Retrofit源码分析

一.分析源码的基本姿势

阅读源码.png

抽茧剥丝看本质

网络请求流程.png

二.Retrofit是什么，有哪些API，有什么好处(what)
1.先看Retrofit的文档 https://square.github.io/retrofit/
A type-safe HTTP client for Android and Java 这里看这个 type-safe，Retrofit通过泛型来约束我们想要的对象，自己不用去解析数据
例子：

public class MainActivity extends AppCompatActivity {
    private TextView textView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textView = findViewById(R.id.text_content);

    }

    public void getHtttp(View view) {

        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("http://gank.io/")
                .addConverterFactory(GsonConverterFactory.create())
                .build();
        GitHubService gitHubService = retrofit.create(GitHubService.class);
        Call>> call = gitHubService.defautBenefits(20, 1);
        call.enqueue(new Callback>>() {
            @Override
            public void onResponse(Call>> call, Response>> response) {
                textView.setText(response.body().results.get(0).getDesc());
            }

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

            }
        });

    }
}

public interface GitHubService {

    @GET("api/data/福利/{pageCount}/{pageIndex}")
    Call>> defautBenefits(
            @Path("pageCount") int pageCount,

            @Path("pageIndex") int pageIndex
    );
}

public class BaseModel {

    public boolean error;
    public T results;
}

public class Benefit {


    /**
     * _id : 5a8e0c41421aa9133298a259
     * createdAt : 2018-02-22T08:18:09.547Z
     * desc : 2-22
     * publishedAt : 2018-02-22T08:24:35.209Z
     * source : chrome
     * type : 福利
     * url : https://ws1.sinaimg.cn/large/610dc034ly1foowtrkpvkj20sg0izdkx.jpg
     * used : true
     * who : 代码家
     */

    private String _id;
    private String createdAt;
    private String desc;
    private String publishedAt;
    private String source;
    private String type;
    private String url;
    private boolean used;
    private String who;

    public String get_id() {
        return _id;
    }

    public void set_id(String _id) {
        this._id = _id;
    }

    public String getCreatedAt() {
        return createdAt;
    }

    public void setCreatedAt(String createdAt) {
        this.createdAt = createdAt;
    }

    public String getDesc() {
        return desc;
    }

    public void setDesc(String desc) {
        this.desc = desc;
    }

    public String getPublishedAt() {
        return publishedAt;
    }

    public void setPublishedAt(String publishedAt) {
        this.publishedAt = publishedAt;
    }

    public String getSource() {
        return source;
    }

    public void setSource(String source) {
        this.source = source;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

    public boolean isUsed() {
        return used;
    }

    public void setUsed(boolean used) {
        this.used = used;
    }

    public String getWho() {
        return who;
    }

    public void setWho(String who) {
        this.who = who;
    }
}

三.debug拎出主线逻辑(how)
debug！debug！debug！

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

retrofit 通过Builder模式来创建，先看看build（）方法

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

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

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

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

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

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

  1.这里先判断callFactory 是否为空，如果为空，则new一个OkHttpClient，那为什么callFactory 只判断是否为空，没有判断callFactory的值呢？这里的工厂模式已经没有意义了，显而易见，Retrofit现在只支持OkHttpClient，不支持HttpClient和HttpConnection
  2.如果没有给我传入Executor ，这里new一个Executor

 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);
      }
    }
  }

在MainThreadExecutor 中，我们声明了一个Handler，创建时我们传入了Looper.getMainLooper()，这里Handler在主线程中运行，execute（）方法也在主线程中执行。
  3.把封装的Call转换成我们想要的Call对象（适配器模式）
  4.converterFactories断点调试可以看出是GsonConvertFactory
最后构建成一个Retrofit。
再看看retrofit.create（），创建一个实现类，看看怎么弄的

public  T create(final Class service) {
    Utils.validateServiceInterface(service);
    if (validateEagerly) {
      eagerlyValidateMethods(service);
    }
//动态代理模式
    return (T) Proxy.newProxyInstance(service.getClassLoader(), new Class[] { service },
        new InvocationHandler() {
          private final Platform platform = Platform.get();
//当调用api方法时，就会触发invoke
          @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);
            }
//通过对注解的处理转换成我们想要的参数
//dapts an invocation of an interface method into an HTTP call. 
//例如：pageCount=20  pageIndex=1  
            ServiceMethod serviceMethod =
                (ServiceMethod) loadServiceMethod(method);
//转换成OkHttpCall
            OkHttpCall