Google Gson

时间：2025-02-13 08:27:46

JackSon简单用法        FastJson简单用法

一、Gson介绍

1、什么是Gson

    Gson 是 Google 开发的Java API，是一个简单基于Java的开源库，可以相互转换Java对象和Json字符串

2、Gson的特点

  • 易使用            ：Gson API提供了一个高级外观来简化常用的用例
  • 无须创建映射 ：Gson API为大部分要序列化的对象提供了默认映射
  • 性能优            ：Gson速度较快，内存占用量低。
  • 无依赖性        ：Gson不需要JDK以外的其他库

二、Maven 依赖

<dependency>
  <groupId></groupId>
  <artifactId>gson</artifactId>
  <version>2.8.6</version>
</dependency>

三、Gson 创建 

1、new 对象

// 使用new方法
Gson gson = new Gson();

2、 使用GsonBuilder

Gson gson = new GsonBuilder().create();

   声明对象的时候可以加规则管控

Gson gson = new GsonBuilder()
         .excludeFieldsWithoutExposeAnnotation() 	//序列化时排除没有@Expose注解的字段
         .enableComplexMapKeySerialization() 		//当Map的key为复杂对象时,需要开启该方法
         .serializeNulls() 							//字段值为空或null时，仍然进行转换
         .setDateFormat("yyyy-MM-dd HH:mm:ss:SSS") 	//时间转化为Pattern的特定格式
         .setPrettyPrinting() 						//对JSON美化
         .disableHtmlEscaping() 					//防止特殊字符出现乱码
         .create();

四、序列化和反序列化

import ;
import ;
import ;
import ;
import .*;
public class GsonTest {
    //测试的实体类
    @Data
    public class TestEntity {
        private String name;
        private int age;
        private String sex;
        private Date birthday;
        private String email;
        private String address;
        public TestEntity() {}
        public TestEntity(String name, int age, String sex, Date birthday, String email, String address) {
             = name;
             = age;
             = sex;
             = birthday;
             = email;
             = address;
        }
    }
    @Test
    public void gsonTset()  {
        //声明Gson对象
        Gson gson = new Gson();
        //声明Java对象，用于序列化
        TestEntity entity  = new TestEntity("盛夏 ",23,"未知",new Date(),"sx @",null);
        TestEntity entity1 = new TestEntity("盛夏1",23,"未知",new Date(),"sx1@",null);
        TestEntity entity2 = new TestEntity("盛夏2",23,"未知",new Date(),"sx2@",null);
        //序列化方法 toJson || 反序列化方法 fromJson


        /*-------序列化 对象 转化为 Json 字符串  -------*/
        String objectToJson = (entity);
        (objectToJson);
        //{"name":"盛夏","age":23,"sex":"未知","birthday":"Apr 26, 2022 11:20:09 AM","email":"sx@"}
        /*-------反序列化 Json 转化为 Java 对象  -------*/
        TestEntity jsonToObject = (objectToJson, );
        (jsonToObject);
        //(name=盛夏 , age=23, sex=未知, birthday=Tue Apr 26 11:34:06 CST 2022, email=sx @, address=null)


        /*-------序列化 Map 转化为 Json 字符串  -------*/
        Map map = new HashMap();
        ("entity1",entity1);
        ("entity2",entity2);
        String mapToJson = (map);
        (mapToJson);
        //{"entity1":{"name":"盛夏1","age":23,"sex":"未知","birthday":"Apr 26, 2022 11:28:49 AM","email":"sx1@"},
        // "entity2":{"name":"盛夏2","age":23,"sex":"未知","birthday":"Apr 26, 2022 11:28:49 AM","email":"sx2@"}}
        /*-------反序列化 Json 转化为 Map 集合  -------*/
        Map jsonToMap = (mapToJson, new TypeToken<Map<String, TestEntity>>() {}.getType());
        (jsonToMap);
        //{entity1=(name=盛夏1, age=23, sex=未知, birthday=Tue Apr 26 11:38:38 CST 2022, email=sx1@, address=null),
        // entity2=(name=盛夏2, age=23, sex=未知, birthday=Tue Apr 26 11:38:38 CST 2022, email=sx2@, address=null)}


        /*-------序列化 List 转化为 Json 字符串  -------*/
        List list = new ArrayList();
        (entity1);
        (entity2);
        String listToJson = (list);
        (listToJson);
        //[{"name":"盛夏1","age":23,"sex":"未知","birthday":"Apr 26, 2022 11:31:37 AM","email":"sx1@"},
        // {"name":"盛夏2","age":23,"sex":"未知","birthday":"Apr 26, 2022 11:31:37 AM","email":"sx2@"}]
        /*-------反序列化 Json 转化为 List 集合  -------*/
        List jsonToList = (listToJson, new TypeToken<List<TestEntity>>() {}.getType());
        (jsonToList);
        // [(name=盛夏1, age=23, sex=未知, birthday=Tue Apr 26 11:41:01 CST 2022, email=sx1@, address=null),
        //  (name=盛夏2, age=23, sex=未知, birthday=Tue Apr 26 11:41:01 CST 2022, email=sx2@, address=null)]
    }
}

五、常用注解

1、@SerializedName注解 用于序列化和反序列化 字段取别名

import ;
import ;
import ;
import ;
import ;
import .*;
public class GsonTest {
    //测试的实体类
    @Data
    public class TestEntity {
        /*---注解SerializedName使用---*/
        // value = "userName" 给实体类字段取别名 ； name --> userName
        // alternate = {"alterName","uName"} 可用于反序列化,{"alterName","uName"}都可给name赋值
        @SerializedName(value = "userName",alternate = {"alterName","uName"})
        private String name;
        private int age;
        private String sex;
        private Date birthday;
        private String email;
        private String address;
        public TestEntity() {}
        public TestEntity(String name, int age, String sex, Date birthday, String email, String address) {
             = name;
             = age;
             = sex;
             = birthday;
             = email;
             = address;
        }
    }
    @Test
    public void gsonTset()  {
        //声明Gson对象
        Gson gson = new Gson();
        //声明Java对象，用于序列化
        TestEntity entity  = new TestEntity("盛夏 ",23,"未知",new Date(),"sx @",null);
        
        // name 序列化为 userName
        String toJson = (entity);
        (toJson);
        //{"userName":"盛夏 ","age":23,"sex":"未知","birthday":"Apr 27, 2022 5:15:57 PM","email":"sx @"}

        // 用 name 反序列化来给 name 赋值 ；会出现赋值不上
        String nameJsonToObject = "{\"name\":\"盛夏 \",\"age\":23,\"sex\":\"未知\",\"birthday\":\"Apr 27, 2022 5:15:57 PM\",\"email\":\"sx @\"}";
        TestEntity entity1 = (nameJsonToObject, );
        (entity1);
        //(name=null, age=23, sex=未知, birthday=Wed Apr 27 17:15:57 CST 2022, email=sx @, address=null)

        // 用 alterName 反序列化来给 name 赋值 ，可赋值成功
        String alterNameJsonToObject = "{\"alterName\":\"盛夏 \",\"age\":23,\"sex\":\"未知\",\"birthday\":\"Apr 27, 2022 5:15:57 PM\",\"email\":\"sx @\"}";
        TestEntity entity2 = (alterNameJsonToObject, );
        (entity2);
        //(name=盛夏 , age=23, sex=未知, birthday=Wed Apr 27 17:15:57 CST 2022, email=sx @, address=null)

        // 用 uName 反序列化来给 name 赋值 ，可赋值成功
        String uNameJsonToObject = "{\"uName\":\"盛夏 \",\"age\":23,\"sex\":\"未知\",\"birthday\":\"Apr 27, 2022 5:15:57 PM\",\"email\":\"sx @\"}";
        TestEntity entity3 = (uNameJsonToObject, );
        (entity3);
        //(name=盛夏 , age=23, sex=未知, birthday=Wed Apr 27 17:15:57 CST 2022, email=sx @, address=null)


        // 用 userName 反序列化来给 name 赋值 ，可赋值成功
        String newJsonToObject = toJson ;
        TestEntity entity4 = (newJsonToObject, );
        (entity4);
        //(name=盛夏 , age=23, sex=未知, birthday=Wed Apr 27 17:20:11 CST 2022, email=sx @, address=null)
    }

}

2、@Expose注解 是否序列化和反序列化【注意Gson声明和不加注解情况】

import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import .*;
public class GsonTest {
    //测试的实体类
    @Data
    public class TestEntity {
        /*---Expose ---*/
        // @Expose(serialize=true) : 序列化的时候是否 序列化该字段 【true：序列化 ；false：不序列化】
        // @Expose(deserialize=true) : 反序列化的时候是否 反序列化该字段 【true：反序列化 ；false：不反序列化】
        @Expose(serialize = true)
        private String name;
        @Expose(deserialize = true)
        private int age;
        @Expose(serialize = false)
        private String sex;
        @Expose(deserialize = false)
        private Date birthday;
        
        private String email;      
        private String address;
        public TestEntity() {}
        public TestEntity(String name, int age, String sex, Date birthday, String email, String address) {
             = name;
             = age;
             = sex;
             = birthday;
             = email;
             = address;
        }
    }
    @Test
    public void gsonTset()  {
        //声明Gson对象
        Gson gson = new Gson();

        //声明Gson对象
        // 不加 @Expose 注解 等于 @Expose(serialize = false , deserialize = false)
        Gson buildGson  = new GsonBuilder().excludeFieldsWithoutExposeAnnotation().create();

        //声明Java对象，用于序列化
        TestEntity entity  = new TestEntity("盛夏 ",23,"未知",new Date(),"sx @",null);

        // 用 gson 序列化 会毫无反映
        String objectToJson = (entity);
        (objectToJson);
        // {"name":"盛夏 ","age":23,"sex":"未知","birthday":"Apr 27, 2022 5:42:21 PM","email":"sx @"}

        // 用 buildGson 序列化
        String objectToBuildJson = (entity);
        // name 字段会被序列化 ；sex 字段不会被序列化
        (objectToBuildJson);
        //{"name":"盛夏 ","age":23,"birthday":"Apr 27, 2022 5:47:20 PM"}

        // 用 buildGson 反序列化
        TestEntity buildEntity = (objectToBuildJson, );
        // age字段 会被反序列化 ； birthday字段 不会被序列化
        (buildEntity);
        //(name=盛夏 , age=23, sex=null, birthday=null, email=null, address=null)
    }
}

3、@Since(double v) 与 @Until(double v) 注解 【版本控制】

不怎么用

4、@JsonAdapter 注解 【一般用于时间转换】

import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import .*;
public class GsonTest {
    //测试的实体类
    @Data
    public class TestEntity {

        private String name;
        private int age;
        private String sex;
        // 这注解不咋会用 参数是个类 这个类要继承TypeAdapter，重写read和write方法，用于序列化和反序列化
        @JsonAdapter()
        private Date birthday;
        private String email;
        private String address;
        public TestEntity() {}
        public TestEntity(String name, int age, String sex, Date birthday, String email, String address) {
             = name;
             = age;
             = sex;
             = birthday;
             = email;
             = address;
        }
    }
    @Test
    public void gsonTset()  {
        //声明Gson对象
        Gson gson = new Gson();      

        //声明Java对象，用于序列化
        TestEntity entity  = new TestEntity("盛夏 ",23,"未知",new Date(),"sx @",null);
        
        String objectToJson = (entity);
        (objectToJson);
        //{"name":"盛夏 ","age":23,"sex":"未知","birthday":2022-04-27-18-25-16,"email":"sx @"}

        TestEntity entity1 = (objectToJson, ());
        (entity1);
        //(name=盛夏 , age=23, sex=未知, birthday=Wed Apr 27 18:25:16 CST 2022, email=sx @, address=null)


    }

    class FormatDate extends TypeAdapter {
        public static final String DATE_FORMAT_DASH_TIME = "yyyy-MM-dd-HH-mm-ss"; // 对格式化有要求，不太会用

        public  FormatDate(){ }

        @Override
        public void write(JsonWriter out, Object value) throws IOException {
            if (value == null) {
                ();
            } else {
                (new SimpleDateFormat(DATE_FORMAT_DASH_TIME).format(value));
            }
        }

        @SneakyThrows
        @Override
        public Object read(JsonReader in) throws IOException {
            return new SimpleDateFormat(DATE_FORMAT_DASH_TIME,).parse(());
        }
    }
}

  另外：可以直接用这个进行日期格式化

​Gson gson = new GsonBuilder().setDateFormat("yyyyMMdd").create();

 

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