Java Jackson ObjectMapper-Annota

Java Jackson ObjectMapper-Annotations

屏蔽相关属性

• @JsonIgnore

/**
 * Created by Jeffy on 16/5/17.
 */
public class Person {

    @JsonIgnore
    private String firstName;

    private String lastName;

    private String personId;

    public String getFirstName() {
        return firstName;
    }
}

测试

/**
 * Created by Jeffy on 16/5/17.
 */
public class JacksonAnnoMain {

    public static void main(String[] args) throws JsonProcessingException {
        ObjectMapper objectMapper  = new ObjectMapper();
        Person person = new Person();
        person.setFirstName("Lee");
        person.setLastName("jeffy");
        person.setPersonId("009xhihis");

        System.err.println(objectMapper.writeValueAsString(person));
    }
}

输出

{"lastName":"jeffy","personId":"009xhihis"}

• @JsonIgnoreProperties

@JsonIgnoreProperties({"firstName","lastName"})
public class Person {

    private String firstName;

    private String lastName;

    private String personId;
    
    }
    

测试

/**
 * Created by Jeffy on 16/5/17.
 */
public class JacksonAnnoMain {

    public static void main(String[] args) throws JsonProcessingException {
        ObjectMapper objectMapper  = new ObjectMapper();
        Person person = new Person();
        person.setFirstName("Lee");
        person.setLastName("jeffy");
        person.setPersonId("009xhihis");

        System.err.println(objectMapper.writeValueAsString(person));
    }
}

输出

{"personId":"009xhihis"}

• @JsonIgnoreType

public class Person {

    private String firstName;

    private String lastName;

    private String personId;

    private Address address;

    @JsonIgnoreType
    public static class Address{
        public String streetName  = null;
        public String houseNumber = null;
    }
}

测试

/**
 * Created by Jeffy on 16/5/17.
 */
public class JacksonAnnoMain {

    public static void main(String[] args) throws JsonProcessingException {
        ObjectMapper objectMapper  = new ObjectMapper();
        Person person = new Person();
        person.setFirstName("Lee");
        person.setLastName("jeffy");
        person.setPersonId("009xhihis");

        System.err.println(objectMapper.writeValueAsString(person));
    }
}

输出

{"firstName":"Lee","lastName":"jeffy","personId":"009xhihis"}

可以看到@JsonIgnoreType 和 @JsonIgnore有相似功能

• @JsonAutoDetect

注释@JsonAutoDetect用于告诉Jackson在读取和写入对象时包括不公开的属性。 这是一个示范课程，向您展示如何使用@JsonAutoDetect注释：

import com.fasterxml.jackson.annotation.JsonAutoDetect;

@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY )
public class PersonAutoDetect {

    private long  personId = 123;
    public String name     = null;

}

常量 有 ANY, DEFAULT, NON_PRIVATE, NONE, PROTECTED_AND_PRIVATE and PUBLIC_ONLY.

• @JsonSetter

解决setter方法和feild字段名称不一致导致的问题

public class Person {


    private String firstName;

    private String lastName;

    private String personId;

    private Address address;

    public String getName() {
        return firstName;
    }

    @JsonSetter("firstName")
    public void setName(String firstName) {
        this.firstName = firstName;
    }
}

如果加上了注解 @JsonSetter("firstName")输出结果为：注意 firstName

{"lastName":"jeffy","personId":"009xhihis","firstName":"Lee"}

如果不加上了注解 @JsonSetter("firstName")输出结果为：注意 name

{"lastName":"jeffy","personId":"009xhihis","name":"Lee"}

• @JsonCreator

使用这个注解可以省略setter方法，使用构造函数

public class PersonImmutable {

    private long   id   = 0;
    private String name = null;

    @JsonCreator
    public PersonImmutable(
            @JsonProperty("id")  long id,
            @JsonProperty("name") String name  ) {

        this.id = id;
        this.name = name;
    }

    public long getId() {
        return id;
    }

    public String getName() {
        return name;
    }

}

• @JacksonInject

使用这个注解是将json字符串中没有包含的字段映射到使用@JacksonInject的字段

demo

public class Person {


    private String firstName;

    private String lastName;

    private String personId;

    private Address address;

    @JacksonInject
    private String source;
    
   ...省略getters和setters
    
 }
 

String tempJson = "{\"firstName\":\"Lee\",\"lastName\":\"jeffy\",\"personId\":\"009xhihis\"}";
        InjectableValues inject = new InjectableValues.Std().addValue(String.class, "viashare.cn");

        Person person2 = new ObjectMapper().reader(inject).forType(Person.class).readValue(tempJson);
        System.err.println(person2.getSource());
        System.err.println(person2.getFirstName());
        

输出

viashare.cn
Lee

注意如果是在Json中有source字段，如下,那么上面的代码在添加source映射时就不是viashare.cn 而是null。

{"firstName":"Lee","lastName":"jeffy","personId":"009xhihis","source":null}

• @JsonDeserialize

字段的转换,比如下面的代码，想要将对boolean字段进行转换，需要重写JsonDeserializer 中的方法 deserialize

public class PersonDeserialize {

    public long    id      = 0;
    public String  name    = null;

    @JsonDeserialize(using = OptimizedBooleanDeserializer.class)
    public boolean enabled = false;
}

public class OptimizedBooleanDeserializer
    extends JsonDeserializer<Boolean> {

    @Override
    public Boolean deserialize(JsonParser jsonParser,
            DeserializationContext deserializationContext) throws
        IOException, JsonProcessingException {

        String text = jsonParser.getText();
        if("0".equals(text)) return false;
        return true;
    }
}

转换时的调用

PersonDeserialize person = objectMapper
        .reader(PersonDeserialize.class)
        .readValue(new File("data/person-optimized-boolean.json"));
        
        

• @JsonInclude

满足一定的条件在进行序列话成json

比如：

import com.fasterxml.jackson.annotation.JsonInclude;

@JsonInclude(JsonInclude.Include.NON_EMPTY)
public class PersonInclude {

    public long  personId = 0;
    public String name     = null;

}

• @JsonGetter

替换属性名称

public class PersonGetter {

    private long  personId = 0;

    @JsonGetter("id")
    public long personId() { return this.personId; }

    @JsonSetter("id")
    public void personId(long personId) { this.personId = personId; }

}

输出

{"id":0}

@JsonAnyGetter

将Object中key-value映射到对象中平级的属性

public class Person {


    private String firstName;

    private String lastName;

    private String personId;

    private Address address;

    private Map<String, Object> properties = new HashMap();
    
     @JsonAnyGetter
    public Map<String, Object> properties() {
        return properties;
    }
    
    
    ...省略其他字段的getter和setter
    
    

/**
 * Created by Jeffy on 16/5/17.
 */
public class JacksonAnnoMain {

    public static void main(String[] args) throws IOException {
        ObjectMapper objectMapper  = new ObjectMapper();
        Person person = new Person();
        person.setFirstName("Lee");
        person.setLastName("jeffy");
        person.setPersonId("009xhihis");

        Map<String,Object> map = new HashMap();
        map.put("classes","classes");
        map.put("school","school");
        person.setProperties(map);
        String json = objectMapper.writeValueAsString(person);
        System.err.println(json);
        
        }
}

输出

{"firstName":"Lee","lastName":"jeffy","personId":"009xhihis","source":null,"school":"school","classes":"classes"}

• @JsonPropertyOrder

对字段进行排序

@JsonPropertyOrder({"name", "personId"})
public class PersonPropertyOrder {

    public long  personId  = 0;
    public String name     = null;

}

• @JsonRawValue

如果字段中是一个json的字符串，在序列化的时候需要。

public class PersonRawValue {

    public long   personId = 0;

    @JsonRawValue
    public String address  =
            "{ \"street\" : \"Wall Street\", \"no\":1}";

}

有注解@JsonRawValue

{"personId":0,"address":{ "street" : "Wall Street", "no":1}}

没有注解@JsonRawValue

{"personId":0,"address":"{ \"street\" : \"Wall Street\", \"no\":1}"}

• @JsonValue

public class Person {


    private String firstName;

    private String lastName;

    private String personId;

    private Address address;

    @JsonValue
    public String toJson(){
        return this.firstName+","+this.lastName;
    }
    
}

测试代码

/**
 * Created by Jeffy on 16/5/17.
 */
public class JacksonAnnoMain {

    public static void main(String[] args) throws IOException {
        ObjectMapper objectMapper  = new ObjectMapper();
        Person person = new Person();
        person.setFirstName("Lee");
        person.setLastName("jeffy");
        person.setPersonId("009xhihis");

//        Map<String,Object> map = new HashMap();
//        map.put("classes","classes");
//        map.put("school","school");
//        person.setProperties(map);
        String json = objectMapper.writeValueAsString(person);
        System.err.println(json);
        }
}

输出

"Lee,jeffy"

• @JsonSerialize

对字段的映射值进行转化

public class PersonSerializer {

    public long   personId = 0;
    public String name     = "John";

    @JsonSerialize(using = OptimizedBooleanSerializer.class)
    public boolean enabled = false;
}

public class OptimizedBooleanSerializer extends JsonSerializer<Boolean> {

    @Override
    public void serialize(Boolean aBoolean, JsonGenerator jsonGenerator, 
        SerializerProvider serializerProvider) 
    throws IOException, JsonProcessingException {

        if(aBoolean){
            jsonGenerator.writeNumber(1);
        } else {
            jsonGenerator.writeNumber(0);
        }
    }
}