Okhttp和Gson结合使用的正确姿势，json返回未 null gson解析报错问题优化。

这篇文章写得很不错，对gson的用法都讲的很详细

 

你真的会用Gson吗？Gson使用指南  https://blog.csdn.net/wsgqp/article/details/51995745

 

当后台返回的数据中带有 为空的值的时候例如  age=

错误实例：

{"data":{"exist":2,"AppEffectSoundSort":""},"message":"ok","status":2000000}

AppEffectSoundSort 这个对象本来应该是list 可是返回一个 “” ，正常的返回结果应该是

BaseBean{status=2000000, message='ok', data=DiyClound{exist=2, AppEffectSoundSort=[]}}

gson在解析的时候就会报错，

特别是在本来要返回list的时候返回为空，如果用gson直接转化为bean就会报错。

所以需要在okttp中处理，要弄清楚原理请认真阅读上面（你真的会用Gson吗？Gson使用指南  https://blog.csdn.net/wsgqp/article/details/51995745）这篇文章：

 

主要的思想：

主要的思想就是利用registerTypeAdapter 和  JsonSerializer与JsonDeserializer 在处理json的时候对返回的数据进行判断处理。

下面直接贴代码：

okhttp中： GsonConverterFactory.create(buildGson()) 

//响应后
        okClient.addInterceptor(new ResponseInterceptor());

        retrofit = new Retrofit.Builder()
                .baseUrl(URL_BASE)
                .client(okClient.build())
                .addConverterFactory(GsonConverterFactory.create(buildGson()))
                .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
                .build();

        server = retrofit.create(RequestServer.class);
    }


    public Gson buildGson() {
        if (gson == null) {
            gson = new GsonBuilder()
                    .registerTypeAdapter(Integer.class, new IntegerDefault0Adapter())
                    .registerTypeAdapter(int.class, new IntegerDefault0Adapter())
                    .registerTypeAdapter(Double.class, new DoubleDefault0Adapter())
                    .registerTypeAdapter(double.class, new DoubleDefault0Adapter())
                    .registerTypeAdapter(Long.class, new LongDefault0Adapter())
                    .registerTypeAdapter(long.class, new LongDefault0Adapter())
                    .registerTypeHierarchyAdapter(List.class, new ListJsonDeserializer())
                    .create();
        }
        return gson;
    }

 

IntegerDefault0Adapter.java

import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;
import com.google.gson.JsonSyntaxException;

import java.lang.reflect.Type;

/**
 * created by Administrator
 * on 2020/6/19
 */

public class IntegerDefault0Adapter implements JsonSerializer, JsonDeserializer {

    @Override
    public Integer deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context)
            throws JsonParseException {
        try {
            if (json.getAsString().equals("") || json.getAsString().equals("null")) {
                //定义为int类型,如果后台返回""或者null,则返回0
                return 0;
            }
        } catch (Exception ignore) {
        }
        try {
            return json.getAsInt();
        } catch (NumberFormatException e) {
            throw new JsonSyntaxException(e);
        }
    }

    @Override
    public JsonElement serialize(Integer src, Type typeOfSrc, JsonSerializationContext context) {
        return new JsonPrimitive(src);
    }
}

LongDefault0Adapter.java

import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;
import com.google.gson.JsonSyntaxException;

import java.lang.reflect.Type;

/**
 * created by Administrator
 * on 2020/6/19
 */

public class LongDefault0Adapter implements JsonSerializer, JsonDeserializer {

    @Override
    public Long deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        try {
            if (json.getAsString().equals("") || json.getAsString().equals("null")) {
                //定义为long类型,如果后台返回""或者null,则返回0
                return Long.valueOf(0);
            }
        } catch (Exception ignore) {
        }
        try {
            return json.getAsLong();
        } catch (NumberFormatException e) {
            throw new JsonSyntaxException(e);
        }
    }

    @Override
    public JsonElement serialize(Long src, Type typeOfSrc, JsonSerializationContext context) {
        return new JsonPrimitive(src);
    }
}

DoubleDefault0Adapter.java

import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import com.google.gson.JsonPrimitive;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;
import com.google.gson.JsonSyntaxException;

import java.lang.reflect.Type;

/**
 * created by Administrator
 * on 2020/6/19
 */

public class DoubleDefault0Adapter implements JsonSerializer, JsonDeserializer {

    @Override
    public Double deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        try {
            if (json.getAsString().equals("") || json.getAsString().equals("null")) {
                //定义为double类型,如果后台返回""或者null,则返回0.00
                return 0.00;
            }
        } catch (Exception ignore) {
        }
        try {
            return json.getAsDouble();
        } catch (NumberFormatException e) {
            throw new JsonSyntaxException(e);
        }
    }

    @Override
    public JsonElement serialize(Double src, Type typeOfSrc, JsonSerializationContext context) {
        return new JsonPrimitive(src);
    }
}

ListJsonDeserializer.java

import com.google.gson.JsonArray;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

/**
 * created by Administrator
 * on 2020/6/19
 */

public class ListJsonDeserializer implements JsonDeserializer> {
    @Override
    public List deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        if (json.isJsonArray()) {
            JsonArray array = json.getAsJsonArray();
            Type itemType = ((ParameterizedType) typeOfT).getActualTypeArguments()[0];
            List list = new ArrayList<>();
            for (int i = 0; i < array.size(); i++) {
                JsonElement element = array.get(i);
                Object item = context.deserialize(element, itemType);
                list.add(item);
            }
            return list;
        } else {
            //和接口类型不符，返回空List
            return Collections.EMPTY_LIST;
        }
    }
}