本文基于java集成retorfit的统一返回类型
第一步构建RetrofitMananger

package com.example.commonui;

import android.content.Context;

import com.example.commonui.adapter.CommonCallAdapter;

import java.io.File;
import java.util.concurrent.TimeUnit;

import javax.inject.Inject;
import javax.inject.Singleton;

import dagger.hilt.android.qualifiers.ApplicationContext;
import okhttp3.Cache;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;

@Singleton
public class RetrofitMananger {
    private long DEFAULT_TIME_OUT = 30;
    private Context context;
    private Retrofit retrofit;
    private String base_url = "https://mock.presstime.cn/";

    @Inject
    public RetrofitMananger(@ApplicationContext Context context) {
        this.context = context;
        init();
    }

    private void init() {
        retrofit = new Retrofit.Builder()
                .client(getOkHttpClientBuilder().build())
                .addCallAdapterFactory(new CommonCallAdapter.Factory())
                .addConverterFactory(GsonConverterFactory.create())
                .baseUrl(base_url)
                .build();
    }

    private OkHttpClient.Builder getOkHttpClientBuilder() {
        File cacheFile = new File(context.getCacheDir(), "cache");
        Cache cache = new Cache(cacheFile, 1024 * 1024 * 100);//100Mb
        OkHttpClient.Builder builder = new OkHttpClient.Builder()
                .connectTimeout(DEFAULT_TIME_OUT, TimeUnit.SECONDS)
                .writeTimeout(DEFAULT_TIME_OUT, TimeUnit.SECONDS)
                .readTimeout(DEFAULT_TIME_OUT, TimeUnit.SECONDS)
                .retryOnConnectionFailure(true)
                .cache(cache)
                .addInterceptor(chain -> {
                    Request request = chain.request();
                    Request newResult = request.newBuilder()
                            .addHeader("Accept-Encoding", "gzip")
                            .addHeader("Accept", "application/json")
                            .addHeader("Content-Type", "application/json; charset=utf-8")
                            .method(request.method(), request.body())
                            .addHeader("Authorization", "Bearer ").build();
                    return chain.proceed(newResult);

                });
        return builder;
    }

    public <T> T create(Class<T> clas){
        return retrofit.create(clas);
    }

}

第二部构建CommonCallAdapter

package com.example.commonui.adapter;

import androidx.annotation.Nullable;

import com.example.commonui.model.CustomCall;

import java.lang.annotation.Annotation;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;

import retrofit2.Call;
import retrofit2.CallAdapter;
import retrofit2.Response;
import retrofit2.Retrofit;

public class CommonCallAdapter<R> implements CallAdapter<R, CustomCall<R>> {
    private Type type;

    public CommonCallAdapter(Type type) {
        this.type = type;
    }

    @Override
    public Type responseType() {
        return type;
    }

    @Override
    public CustomCall<R> adapt(Call<R> call) {
        CustomCall<R> result = CustomCall.unknownError();
        try {
            Response<R> response = null;
            if (call.isCanceled()) {
                result = CustomCall.cancelError();
            } else if ((response = call.execute()).isSuccessful()) {
                result = CustomCall.success(response.code(), response.message(), response.body());
            } else {
                result = CustomCall.error(response.code(), response.message());
            }
        } catch (Exception e) {
            e.printStackTrace();
            result.setMessage(e.getMessage());
        }
        ResultHandler.handlerResult(result);
        return result;
    }

    public static class Factory extends CallAdapter.Factory {

        @Nullable
        @Override
        public CallAdapter<?, ?> get(Type returnType, Annotation[] annotations, Retrofit retrofit) {
            //获取原始类型
            Class<?> rawType = getRawType(returnType);
            if (rawType == CustomCall.class && returnType instanceof ParameterizedType) {
                Type callReturnType = getParameterUpperBound(0, (ParameterizedType) returnType);
                return new CommonCallAdapter<>(callReturnType);
            }
            return null;
        }
    }
}

CustomCall代码如下

package com.example.commonui.model;

public class CustomCall<T> {
    private int code;
    private boolean success;
    private String message;
    private T data;

    public static CustomCall cancelError(){
        return error(-1,"请求被取消");
    }

    public static CustomCall unknownError(){
        return error(-2,"未知错误");
    }

    public static CustomCall error(int code, String message){
        CustomCall<String> customResultInfo = new CustomCall<>();
        customResultInfo.message = message;
        customResultInfo.code = code;
        return customResultInfo;
    }

    public static <T> CustomCall success(int code, String message, T data){
        CustomCall<T> customResultInfo = new CustomCall<>();
        customResultInfo.message = message;
        customResultInfo.code = code;
        customResultInfo.success = true;
        customResultInfo.data = data;
        return customResultInfo;
    }

    public int getCode() {
        return code;
    }

    public boolean isSuccess() {
        return success;
    }

    public String getMessage() {
        return message;
    }

    public void setCode(int code) {
        this.code = code;
    }

    public void setSuccess(boolean success) {
        this.success = success;
    }

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

    public void setData(T data) {
        this.data = data;
    }

    public T getData() {
        return data;
    }
}

ResultHandler代码如下

package com.example.commonui.adapter;

import com.example.commonui.model.CustomCall;
import com.example.commonui.model.Result;

public class ResultHandler {
    public static void handlerResult(CustomCall customCall){
        if(customCall.isSuccess()){
            if(customCall.getData() instanceof Result){
                Result result = (Result)customCall.getData();
                if(result.getData() == null){
                    result.setCode(-3);
                    result.setMessage("返回的json不匹配");
                }
            }
        }else{
            Result<String> result = new Result<>();
            result.setCode(customCall.getCode());
            result.setMessage(customCall.getMessage());
            customCall.setData(result);
        }

    }

}

Result代码如下

package com.example.commonui.model;

public class Result<T> {
    private int code;
    private boolean success;
    private String message;
    private T data;

    public int getCode() {
        return code;
    }

    public void setCode(int code) {
        this.code = code;
    }

    public boolean isSuccess() {
        return success;
    }

    public void setSuccess(boolean success) {
        this.success = success;
    }

    public String getMessage() {
        return message;
    }

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

    public T getData() {
        return data;
    }

    public void setData(T data) {
        this.data = data;
    }

}

UserManager代码如下

package com.example.myapplication.service;

import com.example.commonui.api.UserServiceApi;
import com.example.commonui.hiltModule.User;
import com.example.commonui.model.Result;

import javax.inject.Inject;

public class UserManager {
    private UserServiceApi userServiceApi;
    @Inject
    public UserManager(UserServiceApi userServiceApi){
        this.userServiceApi = userServiceApi;
    }

    public Result<User> getUser(){
        return userServiceApi.getUser().getData();
    }
}

接口定义如下：

package com.example.commonui.api;

import com.example.commonui.hiltModule.User;
import com.example.commonui.model.CustomCall;
import com.example.commonui.model.Result;

import retrofit2.http.GET;

public interface UserServiceApi {
    @GET("mock/61ef6708f5af18001654fe74/example/query")
    CustomCall<Result<User>> getUser();
}