Retrofit简单解析

一：Retrofit用法

支持基本的HTTP请求
主要用法：
(1)一般的Get请求

public interface IUserBiz
{
    @GET("users")
    Call<List<User>> getUsers();
}

Retrofit retrofit = new Retrofit.Builder()
        .baseUrl("http://192.168.31.242:8080/springmvc_users/user/")
        .addConverterFactory(GsonConverterFactory.create())
        .build();
IUserBiz userBiz = retrofit.create(IUserBiz.class);
Call<List<User>> call = userBiz.getUsers();
        call.enqueue(new Callback<List<User>>()
        {
            @Override
            public void onResponse(Call<List<User>> call, Response<List<User>> response)
            {
                Log.e(TAG, "normalGet:" + response.body() + "");
            }

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

            }
        });

(2)动态Url访问(@Path)

/用于访问zhy的信息
http://192.168.1.102:8080/springmvc_users/user/zhy
//用于访问lmj的信息
http://192.168.1.102:8080/springmvc_users/user/lmj

public interface IUserBiz
{
    @GET("{username}")
    Call<User> getUser(@Path("username") String username);
}

//省略了retrofit的构建代码
Call<User> call = userBiz.getUser("zhy");
//Call<User> call = userBiz.getUser("lmj");
call.enqueue(new Callback<User>()
{

    @Override
    public void onResponse(Call<User> call, Response<User> response)
    {
        Log.e(TAG, "getUsePath:" + response.body());
    }

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

    }
});

(3)查询参数设置(@Query)

http://baseurl/users?sortby=username
http://baseurl/users?sortby=id

public interface IUserBiz
{
    @GET("users")
    Call<List<User>> getUsersBySort(@Query("sortby") String sort);
}

//省略retrofit的构建代码
Call<List<User>> call = userBiz.getUsersBySort("username");
//Call<List<User>> call = userBiz.getUsersBySort("id");
//省略call执行相关代码

(4)Post请求体的方式向服务器提交Json字符串(@Body)

public interface IUserBiz
{
 @POST("add")
 Call<List<User>> addUser(@Body User user);
}

//省略retrofit的构建代码
 Call<List<User>> call = userBiz.addUser(new User(1001, "jj", "123,", "jj123", "jj@qq.com"));
//省略call执行相关代码

(5)表单的方式传递键值对FormUrlEncoded

public interface IUserBiz
{
    @POST("login")
    @FormUrlEncoded
    Call<User> login(@Field("username") String username, @Field("password") String password);
}

//省略retrofit的构建代码
Call<User> call = userBiz.login("zhy", "123");
//省略call执行相关代码

(6)单文件上传(@Multipart)

public interface IUserBiz
{
    @Multipart
    @POST("register")
    Call<User> registerUser(@Part MultipartBody.Part photo, @Part("username") RequestBody username, @Part("password") RequestBody password);
}

File file = new File(Environment.getExternalStorageDirectory(), "icon.png");
RequestBody photoRequestBody = RequestBody.create(MediaType.parse("image/png"), file);
MultipartBody.Part photo = MultipartBody.Part.createFormData("photos", "icon.png", photoRequestBody);

Call<User> call = userBiz.registerUser(photo, RequestBody.create(null, "abc"), RequestBody.create(null, "123"));

(7)多文件上传(@PartMap)

public interface IUserBiz
 {
     @Multipart
     @POST("register")
      Call<User> registerUser(@PartMap Map<String, RequestBody> params,  @Part("password") RequestBody password);
}

File file = new File(Environment.getExternalStorageDirectory(), "messenger_01.png");
RequestBody photo = RequestBody.create(MediaType.parse("image/png", file);
Map<String,RequestBody> photos = new HashMap<>();
photos.put("photos\"; filename=\"icon.png", photo);
photos.put("username",  RequestBody.create(null, "abc"));

Call<User> call = userBiz.registerUser(photos, RequestBody.create(null, "123"));

(8)下载文件(@Get("download"))
缺点： 并且onReponse回调虽然在UI线程，但是你还是要处理io操作，也就是说你在这里还要另外开线程操作，或者你可以考虑同步的方式下载。

@GET("download")
Call<ResponseBody> downloadTest();

Call<ResponseBody> call = userBiz.downloadTest();
call.enqueue(new Callback<ResponseBody>()
{
    @Override
    public void onResponse(Call<ResponseBody> call, Response<ResponseBody> response)
    {
        InputStream is = response.body().byteStream();
        //save file
    }

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

    }
});

二：retrofit 源码解析

1 首先构造retrofit，几个核心的参数呢，主要就是baseurl,callFactory(默认okhttpclient),converterFactories,adapterFactories,excallbackExecutor。
2 然后通过create方法拿到接口的实现类，这里利用Java的Proxy类完成动态代理的相关代理
3 在invoke方法内部，拿到我们所声明的注解以及实参等，构造ServiceMethod，ServiceMethod中解析了大量的信息，最痛可以通过toRequest构造出okhttp3.Request对象。有了okhttp3.Request对象就可以很自然的构建出okhttp3.call，最后calladapter对Call进行装饰返回。
4 拿到Call就可以执行enqueue或者execute方法了。