Retrofit响应在onResponse函数（单个JSON对象）中返回null

Question

注册用户后，我试图从改造API获得响应。

我从response.body()函数中获取空值

注册URL：https://apitest10101.000webhostapp.com/alaa-apii/public/createuser（方法POST）

API返回单个对象JSON，如

{
    "error": true,
    "message": "User Already Exists"
}

[“在邮递员中测试后的响应工作”

RegisterActivity.java

public void register(View view) {

       if(Validate())
       {
           Log.d("####", "OKAAAAAY");

            first_name = first_name_edit.getText().toString().trim();
            last_name = last_name_edit.getText().toString().trim();
            email = email_edit.getText().toString().trim();
            password = password_edit.getText().toString().trim();
            phone = Integer.parseInt(phone_edit.getText().toString().trim());
            state = state_edit.getText().toString().trim();
            block = block_edit.getText().toString().trim();
            street = street_edit.getText().toString().trim();
            building = buidling_edit.getText().toString().trim();
            floor = floor_edit.getText().toString().trim();
            flat = flat_edit.getText().toString().trim();


          Call<ResultModel> call = RetrofitClient
                .getInstance()
                .getApi()
                .createUser(first_name, last_name, email, password, phone, postionOfReigon, state, block, street, building, floor, flat);

          call.enqueue(new Callback<ResultModel>() {
              @Override
              public void onResponse(Call<ResultModel> call, Response<ResultModel> response) {

                  boolean error = false;
                  String mass = null;
                  if (response.body() != null) { // response null  !!!!!!!!!!!
                      error = response.body().getError();
                      mass = response.body().getMessage();
                      Log.d("#####", error + "------" + mass);
                  }


                      Log.d("#####", error + "------" + mass);

              }

              @Override
              public void onFailure(Call<ResultModel> call, Throwable t) {
                  Toast.makeText(RegisterActivity.this, t.getMessage(), Toast.LENGTH_LONG).show();

              }
          });


       }
       else
       {
           Log.d("####", "NNNOOTT OKAAAAAY");
       }

    }

如果删除response.body()中的if语句，则在日志中出现此错误

2019-11-10 12:45:51.242 21211-21211/com.example.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.myapplication, PID: 21211
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Boolean com.example.myapplication.ResultModel.getError()' on a null object reference
        at com.example.myapplication.RegisterActivity$2.onResponse(RegisterActivity.java:161)
        at retrofit2.DefaultCallAdapterFactory$ExecutorCallbackCall$1$1.run(DefaultCallAdapterFactory.java:83)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6718)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

ResultModel.java

package com.example.myapplication;

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class ResultModel {

    @SerializedName("error")
    @Expose
    private Boolean error;
    @SerializedName("message")
    @Expose
    private String message;

    public ResultModel(Boolean error, String message) {
        this.error = error;
        this.message = message;
    }

    public Boolean getError() {
        return error;
    }

    public void setError(Boolean error) {
        this.error = error;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

}

RetrofitClient.java

package com.example.myapplication;

import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;

public class RetrofitClient {

    private  static final String BASE_URL = "https://apitest10101.000webhostapp.com/alaa-apii/public/";
    private static RetrofitClient mInstance;
    private Retrofit retrofit;

    private RetrofitClient(){
        retrofit = new Retrofit.Builder()
                .baseUrl(BASE_URL)
                .addConverterFactory(GsonConverterFactory.create())
                .build();
    }

    public static synchronized RetrofitClient getInstance()
    {
        if(mInstance == null)
        {
            mInstance = new RetrofitClient();
        }
        return mInstance;
    }

    public Api getApi()
    {
        return retrofit.create(Api.class);
    }



}

API接口

package com.example.myapplication;


import retrofit2.Call;
import retrofit2.http.Field;
import retrofit2.http.FormUrlEncoded;
import retrofit2.http.POST;

public interface Api {


    @FormUrlEncoded
    @POST("createuser")
    Call<ResultModel> createUser(
            @Field("firstname") String firstname,
            @Field("lastname") String lastname,
            @Field("email") String email,
            @Field("password") String password,
            @Field("phone") int phone,
            @Field("region") int region,
            @Field("state") String state,
            @Field("block") String block,
            @Field("street") String street,
            @Field("building") String building,
            @Field("floor") String floor,
            @Field("flat") String flat
    );
}

build gradle

implementation 'com.squareup.retrofit2:retrofit:2.6.2'
implementation 'com.squareup.retrofit2:converter-gson:2.6.2'

getError()应该返回false或true，而getMessage()应该返回消息用户已存在或用户创建成功。

我使用苗条框架v3.12构建api。

**任何建议**

Answer 1

似乎您正在获得422作为http状态。并非所有2XX状态代码的内容都会通过改版被视为错误，在这种情况下，您可以使用response.errorBody()访问它。

不太好消息是它必须手动转换。一种方法是使用response.errorBody().string()。

请确保只调用一次，因为第一次读取后，它将不再可读。就像行为一样。

Answer 2

您得到的响应代码是422，如果后端和前端一致认为这不是错误，那么可以通过创建自定义Interceptor和让它仍然返回获得响应代码时得到的响应，只需确保将Interceptor添加到Retrofit client