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square公司开源了一系列的优秀库，比如Retrofit,OkHttp,Picasso等，
前面简单分析了Picasso的源码，这里来分析下Retrofit的使用：
compile ‘com.squareup.okhttp:okhttp:2.4.0‘
compile ‘com.squareup.okhttp:okhttp-urlconnection:2.4.0‘
compile ‘com.squareup.okio:okio:1.5.0‘
compile ‘com.google.code.gson:gson:2.2.4‘
compile ‘com.squareup.retrofit:retrofit:2.0.0-beta2‘
compile ‘com.squareup.retrofit:adapter-rxjava:2.0.0-beta2‘
compile ‘com.squareup.retrofit:converter-gson:2.0.0-beta2‘
compile ‘io.reactivex:rxandroid:1.1.0‘
compile ‘io.reactivex:rxjava:1.1.0‘盗两张网上的图：
下面是从创建Retrofit出发，具体的使用流程；Retrofit最终的请求操作都是交由okHttp去执行的，执行的结果返回Response，再根据转换器进行解析成相对应的返回类型T;
Retrofit中使用了动态代理，方便了使用；通过retrofit.create返回的其实是个动态代理类，所有具体的处理逻辑交由MethodHandler进行处理；
下面是Retrofit系统中的整个类图，有点像外观模式，Retrofit持有所有子系统的引用；Retrofit比较重要的是两个Factory，一个使用来生成CallAdapter的CallAdapterFactory；一个是用来转换结果的ConvertFactory；这两个都可以用户自己进行添加。
在自定义的Service中，每一个method对应一个MethodHandler,MethodHandler持有retrofit，前面两个Factory以及生成Request的RequestFactory；在okHttp中，Request需要自己进行定义创建，而Retrofit简化了这个操作，进行了相应的封装，使用注解的方式来定义Request的相关参数信息；注解信息的解析则在RequestFactory中完成，通过RequestFactoryParser对注解信息进行简单解析，RequestBuilderAction是解析method中参数中的注解如@Path这些产生的中间产物，最终通过RequestBuilder来具体产生一个Request，RequestBuilder中持有okHttp中的Request.Builder类的引用，其创建Request过程其实都是交给okHttp来操作的；
生成的Request最终封装成为一个OkHttpCall，OkHttpCall则可以看做是对okHttp中Call的通过，它的enqueue等网络请求操作都是委托个给okHttp来操作的；同时对okHttp的返回Response进行解析，使用convertFactory，将其解析为用户所期望的返回类型；
public interface RetrofirHttpService {
@GET("{user}")
Call<UserInfo> getData(@Path("user") String user);
}
注：UserInfo是自己定义的解析类：
public class UserInfo {
String username;
String password;
}// 原始的CallBack方式
private void getUseCall() {
// 添加拦截器
OkHttpClient client = new OkHttpClient();
client.interceptors().add(new LoggingInterceptor());
Retrofit retrofit = new Retrofit.Builder()
.baseUrl("http://115.156.187.146/TransferServer/")
.client(client) // 添加okHttp
.addConverterFactory(GsonConverterFactory.create()) // GSON进行转换
.build();
RetrofirHttpService apiStores = retrofit.create(RetrofirHttpService.class);
Call<UserInfo> call = apiStores.getData("ServerMain.php");
// 异步调用
call.enqueue(new Callback<UserInfo>() {
@Override
public void onResponse(Response<UserInfo> response, Retrofit retrofit) {
UserInfo data = response.body();
LogUtils.i("Call Result:" + data.m);
}
@Override
public void onFailure(Throwable t) {
LogUtils.e(t.toString());
}
});
}public interface RxHttpService {
@GET("{path}")
Observable<UserInfo> getData(@Path("path") String path);
}// 使用RxJava方式
private void getUseRxJava() {
// 添加拦截器
OkHttpClient client = new OkHttpClient();
client.interceptors().add(new LoggingInterceptor());
Retrofit retrofit = new Retrofit.Builder()
.baseUrl("http://115.156.187.146/TransferServer/")
.client(client) // 添加okHttp
.addConverterFactory(GsonConverterFactory.create()) // GSON进行转换
.addCallAdapterFactory(RxJavaCallAdapterFactory.create())
.build();
RxHttpService apiStores = retrofit.create(RxHttpService.class);
Observable<UserInfo> observable = apiStores.getData("ServerMain.php");
observable.subscribeOn(Schedulers.io())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Observer<UserInfo>() {
@Override
public void onNext(UserInfo user) {
LogUtils.i("Call Result:" + user.m);
}
@Override
public void onCompleted() {
}
@Override
public void onError(Throwable error) {
LogUtils.e(error.toString());
}
});
}RxHttpService apiStores = retrofit.create(RxHttpService.class);动态代理的知识具体见《 设计模式汇总：结构型模型（上）》中的代理模式中的解释。
/** Create an implementation of the API defined by the {@code service} interface. */
@SuppressWarnings("unchecked") // Single-interface proxy creation guarded by parameter safety.
public <T> T create(final Class<T> service) {
Utils.validateServiceInterface(service);
if (validateEagerly) {
eagerlyValidateMethods(service);
}
return (T) Proxy.newProxyInstance(service.getClassLoader(), new Class<?>[]{service},
new InvocationHandler() {
private final Platform platform = Platform.get();
@Override
public Object invoke(Object proxy, Method method, Object... args)
throws Throwable {
// If the method is a method from Object then defer to normal invocation.
if (method.getDeclaringClass() == Object.class) {
return method.invoke(this, args);
}
if (platform.isDefaultMethod(method)) {
return platform.invokeDefaultMethod(method, service, proxy, args);
}
return loadMethodHandler(method).invoke(args);
}
});
}标准的动态代理创建过程；
来看代理类和委托类之间的中间InvocationHandler类的invoke函数具体执行逻辑；
loadMethodHandler(method).invoke(args);
private final Map<Method, MethodHandler<?>> methodHandlerCache = new LinkedHashMap<>();
MethodHandler<?> loadMethodHandler(Method method) {
MethodHandler<?> handler;
synchronized (methodHandlerCache) {
handler = methodHandlerCache.get(method);
if (handler == null) {
handler = MethodHandler.create(this, method);
methodHandlerCache.put(method, handler);
}
}
return handler;
}Retrofit维护了一个method对应的Map，这里将method都封装成一个MethodHandler类（可以当作是委托类）；调用代理类，其实就是调用MethodHandler的invoke;所以具体的实现逻辑都在MethodHandler中；
final class MethodHandler<T> {
// MethodHandler持有一个retrofit对象
private final Retrofit retrofit;
// 类似于Volley中的 Request ，包含了HTTP请求的Url、Header信息，MediaType、Method以及RequestAction数组
private final RequestFactory requestFactory;
// HTTP请求返回数据的类型
private final CallAdapter<T> callAdapter;
// 对返回数据进行转换的类型转换器
private final Converter<ResponseBody, T> responseConverter;
private MethodHandler(Retrofit retrofit, RequestFactory requestFactory,
CallAdapter<T> callAdapter, Converter<ResponseBody, T> responseConverter) {
this.retrofit = retrofit;
this.requestFactory = requestFactory;
this.callAdapter = callAdapter;
this.responseConverter = responseConverter;
}
// 每一次请求的最终具体调用的函数
Object invoke(Object... args) {
// 可以发现最终是调用callAdapter的adapt函数
// 并且将相应的请求事务封装成一个OkHttpCall类进行处理
return callAdapter.adapt(new OkHttpCall<>(retrofit, requestFactory, responseConverter, args));
}
// 调用该静态类创建一个MethodHandler实例
@SuppressWarnings("unchecked")
static MethodHandler<?> create(Retrofit retrofit, Method method) {
// 创建CallAdapter
CallAdapter<Object> callAdapter = (CallAdapter<Object>) createCallAdapter(method, retrofit);
// 根据callAdapter来获取相应的返回类型
Type responseType = callAdapter.responseType();
// 创建结果类型转换器
Converter<ResponseBody, Object> responseConverter =
(Converter<ResponseBody, Object>) createResponseConverter(method, retrofit, responseType);
// 创建RequestFactory
RequestFactory requestFactory = RequestFactoryParser.parse(method, responseType, retrofit);
return new MethodHandler<>(retrofit, requestFactory, callAdapter, responseConverter);
}
// 创建相应的CallAdapter
private static CallAdapter<?> createCallAdapter(Method method, Retrofit retrofit) {
// 这个method即为service中自定义的一个方法，一般返回都是泛型类
Type returnType = method.getGenericReturnType();
if (Utils.hasUnresolvableType(returnType)) {
throw Utils.methodError(method,
"Method return type must not include a type variable or wildcard: %s", returnType);
}
if (returnType == void.class) {
throw Utils.methodError(method, "Service methods cannot return void.");
}
// 获取Method上对应的注解即（GET这些）
Annotation[] annotations = method.getAnnotations();
try {
// 根据注解来获取相应的Adapter
return retrofit.callAdapter(returnType, annotations);
} catch (RuntimeException e) { // Wide exception range because factories are user code.
throw Utils.methodError(e, method, "Unable to create call adapter for %s", returnType);
}
}
// 最后也是调用retrofit来实现的；
private static Converter<ResponseBody, ?> createResponseConverter(Method method,
Retrofit retrofit, Type responseType) {
Annotation[] annotations = method.getAnnotations();
try {
return retrofit.responseConverter(responseType, annotations);
} catch (RuntimeException e) { // Wide exception range because factories are user code.
throw Utils.methodError(e, method, "Unable to create converter for %s", responseType);
}
}
}MethodHandler是系统为定义的每一个Service中的method中创建的一个具体执行类，通过调用其invoke函数，来执行具体的请求的逻辑；
它主要包含四个变量：
Retrofit: MethodHandler持有一个retrofit对象
private final Retrofit retrofit;
RequestFactory: 类似于Volley中的 Request ，包含了HTTP请求的Url、Header信息，MediaType、Method以及RequestAction数组
private final RequestFactory requestFactory;
CallAdapter: HTTP请求返回数据的类型
private final CallAdapter<T> callAdapter;
ResponseConverter: 对返回数据进行转换的类型转换器
private final Converter<ResponseBody, T> responseConverter;
具体来看每个变量的创建；
private final List<CallAdapter.Factory> adapterFactories;
public CallAdapter<?> callAdapter(Type returnType, Annotation[] annotations) {
return nextCallAdapter(null, returnType, annotations);
}
/**
* Returns the {@link CallAdapter} for {@code returnType} from the available {@linkplain
* #callAdapterFactories() factories} except {@code skipPast}.
*/
// 返回相关的可用的CallAdapter（除了指定跳过的skipPast）
public CallAdapter<?> nextCallAdapter(CallAdapter.Factory skipPast, Type returnType,
Annotation[] annotations) {
checkNotNull(returnType, "returnType == null");
checkNotNull(annotations, "annotations == null");
int start = adapterFactories.indexOf(skipPast) + 1;
// 遍历adapterFactories中所有的Factory
for (int i = start, count = adapterFactories.size(); i < count; i++) {
CallAdapter<?> adapter = adapterFactories.get(i).get(returnType, annotations, this);
// 如果找到，则返回该Adapter
if (adapter != null) {
return adapter;
}
}
// 如果获取不到相应的CallAdapter，则抛出异常
StringBuilder builder = new StringBuilder("Could not locate call adapter for ")
.append(returnType)
.append(". Tried:");
for (int i = start, count = adapterFactories.size(); i < count; i++) {
builder.append("\n * ").append(adapterFactories.get(i).getClass().getName());
}
if (skipPast != null) {
builder.append("\nSkipped:");
for (int i = 0; i < start; i++) {
builder.append("\n * ").append(adapterFactories.get(i).getClass().getName());
}
}
throw new IllegalArgumentException(builder.toString());
}RetroFit中有一个adapterFactories保存了所有CallAdapter.Factory,通过遍历这些factory来获取相应符合的CallAdapter;
先来看adapterFactories都保存了哪些Factory；从Retrofit创建开始
private final OkHttpClient client;
private final BaseUrl baseUrl;
private final List<Converter.Factory> converterFactories;
private final List<CallAdapter.Factory> adapterFactories;
private final Executor callbackExecutor;
private final boolean validateEagerly;
private Retrofit(OkHttpClient client, BaseUrl baseUrl, List<Converter.Factory> converterFactories,
List<CallAdapter.Factory> adapterFactories, Executor callbackExecutor,
boolean validateEagerly) {
this.client = client;
this.baseUrl = baseUrl;
this.converterFactories = converterFactories;
this.adapterFactories = adapterFactories;
this.callbackExecutor = callbackExecutor;
this.validateEagerly = validateEagerly;
}
/** Create the {@link Retrofit} instances. */
public Retrofit build() {
if (baseUrl == null) {
throw new IllegalStateException("Base URL required.");
}
// 默认使用OkhttpClient
OkHttpClient client = this.client;
if (client == null) {
client = new OkHttpClient();
}
// 向adapterFactories添加了一个默认的CallAdapterFactory
// 如果前面add了CallAdpterfactory（如RxJavaCallAdapterFactory），则可以看到默认的Factory会添加到用户指定的Factory后面
// 则在遍历的时候，会优先遍历用户指定的Factory
List<CallAdapter.Factory> adapterFactories = new ArrayList<>(this.adapterFactories);
adapterFactories.add(Platform.get().defaultCallAdapterFactory(callbackExecutor));
// Make a defensive copy of the converters.
List<Converter.Factory> converterFactories = new ArrayList<>(this.converterFactories);
return new Retrofit(client, baseUrl, converterFactories, adapterFactories, callbackExecutor,
validateEagerly);
}
/**
* 用户添加自定义的CallAdapterFactory
*/
public Builder addCallAdapterFactory(CallAdapter.Factory factory) {
adapterFactories.add(checkNotNull(factory, "factory == null"));
return this;
}用户可以根据自己需要来添加自定义的CallAdapterFactory，这里来看系统默认的CallAdapterFactory；
Platform.get()是根据系统不同来创建不同的运行环境，比如是再Android上还是Java上运行时由区别的，如下所示：
class Platform {
private static final Platform PLATFORM = findPlatform();
static Platform get() {
return PLATFORM;
}
private static Platform findPlatform() {
// 如果是Android系统
try {
Class.forName("android.os.Build");
if (Build.VERSION.SDK_INT != 0) {
return new Android();
}
} catch (ClassNotFoundException ignored) {
}
// 如果是Java系统
try {
Class.forName("java.util.Optional");
return new Java8();
} catch (ClassNotFoundException ignored) {
}
// 如果是其他系统
return new Platform();
}
static class Android extends Platform {
// 创建默认的CallAdapterFactory过程
@Override CallAdapter.Factory defaultCallAdapterFactory(Executor callbackExecutor) {
if (callbackExecutor == null) {
// 如果没有指定callbackExecutor，或者为null，则新创建一个MainThreadExecutor
callbackExecutor = new MainThreadExecutor();
}
return new ExecutorCallAdapterFactory(callbackExecutor);
}
// 该Executor的主要工作逻辑就是调用主线程的Looper来创建一个对应的Handler
// 执行execute就是操作Handler进行post事件（Runnable）
static class MainThreadExecutor implements Executor {
private final Handler handler = new Handler(Looper.getMainLooper());
@Override public void execute(Runnable r) {
handler.post(r);
}
}
}
}可以看到对应不同的系统平台，Retrofit提供了不同的Platform版本； 默认的CallAdapterFactory是个ExecutorCallAdapterFactory，它是通过callbackExecutor来创建的；
如果用户没有执行相应的callbackExecutor，系统或创建一个默认的MainThreadExecutor，该MainThreadExecutor的主要执行逻辑就是使用主线程的Handler来post Runnable消息；
然后Retrofit把ExecutorCallAdapterFactory实例添加到adapterFactories中；
CallAdapter<?> adapter = adapterFactories.get(i).get(returnType, annotations, this);
final class ExecutorCallAdapterFactory implements CallAdapter.Factory {
private final Executor callbackExecutor;
ExecutorCallAdapterFactory(Executor callbackExecutor) {
this.callbackExecutor = callbackExecutor;
}
@Override
public CallAdapter<Call<?>> get(Type returnType, Annotation[] annotations, Retrofit retrofit) {
// 根据returnType获得具体的返回类型
if (Utils.getRawType(returnType) != Call.class) {
return null;
}
final Type responseType = Utils.getCallResponseType(returnType);
// 返回一个CallAdapter
return new CallAdapter<Call<?>>() {
@Override
public Type responseType() {
return responseType;
}
// 调用adapt返回一个ExecutorCallbackCall类
@Override
public <R> Call<R> adapt(Call<R> call) {
return new ExecutorCallbackCall<>(callbackExecutor, call);
}
};
}将前面所有的逻辑串在一起，使用动态代理创建的代理类使用的InvokeHandler，调用其invoke来实现一个具体的方法调用；委托类是系统自定义创建的MethodHandler，系统根据method来创建相应的MethodHandler;MethodHandler中持有对CallAdapter的引用，CallAdapter是通过相应的CallAdpterFactory来创建的，如果加入了自定义的比如RxJava，最终会添加到Retrofit中的一个factory链表中，系统通过扫描链表来获取合适的CallAdpterFactory来创建CallAdapter;
如果没有自定义CallAdapterFactory，则会默认生成一个CallAdapterFactory;通过这个默认的Factory会创建一个默认的CallAdapter；
代理类的方法实现，是通过InvokeHandler的invoke来实现的；在系统定义的Invokehandler中进而调用MethodHandler的invoke函数，该invoke函数会继续调用CallAdpter的adapt,由上知，最终返回一个ExecutorCallbackCall类；
继续来看ExecutorCallbackCall类：
final class ExecutorCallAdapterFactory implements CallAdapter.Factory {
static final class ExecutorCallbackCall<T> implements Call<T> {
private final Executor callbackExecutor;
private final Call<T> delegate;
// 注意这里的Call传递进来的是一个封装好的OkHttpCall类
ExecutorCallbackCall(Executor callbackExecutor, Call<T> delegate) {
this.callbackExecutor = callbackExecutor;
this.delegate = delegate;
}
@Override public void enqueue(Callback<T> callback) {
delegate.enqueue(new ExecutorCallback<>(callbackExecutor, callback));
}
@Override public Response<T> execute() throws IOException {
return delegate.execute();
}
@Override public void cancel() {
delegate.cancel();
}
@SuppressWarnings("CloneDoesntCallSuperClone") // Performing deep clone.
@Override public Call<T> clone() {
return new ExecutorCallbackCall<>(callbackExecutor, delegate.clone());
}
}
static final class ExecutorCallback<T> implements Callback<T> {
private final Executor callbackExecutor;
private final Callback<T> delegate;
ExecutorCallback(Executor callbackExecutor, Callback<T> delegate) {
this.callbackExecutor = callbackExecutor;
this.delegate = delegate;
}
@Override public void onResponse(final Response<T> response, final Retrofit retrofit) {
callbackExecutor.execute(new Runnable() {
@Override public void run() {
delegate.onResponse(response, retrofit);
}
});
}
@Override public void onFailure(final Throwable t) {
callbackExecutor.execute(new Runnable() {
@Override public void run() {
delegate.onFailure(t);
}
});
}
}
}可以看出来ExecutorCallbackCall也是一个代理类，它的委托类是OkHttpCall；所以使用默认的CallAdapterFactory返回的是一个封装了OkHttpCall的一个Call类，其具体的类型是ExecutorCallbackCall；
final class OkHttpCall<T> implements Call<T> {
private final Retrofit retrofit;
private final RequestFactory requestFactory;
private final Converter<ResponseBody, T> responseConverter;
private final Object[] args;
private volatile com.squareup.okhttp.Call rawCall;
private boolean executed; // Guarded by this.
private volatile boolean canceled;
OkHttpCall(Retrofit retrofit, RequestFactory requestFactory,
Converter<ResponseBody, T> responseConverter, Object[] args) {
this.retrofit = retrofit;
this.requestFactory = requestFactory;
this.responseConverter = responseConverter;
this.args = args;
}
@SuppressWarnings("CloneDoesntCallSuperClone")
// We are a final type & this saves clearing state.
@Override
public OkHttpCall<T> clone() {
return new OkHttpCall<>(retrofit, requestFactory, responseConverter, args);
}
}来看enqueue操作；在用户代码中：
call.enqueue(new Callback<UserInfo>() {
@Override
public void onResponse(Response<UserInfo> response, Retrofit retrofit) {
UserInfo data = response.body();
LogUtils.i("Call Result:" + data.m);
}
@Override
public void onFailure(Throwable t) {
LogUtils.e(t.toString());
}
});由前面知这里的Call对应的是一个ExecutorCallbackCall，来看起enqueue操作：
@Override
public void enqueue(Callback<T> callback) {
delegate.enqueue(new ExecutorCallback<>(callbackExecutor, callback));
}delegate对应的即是OkHttpCall,先来看其enqueue传入的参数： ExecutorCallback
static final class ExecutorCallback<T> implements Callback<T> {
private final Executor callbackExecutor;
private final Callback<T> delegate;
ExecutorCallback(Executor callbackExecutor, Callback<T> delegate) {
this.callbackExecutor = callbackExecutor;
this.delegate = delegate;
}
@Override
public void onResponse(final Response<T> response, final Retrofit retrofit) {
callbackExecutor.execute(new Runnable() {
@Override
public void run() {
delegate.onResponse(response, retrofit);
}
});
}
@Override
public void onFailure(final Throwable t) {
callbackExecutor.execute(new Runnable() {
@Override public void run() {
delegate.onFailure(t);
}
});
}
}ExecutorCallback也是一个代理类，用来封装用户定义的Callback，即类内部的变量delegate；callbackExecutor是查找Platform过程中new Android时创建的，其execute的逻辑较为简单，就是使用主线程对应的Handler来将Runnable事件post出去；可以看到，这里最终的响应都会在主线程中，而且调用用户自定义的onResponse和onFailure;
ExecutorCallback的主要作用就是封装Callback，将Callback的响应切换到主线程中；
@Override
public void enqueue(final Callback<T> callback) {
synchronized (this) {
if (executed) throw new IllegalStateException("Already executed");
executed = true;
}
// 注意okHttp的call和retrofit的Call是不同
com.squareup.okhttp.Call rawCall;
try {
// 创建一个okhttp类型的Call
rawCall = createRawCall();
} catch (Throwable t) {
callback.onFailure(t);
return;
}
// 如果取消
if (canceled) {
rawCall.cancel();
}
this.rawCall = rawCall;
// 将Call中事务全部委托给okHttp来操作
// 调用okHttp的enqueue，使用okHttp的Callback来封装retrofit中的Callback
rawCall.enqueue(new com.squareup.okhttp.Callback() {
// 请求失败的响应
private void callFailure(Throwable e) {
try {
callback.onFailure(e);
} catch (Throwable t) {
t.printStackTrace();
}
}
// 请求成功的响应
private void callSuccess(Response<T> response) {
try {
callback.onResponse(response, retrofit);
} catch (Throwable t) {
t.printStackTrace();
}
}
@Override
public void onFailure(Request request, IOException e) {
callFailure(e);
}
@Override
public void onResponse(com.squareup.okhttp.Response rawResponse) {
Response<T> response;
try {
// 获得结果，并且解析结果
response = parseResponse(rawResponse);
} catch (Throwable e) {
callFailure(e);
return;
}
callSuccess(response);
}
});
}OkHttpCall是对OkHttp里面的Call的封装，将所有的操作都委托给该Call进行操作；这里主要的是通过retrofit的call来创建一个okHttp的Call类；这里通过createRawCall来创建：
private com.squareup.okhttp.Call createRawCall() {
return retrofit.client().newCall(requestFactory.create(args));
}这里是通过okHttpClient来创建的一个Call；首先来看 requestFactory是如何根据args参数来创建一个相应的Call的；
先来看requestFactory，它是MethodHandler中创建传递过来的；
RequestFactory requestFactory = RequestFactoryParser.parse(method, responseType, retrofit);
final class RequestFactoryParser {
private final Method method;
static RequestFactory parse(Method method, Type responseType, Retrofit retrofit) {
RequestFactoryParser parser = new RequestFactoryParser(method);
// Method对应的注解这里解析
parser.parseMethodAnnotations(responseType);
parser.parseParameters(retrofit);
// 创建一个RequestFactory
return parser.toRequestFactory(retrofit.baseUrl());
}
private RequestFactoryParser(Method method) {
this.method = method;
}
}RequestFactoryParser主要是根据method对应的注解及返回类型进行相应解析，得出相应的解析结果，然后创建一个RequestFactory来保存所有解析后结果，供创建OkHttpCall来使用。
// 这里是对注解进行解析的核心代码
// 根据注解类型的不同（即请求类型类型的不同进行相应解析）
// 这里也对应的retrofit的基本用法
private void parseMethodAnnotations(Type responseType) {
for (Annotation annotation : method.getAnnotations()) {
if (annotation instanceof DELETE) {
parseHttpMethodAndPath("DELETE", ((DELETE) annotation).value(), false);
} else if (annotation instanceof GET) {
parseHttpMethodAndPath("GET", ((GET) annotation).value(), false);
} else if (annotation instanceof HEAD) {
parseHttpMethodAndPath("HEAD", ((HEAD) annotation).value(), false);
if (!Void.class.equals(responseType)) {
throw methodError(method, "HEAD method must use Void as response type.");
}
} else if (annotation instanceof PATCH) {
parseHttpMethodAndPath("PATCH", ((PATCH) annotation).value(), true);
} else if (annotation instanceof POST) {
parseHttpMethodAndPath("POST", ((POST) annotation).value(), true);
} else if (annotation instanceof PUT) {
parseHttpMethodAndPath("PUT", ((PUT) annotation).value(), true);
} else if (annotation instanceof HTTP) {
HTTP http = (HTTP) annotation;
parseHttpMethodAndPath(http.method(), http.path(), http.hasBody());
} else if (annotation instanceof Headers) {
// 只有Headers是通过parseHeaders来解析的
String[] headersToParse = ((Headers) annotation).value();
if (headersToParse.length == 0) {
throw methodError(method, "@Headers annotation is empty.");
}
headers = parseHeaders(headersToParse);
} else if (annotation instanceof Multipart) {
// 可以看到Multipart和FormUrlEncoded不能同时定义
if (isFormEncoded) {
throw methodError(method, "Only one encoding annotation is allowed.");
}
isMultipart = true;
} else if (annotation instanceof FormUrlEncoded) {
if (isMultipart) {
throw methodError(method, "Only one encoding annotation is allowed.");
}
isFormEncoded = true;
}
}
if (httpMethod == null) {
throw methodError(method, "HTTP method annotation is required (e.g., @GET, @POST, etc.).");
}
// 如果不存在实体，但是用户定义为isMultipart或者isFormEncoded类型，则会抛出异常
if (!hasBody) {
if (isMultipart) {
throw methodError(method,
"Multipart can only be specified on HTTP methods with request body (e.g., @POST).");
}
if (isFormEncoded) {
throw methodError(method,
"FormUrlEncoded can only be specified on HTTP methods with request body "
+ "(e.g., @POST).");
}
}
}这里是对注解进行解析的核心代码 ，根据注解类型的不同（即请求类型类型的不同） 进行相应解析，这里也对应的retrofit的基本用法；
可以看到除了headers使用的parseheader进行解析外，其他都是通过 parseHttpMethodAndPath进行解析的；这里来重点分析下parseHttpMethodAndPath；
// 这个函数只是先做了一个前期判断
private void parseHttpMethodAndPath(String httpMethod, String value, boolean hasBody) {
if (this.httpMethod != null) {
throw methodError(method, "Only one HTTP method is allowed. Found: %s and %s.",
this.httpMethod, httpMethod);
}
// 对应"GET","POST"等
this.httpMethod = httpMethod;
// 标注有没有实体
this.hasBody = hasBody;
// 注解值为空直接返回
if (value.isEmpty()) {
return;
}
// 判断URL是否已经有查询字符串query string
// Get the relative URL path and existing query string, if present.
int question = value.indexOf(‘?‘);
if (question != -1 && question < value.length() - 1) {
// 保证URL的查询字符串中没有{...}之类的字符
// Ensure the query string does not have any named parameters.
String queryParams = value.substring(question + 1);
Matcher queryParamMatcher = PARAM_URL_REGEX.matcher(queryParams);
if (queryParamMatcher.find()) {
throw methodError(method, "URL query string \"%s\" must not have replace block. "
+ "For dynamic query parameters use @Query.", queryParams);
}
}
// 具体的解析继续由parsePathParameters来完成
this.relativeUrl = value;
this.relativeUrlParamNames = parsePathParameters(value);
}这个函数仅是做了一个简单的前期判断，将method对应的请求类型（httpMethod） ，注解值（relativeUrl），以及是否包含实体信息（hasBody）赋值给该RequestFactoryParser;
来看POST和GET的简单调用实例：
parseHttpMethodAndPath("GET", ((GET) annotation).value(), false);
parseHttpMethodAndPath("POST", ((POST) annotation).value(), true);
继续来看解析函数parsePathParameters :
private static final String PARAM = "[a-zA-Z][a-zA-Z0-9_-]*";
private static final Pattern PARAM_NAME_REGEX = Pattern.compile(PARAM);
private static final Pattern PARAM_URL_REGEX = Pattern.compile("\\{(" + PARAM + ")\\}");
/**
* Gets the set of unique path parameters used in the given URI. If a parameter is used twice
* in the URI, it will only show up once in the set.
*/
// 检测出路径中所有{..}的字段，如{user}等，添加到一个Set中（因此不会重复添加）
static Set<String> parsePathParameters(String path) {
Matcher m = PARAM_URL_REGEX.matcher(path);
Set<String> patterns = new LinkedHashSet<>();
while (m.find()) {
patterns.add(m.group(1));
}
return patterns;
}这一步仅是根据正则表达式获取URL中所有{…}类型的数据，添加到patterns这个Set中，然后返回给RequestFactoryParser，对relativeUrlParamNames进行赋值；
第一步解析完毕，来到第二步parseParameters：
private final Method method;
private void parseParameters(Retrofit retrofit) {
Type[] methodParameterTypes = method.getGenericParameterTypes();
// 获取method所有参数中的所有的注解信息
Annotation[][] methodParameterAnnotationArrays = method.getParameterAnnotations();
boolean gotField = false;
boolean gotPart = false;
boolean gotBody = false;
boolean gotPath = false;
boolean gotQuery = false;
boolean gotUrl = false;
int count = methodParameterAnnotationArrays.length;
// 这里是一个重要的类
RequestBuilderAction[] requestBuilderActions = new RequestBuilderAction[count];
for (int i = 0; i < count; i++) {
Type methodParameterType = methodParameterTypes[i];
Annotation[] methodParameterAnnotations = methodParameterAnnotationArrays[i];
if (methodParameterAnnotations != null) {
for (Annotation methodParameterAnnotation : methodParameterAnnotations) {
RequestBuilderAction action = null;
// 解析URL
if (methodParameterAnnotation instanceof Url) {
if (gotUrl) {
throw parameterError(i, "Multiple @Url method annotations found.");
}
if (gotPath) {
throw parameterError(i, "@Path parameters may not be used with @Url.");
}
if (gotQuery) {
throw parameterError(i, "A @Url parameter must not come after a @Query");
}
if (methodParameterType != String.class) {
throw parameterError(i, "@Url must be String type.");
}
if (relativeUrl != null) {
throw parameterError(i, "@Url cannot be used with @%s URL", httpMethod);
}
gotUrl = true;
action = new RequestBuilderAction.Url();
} else if (methodParameterAnnotation instanceof Path) { // 解析Path注解
if (gotQuery) {
throw parameterError(i, "A @Path parameter must not come after a @Query.");
}
if (gotUrl) {
throw parameterError(i, "@Path parameters may not be used with @Url.");
}
if (relativeUrl == null) {
throw parameterError(i, "@Path can only be used with relative url on @%s",
httpMethod);
}
gotPath = true;
Path path = (Path) methodParameterAnnotation;
String name = path.value();
validatePathName(i, name);
action = new RequestBuilderAction.Path(name, path.encoded());
} else if (methodParameterAnnotation instanceof Query) { // 解析Query注解
Query query = (Query) methodParameterAnnotation;
action = new RequestBuilderAction.Query(query.value(), query.encoded());
gotQuery = true;
} else if (methodParameterAnnotation instanceof QueryMap) { // 解析QueryMap注解
if (!Map.class.isAssignableFrom(Utils.getRawType(methodParameterType))) {
throw parameterError(i, "@QueryMap parameter type must be Map.");
}
QueryMap queryMap = (QueryMap) methodParameterAnnotation;
action = new RequestBuilderAction.QueryMap(queryMap.encoded());
} else if (methodParameterAnnotation instanceof Header) { // 解析header注解
Header header = (Header) methodParameterAnnotation;
action = new RequestBuilderAction.Header(header.value());
} else if (methodParameterAnnotation instanceof Field) { // 解析Field注解
if (!isFormEncoded) {
throw parameterError(i, "@Field parameters can only be used with form encoding.");
}
Field field = (Field) methodParameterAnnotation;
action = new RequestBuilderAction.Field(field.value(), field.encoded());
gotField = true;
} else if (methodParameterAnnotation instanceof FieldMap) { // 解析FieldMap
if (!isFormEncoded) {
throw parameterError(i, "@FieldMap parameters can only be used with form encoding.");
}
if (!Map.class.isAssignableFrom(Utils.getRawType(methodParameterType))) {
throw parameterError(i, "@FieldMap parameter type must be Map.");
}
FieldMap fieldMap = (FieldMap) methodParameterAnnotation;
action = new RequestBuilderAction.FieldMap(fieldMap.encoded());
gotField = true;
} else if (methodParameterAnnotation instanceof Part) { // 解析Part
if (!isMultipart) {
throw parameterError(i, "@Part parameters can only be used with multipart encoding.");
}
Part part = (Part) methodParameterAnnotation;
com.squareup.okhttp.Headers headers = com.squareup.okhttp.Headers.of(
"Content-Disposition", "form-data; name=\"" + part.value() + "\"",
"Content-Transfer-Encoding", part.encoding());
Converter<?, RequestBody> converter;
try {
converter =
retrofit.requestConverter(methodParameterType, methodParameterAnnotations);
} catch (RuntimeException e) { // Wide exception range because factories are user code.
throw parameterError(e, i, "Unable to create @Part converter for %s",
methodParameterType);
}
action = new RequestBuilderAction.Part<>(headers, converter);
gotPart = true;
} else if (methodParameterAnnotation instanceof PartMap) { //解析PartMap
if (!isMultipart) {
throw parameterError(i,
"@PartMap parameters can only be used with multipart encoding.");
}
if (!Map.class.isAssignableFrom(Utils.getRawType(methodParameterType))) {
throw parameterError(i, "@PartMap parameter type must be Map.");
}
PartMap partMap = (PartMap) methodParameterAnnotation;
action = new RequestBuilderAction.PartMap(retrofit, partMap.encoding(),
methodParameterAnnotations);
gotPart = true;
} else if (methodParameterAnnotation instanceof Body) { // 解析Body
if (isFormEncoded || isMultipart) {
throw parameterError(i,
"@Body parameters cannot be used with form or multi-part encoding.");
}
if (gotBody) {
throw parameterError(i, "Multiple @Body method annotations found.");
}
Converter<?, RequestBody> converter;
try {
converter =
retrofit.requestConverter(methodParameterType, methodParameterAnnotations);
} catch (RuntimeException e) { // Wide exception range because factories are user code.
throw parameterError(e, i, "Unable to create @Body converter for %s",
methodParameterType);
}
action = new RequestBuilderAction.Body<>(converter);
gotBody = true;
}
if (action != null) {
if (requestBuilderActions[i] != null) {
throw parameterError(i, "Multiple Retrofit annotations found, only one allowed.");
}
requestBuilderActions[i] = action;
}
}
}
if (requestBuilderActions[i] == null) {
throw parameterError(i, "No Retrofit annotation found.");
}
}
if (relativeUrl == null && !gotUrl) {
throw methodError(method, "Missing either @%s URL or @Url parameter.", httpMethod);
}
if (!isFormEncoded && !isMultipart && !hasBody && gotBody) {
throw methodError(method, "Non-body HTTP method cannot contain @Body.");
}
if (isFormEncoded && !gotField) {
throw methodError(method, "Form-encoded method must contain at least one @Field.");
}
if (isMultipart && !gotPart) {
throw methodError(method, "Multipart method must contain at least one @Part.");
}
this.requestBuilderActions = requestBuilderActions;
}这里是根据method里面对应的参数中的注解比如@(Url,Path,Query,QueryMap,Header,Field,FieldMap,Part,PartMap,Body)，它们的解析操作都是通过创建一个RequestBuilderAction类进行相应的解析，比如@Path，解析则调用的是创建一个RequestBuilderAction.Path，Path类是RequestBuilderAction的静态内部类，继承了RequestBuilderAction；最后所有参数中的注解对应一个RequestBuilderAction数组requestBuilderActions，把这个数组赋值给RequestFactoryParser;
abstract class RequestBuilderAction {
abstract void perform(RequestBuilder builder, Object value);
}RequestBuilderAction是个抽象类，它内部有一个perform的抽象方法；还有一些具体的内部类继承该方法，根据不同的注解，来创建不同的静态内部类，这些静态内部类都继承了RequestBuilderAction，并且重写了自己的perform方法；
如Path:
static final class Path extends RequestBuilderAction {
private final String name;
private final boolean encoded;
Path(String name, boolean encoded) {
this.name = checkNotNull(name, "name == null");
this.encoded = encoded;
}
@Override void perform(RequestBuilder builder, Object value) {
if (value == null) {
throw new IllegalArgumentException(
"Path parameter \"" + name + "\" value must not be null.");
}
builder.addPathParam(name, value.toString(), encoded);
}
}可以看到这里涉及到一个 RequestBuilder的概念，等到具体使用的时候再进行分析；
private RequestFactory toRequestFactory(BaseUrl baseUrl) {
return new RequestFactory(httpMethod, baseUrl, relativeUrl, headers, contentType, hasBody,
isFormEncoded, isMultipart, requestBuilderActions);
}最后一步将所有解析完的信息封装成一个 RequestFactory；
则继续来看第（三）步中okHttp创建Call是传递进来的参数：requestFactory.create(args)
final class RequestFactory {
private final String method;
private final BaseUrl baseUrl;
private final String relativeUrl;
private final Headers headers;
private final MediaType contentType;
private final boolean hasBody;
private final boolean isFormEncoded;
private final boolean isMultipart;
private final RequestBuilderAction[] requestBuilderActions;
RequestFactory(String method, BaseUrl baseUrl, String relativeUrl, Headers headers,
MediaType contentType, boolean hasBody, boolean isFormEncoded, boolean isMultipart,
RequestBuilderAction[] requestBuilderActions) {
this.method = method;
this.baseUrl = baseUrl;
this.relativeUrl = relativeUrl;
this.headers = headers;
this.contentType = contentType;
this.hasBody = hasBody;
this.isFormEncoded = isFormEncoded;
this.isMultipart = isMultipart;
this.requestBuilderActions = requestBuilderActions;
}
Request create(Object... args) {
// 创建一个RequestBuilder，它是真正创建Request的类
RequestBuilder requestBuilder =
new RequestBuilder(method, baseUrl.url(), relativeUrl, headers, contentType, hasBody,
isFormEncoded, isMultipart);
if (args != null) {
// 前面解析method参数中的注解获取到的RequestBuilderAction
RequestBuilderAction[] actions = requestBuilderActions;
if (actions.length != args.length) {
throw new IllegalArgumentException("Argument count ("
+ args.length
+ ") doesn‘t match action count ("
+ actions.length
+ ")");
}
for (int i = 0, count = args.length; i < count; i++) {
// 这里调用RequestBuilderAction的perform进行创建
actions[i].perform(requestBuilder, args[i]);
}
}
// 建造者模型，返回一个build
return requestBuilder.build();
}
}可以看到RequestFactory在create时创建了一个RequestBuilder，它是一个典型的Builder模式，也就是类似OkHttp的Request Buidler模式，由用户调用builder自定义来转化为通过注解方式进行定义，而Retrofit通过解析注解信息，分析用户行为，然后将解析信息添加到requestBuidler中来自行构造Request；它暴漏出注解定义的方式，而将具体的Request Builder细节隐藏了。
这里终点来看RequestBuidler，前面分析method参数类型获得的RequestBuilderAction，其具体的perform也是通过RequestBuilderAction来实现的；
final class RequestBuilder {
// 注意这里的Request对应的是okHttp的request
private final Request.Builder requestBuilder;
RequestBuilder(String method, HttpUrl baseUrl, String relativeUrl, Headers headers,
MediaType contentType, boolean hasBody, boolean isFormEncoded, boolean isMultipart) {
this.method = method;
this.baseUrl = baseUrl;
this.relativeUrl = relativeUrl;
this.requestBuilder = new Request.Builder();
this.contentType = contentType;
this.hasBody = hasBody;
if (headers != null) {
requestBuilder.headers(headers);
}
if (isFormEncoded) {
// Will be set to ‘body‘ in ‘build‘.
formEncodingBuilder = new FormEncodingBuilder();
} else if (isMultipart) {
// Will be set to ‘body‘ in ‘build‘.
multipartBuilder = new MultipartBuilder();
multipartBuilder.type(MultipartBuilder.FORM);
}
}
}Retrofit默认是通过okHttp来实现的，RequestBuidler其实将所有Request创建的任务交给真正的类Okhttp中的Request.Builder进行构造器request；相应的FormEncodingBuilder以及MultipartBuilder也都是okHttp内部的；
RequestBuilderAction中的perform也都是通过RequestBuidler的函数来实现的，比如@Path:
static final class Path extends RequestBuilderAction {
private final String name;
private final boolean encoded;
Path(String name, boolean encoded) {
this.name = checkNotNull(name, "name == null");
this.encoded = encoded;
}
@Override void perform(RequestBuilder builder, Object value) {
if (value == null) {
throw new IllegalArgumentException(
"Path parameter \"" + name + "\" value must not be null.");
}
builder.addPathParam(name, value.toString(), encoded);
}
}可以看到调用的RequestBuilder的addPathParam方法：
void addPathParam(String name, String value, boolean encoded) {
if (relativeUrl == null) {
// The relative URL is cleared when the first query parameter is set.
throw new AssertionError();
}
relativeUrl = relativeUrl.replace("{" + name + "}", canonicalize(value, encoded));
}再来看RequestFactory#create的返回值，即RequestBuilder.builder:
Request build() {
HttpUrl url;
HttpUrl.Builder urlBuilder = this.urlBuilder;
if (urlBuilder != null) {
url = urlBuilder.build();
} else {
// No query parameters triggered builder creation, just combine the relative URL and base URL.
url = baseUrl.resolve(relativeUrl);
}
RequestBody body = this.body;
if (body == null) {
// Try to pull from one of the builders.
if (formEncodingBuilder != null) {
body = formEncodingBuilder.build();
} else if (multipartBuilder != null) {
body = multipartBuilder.build();
} else if (hasBody) {
// Body is absent, make an empty body.
body = RequestBody.create(null, new byte[0]);
}
}
MediaType contentType = this.contentType;
if (contentType != null) {
if (body != null) {
body = new ContentTypeOverridingRequestBody(body, contentType);
} else {
requestBuilder.addHeader("Content-Type", contentType.toString());
}
}
return requestBuilder
.url(url)
.method(method, body)
.build();
} 可想而知最后调用的是okHttp总的builder来具体创建一个Request,具体的创建细节见okHttp源码解析；
因此返回的是一个okHttp中的Request；来看具体的创建：
retrofit.client().newCall(requestFactory.create(args));
OkHttpClient#newCall:
/**
* Prepares the {@code request} to be executed at some point in the future.
*/
public Call newCall(Request request) {
return new Call(this, request);
}将Request封装成一个Call；因此，接下来的所有网络请求操作都交由okHttp进行处理；
在调用OkHttpCall的enqueue时，可以看到Callback中会对结果Response(okHttp中的)进行进一步解析，然后将解析后的结果通过Retrofit中定义的callback进行返回，返回的结果为Response:
rawCall.enqueue(new com.squareup.okhttp.Callback() {
private void callFailure(Throwable e) {
try {
callback.onFailure(e);
} catch (Throwable t) {
t.printStackTrace();
}
}
private void callSuccess(Response<T> response) {
try {
callback.onResponse(response, retrofit);
} catch (Throwable t) {
t.printStackTrace();
}
}
@Override public void onFailure(Request request, IOException e) {
callFailure(e);
}
@Override public void onResponse(com.squareup.okhttp.Response rawResponse) {
Response<T> response;
try {
response = parseResponse(rawResponse);
} catch (Throwable e) {
callFailure(e);
return;
}
callSuccess(response);
}
});可以看到主要解析过程则在于parseResponse中；
private Response<T> parseResponse(com.squareup.okhttp.Response rawResponse) throws IOException {
ResponseBody rawBody = rawResponse.body();
// Remove the body‘s source (the only stateful object) so we can pass the response along.
rawResponse = rawResponse.newBuilder()
.body(new NoContentResponseBody(rawBody.contentType(), rawBody.contentLength()))
.build();
int code = rawResponse.code();
// 如果请求失败
if (code < 200 || code >= 300) {
try {
// Buffer the entire body to avoid future I/O.
ResponseBody bufferedBody = Utils.readBodyToBytesIfNecessary(rawBody);
return Response.error(bufferedBody, rawResponse);
} finally {
closeQuietly(rawBody);
}
}
// 没有数据返回情况，则不用进行解析
if (code == 204 || code == 205) {
return Response.success(null, rawResponse);
}
// ExceptionCatchingRequestBody是对okHttp的RequestBody类的一个封装
ExceptionCatchingRequestBody catchingBody = new ExceptionCatchingRequestBody(rawBody);
try {
// 利用变换器进行转换
T body = responseConverter.convert(catchingBody);
// 将转换后的实体结果和原Response封装成一个Response<T>
return Response.success(body, rawResponse);
} catch (RuntimeException e) {
// If the underlying source threw an exception, propagate that rather than indicating it was
// a runtime exception.
catchingBody.throwIfCaught();
throw e;
}
}当请求发生错误，获取204情况没有实体返回时，自然不用对实体进行转化；而对于实体的转换是通过最初定义的转换器来（这里用的是GSON）来进行covert的；然后将转换后的结果同原始okHttp返回的Response封装成一个Response进行返回；
先来看传递进来的转换器：
是通过在build retrofit的时候添加的：
Retrofit retrofit = new Retrofit.Builder()
.baseUrl("http://115.156.187.146/TransferServer/")
.client(client) // 添加okHttp
.addConverterFactory(GsonConverterFactory.create()) // GSON进行转换
.build();
Retrofit#ConverterFactory:
/** Add converter factory for serialization and deserialization of objects. */
public Builder addConverterFactory(Converter.Factory converterFactory) {
converterFactories.add(checkNotNull(converterFactory, "converterFactory == null"));
return this;
}由前面的分析知，在创建MethodHandler时，
static MethodHandler<?> create(Retrofit retrofit, Method method) {
CallAdapter<Object> callAdapter = (CallAdapter<Object>) createCallAdapter(method, retrofit);
Type responseType = callAdapter.responseType();
// 创建转换器
Converter<ResponseBody, Object> responseConverter =
(Converter<ResponseBody, Object>) createResponseConverter(method, retrofit, responseType);
RequestFactory requestFactory = RequestFactoryParser.parse(method, responseType, retrofit);
return new MethodHandler<>(retrofit, requestFactory, callAdapter, responseConverter);
}
private static Converter<ResponseBody, ?> createResponseConverter(Method method,
Retrofit retrofit, Type responseType) {
Annotation[] annotations = method.getAnnotations();
try {
return retrofit.responseConverter(responseType, annotations);
} catch (RuntimeException e) { // Wide exception range because factories are user code.
throw Utils.methodError(e, method, "Unable to create converter for %s", responseType);
}
}进而根据返回数据类型调用Retrofit.responseConverter来创建；下面基本上和CallAdapterFactory基本相同的流程；通过遍历converterFactories链表进行获取相应的解析Converter:
public <T> Converter<ResponseBody, T> responseConverter(Type type, Annotation[] annotations) {
checkNotNull(type, "type == null");
checkNotNull(annotations, "annotations == null");
for (int i = 0, count = converterFactories.size(); i < count; i++) {
// 重点看这个解析函数
Converter<ResponseBody, ?> converter =
converterFactories.get(i).fromResponseBody(type, annotations);
if (converter != null) {
//noinspection unchecked
return (Converter<ResponseBody, T>) converter;
}
}
StringBuilder builder = new StringBuilder("Could not locate ResponseBody converter for ")
.append(type)
.append(". Tried:");
for (Converter.Factory converterFactory : converterFactories) {
builder.append("\n * ").append(converterFactory.getClass().getName());
}
throw new IllegalArgumentException(builder.toString());
}主要的逻辑在：
// 重点看这个解析函数
Converter<ResponseBody, ?> converter =
converterFactories.get(i).fromResponseBody(type, annotations);
这里的converterFactories.get(i)即是通过GsonConverterFactory.create()创建的GSON转换器；来看其具体细节；public final class GsonConverterFactory extends Converter.Factory {
/**
* Create an instance using a default {@link Gson} instance for conversion. Encoding to JSON and
* decoding from JSON (when no charset is specified by a header) will use UTF-8.
*/
public static GsonConverterFactory create() {
return create(new Gson());
}
/**
* Create an instance using {@code gson} for conversion. Encoding to JSON and
* decoding from JSON (when no charset is specified by a header) will use UTF-8.
*/
public static GsonConverterFactory create(Gson gson) {
return new GsonConverterFactory(gson);
}
private final Gson gson;
private GsonConverterFactory(Gson gson) {
if (gson == null) throw new NullPointerException("gson == null");
this.gson = gson;
}
@Override
public Converter<ResponseBody, ?> fromResponseBody(Type type, Annotation[] annotations) {
return new GsonResponseBodyConverter<>(gson, type);
}
@Override public Converter<?, RequestBody> toRequestBody(Type type, Annotation[] annotations) {
return new GsonRequestBodyConverter<>(gson, type);
}
}这个Factory很简单，就是持有了一个GSON实例对象；
上面调用了fromResponseBody，这里根据returntype来创建一个GsonRequestBodyConverter：
final class GsonRequestBodyConverter<T> implements Converter<T, RequestBody> {
private static final MediaType MEDIA_TYPE = MediaType.parse("application/json; charset=UTF-8");
private static final Charset UTF_8 = Charset.forName("UTF-8");
private final Gson gson;
private final Type type;
GsonRequestBodyConverter(Gson gson, Type type) {
this.gson = gson;
this.type = type;
}
@Override
public RequestBody convert(T value) throws IOException {
Buffer buffer = new Buffer();
Writer writer = new OutputStreamWriter(buffer.outputStream(), UTF_8);
try {
gson.toJson(value, type, writer);
writer.flush();
} catch (IOException e) {
throw new AssertionError(e); // Writing to Buffer does no I/O.
}
return RequestBody.create(MEDIA_TYPE, buffer.readByteString());
}
}其转换函数convert逻辑也较为简单，将工作交给gson就可以了；所以Retrofit的解析工作在okHttp的Call返回结果时，在其okHttp的Callback中进行解析，解析过程也较为简单，通过获取返回类型Returntype，然后使用gson进行解析即可；
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原文地址：http://blog.csdn.net/woliuyunyicai/article/details/51479011
