网络请求框架：Retrofit

Retrofit的使用

1. 定义
   Retrofit可以通过接口方法注解的方式完成Http请求。
2. 实现方法
   第一步：定义一个接口，接口中包含请求的方法，通过使用注解，将请求进行描述。
   第二步：通过Retrofit.Builder完成Retrofit对象的实例化。
   第三步：通过Retrofit对象的create方法传入接口的方式，完成接口的实例化。
   第四步：通过接口对象调用相应的方法，完成网络的请求。
3. 示例

第一步：public interface ServerApi{    @GET("/square/okhttp/master/README.md")    Call<ResponseBody> getOkHttpReadMeMessage();}第二步： Retrofit retrofit = new Retrofit.Builder()     .baseUrl("https://raw.github.com")     .addConverterFactory(GsonConverterFactory.create())     .build();第三步：    ServerApi serverApi = retrofit.create(ServerApi.class);第四步：    serverApi.getOkHttpReadMeMessage().enqueue(new retrofit2.Callback<ResponseBody>() {            @Override            public void onResponse(retrofit2.Call<ResponseBody> call,    retrofit2.Response<ResponseBody> response) {            }            @Override            public void onFailure(retrofit2.Call<ResponseBody> call, Throwable t) {            }        });    };

Important Notice：
1）addConverterFactory（Converter.Factory factory）
2）addCallAdapterFactory(CallAdapter.Factory factory)

注意上述示例的返回类型：Call，这是默认情况下的返回结果，Call是Retofit的请求和响应的类型，ResponseBody代表成功请求后的响应体。

比较常用的转换如下：
.addCallAdapterFactory(RxJavaCallAdapterFactory.create())
.addConverterFactory(GsonConverterFactory.create());

These are called call adapters, and Retrofit includes a few first-party modules for popular frameworks:

RxJava Observable & Single - com.squareup.retrofit2:adapter-rxjava
Guava ListenableFuture - com.squareup.retrofit2:adapter-guava
Java 8 CompleteableFuture - com.squareup.retrofit2:adapter-java8

Various third-party adapters have been created by the community for other libraries:
Bolts
Agera

These are called converters, and Retrofit includes a few first-party modules for popular frameworks:

Gson - com.squareup.retrofit2:converter-gson
Jackson - com.squareup.retrofit2:converter-jackson
Moshi - com.squareup.retrofit2:converter-moshi
Protobuf - com.squareup.retrofit2:converter-protobuf
Wire - com.squareup.retrofit2:converter-wire
Simple Framework - com.squareup.retrofit2:converter-simpleframework
Scalars - com.squareup.retrofit2:converter-scalars
Various third-party converters have been created by the community for other libraries and serialization formats:

LoganSquare - com.github.aurae.retrofit2:converter-logansquare
FastJson - org.ligboy.retrofit2:converter-fastjson or org.ligboy.retrofit2:converter-fastjson-android

3）baseUrl(String baseUrl)中的baseUrl+endpoint的组合规则，注意加粗部分

BaseUrl: http://example.com/api/
EndPoint: foot/bar/
Result : http://example.com/api/foot/bar/

BaseUrl:http://example.com/api/
EndPoint: /foot/bar/
Result : http://example.com/foot/bar/

BaseUrl: http://example.com/
EndPoint:/foot/bar
Result:http://example.com/foot/bar

BaseUrl:http://example.com/
EndPoint:https://github.com/suqare/retrofit/
Result:https://github.com/suqare/retrofit/

BaseUrl:**http://**example.com
EndPoint://github.com/square/retrofit/
Result:http://github.com/square/retrofit/