gson操作json格式字符串

测试数据(test.json)

[
  {
    "id": 91234,
    "text": "How do I read a JSON stream in Java?",
    "geo": null,
    "user": {
      "name": "json_newb",
      "followers_count": 41
    }
  },
  {
    "id": 91235,
    "text": "@json_newb just use JsonReader!",
    "geo": [50.454722, -104.606667],
    "user": {
      "name": "jesse",
      "followers_count": 2
    }
  }
]

存储数据的类(Message.java和User.java)

• Message.java

package json;

import java.util.List;

public class Message {
   private int id;
   private String text;
   private List<Double> geo;
   private User user;

   public Message(){}

   public Message(int id, String text, List<Double> geo,User user) {
       this.id = id;
       this.text = text;
       this.geo = geo;
       this.user=user;
   }

   public User getUser() {
       return user;
   }

   public void setUser(User user) {
       this.user = user;
   }

   public int getId() {
       return id;
   }

   public void setId(int id) {
       this.id = id;
   }

   public String getText() {
       return text;
   }

   public void setText(String text) {
       this.text = text;
   }

   public List<Double> getGeo() {
       return geo;
   }

   public void setGeo(List<Double> geo) {
       this.geo = geo;
   }

   @Override
   public String toString() {
       return "Message{" +
               "id=" + id +
               ", text='" + text + '\'' +
               ", geo=" + geo +
               ", user=" + user +
               '}';
   }
}

• User.java

package json;

public class User {
   private String name;
   private int followers_count;

   @Override
   public String toString() {
       return "User{" +
               "name='" + name + '\'' +
               ", followers_count=" + followers_count +
               '}';
   }

   public String getName() {
       return name;
   }

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

   public int getFollowers_count() {
       return followers_count;
   }

   public void setFollowers_count(int followers_count) {
       this.followers_count = followers_count;
   }
}

使用JsonReader类读取json

• JsonReaderTest.java

package json;

import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonToken;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class JsonReaderTest {
    public static void main(String[] args)throws IOException {
        InputStream in = Thread.currentThread().getContextClassLoader().getResourceAsStream("json/test.json");
        JsonReader jsonReader = new JsonReader(new InputStreamReader(in));
        jsonReader.beginArray();
        List<Message> list=new ArrayList<>();
        while (jsonReader.hasNext()){
            Message msg=getMessage(jsonReader);
            list.add(msg);
        }
        jsonReader.endArray();
        System.out.println(Arrays.toString(list.toArray()));
    }

    //获取message对象
    public static Message getMessage(JsonReader jsonReader)throws IOException{
        Message msg=new Message();
        jsonReader.beginObject();
        while (jsonReader.hasNext()){
            String name = jsonReader.nextName();
            if(name.equals("id")){
                msg.setId(Integer.parseInt(jsonReader.nextString()));
            }else if(name.equals("text")){
                msg.setText(jsonReader.nextString());
            }else if(name.equals("geo")&&jsonReader.peek()!= JsonToken.NULL){
                msg.setGeo(getGeoList(jsonReader));
            }else if(name.equals("user")){
                msg.setUser(getUser(jsonReader));
            }else {
                jsonReader.skipValue();
            }
        }
        jsonReader.endObject();
        return msg;
    }

    //获取geo列表
    public static List<Double> getGeoList(JsonReader jsonReader)throws IOException{
        jsonReader.beginArray();
        List<Double> list=new ArrayList<>();
        while (jsonReader.hasNext()){
            list.add(jsonReader.nextDouble());
        }
        jsonReader.endArray();
        return list;
    }

    //获取User对象
    public static User getUser(JsonReader jsonReader)throws IOException{
        User user = new User();
        jsonReader.beginObject();
        while (jsonReader.hasNext()){
            String name = jsonReader.nextName();
            if (name.equals("name")){
                user.setName(jsonReader.nextString());
            }else if(name.equals("followers_count")){
                user.setFollowers_count(jsonReader.nextInt());
            }else {
                jsonReader.skipValue();
            }
        }
        jsonReader.endObject();
        return user;
    }
}

• 结果

"C:\Program Files\Java\jdk-9.0.4\bin\java.exe" "-javaagent:D:\Program Files\JetBrains\IntelliJ IDEA 2018.3.4\lib\idea_rt.jar=4735:D:\Program Files\JetBrains\IntelliJ IDEA 2018.3.4\bin" -Dfile.encoding=UTF-8 -classpath "D:\java\test\bin;D:\java\test\libs\guava-27.0-jre.jar;D:\Program Files\JetBrains\IntelliJ IDEA 2018.3.4\lib\junit.jar;D:\java\test\libs\apache-mina-2.0.20\dist\mina-core-2.0.20.jar;D:\java\test\libs\apache-mina-2.0.20\lib\slf4j-api-1.7.26.jar;D:\java\test\libs\jdom-2.0.6.jar;D:\java\test\libs\dom4j-2.0.2.jar;D:\java\test\libs\xstream-1.4.11.1.jar;D:\java\test\libs\xpp3-1.1.3.4.C.jar;D:\java\test\libs\gson-2.8.4.jar" json.JsonReaderTest
[Message{id=91234, text='How do I read a JSON stream in Java?', geo=null, user=User{name='json_newb', followers_count=41}}, Message{id=91235, text='@json_newb just use JsonReader!', geo=[50.454722, -104.606667], user=User{name='jesse', followers_count=2}}]

使用Gson读写json

• GsonTest.java

package json;

import com.google.gson.Gson;
import com.google.gson.JsonArray;
import com.google.gson.JsonObject;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonToken;
import com.google.gson.stream.JsonWriter;

import java.io.*;
import java.util.List;

public class GsonTest {
   public static void main(String[] args) throws FileNotFoundException,IOException {
       Gson gson = new Gson();
       JsonArray jsonArray = new JsonArray();

       JsonObject obj = new JsonObject();
       obj.addProperty("id",2222);
       obj.addProperty("text","hello");
       JsonArray geoArray=new JsonArray();
       geoArray.add(234);
       geoArray.add(567);
       obj.add("geo",geoArray);

       JsonObject obj1 = new JsonObject();
       obj1.addProperty("id",3333);
       obj1.addProperty("text","world");
       JsonArray geoArray1=new JsonArray();
       geoArray1.add(234);
       geoArray1.add(567);
       obj.add("geo",geoArray1);
       jsonArray.add(obj);
       jsonArray.add(obj1);
       
       FileWriter out=new FileWriter("gson_test.json");
       out.write(jsonArray.toString());
       out.flush();
       //gson.toJson(jsonArray,in);不能写入文件

       FileReader in = new FileReader("gson_test.json");
       TypeToken<List<Message>> typeToken=new TypeToken<>(){};
       List<Message> list=gson.fromJson(in, typeToken.getType());
       for (Message msg:list){
           System.out.println(msg);
       }
   }
}

• 结果

"C:\Program Files\Java\jdk-9.0.4\bin\java.exe" "-javaagent:D:\Program Files\JetBrains\IntelliJ IDEA 2018.3.4\lib\idea_rt.jar=4832:D:\Program Files\JetBrains\IntelliJ IDEA 2018.3.4\bin" -Dfile.encoding=UTF-8 -classpath "D:\java\test\bin;D:\java\test\libs\guava-27.0-jre.jar;D:\Program Files\JetBrains\IntelliJ IDEA 2018.3.4\lib\junit.jar;D:\java\test\libs\apache-mina-2.0.20\dist\mina-core-2.0.20.jar;D:\java\test\libs\apache-mina-2.0.20\lib\slf4j-api-1.7.26.jar;D:\java\test\libs\jdom-2.0.6.jar;D:\java\test\libs\dom4j-2.0.2.jar;D:\java\test\libs\xstream-1.4.11.1.jar;D:\java\test\libs\xpp3-1.1.3.4.C.jar;D:\java\test\libs\gson-2.8.4.jar" json.GsonTest
Message{id=2222, text='hello', geo=[234.0, 567.0], user=null}
Message{id=3333, text='world', geo=null, user=null}