Retrofit 使用例子
下面只展示了异步请求示例
Retrofit retrofit = new Retrofit.Builder()
.baseUrl("https://api.github.com")
.build();
GitHubService service = retrofit.create(GitHubService.class);
service.search().enqueue(new retrofit2.Callback<String>() {
@Override
public void onResponse(retrofit2.Call<String> call, retrofit2.Response<String> response) {
}
@Override
public void onFailure(retrofit2.Call<String> call, Throwable t) {
}
});源码分析
Retrofit 中使用了 OkHttp, 分析到后面就可以看到。
先来看创建 Retrofit 吧：
public Retrofit build() {
// ...
okhttp3.Call.Factory callFactory = this.callFactory;
if (callFactory == null) {
// 创建 callFactory 对象，也就是 Retrofit 的 callFactory.
callFactory = new OkHttpClient();
}
Executor callbackExecutor = this.callbackExecutor;
if (callbackExecutor == null) {
// 创建 callbackExecutor 对象，platform 是 Android 的实例，其 defaultCallbackExecutor 方法返回的是 ExecutorCallAdapterFactory 对象
callbackExecutor = platform.defaultCallbackExecutor();
}
List<CallAdapter.Factory> callAdapterFactories = new ArrayList<>(this.callAdapterFactories);
// 把上面创建的 callbackExecutor 添加到 callAdapterFactories 中
callAdapterFactories.add(platform.defaultCallAdapterFactory(callbackExecutor));
// ...
return new Retrofit(callFactory, baseUrl, unmodifiableList(converterFactories),
unmodifiableList(callAdapterFactories), callbackExecutor, validateEagerly);
}上面代码主要创建了 retrofit 对象，还创建了这几个稍等分析会用到的对象，callFactory、callbackExecutor.
下面接着往下看 retrofit.create 方法，这里使用了代理模式，create 创建的 GitHubService 对象可以调用 search 方法，search 方法的执行就在代理的实现里面，这个就一起分析了。
public <T> T create(final Class<T> service) {
Utils.validateServiceInterface(service);
if (validateEagerly) {
eagerlyValidateMethods(service);
}
// 代理实现, service.search 走的就是这里的 invoke 方法
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, @Nullable 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);
}
// 这里是主要内容
/* 封装 ServiceMethod 对象，创建 ServiceMethod 对象时创建了 callAdapter 实例，callAdapter 是 retrofit.callAdapter(returnType, annotations), 再往里看就是 retrofit 的成员变量 callAdapterFactories.get(i).get(returnType, annotations, this), callAdapterFactories 是在创建 retrofit 时，里面存的是 ExecutorCallAdapterFactory 对象
return new CallAdapter<Object, Call<?>>() {
@Override public Type responseType() {
return responseType;
}
@Override public Call<Object> adapt(Call<Object> call) {
return new ExecutorCallbackCall<>(callbackExecutor, call);
}
};
这就是 ServiceMethod 的 callAdapter 对象
*/
ServiceMethod<Object, Object> serviceMethod =
(ServiceMethod<Object, Object>) loadServiceMethod(method);
// 创建 OkHttpCall
OkHttpCall<Object> okHttpCall = new OkHttpCall<>(serviceMethod, args);
// 其中 callAdapter 在封装 ServiceMethod 对象时创建的，执行的 callAdapter.adapt(call) 返回的就是 new ExecutorCallbackCall<>(callbackExecutor, call)
return serviceMethod.adapt(okHttpCall);
}
});
}可以看到 service.search 返回的是 ExecutorCallbackCall 对象，它的成员变量 delegate 是上面创建的 OkHttpCall 对象，那么接下来的 enqueue 方法就是 ExecutorCallbackCall 的 enqueue 了。
@Override public void enqueue(final Callback<T> callback) {
checkNotNull(callback, "callback == null");
// 主要看下面这一点，delegata.enqueue, delegate 是 OkHttpCall 对象，那接着看下一个 OkHttpCall 的 enqueue 方法把
delegate.enqueue(new Callback<T>() {
@Override public void onResponse(Call<T> call, final Response<T> response) {
callbackExecutor.execute(new Runnable() {
@Override public void run() {
if (delegate.isCanceled()) {
// Emulate OkHttp's behavior of throwing/delivering an IOException on cancellation.
callback.onFailure(ExecutorCallbackCall.this, new IOException("Canceled"));
} else {
callback.onResponse(ExecutorCallbackCall.this, response);
}
}
});
}
@Override public void onFailure(Call<T> call, final Throwable t) {
callbackExecutor.execute(new Runnable() {
@Override public void run() {
callback.onFailure(ExecutorCallbackCall.this, t);
}
});
}
});
}
@Override public void enqueue(final Callback<T> callback) {
checkNotNull(callback, "callback == null");
okhttp3.Call call;
Throwable failure;
synchronized (this) {
if (executed) throw new IllegalStateException("Already executed.");
executed = true;
call = rawCall;
failure = creationFailure;
if (call == null && failure == null) {
try {
// 创建 call 对象，serviceMethod.toCall -> callFactory.newCall(callFactory 就是在最开始创建 retrofit 对象的 OkHttpClient 实例) -> okHttpClient.newCall(这里使用的就是 OkHttp 框架的了) -> RealCall
call = rawCall = createRawCall();
} catch (Throwable t) {
throwIfFatal(t);
failure = creationFailure = t;
}
}
}
if (failure != null) {
callback.onFailure(this, failure);
return;
}
if (canceled) {
call.cancel();
}
// call 是 RealCall 对象，接下来的 enqueue 方法跟分析 OkHttp 的就一样了
call.enqueue(new okhttp3.Callback() {
@Override public void onResponse(okhttp3.Call call, okhttp3.Response rawResponse) {
Response<T> response;
try {
response = parseResponse(rawResponse);
} catch (Throwable e) {
callFailure(e);
return;
}
try {
callback.onResponse(OkHttpCall.this, response);
} catch (Throwable t) {
t.printStackTrace();
}
}
@Override public void onFailure(okhttp3.Call call, IOException e) {
callFailure(e);
}
private void callFailure(Throwable e) {
try {
callback.onFailure(OkHttpCall.this, e);
} catch (Throwable t) {
t.printStackTrace();
}
}
});
}