处理gson解析时类型不匹配或者空值问题

由于近期对平台内容进行审核,导致之前的这篇文章无法访问,所以重新发一次

android开发的数据几乎都是通过请求拿到后台的json数据,然后将数据解析成对应的Bean

通常我们会将请求结果封装成一个BaseResponse,比如这样

package com.mjt.factory.base;

import com.google.gson.annotations.SerializedName;

import java.io.Serializable;

/**
 * Author: zhangsiqi
 * Email: [email protected]
 * Date: 2018/1/25
 * Time: 11:09
 * Desc:
 */
public class BaseResponse implements Serializable {

    public BaseResponse(int ret, String message, Error error) {
        this.ret = ret;
        this.message = message;
        this.error = error;
    }

    public BaseResponse(int ret, String message, T data) {
        this.ret = ret;
        this.message = message;
        this.data = data;
    }

    @SerializedName("ret")
    private int ret;

    @SerializedName("msg")
    private String message;

    @SerializedName("data")
    private T data;

    @SerializedName("error")
    private Error error;

    public Error getError() {
        return error;
    }

    public int getRet() {
        return ret;
    }

    public String getMessage() {
        return message;
    }

    public T getData() {
        return data;
    }

    public static class Error {

        public Error(int code, String msg) {
            this.code = code;
            this.msg = msg;
        }

        @SerializedName("code")
        private int code;
        @SerializedName("msg")
        private String msg = "";

        public int getCode() {
            return code;
        }

        public String getMsg() {
            return msg;
        }
    }
}

可以看到BaseResponse里data是object类型

但是遇到开发不规范的后台,如果object为空他会返回给你""或者"null"这样一个空字符串,这时候我们用object类型类接收就会抛一个java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING 的异常

那么怎么动态的处理这种问题呢

gson有一个TypeAdapter是可以让开发者自定义处理类型问题的

package com.mjt.common.utils.gson;

import com.google.gson.Gson;
import com.google.gson.TypeAdapter;
import com.google.gson.TypeAdapterFactory;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonToken;
import com.google.gson.stream.JsonWriter;

import java.io.IOException;

/**
 * Copyright:mjt_pad_android
 * Author: liyang 
* Date:2019/3/4 2:35 PM
* Desc:
*/ public class GsonTypeAdapterFactory implements TypeAdapterFactory { @Override public TypeAdapter create(Gson gson, TypeToken type) { final TypeAdapter adapter = gson.getDelegateAdapter(this, type); return new TypeAdapter() { @Override public void write(JsonWriter out, T value) throws IOException { adapter.write(out, value); } @Override public T read(JsonReader in) throws IOException { try { return adapter.read(in); } catch (Throwable e) { consumeAll(in); return null; } } private void consumeAll(JsonReader in) throws IOException { if (in.hasNext()) { JsonToken peek = in.peek(); if (peek == JsonToken.STRING) { in.nextString(); } else if (peek == JsonToken.BEGIN_ARRAY) { in.beginArray(); consumeAll(in); in.endArray(); } else if (peek == JsonToken.BEGIN_OBJECT) { in.beginObject(); consumeAll(in); in.endObject(); } else if (peek == JsonToken.END_ARRAY) { in.endArray(); } else if (peek == JsonToken.END_OBJECT) { in.endObject(); } else if (peek == JsonToken.NUMBER) { in.nextString(); } else if (peek == JsonToken.BOOLEAN) { in.nextBoolean(); } else if (peek == JsonToken.NAME) { in.nextName(); consumeAll(in); } else if (peek == JsonToken.NULL) { in.nextNull(); } } } }; } }

接下来我们来测试一下这个东西起不起作用呢

json数据正常的情况下是这样
main方法

 public static void main(String[] args) {
             String jsonStr="{\"name\":\"Coder\",\"friends\":{\"name\":\"庄长鹏\",\"relation\":\"好朋友\"},\"relation\":\"自己\",\"family\":[{\"name\":\"李克亮\",\"relation\":\"爸爸\"}]}";

//        Gson gson=new GsonBuilder().registerTypeAdapterFactory(new GsonTypeAdapterFactory()).create();
//        User json=gson.fromJson(jsonStr,User.class);
        User json=new Gson().fromJson(jsonStr,User.class);
        System.out.println(json);

 }

User类

    static class User implements Serializable{
        String name;

        User friends;

        String relation;

        List family;

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public User getFriends() {
            return friends;
        }

        public void setFriends(User friends) {
            this.friends = friends;
        }

        public List getFamily() {
            return family;
        }

        public void setFamily(List family) {
            this.family = family;
        }

        public String getRelation() {
            return relation;
        }

        public void setRelation(String relation) {
            this.relation = relation;
        }

        @Override
        public String toString() {
            return "User{" +
                    "name='" + name + '\'' +
                    ", friends=" + friends +
                    ", relation='" + relation + '\'' +
                    ", family=" + family +
                    '}';
        }
    }
此时的执行结果为

User{name='Coder', friends=User{name='庄长鹏', friends=null, relation='好朋友', family=null}, relation='自己', family=[User{name='李克亮', friends=null, relation='爸爸', family=null}]}


情况一

如果此时我们将jsonStr改为这样,可以看到name明明是个字符串,但是被我改为{}这样就是object类型了
  public static void main(String[] args) {
        String jsonStr="{\"name\":{},\"friends\":{\"name\":\"庄长鹏\",\"relation\":\"好朋友\"},\"relation\":\"自己\",\"family\":[{\"name\":\"李克亮\",\"relation\":\"爸爸\"}]}";

//        Gson gson=new GsonBuilder().registerTypeAdapterFactory(new GsonTypeAdapterFactory()).create();
//        User json=gson.fromJson(jsonStr,User.class);
        User json=new Gson().fromJson(jsonStr,User.class);
        System.out.println(json);

    }
这时就进行解析就抛了异常了
Exception in thread "main" com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected STRING but was BEGIN_OBJECT at line 1 column 85 path $.family
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:226)
    at com.google.gson.Gson.fromJson(Gson.java:927)
    at com.google.gson.Gson.fromJson(Gson.java:892)
    at com.google.gson.Gson.fromJson(Gson.java:841)
    at com.google.gson.Gson.fromJson(Gson.java:813)

情况二

我们再将jsonStr改为这样
    public static void main(String[] args) {
        String jsonStr="{\"name\":\"Coder\",\"friends\":\"\",\"relation\":\"自己\",\"family\":[{\"name\":\"李克亮\",\"relation\":\"爸爸\"}]}";

//        Gson gson=new GsonBuilder().registerTypeAdapterFactory(new GsonTypeAdapterFactory()).create();
//        User json=gson.fromJson(jsonStr,User.class);
        User json=new Gson().fromJson(jsonStr,User.class);
        System.out.println(json);

    }
此时执行又抛异常了
Exception in thread "main" com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 28 path $.friends
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:226)
    at com.google.gson.Gson$FutureTypeAdapter.read(Gson.java:1011)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:131)
    at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:222)
    at com.google.gson.Gson.fromJson(Gson.java:927)
    at com.google.gson.Gson.fromJson(Gson.java:892)
    at com.google.gson.Gson.fromJson(Gson.java:841)
    at com.google.gson.Gson.fromJson(Gson.java:813)
解析又出错了,因为User类中的friends是一个object类型,而jsonStr中的friends却是一个""空字符串

接下来我们使用TypeAdapter来对上述两种情况进行处理

 public static void main(String[] args) {
        String jsonStr="{\"name\":\"Coder\",\"friends\":\"\",\"relation\":\"自己\",\"family\":[{\"name\":\"李克亮\",\"relation\":\"爸爸\"}]}";

        Gson gson=new GsonBuilder().registerTypeAdapterFactory(new GsonTypeAdapterFactory()).create();
        User json=gson.fromJson(jsonStr,User.class);
//        User json=new Gson().fromJson(jsonStr,User.class);
        System.out.println(json);

    }

执行结果为
User{name='Coder', friends=null, relation='自己', family=[User{name='李克亮', friends=null, relation='爸爸', family=null}]}
嗯 friends虽然类型不匹配,但是并不影响其他字段的解析

我们再对第一种情况进行处理
public static void main(String[] args) {
        String jsonStr="{\"name\":{},\"friends\":{\"name\":\"庄长鹏\",\"relation\":\"好朋友\"},\"relation\":\"自己\",\"family\":[{\"name\":\"李克亮\",\"relation\":\"爸爸\"}]}";

        Gson gson=new GsonBuilder().registerTypeAdapterFactory(new GsonTypeAdapterFactory()).create();
       User json=gson.fromJson(jsonStr,User.class);
 //       User json=new Gson().fromJson(jsonStr,User.class);
        System.out.println(json);

    }

执行的结果为
User{name='null', friends=User{name='庄长鹏', friends=null, relation='好朋友', family=null}, relation='自己', family=[User{name='李克亮', friends=null, relation='爸爸', family=null}]}
嗯 json字符串中的name字段虽然变成了{}对象,但是并不影响其他字段的解析


回头我们来看看

GsonTypeAdapterFactory是怎么处理的呢

  • gson 库会通过JsonReader对json对象的每个字段进项读取,当发现类型不匹配时抛出异常
  • 那么我们就在它抛出异常的时候进行处理,让它继续不中断接着往下读取其他的字段就好了
/**
 * Copyright:mjt_pad_android
 * Author: liyang 
* Date:2019/3/4 2:35 PM
* Desc:
*/ public class GsonTypeAdapterFactory implements TypeAdapterFactory { @Override public TypeAdapter create(Gson gson, TypeToken type) { final TypeAdapter adapter = gson.getDelegateAdapter(this, type); return new TypeAdapter() { @Override public void write(JsonWriter out, T value) throws IOException { adapter.write(out, value); } @Override public T read(JsonReader in) throws IOException { //gson 库会通过JsonReader对json对象的每个字段进项读取,当发现类型不匹配时抛出异常 try { return adapter.read(in); } catch (Throwable e) { //那么我们就在它抛出异常的时候进行处理,让它继续不中断接着往下读取其他的字段就好了 consumeAll(in); return null; } } private void consumeAll(JsonReader in) throws IOException { if (in.hasNext()) { JsonToken peek = in.peek(); if (peek == JsonToken.STRING) { in.nextString(); } else if (peek == JsonToken.BEGIN_ARRAY) { in.beginArray(); consumeAll(in); in.endArray(); } else if (peek == JsonToken.BEGIN_OBJECT) { in.beginObject(); consumeAll(in); in.endObject(); } else if (peek == JsonToken.END_ARRAY) { in.endArray(); } else if (peek == JsonToken.END_OBJECT) { in.endObject(); } else if (peek == JsonToken.NUMBER) { in.nextString(); } else if (peek == JsonToken.BOOLEAN) { in.nextBoolean(); } else if (peek == JsonToken.NAME) { in.nextName(); consumeAll(in); } else if (peek == JsonToken.NULL) { in.nextNull(); } } } }; } }

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