Retrofit2源码学习之Retrofit

综述

Retrofit采用Builder模式构建

类图 来源[第一篇:Retrofit主要类UML图](http://www.cnblogs.com/wlrhnh/p/5466928.html)

源码研究

Retrofit类的源码本身比较简单，简单分析下build()和create（）两个主要方法

build()

build是构建一个Retrofit实例的方法

public Retrofit build() {
      //baseUrl判空处理
      if (baseUrl == null) {
        throw new IllegalStateException("Base URL required.");
      }
      //加载Call，可以用client(OkHttpClient client)替换默认Call
      okhttp3.Call.Factory callFactory = this.callFactory;
      if (callFactory == null) {
        callFactory = new OkHttpClient();
      }
    
      Executor callbackExecutor = this.callbackExecutor;
      if (callbackExecutor == null) {
        //默认callbackExecutor在Platform中实现 
        //Android对应的就是MainThreadExecutor
        callbackExecutor = platform.defaultCallbackExecutor();
      }

      // Make a defensive copy of the adapters and add the default Call adapter.
      List adapterFactories = new ArrayList<>(this.adapterFactories);
      //添加默认的CallAdapter
      //Android平台默认ExecutorCallAdapterFactory   
      adapterFactories.add(platform.defaultCallAdapterFactory(callbackExecutor));

      // Make a defensive copy of the converters.
      //添加用户自定义Converter.Factory
      List converterFactories = new ArrayList<>(this.converterFactories);
      
      return new Retrofit(callFactory, baseUrl, converterFactories, adapterFactories,
          callbackExecutor, validateEagerly);
    }

create()

create用于创建用户定义的ApiService动态代理对象

  public  T create(final Class service) {
    //判断是否合法的service
    Utils.validateServiceInterface(service);
    //是否在调用ApiService具体方法前提前创建ServiceMethod
    //一般用于在ApiService调用方法时不需要传递参数的Service，默认为false
    if (validateEagerly) {
      eagerlyValidateMethods(service);
    }
    //返回动态代理对象
    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);
            }
            //将service中的注释适配成URL组件
            ServiceMethod serviceMethod =
                (ServiceMethod) loadServiceMethod(method);
            //用serviceMethod 创建转化OKHttpCall
            OkHttpCall