Retrofit源码分析

川长思鸟来 2022-05-27 09:49 201阅读 0赞

# Retrofit源码分析 #

--------------------

# 前言 #

> retrofit是基于okhttp3的[（推荐先看OkHttp3源码解析)][OkHttp3]，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。  
> ![这里写图片描述][70]

# 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<GankBeautyResult> 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<GankBeautyResult> call = testApi.getBeauties(100, 1);
    
    call.enqueue(new Callback<GankBeautyResult>() {
        @Override
        public void onResponse(Call<GankBeautyResult> call, Response<GankBeautyResult> 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<CallAdapter.Factory> adapterFactories = new ArrayList<>(this.adapterFactories);
          adapterFactories.add(platform.defaultCallAdapterFactory(callbackExecutor));
    
          // Make a defensive copy of the converters.
          List<Converter.Factory> 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> 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, 
              @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<Object, Object> serviceMethod =
                    (ServiceMethod<Object, Object>) loadServiceMethod(method);
                OkHttpCall<Object> okHttpCall = new OkHttpCall<>(serviceMethod, args);
                return serviceMethod.callAdapter.adapt(okHttpCall);
              }
            });
      }
    
      Call<GankBeautyResult> call = testApi.getBeauties(100, 1);
    
      ServiceMethod<?, ?> loadServiceMethod(Method method) {
            ServiceMethod<?, ?> result = serviceMethodCache.get(method);
            if (result != null) return result;
    
            synchronized (serviceMethodCache) {
              result = serviceMethodCache.get(method);
              if (result == null) {
                result = new ServiceMethod.Builder<>(this, method).build();
                serviceMethodCache.put(method, result);
              }
            }
            return result;
      }
    
      Builder(Retrofit retrofit, Method method) {
          this.retrofit = retrofit;
          this.method = method;
          this.methodAnnotations = method.getAnnotations();
          this.parameterTypes = method.getGenericParameterTypes();
          this.parameterAnnotationsArray = method.getParameterAnnotations();
        }
    
        public ServiceMethod build() {
          callAdapter = createCallAdapter();
          responseType = callAdapter.responseType();
          if (responseType == Response.class || responseType == okhttp3.Response.class) {
            throw methodError("'"
                + Utils.getRawType(responseType).getName()
                + "' is not a valid response body type. Did you mean ResponseBody?");
          }
          responseConverter = createResponseConverter();
    
          for (Annotation annotation : methodAnnotations) {
            parseMethodAnnotation(annotation);
          }
    
          if (httpMethod == null) {
            throw methodError("HTTP method annotation is required (e.g., @GET, @POST, etc.).");
          }
    
          if (!hasBody) {
            if (isMultipart) {
              throw methodError(
                  "Multipart can only be specified on HTTP methods with request body (e.g., @POST).");
            }
            if (isFormEncoded) {
              throw methodError("FormUrlEncoded can only be specified on HTTP methods with "
                  + "request body (e.g., @POST).");
            }
          }
    
          int parameterCount = parameterAnnotationsArray.length;
          parameterHandlers = new ParameterHandler<?>[parameterCount];
          for (int p = 0; p < parameterCount; p++) {
            Type parameterType = parameterTypes[p];
            if (Utils.hasUnresolvableType(parameterType)) {
              throw parameterError(p, "Parameter type must not include a type variable or wildcard: %s",
                  parameterType);
            }
    
            Annotation[] parameterAnnotations = parameterAnnotationsArray[p];
            if (parameterAnnotations == null) {
              throw parameterError(p, "No Retrofit annotation found.");
            }
    
            parameterHandlers[p] = parseParameter(p, parameterType, parameterAnnotations);
          }
    
          if (relativeUrl == null && !gotUrl) {
            throw methodError("Missing either @%s URL or @Url parameter.", httpMethod);
          }
          if (!isFormEncoded && !isMultipart && !hasBody && gotBody) {
            throw methodError("Non-body HTTP method cannot contain @Body.");
          }
          if (isFormEncoded && !gotField) {
            throw methodError("Form-encoded method must contain at least one @Field.");
          }
          if (isMultipart && !gotPart) {
            throw methodError("Multipart method must contain at least one @Part.");
          }
    
          return new ServiceMethod<>(this);
        }
    
         @Override public Call<Object> adapt(Call<Object> call) {
            return new ExecutorCallbackCall<>(callbackExecutor, call);
         }

## 进行请求 ##

> 由上，call为ExecutorCallbackCall对象，由14行，传入一个接口调用delegate.enqueue(callback)这里的delegate是OkHttpCall对象；由38-71行，我们看OkHttpCall.enqueue(final Callback callback)方法，由40-43行，是不是很熟悉？是的这里就是开始调用OkHttp3了[（推荐看OkHttp3源码解析)][OkHttp3]通过request和OkHttpClient创建okhttp3.Call对象；由49行，这里就是调用Okhttp3异步请求，我们直接看onResponse回调方法是怎么处理的；由54行，通过parseResponse(okhttp3.Response)中body通过serviceMethod.toResponse(catchingBody)处理成对应的实例body；然后将该body跟okhttp3.Response一起封装成retrofit的Response对象；由59行，通过callSuccess(Response response)最终回调结果；由15-25行，ExecutorCallbackCall.enqueue方法的callback接口的onResponse回调方法收到对应的结果，这里会通过callbackExecutor切换到ui主线程执行用户传入的接口回调方法；callbackExecutor为MainThreadExecutor对象(上面有提到，你可以往上翻）该对象通过execute(runnable)继而通过方法里的 handler.post(r)切换到了主线程。（handler创建的时候是指定了主线程looper)->[(你可以看看Handler消息机制以及源码分析Handle Looper MessageQueue)][Handler_Handle Looper MessageQueue]

call.enqueue(new Callback<GankBeautyResult>() {
            @Override
            public void onResponse(Call<GankBeautyResult> call, Response<GankBeautyResult> response) {
                System.out.println("response content:" + response.body().beauties.size());
            }
            @Override
            public void onFailure(Call call, Throwable t) {
    
            }
    });
    
     @Override public void enqueue(final Callback<T> callback) {
          checkNotNull(callback, "callback == null");
          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;
        ...
            try {
              call = rawCall = createRawCall();
            } catch (Throwable t) {
              failure = creationFailure = t;
            }
         ....
    
        call.enqueue(new okhttp3.Callback() {
          @Override public void onResponse(okhttp3.Call call, okhttp3.Response rawResponse)
              throws IOException {
            Response<T> response;
            try {
              response = parseResponse(rawResponse);
            } catch (Throwable e) {
              callFailure(e);
              return;
            }
            callSuccess(response);
          }
    
          @Override public void onFailure(okhttp3.Call call, IOException e) {
            try {
              callback.onFailure(OkHttpCall.this, e);
            } catch (Throwable t) {
              t.printStackTrace();
            }
          }
        .....
        });
      }

[OkHttp3]: https://blog.csdn.net/yang_yang1994/article/details/79857629
[70]: /images/20220527/f30c951c668b4793ada83c9705e59345.png
[Handler_Handle Looper MessageQueue]: https://blog.csdn.net/yang_yang1994/article/details/79018552