Retrofit源码分析

Retrofit源码分析

---

前言

retrofit是基于okhttp3的（推荐先看OkHttp3源码解析)，没图说个jb？下面附图一张（感谢这是一份很详细的 Retrofit 2.0 使用教程（含实例讲解）这篇博客友情提供); 接着我会用一个简单的实例，进行源码的分析以及讲解。

实例

1. 导入一些必要的第三方库

   compile 'com.squareup.retrofit2:retrofit:2.3.0'
   compile 'com.squareup.retrofit2:converter-gson:2.3.0'
   compile 'com.squareup.retrofit2:adapter-rxjava2:2.3.0'

2. 接着创建ServiceInterface（动态代理接口）

public interface TestApi {
    @GET("data/福利/{number}/{page}")
    Call getBeauties(@Path("number") int number, @Path("page") int page);
}

3.请求实例

Retrofit retrofit = new Retrofit.Builder()
        .client(new OkHttpClient())
        .baseUrl("http://gank.io/api/")
        .addConverterFactory(GsonConverterFactory.create())
        .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
        .build();
TestApi testApi = retrofit.create(TestApi.class);
Call call = testApi.getBeauties(100, 1);

call.enqueue(new Callback() {
    @Override
    public void onResponse(Call call, Response response) {
        System.out.println("response content:" + response.body().beauties.size());
    }
    @Override
    public void onFailure(Call call, Throwable t) {

    }
});

实例源码分析

初始化retrofit实例

根据实例代码，通过建造者模式创建一个retrofit实例如下；其中baseUrl属性是必须指定的；由1行，Retrofit.Builder()实例方法首先通过Platform的静态方法get()得到Android实例(通过18-57行),然后调用重载方法Builder(Platform);由2-4行，一些参数的赋值；由5行，由60-62行，baseUrl属性是必须指定的；由64-67行，如果没有指定OkHttpClient,那么就创建一个OkhttpClient;由69-72行，通过刚刚得到的Android实例获取callbackExecutor；由75-79行，一些CallAdapter和Converter的保存，最后把上述传入创建Retrofit对象。

Retrofit retrofit = new Retrofit.Builder()
        .baseUrl("http://gank.io/api/")
        .addConverterFactory(GsonConverterFactory.create())
        .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
        .build();

public Builder() {
  this(Platform.get());
}

Builder(Platform platform) {
      this.platform = platform;
      // Add the built-in converter factory first. This prevents overriding its behavior but also
      // ensures correct behavior when using converters that consume all types.
      converterFactories.add(new BuiltInConverters());
}

 static Platform get() {
    return PLATFORM;
  }

private static final Platform PLATFORM = findPlatform();

private static Platform findPlatform() {
    try {
      Class.forName("android.os.Build");
      if (Build.VERSION.SDK_INT != 0) {
        return new Android();
      }
    } catch (ClassNotFoundException ignored) {
    }
    try {
      Class.forName("java.util.Optional");
      return new Java8();
    } catch (ClassNotFoundException ignored) {
    }
    return new Platform();
}

static class Android extends Platform {
    @Override public Executor defaultCallbackExecutor() {
      return new MainThreadExecutor();
    }

    @Override CallAdapter.Factory defaultCallAdapterFactory(@Nullable Executor callbackExecutor) {
      if (callbackExecutor == null) throw new AssertionError();
      return new ExecutorCallAdapterFactory(callbackExecutor);
    }

    static class MainThreadExecutor implements Executor {
      private final Handler handler = new Handler(Looper.getMainLooper());

      @Override public void execute(Runnable r) {
        handler.post(r);
      }
    }
  }

 public Retrofit build() {
      if (baseUrl == null) {
        throw new IllegalStateException("Base URL required.");
      }

      okhttp3.Call.Factory callFactory = this.callFactory;
      if (callFactory == null) {
        callFactory = new OkHttpClient();
      }

      Executor callbackExecutor = this.callbackExecutor;
      if (callbackExecutor == null) {
        callbackExecutor = platform.defaultCallbackExecutor();
      }

      // Make a defensive copy of the adapters and add the default Call adapter.
      List adapterFactories = new ArrayList<>(this.adapterFactories);
      adapterFactories.add(platform.defaultCallAdapterFactory(callbackExecutor));

      // Make a defensive copy of the converters.
      List converterFactories = new ArrayList<>(this.converterFactories);

      return new Retrofit(callFactory, baseUrl, converterFactories, adapterFactories,
          callbackExecutor, validateEagerly);
}

代理代理(接口的代理)

由1行，通过动态代理，生成代理对象testApi; 动态代理的原理自行Google，当调用该代理对象的方法时，会执行内部匿名类InvocationHandler的invoke(…)方法。
由30行，我们看invoke方法里面，由16-21行，一些必要的拦截；由22行，通过loadServiceMethod（method)方法获取ServiceMethod对象；由32-44行，该方法通过Map

TestApi testApi = retrofit.create(TestApi.class);

public  T create(final Class 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, 
          @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);
            }
            ServiceMethod serviceMethod =
                (ServiceMethod) loadServiceMethod(method);
            OkHttpCall