Gson是Google公司发布的一个开发源码的Java库，可用于将Java对象转换为JSON字符串，也可用于将JSON字符串转换为对应的Java对象。本介绍下Gson的基本使用方法，包括序列化和反序列化；文中所使用到的软件版本：Java 1.8.0_191、Gson 2.8.6。

1、引入依赖

<dependency>
  <groupId>com.google.code.gson</groupId>
  <artifactId>gson</artifactId>
  <version>2.8.6</version>
</dependency>

2、序列化

public static String serialize() {
        MyBean bean = new MyBean();
        bean.setS("测试字符串");
        Calendar calendar = Calendar.getInstance();
        calendar.add(Calendar.HOUR_OF_DAY, -1);
        bean.setD(calendar.getTime());

        List<MyBean> list = new ArrayList<MyBean>();
        list.add(bean);
        Map<String, List<MyBean>> map = new HashMap<String, List<MyBean>>();
        map.put("data", list);

        Gson gson = new GsonBuilder()
                .serializeNulls() //序列化值为null的字段
                .setDateFormat("yyyy-MM-dd HH:mm:ss") //设置日期格式
                .excludeFieldsWithModifiers(Modifier.STATIC)//根据修饰符过滤字段
                .create();
        String result = gson.toJson(map);
        System.out.println(result);
        return result;
    }

3、反序列化

public static void deserialize() {
        String s = serialize();
        Gson gson = new GsonBuilder()
                .setDateFormat("yyyy-MM-dd HH:mm:ss") //设置日期格式
                .create();
        Type type = new TypeToken<Map<String, List<MyBean>>>(){}.getType();
        Map<String, List<MyBean>> map =  gson.fromJson(s, type);
        System.out.println(map);
        
        //直接通过api获取相应数据
        JsonElement element = JsonParser.parseString(s);
        JsonArray data = element.getAsJsonObject().getAsJsonArray("data");
        JsonObject bean = data.get(0).getAsJsonObject();
        System.out.println(bean.get("s").getAsString());
        //...
    }

4、完整例子

package com.inspur.demo.json;

import java.lang.reflect.Modifier;
import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.Calendar;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonArray;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParser;
import com.google.gson.reflect.TypeToken;

/**
 * Gson操作JSON数据
 */
public class GsonCase {
    /**
     * 序列化
     */
    public static String serialize() {
        MyBean bean = new MyBean();
        bean.setS("测试字符串");
        Calendar calendar = Calendar.getInstance();
        calendar.add(Calendar.HOUR_OF_DAY, -1);
        bean.setD(calendar.getTime());

        List<MyBean> list = new ArrayList<MyBean>();
        list.add(bean);
        Map<String, List<MyBean>> map = new HashMap<String, List<MyBean>>();
        map.put("data", list);

        Gson gson = new GsonBuilder()
                .serializeNulls() //序列化值为null的字段
                .setDateFormat("yyyy-MM-dd HH:mm:ss") //设置日期格式
                .excludeFieldsWithModifiers(Modifier.STATIC)//根据修饰符过滤字段
                .create();
        String result = gson.toJson(map);
        System.out.println(result);
        return result;
    }

    /**
     * 反序列化
     */
    public static void deserialize() {
        String s = serialize();
        Gson gson = new GsonBuilder()
                .setDateFormat("yyyy-MM-dd HH:mm:ss") //设置日期格式
                .create();
        Type type = new TypeToken<Map<String, List<MyBean>>>(){}.getType();
        Map<String, List<MyBean>> map =  gson.fromJson(s, type);
        System.out.println(map);
        
        //直接通过api获取相应数据
        JsonElement element = JsonParser.parseString(s);
        JsonArray data = element.getAsJsonObject().getAsJsonArray("data");
        JsonObject bean = data.get(0).getAsJsonObject();
        System.out.println(bean.get("s").getAsString());
        //...
    }
    
    public static void main(String[] args) {
        serialize();
        deserialize();
    }

}

GsonCase

package com.inspur.demo.json;

import java.util.Arrays;
import java.util.Date;

public class MyBean {
    private String s = "字符串";
    private String s2;
    private String s3 = "字符串3";
    private int i = 123;
    private Integer i2;
    private char c = '到';
    private char[] c2 = new char[]{'a', 'b'};
    private Date d = new Date();
    private Date[] d2 = new Date[]{new Date(), new Date()};
    public String getS() {
        return s;
    }
    public void setS(String s) {
        this.s = s;
    }
    public String getS2() {
        return s2;
    }
    public void setS2(String s2) {
        this.s2 = s2;
    }
    public String getS3() {
        return s3;
    }
    public void setS3(String s3) {
        this.s3 = s3;
    }
    public int getI() {
        return i;
    }
    public void setI(int i) {
        this.i = i;
    }
    public Integer getI2() {
        return i2;
    }
    public void setI2(Integer i2) {
        this.i2 = i2;
    }
    public char getC() {
        return c;
    }
    public void setC(char c) {
        this.c = c;
    }
    public char[] getC2() {
        return c2;
    }
    public void setC2(char[] c2) {
        this.c2 = c2;
    }
    public Date getD() {
        return d;
    }
    public void setD(Date d) {
        this.d = d;
    }
    public Date[] getD2() {
        return d2;
    }
    public void setD2(Date[] d2) {
        this.d2 = d2;
    }
    @Override
    public String toString() {
        return "MyBean [s=" + s + ", s2=" + s2 + ", s3=" + s3 + ", i=" + i + ", i2=" + i2 + ", c=" + c + ", c2="
                + Arrays.toString(c2) + ", d=" + d + ", d2=" + Arrays.toString(d2) + "]";
    }
}

MyBean