package cc.vv;
import java.io.File;
import java.io.InputStream;
import java.io.OutputStream;
import libcore.io.DiskLruCache;
import libcore.io.Utils;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.widget.ImageView;
import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
/**
* Demo描述:
* DiskLruCache学习示例
*
* DiskLruCache用于本地缓存.
* 比如在网络可用时加载一张网络图片，当网络不可用时依然可以显示该图片。
* 实现的原理是将图片保存到本地；当网络不可用时从本地加载图片。
* 在此简单模拟该过程，步骤如下:
* 1 从网络下载图片且保存至DiskLruCache
* 2 从DiskLruCache中获取缓存图片进行显示
*
*
* 学习备注:
* 1 DiskLruCache的本地缓存文件路径为:
* /sdcard/Android/data/<application package>/cache
* 当应用被卸载时该文件亦会被删除
* 2 新闻类APP一般的做法.从新闻列表(ListView)中点击某条新闻跳转到详细画面.
* 在详细画面一般有图片和文字.此时可以将图片和文字用同一个key存到不同的缓存文件夹下.
* 在断网时浏览该新闻时候依据该key分别取出对应的图片和文字即可.
* 3 在示例中用到了DiskLruCache的存和取的相关API.在此对其余重要API简要整理:
* 3.1 remove(String key) 删除某个已缓存的对象.
* 3.2 size() 得到缓存路径下缓存的总大小.这个很常见.许多APP都提示当前有多少缓存.
* 3.3 flush() 将内存中的操作记录同步到日志文件(也就是journal文件)中
* 一般在Activity的onPause()中调用该方法.
* 3.4 close() 关闭DiskLruCache.该方法与open方法对应.
* 一般在Activity的onDestory()中调用该方法.
* 3.5 delete() 将缓存数据全部删除.
*
*
* 学习资源:
* http://blog.csdn.net/guolin_blog/article/details/28863651
* Thank you very much
*/
public class MainActivity extends Activity {
private ImageView mImageView;
private DiskLruCache mDiskLruCache;
private Context mContext;
//DiskLruCache中对于图片的最大缓存值.
private int maxSize=20*1024*1024;
private String mImagePath="http://www.baidu.com/img/bdlogo.png";
private Handler mHandler;
private final int FINISH=9527;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
init();
}
private void init(){
try {
mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
super.handleMessage(msg);
if (msg.what==FINISH) {
getDataFromDiskLruCache();
}
}
};
mContext=this;
mImageView=(ImageView) findViewById(R.id.imageView);
initDiskLruCache();
} catch (Exception e) {
// TODO: handle exception
}
}
/**
* 初始化DiskLruCache
*/
private void initDiskLruCache(){
try {
File cacheDir=Utils.getDiskLruCacheDir(mContext, "bitmap");
if (!cacheDir.exists()) {
cacheDir.mkdirs();
}
int versionCode=Utils.getAppVersionCode(mContext);
mDiskLruCache=DiskLruCache.open(cacheDir, versionCode, 1, maxSize);
saveDataToDiskLruCache();
} catch (Exception e) {
// TODO: handle exception
}
}
// 将数据写入DiskLruCache
private void saveDataToDiskLruCache() {
new Thread(new Runnable() {
@Override
public void run() {
try {
//第一步:获取将要缓存的图片的对应唯一key值.
String key = Utils.getStringByMD5(mImagePath);
//第二步:获取DiskLruCache的Editor
DiskLruCache.Editor editor = mDiskLruCache.edit(key);
if (editor!=null) {
//第三步:从Editor中获取OutputStream
OutputStream outputStream=editor.newOutputStream(0);
//第四步:下载网络图片且保存至DiskLruCache图片缓存中
boolean isSuccessfull=Utils.getBitmapFromNetWorkAndSaveToDiskLruCache(mImagePath, outputStream);
if (isSuccessfull) {
editor.commit();
mHandler.sendEmptyMessage(FINISH);
}else{
editor.abort();
}
mDiskLruCache.flush();
}
} catch (Exception e) {
}
}
}).start();
}
//从DiskLruCache中读取数据
private void getDataFromDiskLruCache(){
try {
//第一步:获取已缓存的图片的对应唯一key值.
String key = Utils.getStringByMD5(mImagePath);
//第二步:依据key获取到其对应的snapshot
DiskLruCache.Snapshot snapshot=mDiskLruCache.get(key);
if (snapshot!=null) {
//第三步:从snapshot中获取到InputStream
InputStream inputStream=snapshot.getInputStream(0);
Bitmap bitmap=BitmapFactory.decodeStream(inputStream);
mImageView.setImageBitmap(bitmap);
}
} catch (Exception e) {
}
}
}
Utils如下:
package libcore.io;
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import org.apache.http.HttpStatus;
import android.content.Context;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.content.pm.PackageManager.NameNotFoundException;
import android.os.Environment;
public class Utils {
/**
* 获取DiskLruCache的缓存文件夹
* 注意第二个参数dataType
* DiskLruCache用一个String类型的唯一值对不同类型的数据进行区分.
* 比如bitmap,object等文件夹.其中在bitmap文件夹中缓存了图片.
*
* 缓存数据的存放位置为:
* /sdcard/Android/data/<application package>/cache
* 如果SD卡不存在时缓存存放位置为:
* /data/data/<application package>/cache
*
*/
public static File getDiskLruCacheDir(Context context, String dataType) {
String dirPath;
File cacheFile = null;
if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState()) ||
!Environment.isExternalStorageRemovable()) {
dirPath=context.getExternalCacheDir().getPath();
} else {
dirPath=context.getCacheDir().getPath();
}
cacheFile=new File(dirPath+File.separator+dataType);
return cacheFile;
}
/**
* 获取APP当前版本号
* @param context
* @return
*/
public static int getAppVersionCode(Context context){
int versionCode=1;
try {
String packageName=context.getPackageName();
PackageManager packageManager=context.getPackageManager();
PackageInfo packageInfo=packageManager.getPackageInfo(packageName, 0);
versionCode=packageInfo.versionCode;
} catch (NameNotFoundException e) {
e.printStackTrace();
}
return versionCode;
}
/**
* 将字符串用MD5编码.
* 比如在改示例中将url进行MD5编码
*/
public static String getStringByMD5(String string) {
String md5String = null;
try {
// Create MD5 Hash
MessageDigest messageDigest = MessageDigest.getInstance("MD5");
messageDigest.update(string.getBytes());
byte messageDigestByteArray[] = messageDigest.digest();
if (messageDigestByteArray == null || messageDigestByteArray.length == 0) {
return md5String;
}
// Create hexadecimal String
StringBuffer hexadecimalStringBuffer = new StringBuffer();
int length = messageDigestByteArray.length;
for (int i = 0; i < length; i++) {
hexadecimalStringBuffer.append(Integer.toHexString(0xFF & messageDigestByteArray[i]));
}
md5String = hexadecimalStringBuffer.toString();
return md5String;
} catch (NoSuchAlgorithmException e) {
e.printStackTrace();
}
return md5String;
}
/**
* 从网络获取图片且保存至SD卡中的缓存
*/
public static boolean getBitmapFromNetWorkAndSaveToDiskLruCache(String imageUrl,OutputStream outputStream){
boolean isSuccessfull=false;
URL url=null;
HttpURLConnection httpURLConnection=null;
BufferedOutputStream bufferedOutputStream=null;
InputStream inputStream=null;
BufferedInputStream bufferedInputStream=null;
try {
url=new URL(imageUrl);
httpURLConnection=(HttpURLConnection) url.openConnection();
httpURLConnection.setConnectTimeout(5*1000);
httpURLConnection.setReadTimeout(10*1000);
httpURLConnection.setDoInput(true);
httpURLConnection.setDoOutput(true);
if (httpURLConnection.getResponseCode()==HttpStatus.SC_OK) {
bufferedOutputStream=new BufferedOutputStream(outputStream);
inputStream=httpURLConnection.getInputStream();
bufferedInputStream=new BufferedInputStream(inputStream);
int len=0;
byte [] buffer=new byte[1024];
while((len=bufferedInputStream.read(buffer))!=-1){
bufferedOutputStream.write(buffer, 0, len);
bufferedOutputStream.flush();
}
isSuccessfull=true;
} else {
isSuccessfull=false;
System.out.println("图片请求失败");
}
} catch (Exception e) {
isSuccessfull=false;
System.out.println("e="+e.toString());
}finally{
try {
if (bufferedOutputStream!=null) {
bufferedOutputStream.close();
}
if (inputStream!=null) {
inputStream.close();
}
if (bufferedInputStream!=null) {
bufferedInputStream.close();
}
if (httpURLConnection!=null) {
httpURLConnection.disconnect();
}
} catch (Exception e) {
System.out.println("e="+e.toString());
}
}
return isSuccessfull;
}
}
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<ImageView
android:id="@+id/imageView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true" />
</RelativeLayout>
Android本地缓存DiskLruCache完整详细学习示例
原文地址：http://blog.csdn.net/lfdfhl/article/details/42557301
