JSON转换常用类库

------------------jackson-------------------------------
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-core</artifactId>
    <version>2.9.1</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-annotations</artifactId>
    <version>2.9.1</version>
</dependency>
<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.9.1</version>
</dependency>
------------------fastjson-------------------------------
 <dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.2.4</version>
</dependency>
------------------gson-------------------------------
<dependency>  
    <groupId>com.google.code.gson</groupId>  
    <artifactId>gson</artifactId>  
    <version>2.8.2</version>  
</dependency>  

//实体类
public class Users {
    private String name;
    private Integer age;
    private Date birthday;
    private String email;
    ...
@Test
public void testJoinne2r() throws IOException{
    //JAVA对象转JSON[JSON序列化]
    Users user = new Users();
    user.setName("小民");
    user.setEmail("xiaomin@sina.com");
    user.setAge(20);
    System.out.println(objectMapper.writeValueAsString(user));
    //{"name":"小民","age":20,"birthday":null,"email":"xiaomin@sina.com"}
    //JSON转Java类[JSON反序列化]
    String jsonstr = objectMapper.writeValueAsString(user);
    Users u = objectMapper.readValue(jsonstr,Users.class);
    System.out.println(u.toString());
    //Users{name='小民', age=20, birthday=null, email='xiaomin@sina.com'}
}    

//对象序列化
Map<String, Object> map = ImmutableMap.of("key1", "One","key2", "Two");
System.out.println(JSON.toJSONString(map));
//{"key1":"One","key2":"Two"}
//传入一个对象和一个布尔类型（是否格式化），将对象转成格式化后的JSON字符串。
JSON.toJSONString(map,true)
//反序列化对象
String jsonstr = JSON.toJSONString(map);
Map<String, Object> resultMap = JSONObject.parseObject(jsonstr ,Map.class);
System.out.println(resultMap);//{key1=One, key2=Two}
//日期格式化
String dateJson = JSON.toJSONString(new Date(), SerializerFeature.WriteDateUseDateFormat);
System.out.println(dateJson);//"2021-06-29 15:28:55"
//集合的反序列化
List<Map<String,Object>> list = Lists.newArrayList();
Map<String, Object> map = ImmutableMap.of("key1", "One","key2", "Two");
list.add(map);
String jsonstr = JSON.toJSONString(list,true);
List<Map<String,Object>> result = JSONArray.parseObject(jsonstr ,List.class);
System.out.println(result);//[{"key1":"One","key2":"Two"}]

public class MyJsonUtil {
    private static final SerializerFeature[] features = {SerializerFeature.WriteMapNullValue, // 输出空置字段
             SerializerFeature.WriteNullListAsEmpty,
            // // list字段如果为null，输出为[]，而不是null
             SerializerFeature.WriteNullNumberAsZero,
             // 数值字段如果为null，输出为0，而不是null
             SerializerFeature.WriteNullBooleanAsFalse,
            // // Boolean字段如果为null，输出为false，而不是null
             SerializerFeature.WriteNullStringAsEmpty,
            // // 字符类型字段如果为null，输出为""，而不是null
            SerializerFeature.WriteDateUseDateFormat // 日期格式化yyyy-MM-dd
            // HH:mm:ss
    };
    public static String toJson(Object object) {
        return JSON.toJSONString(object, features);
    }
}

public class User {
    //省略其它
    public String name;
    public int age;
    public String emailAddress;
}
//生成JSON：　
Gson gson = new Gson();
User user = new User("张三",24);
String jsonObject = gson.toJson(user); // {"name":"张三kidou","age":24}
//解析JSON：
Gson gson = new Gson();
String jsonString = "{\"name\":\"张三\",\"age\":24}";
User user = gson.fromJson(jsonString, User.class);
//属性重命名 @SerializedName 注解的使用
@SerializedName("email_address")
public String emailAddress;