Retrofit2源码阅读

声明:本文章基于retrofit:2.3.0

一.Retrofit2中类的介绍

1.retrofit2/http包下的注解 Retrofit2大都是用于构造请求的, 这些注解可以分为三类 :"Http请求方法类","标记类","参数类",具体会在三中描述

2.Call:(接口)类似于OKHttp的Call就是对一个请求的封装,我们一般在接口文件中定义的方法其返回值就是Call 类型.

3.CallAdapter:(接口其中有一个抽象内部类Factory):用于对Call进行操作,包装的类,Retrofit2提供了很多CallAdapter在五中会有描述

4.DefaultCallAdapterFactory:是对CallAdapter.Factory的实现

5.Converter:(接口其中有一个抽象内部类Factory)用于转换数据,如将请求网络返回的Response转换成我们需要的javaBean,Retrofit2提供了很多Converter在四中会有描述.当然不仅仅是针对返回的数据，还能用于一般备注解的参数的转化例如@Body标识的对象做一些操作

6.BuiltInConverters:(实现了Converter.Factory) 是Retrofit2中Converter的默认实现

7.Platform:Android,java8等平台信息的封装,可获取平台信息,并且每个平台都有对应的回调接口,比如Android平台就会具有回调到主线程的接口.

8.ServiceMethod:从接口方法到Http请求(OKHttp的Call)的转换器,也是使用的构造器模式.

二.对最简单的Retrofit2访问网络的代码进行源码阅读

    //配置Retrofit,并获取Retrofit实例
    Retrofit.Builder builder = new Retrofit.Builder();
    builder .addConverterFactory(GsonConverterFactory.create());
    builder .baseUrl("http://www.ccholterserver.com:44444/");
    Retrofit retrofit =builder .build();
    //获取接口实例
    RetrofitDemo retrofitDemo = retrofit.create(RetrofitDemo.class);
    Call call = retrofitDemo.getImage();
    //执行请求
    call.enqueue(new Callback() {
        @Override
        public void onResponse(Call call, Response response) {
            ResponseBody body = response.body();
            try {
                Log.e("MainActivity", body.string());
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        @Override
        public void onFailure(Call call, Throwable t) {}
    });

1.在执行第一句代码创建Retrofit.Builder的时候

Retrofit.Builder builder = new Retrofit.Builder();

系统首先会调用Platform.get()判断当前的平台是什么,

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

然后对平台信息进行记录,并为Retrofit2添加一个默认的ConverterFactory(转换器)

Builder(Platform platform) {
  this.platform = platform;
  converterFactories.add(new BuiltInConverters());
}

在Retrofit中有一个存储ConverterFactory的集合

private final List converterFactories = new ArrayList<>();

2.第二句第三句代码是对Retrofit.Builder进行配置

 builder .addConverterFactory(GsonConverterFactory.create());
 builder .baseUrl("http://www.ccholterserver.com:44444/");

在执行 builder .addConverterFactory(GsonConverterFactory.create());的时候也就是给converterFactories 集合中再添加了一个ConverterFactory.

/** Add converter factory for serialization and deserialization of objects. */
public Builder addConverterFactory(Converter.Factory factory) {
  converterFactories.add(checkNotNull(factory, "factory == null"));
  return this;
}

在执行builder .baseUrl("http://www.ccholterserver.com:44444/");这句代码的时候首先会对baseUrl进行检查,如果没有问题则转换为HttpUrl然后进行记录到Builder中

public Builder baseUrl(String baseUrl) {
  //检查baseUrl 是否为null
  checkNotNull(baseUrl, "baseUrl == null");
  //将String型的baseUrl转换成HttpUrl
  HttpUrl httpUrl = HttpUrl.parse(baseUrl);
  if (httpUrl == null) {
    throw new IllegalArgumentException("Illegal URL: " + baseUrl);
  }
  return baseUrl(httpUrl);
}

public Builder baseUrl(HttpUrl baseUrl) {
  //检查baseUrl 
  checkNotNull(baseUrl, "baseUrl == null");
  List pathSegments = baseUrl.pathSegments();
  if (!"".equals(pathSegments.get(pathSegments.size() - 1))) {
    throw new IllegalArgumentException("baseUrl must end in /: " + baseUrl);
  }
  //对baseUrl 进行记录
  this.baseUrl = baseUrl;
  return this;
}

3.第四句代码** Retrofit retrofit =builder .build();**执行了builder.build()方法,这个就是创建一个Retrofit然后将builder记录的数据传递给Retrofit.

public Retrofit build() {
  //如果baseUrl 为空 就抛异常
  if (baseUrl == null) {
    throw new IllegalStateException("Base URL required.");
  }

  //如果用户没有设置OkHttpClient的话,Retrofit会自己创建一个        
  //OkHttpClient对象
  okhttp3.Call.Factory callFactory = this.callFactory;
  if (callFactory == null) {
    callFactory = new OkHttpClient();
  }
  
  //如果用户没有设置callbackExecutor,那么Retrofit就会将该平台默认    
  //的Executor设置给自己
  Executor callbackExecutor = this.callbackExecutor;
  if (callbackExecutor == null) {
    callbackExecutor = platform.defaultCallbackExecutor();
  }

  // 将用户设置的CallAdapter.Factory进行拷贝并添加该平台默认的
  //CallAdapter.Factory
  List adapterFactories = new ArrayList<>(this.adapterFactories);
  adapterFactories.add(platform.defaultCallAdapterFactory(callbackExecutor));

  // 将用户设置的Converter.Factory进行拷贝,默认的Converter.Factory
  //已经在创建Builder的时候设置了
  List converterFactories = new ArrayList<>(this.converterFactories);

  //创建一个Retrofit实例,并返回
  return new Retrofit(callFactory, baseUrl, converterFactories, adapterFactories,
      callbackExecutor, validateEagerly);
}


//在创建Retrofit实例的时候其实也没有做其他的事情,只是将从Builder中传
//递过来的参数进行了记录

Retrofit(okhttp3.Call.Factory callFactory, HttpUrl baseUrl, List converterFactories, List adapterFactories,
  @Nullable Executor callbackExecutor, boolean validateEagerly) {
this.callFactory = callFactory;
this.baseUrl = baseUrl;
this.converterFactories = unmodifiableList(converterFactories); // Defensive copy at call site.
this.adapterFactories = unmodifiableList(adapterFactories); // Defensive copy at call site.
this.callbackExecutor = callbackExecutor;
this.validateEagerly = validateEagerly;
}

4.下面执行的第五局代码** RetrofitDemo retrofitDemo = retrofit.create(RetrofitDemo.class);**就是通过Retrofit实例将我们写url的接口文件进行实例化.其实里面是通过动态代理来对接口进行实例化,然后在调用接口中方法的时候都会先调用代理中InvocationHandler中的invoke()方法.

 public  T create(final Class service) {
//对传入的interface进行检查
Utils.validateServiceInterface(service);
//如果我们设置了validateEagerly为true,那么Retrofit就会提前检查传入  
//Interface中的方法
if (validateEagerly) {
  eagerlyValidateMethods(service);
}
//返回传入interface的实例
return (T) Proxy.newProxyInstance(service.getClassLoader(), new Class[] { service },
    new InvocationHandler() {
      //获取平台信息
      private final Platform platform = Platform.get();

      @Override public Object invoke(Object proxy, Method method, @Nullable Object[] args)
          throws Throwable {
        //如果传入的method是object的中定义的方法那就直接执行
        if (method.getDeclaringClass() == Object.class) {
          return method.invoke(this, args);
        }
        //isDefaultMethod()这个方法其实只是对java8平台上的有效,Android平台上直接返回的是false
        if (platform.isDefaultMethod(method)) {
          return platform.invokeDefaultMethod(method, service, proxy, args);
        }
        
        //将接口中定义的方法封装成ServiceMethod,其实也就是获取到接口中方法的注解,和参数来进行转换
        ServiceMethod serviceMethod =
            (ServiceMethod) loadServiceMethod(method);
      
        //将ServiceMethod再次封装成OkHttpCall(实现了Retrofit的Call接口)
        OkHttpCall