

对一个request的重新请求策略的设置，不同的项目是否需要重新请求，重新请求几次，请求超时的时间，这些就在这设置到里面。

　　/**
     * Sets the retry policy for this request.
     *
     * @return This Request object to allow for chaining.
     */
    public Request<?> setRetryPolicy(RetryPolicy retryPolicy) {
        mRetryPolicy = retryPolicy;
        return this;
    }

从上面的源码可以看出，这里需要传入一个RetryPlicy的子类，就是重新请求策略的子类，Volley会在构造Request时传一个默认的对象，叫做DefaultRetryPolicy。

    /**
     * Creates a new request with the given method (one of the values from {@link Method}),
     * URL, and error listener.  Note that the normal response listener is not provided here as
     * delivery of responses is provided by subclasses, who have a better idea of how to deliver
     * an already-parsed response.
     */
    public Request(int method, String url, Response.ErrorListener listener) {
        mMethod = method;
        mUrl = url;
        mErrorListener = listener;
        setRetryPolicy(new DefaultRetryPolicy());

        mDefaultTrafficStatsTag = findDefaultTrafficStatsTag(url);
    }

如果你对于网络请求有具体的要求，可以实现RetryPolicy接口，进行自由的配置。下面贴一下DefaultRetryPolicy源码，方便参考。

 

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.volley;

/**
 * Default retry policy for requests.
 */
public class DefaultRetryPolicy implements RetryPolicy {
    /** The current timeout in milliseconds. */
    private int mCurrentTimeoutMs;

    /** The current retry count. */
    private int mCurrentRetryCount;

    /** The maximum number of attempts. */
    private final int mMaxNumRetries;

    /** The backoff multiplier for the policy. */
    private final float mBackoffMultiplier;

    /** The default socket timeout in milliseconds */
    public static final int DEFAULT_TIMEOUT_MS = 2500;

    /** The default number of retries */
    public static final int DEFAULT_MAX_RETRIES = 1;

    /** The default backoff multiplier */
    public static final float DEFAULT_BACKOFF_MULT = 1f;

    /**
     * Constructs a new retry policy using the default timeouts.
     */
    public DefaultRetryPolicy() {
        this(DEFAULT_TIMEOUT_MS, DEFAULT_MAX_RETRIES, DEFAULT_BACKOFF_MULT);
    }

    /**
     * Constructs a new retry policy.
     * @param initialTimeoutMs The initial timeout for the policy.
     * @param maxNumRetries The maximum number of retries.
     * @param backoffMultiplier Backoff multiplier for the policy.
     */
    public DefaultRetryPolicy(int initialTimeoutMs, int maxNumRetries, float backoffMultiplier) {
        mCurrentTimeoutMs = initialTimeoutMs;
        mMaxNumRetries = maxNumRetries;
        mBackoffMultiplier = backoffMultiplier;
    }

    /**
     * Returns the current timeout.
     */
    @Override
    public int getCurrentTimeout() {
        return mCurrentTimeoutMs;
    }

    /**
     * Returns the current retry count.
     */
    @Override
    public int getCurrentRetryCount() {
        return mCurrentRetryCount;
    }

    /**
     * Returns the backoff multiplier for the policy.
     */
    public float getBackoffMultiplier() {
        return mBackoffMultiplier;
    }

    /**
     * Prepares for the next retry by applying a backoff to the timeout.
     * @param error The error code of the last attempt.
     */
    @Override
    public void retry(VolleyError error) throws VolleyError {
        mCurrentRetryCount++;
        mCurrentTimeoutMs += (mCurrentTimeoutMs * mBackoffMultiplier);
        if (!hasAttemptRemaining()) {
            throw error;
        }
    }

    /**
     * Returns true if this policy has attempts remaining, false otherwise.
     */
    protected boolean hasAttemptRemaining() {
        return mCurrentRetryCount <= mMaxNumRetries;
    }
}

 

2.3 产生Request对象

虽然我们在代码中都会初始化一个Request对象，但是我们要在把他添加到响应队列中后才能得到它的完整体。

public <T> Request<T> add(Request<T> request) {

举例：

com.android.volley.Request<Bitmap> bitmapRequest = mQueue.add(imageRequest);

说明：如果你要设定这个request是不需要进行磁盘缓存的，那么请在把它添加到响应队列之前就进行设置，否则会得到不想要的效果。原因：源码在添加队列时会判断是否需要缓存。

    /**
     * Adds a Request to the dispatch queue.
     * @param request The request to service
     * @return The passed-in request
     */
    public <T> Request<T> add(Request<T> request) {
        // Tag the request as belonging to this queue and add it to the set of current requests.
        request.setRequestQueue(this);
        synchronized (mCurrentRequests) {
            mCurrentRequests.add(request);
        }

        // Process requests in the order they are added.
        request.setSequence(getSequenceNumber());
        request.addMarker("add-to-queue");

        // If the request is uncacheable, skip the cache queue and go straight to the network.
        if (!request.shouldCache()) {
            mNetworkQueue.add(request);
            return request; // 如果不需要缓存，直接返回request对象，不会执行下面的代码
        }

        // Insert request into stage if there‘s already a request with the same cache key in flight.
        synchronized (mWaitingRequests) {
            String cacheKey = request.getCacheKey();
            if (mWaitingRequests.containsKey(cacheKey)) {
                // There is already a request in flight. Queue up.
                Queue<Request<?>> stagedRequests = mWaitingRequests.get(cacheKey);
                if (stagedRequests == null) {
                    stagedRequests = new LinkedList<Request<?>>();
                }
                stagedRequests.add(request);
                mWaitingRequests.put(cacheKey, stagedRequests);
                if (VolleyLog.DEBUG) {
                    VolleyLog.v("Request for cacheKey=%s is in flight, putting on hold.", cacheKey);
                }
            } else {
                // Insert ‘null‘ queue for this cacheKey, indicating there is now a request in
                // flight.
                mWaitingRequests.put(cacheKey, null);
                mCacheQueue.add(request);
            }
            return request;
        }
    }

 

 

详细解读Volley（三）—— ImageLoader & NetworkImageView

ImageLoader是一个加载网络图片的封装类，其内部还是由ImageRequest来实现的。但因为源码中没有提供磁盘缓存的设置，所以咱们还需要去源码中进行修改，让我们可以更加自如的设定是否进行磁盘缓存。

 

2. ImageLoader的用法

如果你觉得ImageRequest已经非常好用了，那我只能说你太容易满足了 ^_^。实际上，Volley在请求网络图片方面可以做到的还远远不止这些，而ImageLoader就是一个很好的例子。ImageLoader也可以 用于加载网络上的图片，并且它的内部也是使用ImageRequest来实现的，不过ImageLoader明显要比ImageRequest更加高效， 因为它不仅可以帮我们对图片进行缓存，还可以过滤掉重复的链接，避免重复发送请求。

由于ImageLoader已经不是继承自Request的了，所以它的用法也和我们之前学到的内容有所不同，总结起来大致可以分为以下四步：

1. 创建一个RequestQueue对象。

2. 创建一个ImageLoader对象。

3. 获取一个ImageListener对象。

4. 调用ImageLoader的get()方法加载网络上的图片。

下面我们就来按照这个步骤，学习一下ImageLoader的用法吧。首先第一步的创建RequestQueue对象我们已经写过很多遍了，相信已经不用再重复介绍了，那么就从第二步开始学习吧，新建一个ImageLoader对象，代码如下所示：

    ImageLoader imageLoader = new ImageLoader(mQueue, new ImageCache() {  
        @Override  
        public void putBitmap(String url, Bitmap bitmap) {  
        }  
      
        @Override  
        public Bitmap getBitmap(String url) {  
            return null;  
        }  
    });  

 

可以看到，ImageLoader的构造函数接收两个参数，第一个参数就是RequestQueue对象，第二个参数是一个ImageCache对象，这里我们先new出一个空的ImageCache的实现即可。

 

接下来需要获取一个ImageListener对象，代码如下所示：

    ImageListener listener = ImageLoader.getImageListener(imageView,  
            R.drawable.default_image, R.drawable.failed_image);  

 

我 们通过调用ImageLoader的getImageListener()方法能够获取到一个ImageListener对 象，getImageListener()方法接收三个参数，第一个参数指定用于显示图片的ImageView控件，第二个参数指定加载图片的过程中显示 的图片，第三个参数指定加载图片失败的情况下显示的图片。

 

最后，调用ImageLoader的get()方法来加载图片，代码如下所示：

    imageLoader.get("http://img.my.csdn.net/uploads/201404/13/1397393290_5765.jpeg", listener);  

 

get()方法接收两个参数，第一个参数就是图片的URL地址，第二个参数则是刚刚获取到的ImageListener对象。当然，如果你想对图片的大小进行限制，也可以使用get()方法的重载，指定图片允许的最大宽度和高度，如下所示：

    imageLoader.get("http://img.my.csdn.net/uploads/201404/13/1397393290_5765.jpeg",  
                    listener, 200, 200);  

 

 

现在运行一下程序并开始加载图片，你将看到ImageView中会先显示一张默认的图片，等到网络上的图片加载完成后，ImageView则会自动显示该图，效果如下图所示。

虽然现在我们已经掌握了ImageLoader的用法，但是刚才介绍的ImageLoader的优点却还没有使用到。为什么呢？因为这里创建的 ImageCache对象是一个空的实现，完全没能起到图片缓存的作用。其实写一个ImageCache也非常简单，但是如果想要写一个性能非常好的 ImageCache，最好就要借助Android提供的LruCache功能了，如果你对LruCache还不了解，可以参考我之前的一篇博客Android高效加载大图、多图解决方案，有效避免程序OOM。

这里我们新建一个BitmapCache并实现了ImageCache接口，如下所示：

    public class BitmapCache implements ImageCache {  
      
        private LruCache<String, Bitmap> mCache;  
      
        public BitmapCache() {  
            int maxSize = 10 * 1024 * 1024;  
            mCache = new LruCache<String, Bitmap>(maxSize) {  
                @Override  
                protected int sizeOf(String key, Bitmap bitmap) {  
                    return bitmap.getRowBytes() * bitmap.getHeight();  
                }  
            };  
        }  
      
        @Override  
        public Bitmap getBitmap(String url) {  
            return mCache.get(url);  
        }  
      
        @Override  
        public void putBitmap(String url, Bitmap bitmap) {  
            mCache.put(url, bitmap);  
        }  
      
    }  

 

可以看到，这里我们将缓存图片的大小设置为10M。接着修改创建ImageLoader实例的代码，第二个参数传入BitmapCache的实例，如下所示：

ImageLoader imageLoader = new ImageLoader(mQueue, new BitmapCache());

 

  这样我们就把ImageLoader的功能优势充分利用起来了

一、添加对磁盘缓存的控制

我们默默的打开源码，添加如下代码：

    private boolean mShouldCache = true;
    /**
     * Set whether or not responses to this request should be cached(Disk Cache).
     *
     * @return This Request object to allow for chaining.
     */
    public void setShouldCache(boolean shouldCache) {
        mShouldCache = shouldCache;
    }
    
    /**
     * Returns true if responses to this request should be cached.
     */
    public final boolean shouldCache() {
        return mShouldCache;
    }

定位到get方法

public ImageContainer get(String requestUrl, ImageListener imageListener,
int maxWidth, int maxHeight) 

找到初始化Request<Bitmap>的地方。

    public ImageContainer get(String requestUrl, ImageListener imageListener,
            int maxWidth, int maxHeight) {
        // only fulfill requests that were initiated from the main thread.
        throwIfNotOnMainThread();

        final String cacheKey = getCacheKey(requestUrl, maxWidth, maxHeight);

        // Try to look up the request in the cache of remote images.
        Bitmap cachedBitmap = mCache.getBitmap(cacheKey);
        if (cachedBitmap != null) {
            // Return the cached bitmap.
            ImageContainer container = new ImageContainer(cachedBitmap, requestUrl, null, null);
            imageListener.onResponse(container, true);
            return container;
        }

        // The bitmap did not exist in the cache, fetch it!
        ImageContainer imageContainer =
                new ImageContainer(null, requestUrl, cacheKey, imageListener);

        // Update the caller to let them know that they should use the default bitmap.
        imageListener.onResponse(imageContainer, true);

        // Check to see if a request is already in-flight.
        BatchedImageRequest request = mInFlightRequests.get(cacheKey);
        if (request != null) {
            // If it is, add this request to the list of listeners.
            request.addContainer(imageContainer);
            return imageContainer;
        }

        // The request is not already in flight. Send the new request to the network and
        // track it.
        Request<Bitmap> newRequest = makeImageRequest(requestUrl, maxWidth, maxHeight, cacheKey);
        mRequestQueue.add(newRequest);

        mInFlightRequests.put(cacheKey,
                new BatchedImageRequest(newRequest, imageContainer));
        return imageContainer;
    }

把红色代码中间添加：newRequest.setShouldCache(mShouldCache);最终效果如下：

　　　　　// The request is not already in flight. Send the new request to the network and
        // track it.
        Request<Bitmap> newRequest = makeImageRequest(requestUrl, maxWidth, maxHeight, cacheKey);
        newRequest.setShouldCache(mShouldCache);
        mRequestQueue.add(newRequest);

 

二、ImageLoader

    /**
     * Constructs a new ImageLoader.
     * @param queue The RequestQueue to use for making image requests.
     * @param imageCache The cache to use as an L1 cache.
     */
    public ImageLoader(RequestQueue queue, ImageCache imageCache) {
        mRequestQueue = queue;
        mCache = imageCache;
    }

初始化要传入两个参数：①RequestQueue对象；②ImageCache对象（不能传null！！！！）

RequestQueue这个我就不多说了，之前的文章已经讲解过了，下面来说说ImageCache这个对象。

 

2.1 建立ImageCache对象来实现内存缓存

ImageCache是一个图片的内存缓存对象，源码中叫做L1缓存，其实缓存分为L1、L2两种，L1就是所谓的内存缓存，将展示过的图片放入内存中进行缓存，L2就是磁盘缓存，如果这个图片下载完成，它可以被存放到磁盘中，在没有网络的时候就可以调出来使用了。

为了简单我先空实现ImageCache接口，产生一个MyImageCache对象

    class MyImageCache implements ImageCache {

        @Override
        public Bitmap getBitmap(String url) {
            return null;
        }

        @Override
        public void putBitmap(String url, Bitmap bitmap) {
        }
    }

这个接口提供的方法简单明了，今后我们可以用自己的内存缓存来完善这个类，当前getBitmap返回的是null，说明这个内存缓存没啥用处，和没缓存一样。

 

2.2 实现加载网络图片

        ImageLoader imageLoader = new ImageLoader(mQueue, new MyImageCache());
        ImageListener listener = ImageLoader.getImageListener(iv, R.drawable.default_photo, R.drawable.error_photo);
        imageLoader.setShouldCache(true);
        imageLoader.get("http://img5.duitang.com/uploads/item/201409/14/20140914162144_MBEmX.jpeg", listener);

代码的思路是产生ImageLoader后，再初始化一个监听器，监听器中传入imageview对象，还有默认的图片，出错时展示的图片，这个很好理解。最后在imageLoader的get方法中传入URL，还有监听器对象即可。

值得注意的是，get方法还有一种变体：

imageLoader.get("http://img5.duitang.com/uploads/item/201409/14/20140914162144_MBEmX.jpeg", listener, 0 ,0);

这里最后传入的数值是得到图片的最大宽、高，其意义和ImageRequest中的宽、高完全一致，可以参考之前的文章。其实，如果你去源码中找找的话，你会发现这两个参数最终都是传给ImageRequest的，所以在此就不做过多讲解了。

 

2.3 设置缓存

因为我们一上来就修改了源码，所以当我们在执行get()方法前可以通过setShouldCache(false)来取消磁盘缓存，如果你不进行设置的话默认是执行磁盘缓存的。那么如何配置L1缓存呢？刚刚我们的MyImageCache仅仅是一个空实现，现在就开始来完善它。

我的想法是通过LruCache进行图片缓存，分配的缓存空间是5m。如果对LruCache不是很了解，可以看看我之前的文章：详细解读LruCache类

class MyImageCache implements ImageCache {

        private LruCache<String, Bitmap> mCache;  
        
        public MyImageCache() {
            int maxSize = 5 * 1024 * 1024;  
            mCache = new LruCache<String, Bitmap>(maxSize) {  
                @Override  
                protected int sizeOf(String key, Bitmap bitmap) {  
                    return bitmap.getRowBytes() * bitmap.getHeight();  
                }  
            };
        }
        
        @Override
        public Bitmap getBitmap(String url) {
            return mCache.get(url);  
            
        }

        @Override
        public void putBitmap(String url, Bitmap bitmap) {
            mCache.put(url, bitmap); 
        }

    }

每次执行get方法时，Volley会到MyImageCache中调用getBitmap()，看看有没有内存缓存，如果你返回了null，那么Volley就会从网络上下载，如果不为null，Volley会直接把取得的bitmap展示到imageview中。当图片展示到屏幕上后（无论是这个图片是从内存中读的，还是从磁盘中读的，或者是从网络上下载的），Volley都会自动调用putBitmap，把图片放入内存中缓存起来。

说明：缓存的size是：bitmap.getRowBytes() * bitmap.getHeight()，这里getRowBytes()是返回图片每行的字节数，图片的size应该乘以高度。

 

注意：imageLoader.setShouldCache(false);仅仅是设置了不实用磁盘缓存，和内存缓存没有任何关系。如果你想要不实用内存缓存，请在自定义的ImageCache中进行处理。

 

2.4 其他方法

public final boolean shouldCache()

查看是否已经做了磁盘缓存。

 

void setShouldCache(boolean shouldCache)

设置是否运行磁盘缓存，此方法需要在get方法前使用

 

public boolean isCached(String requestUrl, int maxWidth, int maxHeight)

判断对象是否已经被缓存，传入url，还有图片的最大宽高

 

public void setBatchedResponseDelay(int newBatchedResponseDelayMs)

Sets the amount of time to wait after the first response arrives before delivering all responses. Batching can be disabled entirely by passing in 0.

设置第一次响应到达后到分发所有响应之前的整体时间，单位ms，如果你设置的时间是0，那么Batching将不可用。

 

三、NetworkImageView

NetworkImageView继承自ImageView，你可以认为它是一个可以实现加载网络图片的imageview，十分简单好用。这个控件在被从父控件分离的时候，会自动取消网络请求的，即完全不用我们担心相关网络请求的生命周期问题。

3.1 XML

    <com.android.volley.toolbox.NetworkImageView
        android:id="@+id/network_image_view"
        android:layout_width="200dp"
        android:layout_height="200dp"
        android:layout_gravity="center_horizontal" />

 

3.2 JAVA

　　　　 NetworkImageView networkImageView = (NetworkImageView) findViewById(R.id.network_image_view);
        networkImageView.setDefaultImageResId(R.drawable.default_photo);
        networkImageView.setErrorImageResId(R.drawable.error_photo);
        networkImageView.setImageUrl("http://img5.duitang.com/uploads/item/201409/14/20140914162144_MBEmX.jpeg", imageLoader);

 

3.3 设置图片的宽高

NetworkImageView没有提供任何设置图片宽高的方法，这是由于它是一个控件，在加载图片的时候它会自动获取自身的宽高，然后对比网络图片的宽度，再决定是否需要对图片进行压缩。也就是说，压缩过程是在内部完全自动化的，并不需要我们关心。NetworkImageView最终会始终呈现给我们一张大小比控件尺寸略大的网络图片，因为它会根据控件宽高来等比缩放原始图片，这点需要注意，如果你想要了解详细原理，请看我之前的ImageRequest介绍。

如果你不想对图片进行压缩的话，只需要在布局文件中把NetworkImageView的layout_width和layout_height都设置成wrap_content就可以了，这样它就会将该图片的原始大小展示出来，不会进行任何压缩。

 

参考自：

http://blog.csdn.net/guolin_blog/article/details/17482165

 

 

详细解读Volley（四）—— 自定义Request

Volley中提供了几个Request，如果我们有特殊的需求，完全可以自定义Request的，自定义Request自然要继承Request，那么本篇就教大家来一步一步地定义一个自己的Request类。

 

一、继承Request

如果我们的request的对象不是string，也不是JsonObject，而是一个奇怪的对象呢？我这里建立了一个类，叫做：Kale，然后定义了一个CustomReqeust去继承Reqeust，得到如下的代码。

package com.kale.volleytest;

import com.android.volley.NetworkResponse;
import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.Response.ErrorListener;
import com.android.volley.Response.Listener;

public class CustomReqeust extends Request<Kale>{
    
    public CustomReqeust(int method, String url, ErrorListener listener) {
        super(method, url, listener);
    }

    @Override
    protected Response<Kale> parseNetworkResponse(NetworkResponse response) {
        // TODO 自动生成的方法存根
        return null;
    }

    @Override
    protected void deliverResponse(Kale response) {
        // TODO 自动生成的方法存根
        
    }

}

分析：

public CustomReqeust(int method, String url, ErrorListener listener)

构造函数中调用了父类的方法，初始化了当前对象。传入三个参数：①请求方式，即POST/GET，②请求的URL，③出错时的回调监听器

 

protected Response<Kale> parseNetworkResponse(NetworkResponse response)

解析网络响应的结果，从NetworkResponse的代码中我们就可以知道它里面有什么东西了。

/**
 * Data and headers returned from {@link Network#performRequest(Request)}.
 */
public class NetworkResponse {
    /**
     * Creates a new network response.
     * @param statusCode the HTTP status code
     * @param data Response body
     * @param headers Headers returned with this response, or null for none
     * @param notModified True if the server returned a 304 and the data was already in cache
     * @param networkTimeMs Round-trip network time to receive network response
     */
    public NetworkResponse(int statusCode, byte[] data, Map<String, String> headers,
            boolean notModified, long networkTimeMs)

响应码啊，请求头什么的，最最主要的就是这个比特数组的data，响应的结果就在里面。我们可以自由的进行处理了~

 

protected void deliverResponse(Kale response)

分发响应的结果，我们可以通过将这个response放到监听器里来获取响应结果。

 

二、分析StringRequest

我们现在已经对request的子类有了基本的认识，现在就来看看StringRequest的源码吧，别担心，很短！

package com.android.volley.toolbox;public class StringRequest extends Request<String> {
    // 建立监听器来获得响应成功时返回的结果
    private final Listener<String> mListener; 


    // 传入请求方法，url，成功时的监听器，失败时的监听器
    public StringRequest(int method, String url, Listener<String> listener,
            ErrorListener errorListener) {
        super(method, url, errorListener);
        // 初始化成功时的监听器
        mListener = listener;
    }

    /**
     * Creates a new GET request.
     * 建立一个默认的GET请求，调用了上面的构造函数
     */
    public StringRequest(String url, Listener<String> listener, ErrorListener errorListener) {
        this(Method.GET, url, listener, errorListener);
    }

    @Override
    protected void deliverResponse(String response) {
        // 用监听器的方法来传递下响应的结果
        mListener.onResponse(response);
    }

    @Override
    protected Response<String> parseNetworkResponse(NetworkResponse response) {
        String parsed;
        try {
            // 调用了new String(byte[] data, String charsetName) 这个构造函数来构建String对象，
            // 将byte数组按照特定的编码方式转换为String对象
            // 主要部分是data
            parsed = new String(response.data, HttpHeaderParser.parseCharset(response.headers));
        } catch (UnsupportedEncodingException e) {
            parsed = new String(response.data);
        }
        return Response.success(parsed, HttpHeaderParser.parseCacheHeaders(response));
    }
}

分析完代码我们应该就能知道改如何自定义Request了，其实没啥高深的东西。

 

三、自定义XMLRequest

代码来自：http://blog.csdn.net/guolin_blog/article/details/17612763

public class XMLRequest extends Request<XmlPullParser> {  
  
    private final Listener<XmlPullParser> mListener;  
  
    public XMLRequest(int method, String url, Listener<XmlPullParser> listener,  
            ErrorListener errorListener) {  
        super(method, url, errorListener);  
        mListener = listener;  
    }  
  
    public XMLRequest(String url, Listener<XmlPullParser> listener, ErrorListener errorListener) {  
        this(Method.GET, url, listener, errorListener);  
    }  
  
    @Override  
    protected Response<XmlPullParser> parseNetworkResponse(NetworkResponse response) {  
        try {  
            String xmlString = new String(response.data,  
                    HttpHeaderParser.parseCharset(response.headers));  
            XmlPullParserFactory factory = XmlPullParserFactory.newInstance();  
            XmlPullParser xmlPullParser = factory.newPullParser();  
            xmlPullParser.setInput(new StringReader(xmlString));  
            return Response.success(xmlPullParser, HttpHeaderParser.parseCacheHeaders(response));  
        } catch (UnsupportedEncodingException e) {  
            return Response.error(new ParseError(e));  
        } catch (XmlPullParserException e) {  
            return Response.error(new ParseError(e));  
        }  
    }  
  
    @Override  
    protected void deliverResponse(XmlPullParser response) {  
        mListener.onResponse(response);  
    }  
  
} 

这里用到了XmlPull的知识，如果不是很了解，可以去这篇文章看看：http://www.cnblogs.com/tianzhijiexian/p/4020250.html

测试代码：

XMLRequest xmlRequest = new XMLRequest(  
                "http://flash.weather.com.cn/wmaps/xml/china.xml",  
                new Response.Listener<XmlPullParser>() {  
                    @Override  
                    public void onResponse(XmlPullParser response) {  
                        try {  
                            int eventType = response.getEventType();  
                            while (eventType != XmlPullParser.END_DOCUMENT) {  
                                switch (eventType) {  
                                case XmlPullParser.START_TAG:  
                                    String nodeName = response.getName();  
                                    if ("city".equals(nodeName)) {  
                                        String pName = response.getAttributeValue(0);  
                                        Log.d("TAG", "pName is " + pName);  
                                    }  
                                    break;  
                                }  
                                eventType = response.next();  
                            }  
                        } catch (XmlPullParserException e) {  
                            e.printStackTrace();  
                        } catch (IOException e) {  
                            e.printStackTrace();  
                        }  
                    }  
                }, new Response.ErrorListener() {  
                    @Override  
                    public void onErrorResponse(VolleyError error) {  
                        Log.e("TAG", error.getMessage(), error);  
                    }  
                });  
        mQueue.add(xmlRequest);

结果：

 

四、自定义GsonRequest

代码来自：http://blog.csdn.net/guolin_blog/article/details/17612763

public class GsonRequest<T> extends Request<T> {

    private final Listener<T> mListener;

    private Gson mGson;

    private Class<T> mClass;

    public GsonRequest(int method, String url, Class<T> clazz, Listener<T> listener,
            ErrorListener errorListener) {
        super(method, url, errorListener);
        mGson = new Gson();
        mClass = clazz;
        mListener = listener;
    }

    public GsonRequest(String url, Class<T> clazz, Listener<T> listener,
            ErrorListener errorListener) {
        this(Method.GET, url, clazz, listener, errorListener);
    }

    @Override
    protected Response<T> parseNetworkResponse(NetworkResponse response) {
        try {
            String jsonString = new String(response.data,
                    HttpHeaderParser.parseCharset(response.headers));
            return Response.success(mGson.fromJson(jsonString, mClass),
                    HttpHeaderParser.parseCacheHeaders(response));
        } catch (UnsupportedEncodingException e) {
            return Response.error(new ParseError(e));
        }
    }

    @Override
    protected void deliverResponse(T response) {
        mListener.onResponse(response);
    }

}

代码十分简单，先是将服务器响应的数据解析出来，然后通过调用Gson的fromJson方法将数据组装成对象。在deliverResponse方法中仍然是将最终的数据进行回调。

用法：

建立一个对象类，比如这里的weather、WeatherInfo类，然后初始化GsonRequest对象，最后把GsonRequest对象添加到队列中。

Weather：

 

public class Weather {

    private WeatherInfo weatherinfo;

    public WeatherInfo getWeatherinfo() {
        return weatherinfo;
    }

    public void setWeatherinfo(WeatherInfo weatherinfo) {
        this.weatherinfo = weatherinfo;
    }

}

 

 

 

WeatherInfo：

public class WeatherInfo {

    private String city;

    private String temp;

    private String time;

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public String getTemp() {
        return temp;
    }

    public void setTemp(String temp) {
        this.temp = temp;
    }

    public String getTime() {
        return time;
    }

    public void setTime(String time) {
        this.time = time;
    }

}

 

Java测试代码：

GsonRequest<Weather> gsonRequest = new GsonRequest<Weather>(  
        "http://www.weather.com.cn/data/sk/101010100.html", Weather.class,  
        new Response.Listener<Weather>() {  
            @Override  
            public void onResponse(Weather weather) {  
                WeatherInfo weatherInfo = weather.getWeatherinfo();  
                Log.d("TAG", "city is " + weatherInfo.getCity());  
                Log.d("TAG", "temp is " + weatherInfo.getTemp());  
                Log.d("TAG", "time is " + weatherInfo.getTime());  
            }  
        }, new Response.ErrorListener() {  
            @Override  
            public void onErrorResponse(VolleyError error) {  
                Log.e("TAG", error.getMessage(), error);  
            }  
        });  
mQueue.add(gsonRequest); 

 

五、重写getBody()方法来添加post参数

我们可以在JsonRequest类中发现如下代码：

/** 
  * Returns the raw POST or PUT body to be sent. 
  * 
  * @throws AuthFailureError in the event of auth failure 
  */  
 @Override  
 public byte[] getBody() {  
     try {  
         return mRequestBody == null ? null : mRequestBody.getBytes(PROTOCOL_CHARSET);  
     } catch (UnsupportedEncodingException uee) {  
         VolleyLog.wtf("Unsupported Encoding while trying to get the bytes of %s using %s",  
                 mRequestBody, PROTOCOL_CHARSET);  
         return null;  
     }  
 }  

不用看代码，直接看注释，说明这里执行post请求，所以我们可以在这里设置post参数。这里

return mRequestBody == null ? null : mRequestBody.getBytes(PROTOCOL_CHARSET); 

返回的就是post参数了。

如果我们想要传递POST数据，可以参考上面的代码，重写Request的getBody()方法，放入自己的参数，举例如下：

　　 /** http请求编码方式 */  
    private static final String PROTOCOL_CHARSET = "utf-8";  
  
    private String mUserName; 

@Override  
    public byte[] getBody() {  
        try {  
            return mUserName == null ? null : mUserName.getBytes(PROTOCOL_CHARSET);  
        } catch (UnsupportedEncodingException uee) {  
            VolleyLog.wtf("Unsupported Encoding while trying to get the bytes of %s using %s", mUserName, PROTOCOL_CHARSET);  
            return null;  
        }  
    }  

完整代码（来自：http://blog.csdn.net/ttdevs/article/details/17586205）：

 

public class CustomReqeust extends Request<String> {  
    /** http请求编码方式 */  
    private static final String PROTOCOL_CHARSET = "utf-8";  
  
    private Listener<String> mListener;  
    private String mUserName;  
  
    public CustomReqeust(String url, String userName, Listener<String> listener, ErrorListener errorListener) {  
        super(Method.POST, url, errorListener);  
        mUserName = userName;  
        mListener = listener;  
    }  
  
    @Override  
    protected Response<String> parseNetworkResponse(NetworkResponse response) {  
        String parsed;  
        try {  
            parsed = new String(response.data, HttpHeaderParser.parseCharset(response.headers));  
        } catch (UnsupportedEncodingException e) {  
            parsed = new String(response.data);  
        }  
        return Response.success(parsed, HttpHeaderParser.parseCacheHeaders(response));  
    }  
  
    @Override  
    protected void deliverResponse(String response) {  
        mListener.onResponse(response);  
    }  
  
    @Override  
    public byte[] getBody() {  
        try {  
            return mUserName == null ? null : mUserName.getBytes(PROTOCOL_CHARSET);  
        } catch (UnsupportedEncodingException uee) {  
            VolleyLog.wtf("Unsupported Encoding while trying to get the bytes of %s using %s", mUserName, PROTOCOL_CHARSET);  
            return null;  
        }  
    }  
}

 

 

 

测试代码：

private void customRequest() {  
    CustomReqeust request = new CustomReqeust(URL, "CustomVolley", new Listener<String>() {  
  
        @Override  
        public void onResponse(String arg0) {  
            Toast.makeText(getApplicationContext(), arg0, Toast.LENGTH_LONG).show();  
            Log.d("onResponse", arg0);  
        }  
    }, new ErrorListener() {  
  
        @Override  
        public void onErrorResponse(VolleyError arg0) {  
            Toast.makeText(getApplicationContext(), arg0.toString(), Toast.LENGTH_LONG).show();  
            Log.d("onErrorResponse", arg0.toString());  
        }  
    });  
    mQueue.add(request);  
}  

抓包结果：

得到了传递的username = CustomVolley

 

 

参考自：

http://blog.csdn.net/t12x3456/article/details/9221611

http://blog.csdn.net/guolin_blog/article/details/17612763

http://blog.csdn.net/ttdevs/article/details/17586205