Android - retrofit 源码分析

一. retrofit的简单使用

先看下涉及到的类:

首先定义个接口ApiService,所有的请求方法的定义.

public interface ApiService {

    @POST("doPost")
    Call doPost(@Query("name") String name,
                              @Query("email") String e
    );

    @GET("doGet")
    Call doGet(@Query("name") String name,
               @Query("age") int age
    );
}

对retrofit的配置类,不建议每次都去创建retrofit的实例. OkHttpClient 也要保证整个工程只有一个实例,官方推荐也是这么做的.

/**
 * Created by CaiRR on 2017-10-25.
 */

public class ApiClient {
    private static OkHttpClient mOkHttpClient = null;
    private static Retrofit mRetrofit;
    private static ApiService mApiService;
    private static final boolean isDebug = true;
    private static final String HTTP_BASE_URL = "http://192.168.6.21:9090";

    public static ApiClient getInstance() {
        return SingletonHolder.INSTANCE;
    }

    private static class SingletonHolder {
        private static final ApiClient INSTANCE = new ApiClient();
    }

    private ApiClient() {
        initOkHttpClient();
        mRetrofit = new Retrofit.Builder()
                .baseUrl(HTTP_BASE_URL)
                //设置 Json 转换器
                .addConverterFactory(GsonConverterFactory.create())
                .client(mOkHttpClient)
                .build();
        mApiService = mRetrofit.create(ApiService.class);
    }

    private void initOkHttpClient() {
        OkHttpClient.Builder builder = new OkHttpClient.Builder();
        if (isDebug) {
            // Log信息拦截器
            HttpLoggingInterceptor loggingInterceptor = new HttpLoggingInterceptor();
            loggingInterceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
            //设置 Debug Log 模式
            builder.addInterceptor(loggingInterceptor);
        }
        //设置超时
        builder.connectTimeout(15, TimeUnit.SECONDS);
        builder.readTimeout(60, TimeUnit.SECONDS);
        builder.writeTimeout(60, TimeUnit.SECONDS);
        //错误重连
        builder.retryOnConnectionFailure(true);
        mOkHttpClient = builder.build();
    }

    public ApiService getApiService() {
        return mApiService;
    }

    public OkHttpClient getOkhttpClient() {
        if (mOkHttpClient == null) {
            initOkHttpClient();
        }
        return mOkHttpClient;
    }

}

在这里简单的使用 post 和 get 请求,分别用同步和异步的形式.

public class TestRetrofitActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_test_retrofit);

        findViewById(R.id.btn_get).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                doGet();
            }
        });


        findViewById(R.id.btn_post).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                doPost();
            }
        });
    }

    private void doPost() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Response response = ApiClient.getInstance().getApiService().doPost("xiaocai", "[email protected]").execute();
                    String data = response.body().string();
                    Log.d("xiaocai", data);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }

    private void doGet() {
        ApiClient.getInstance().getApiService().doGet("xiaocai", 25).enqueue(new Callback() {
            @Override
            public void onResponse(Call call, Response response) {
                try {
                    String data = response.body().string();
                    Log.d("xiaocai", data);
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

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

    }
}

在spring boot中简单的做下处理:

@RestController
public class HelloController {
    private final static org.slf4j.Logger log = LoggerFactory.getLogger("xiaocai");

    @RequestMapping("/sayHello")
    public String sayHello() {
        return JsonHelper.success("hello world");
    }

    @GetMapping("/doGet")
    public String testGet(@RequestParam(value = "name") String name,
                          @RequestParam(value = "age", required = false) int age) {
        String data = "name:" + name + " age:" + age;
        log.debug(data);
        return JsonHelper.success(data);
    }

    @PostMapping("/doPost")
    public String testPost(@RequestParam(value = "name") String name,
                          @RequestParam(value = "email", required = false) String email) {
        String data = "name:" + name + " email:" + email;
        log.debug(data);
        return JsonHelper.success(data);
    }
}

日志输出:

 // post 请求
 D/OkHttp: --> POST http://192.168.6.21:9090/[email protected] http/1.1
 D/OkHttp: Content-Length: 0
 D/OkHttp: --> END POST (0-byte body)
 D/OkHttp: <-- 200  http://192.168.6.21:9090/[email protected] (31ms)
 D/OkHttp: Content-Type: text/plain;charset=UTF-8
 D/OkHttp: Content-Length: 82
 D/OkHttp: Date: Wed, 25 Oct 2017 07:43:47 GMT
 D/OkHttp: {"msg":"成功","code":0,"data":"name:xiaocai email:[email protected]","status":"0"}
 D/OkHttp: <-- END HTTP (82-byte body)
 D/xiaocai: {"msg":"成功","code":0,"data":"name:xiaocai email:[email protected]","status":"0"}
 
 // get 请求
 D/OkHttp: --> GET http://192.168.6.21:9090/get?name=xiaocai&age=25 http/1.1
 D/OkHttp: --> END GET
 D/OkHttp: <-- 200  http://192.168.6.21:9090/get?name=xiaocai&age=25 (18ms)
 D/OkHttp: Content-Type: text/plain;charset=UTF-8
 D/OkHttp: Content-Length: 67
 D/OkHttp: Date: Wed, 25 Oct 2017 07:44:13 GMT
 D/OkHttp: {"msg":"成功","code":0,"data":"name:xiaocai age:25","status":"0"}
 D/OkHttp: <-- END HTTP (67-byte body)
 D/xiaocai: {"msg":"成功","code":0,"data":"name:xiaocai age:25","status":"0"}

整个过程还是比较清爽的.

其他的使用方式可以直接看官网的说明:
retrofit的使用

二. 源码分析

我们在使用 retrofit 的时候,基本上都会:

  mRetrofit = new Retrofit.Builder()
          .baseUrl(HTTP_BASE_URL)
          //设置 Json 转换器
          .addConverterFactory(GsonConverterFactory.create())
          .client(mOkHttpClient)
          .build();
  mApiService = mRetrofit.create(ApiService.class);

从 create 方法作为入口进行分析:

  public  T create(final Class service) {
    Utils.validateServiceInterface(service); // 校验是否为接口且不能继承接口
    if (validateEagerly) {
      eagerlyValidateMethods(service); 
    }
    // 使用动态代理
    return (T) Proxy.newProxyInstance(service.getClassLoader(), new Class[] { service },
        new InvocationHandler() {
          private final Platform platform = Platform.get();

          // 每次请求都会走(执行方法)
          @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) { // 校验
              return method.invoke(this, args);
            }
            if (platform.isDefaultMethod(method)) { // 校验平台
              return platform.invokeDefaultMethod(method, service, proxy, args);
            }
            
            // 处理接口中定义的方法,serviceMethod解析注解
            ServiceMethod serviceMethod =
                (ServiceMethod) loadServiceMethod(method);
            // args 是具体的参数值
            OkHttpCall