FastJSON解析-----@JSONField注解详解_jsonfield alternatenames

一、依赖

<dependency>
      <groupId>com.alibaba</groupId>
      <artifactId>fastjson</artifactId>
      <version>1.2.21</version>
</dependency>

二、FastJson序列化方式  

    PS：这里只陈述第一种方式。

• 通过@JSONField定制序列化-----配置在字段或者getter/setter方法上。
• 通过@JSONType定制序列化-----配置在类上
• 通过SerializeFilter定制序列化 
• 通过ParseProcess定制反序列化

三、@JSONField

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD, ElementType.FIELD, ElementType.PARAMETER})//一般作用在字段上
public @interface JSONField {
    int ordinal() default 0;//配置序列化和反序列化的顺序
 
    String name() default "";//配置序列化和反序列化时字段的名字
 
    String format() default "";//字段格式化，对日期很有用
 
    boolean serialize() default true;//是否序列化
 
    boolean deserialize() default true;//是否反序列化
 
    SerializerFeature[] serialzeFeatures() default {};//控制序列化的一些规则，如NULL的处理
 
    Feature[] parseFeatures() default {};//控制反序列化的一些规则
 
    String label() default "";
 
    boolean jsonDirect() default false;//当有一个字段是字符串类型，里面是json格式数据，希望直接输入，而不是经过转义之后再输出。
 
    Class<?> serializeUsing() default Void.class;//对某一个类的某个属性定制序列化
 
    Class<?> deserializeUsing() default Void.class;//对某一个类的某个属性定制反序列化
 
    String[] alternateNames() default {};//反序列化时使用多个不同的字段名称
}

• ordinal

@Data
public class User {
    @JSONField(ordinal = 2)
    private String name;
 
    @JSONField(ordinal = 3)
    private String sex;
 
    @JSONField(ordinal = 1)
    private Integer age;
}
//序列化结果：顺序为age、name、sex
{"age":20,"name":"zhangsan","sex":"男"}

•  name

@Data
public class User {
    @JSONField(ordinal = 2 , name="userName")
    private String name;
 
    @JSONField(ordinal = 3)
    private String sex;
 
    @JSONField(ordinal = 1)
    private Integer age;
}
//序列化结果：name变为userName
{"age":20,"userName":"zhangsan","sex":"男"}

•  format

@Data
public class User {
    @JSONField(ordinal = 2 , name="userName")
    private String name;
 
    @JSONField(ordinal = 3 , format = "yyyy-MM-dd HH:mm:ss")
    private Date birthDay;
 
    @JSONField(ordinal = 1)
    private Integer age;
}
//序列化结果：
{"age":20,"userName":"zhangsan","birthDay":"2018-11-05 18:26:46"}

•  serialize

    默认情况下，是true，也就是所有字段都会被序列化。

@Data
public class User {
    @JSONField(ordinal = 2 , name="userName")
    private String name;
 
    @JSONField(ordinal = 3 , format = "yyyy-MM-dd HH:mm:ss")
    private Date birthDay;
 
    @JSONField(ordinal = 1 , serialize = false)
    private Integer age;
}
//序列化结果：age没有被序列化
{"userName":"zhangsan","birthDay":"2018-11-05 18:29:19"}

• deserialize

@Data
public class User {
    @JSONField(ordinal = 2 , name="userName")
    private String name;
 
    @JSONField(ordinal = 3 , format = "yyyy-MM-dd HH:mm:ss")
    private Date birthDay;
 
    @JSONField(ordinal = 1 , serialize = false)
    private Integer age;
}
 
@Test
    public void deserialize(){
        String str = "{\"age\":20,\"userName\":\"zhangsan\",\"birthDay\":\"2018-11-05 18:26:46\"}";
        User user = JSON.parseObject(str, User.class);
        System.out.println(user);
    }
 
//反序列化结果：
User(name=zhangsan, birthDay=Mon Nov 05 18:26:46 CST 2018, age=20)

•  serialzeFreature

默认的序列化规则是当你的字段的值为null的时候，它是不会给你序列化这个字段的。我们可以通过serialzeFeatures的属性值SerializerFeature.WriteMapNullValue来控制，当属性的值为null时也输出该字段，字段的值为null。

@Data
public class User {
    @JSONField(ordinal = 2 , name="userName")
    private String name;
 
    @JSONField(ordinal = 3 , format = "yyyy-MM-dd HH:mm:ss" , serialzeFeatures = SerializerFeature.WriteMapNullValue)
    private Date birthDay;
 
    @JSONField(ordinal = 1 , serialize = false)
    private Integer age;
}
 
//JSON.toJSONString(user)序列化的结果:
{"userName":"zhangsan","birthDay":null}
 
//也可以如下使用，不在字段上做限制。这种情况针对所有字段。
@Test
public void test(){
     User user = initUser();
     String jsonStr = JSON.toJSONString(user , SerializerFeature.WriteMapNullValue,SerializerFeature.WriteNullNumberAsZero);
     System.out.println(jsonStr);
}
//输出结果：
{"age":0,"userName":"zhangsan","birthDay":null}

 当然SerializerFeature类中还有很多其他的属性：

• parseFeatures 

    略............

• jsonDirect

@Data
public class Group {
    private String name;
    @JSONField(jsonDirect = true)
    private String userDetail;
}
@Data
public class User {
    @JSONField(ordinal = 2 , name="userName")
    private String name;
 
    @JSONField(ordinal = 3 , format = "yyyy-MM-dd HH:mm:ss")
    private Date birthDay;
 
    @JSONField(ordinal = 1 )
    private Integer age;
}
//测试
    @Test
    public void jsonDirect(){
        User user = new User();
        user.setName("zhangsan");
        user.setBirthDay(new Date());
        user.setAge(10);
        String userJSON = JSON.toJSONString(user);
        Group group = new Group();
        group.setName("1组");
        group.setUserDetail(userJSON);
        String grouJson = JSON.toJSONString(group);
        System.out.println(grouJson);
    }
//输出结果：
{"name":"1组","userDetail":{"birthDay":"2018-11-05 19:16:18","userName":"zhangsan","age":10}}
//而不是：
{"name":"1组","userDetail":"{\"age\":10,\"userName\":\"zhangsan\",\"birthDay\":\"2018-11-05 19:18:33\"}"}

•  serializeUsing

    如果实体类某字段是String类型，但第三方的相同字段是Interger类型，那么，就需要我们传过去的JSON串中该字段作为key对应的值不可以带双引号。这种情况，也可以用此方法解决。

//实体类
@Data
public class User {
    @JSONField(ordinal = 2 , name="userName")
    private String name;
 
    @JSONField(ordinal = 3 , format = "yyyy-MM-dd HH:mm:ss")
    private Date birthDay;
 
    @JSONField(ordinal = 1 , serializeUsing = ModelValueSerializer.class)
    private Integer age;
}
 
//工具类---需要实现ObjectSerializer重写write方法
public class ModelValueSerializer implements ObjectSerializer {
    @Override
    public void write(JSONSerializer jsonSerializer, Object o, Object o1, Type type, int i) throws IOException {
        Integer value = (Integer) o;
        String text = value + "岁";
        jsonSerializer.write(text);
    }
}
 
//测试
    @Test
    public void test(){
        User user = new User();
        user.setName("zhangsan");
        user.setBirthDay(new Date());
        user.setAge(10);
        String jsonStr = JSON.toJSONString(user);
        System.out.println(jsonStr);
    }
//结果：
{"age":"10岁","userName":"zhangsan","birthDay":"2018-11-05 19:26:24"}

• deserializeUsing

     略.........................

• alternateNames

@Data
public class User {
    @JSONField(ordinal = 2 , name="userName" ,alternateNames = {"userName","studentName"})
    private String name;
 
    @JSONField(ordinal = 3 , format = "yyyy-MM-dd HH:mm:ss")
    private Date birthDay;
 
    @JSONField(ordinal = 1 , serializeUsing = ModelValueSerializer.class)
    private Integer age;
}
 
   @Test
    public void alternateNames(){
        String jsonVal0 = "{\"age\":"10",\"name\":\"zhangsan\",\"birthDay\":\"2018-11-05 19:41:47\"}";
        String jsonVal1 = "{\"age\":11,\"userName\":\"lisi\",\"birthDay\":\"2018-11-05 19:41:47\"}";
        String jsonVal2 = "{\"age\":12,\"studentName\":\"wangwu\",\"birthDay\":\"2018-11-05 19:41:47\"}";
 
        User obj0 = JSON.parseObject(jsonVal0, User.class);
        System.out.println(obj0);
        User obj1 = JSON.parseObject(jsonVal1, User.class);
        System.out.println(obj1);
        User obj2 = JSON.parseObject(jsonVal2, User.class);
        System.out.println(obj2);
    }
 
//输出结果：
User(name=null, birthDay=Mon Nov 05 19:41:47 CST 2018, age=10)
User(name=lisi, birthDay=Mon Nov 05 19:41:47 CST 2018, age=11)
User(name=wangwu, birthDay=Mon Nov 05 19:41:47 CST 2018, age=12)

 发现，JSON串中如果是name的话，反序列化的话会是null。但如果是userName或者studentName的话，则会成功反序列化。

 并且，JSON串中age的值是带引号的"10"，也就是String类型，而User类中age是Interger类型，这样也可以反序列化成功。