Jackson使用手册

Posted 2021-12-09 miaosj

引用jar：jackson-core，jackson-databind，jackson-annotations

http://central.maven.org/maven2/com/fasterxml/jackson/core/jackson-annotations/2.9.9/jackson-annotations-2.9.9.jar

http://central.maven.org/maven2/com/fasterxml/jackson/core/jackson-core/2.9.9/jackson-core-2.9.9.jar

http://central.maven.org/maven2/com/fasterxml/jackson/core/jackson-databind/2.9.9/jackson-databind-2.9.9.jar

1、jackson基本使用

1.1、创建Person对象

public class Person {
    private String name;
    private Integer age;

    public Person(String name, Integer age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }
}

1.2、Main方法调用

备注：对象转json需要属性拥有get方法（注解方法除外）

import com.fasterxml.jackson.databind.ObjectMapper;

public class Main {
    public static void main(String[] arges) throws Exception {
        ObjectMapper mapper = new ObjectMapper();
        Person person = new Person("jackson",20);
        System.out.println(mapper.writeValueAsString(person));
    }
}

输出结果为：

{"name":"jackson"}

2、注解使用

2.1、@JsonProperty注解使用

@JsonProperty注解类似于sql里字段的别名，用于序列化，使用注解字段属性，替代原字段属性

@JsonProperty("userName")
    private String name;

序列化结果为：在序列化的json串中，userName替代了name

{"userName":"jackson"}

2.2、@JsonIgnore注解使用

@JsonIgnore注解是在序列化时忽略该字段

  @JsonIgnore
    @JsonProperty("userName")
    private String name;
    @JsonProperty("userAge")
    private Integer age;

序列化结果为：{"userAge":20}

{"userAge":20}

2.3、@JsonIgnoreProperties注解使用

2.3.1、序列化@JsonIgnoreProperties与@JsonIgnore类似，用于类上，注解使用的是字段别名

import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.annotation.JsonProperty;

@JsonIgnoreProperties(value={"name","userAge"})
public class Person {
    @JsonIgnore
    @JsonProperty("userName")
    private String name;
    @JsonProperty("userAge")
    private Integer age;
    @JsonProperty("userHeight")
    private Integer height;

    public Person(String name, Integer age, Integer height) {
        this.name = name;
        this.age = age;
        this.height = height;
    }
}

ObjectMapper mapper = new ObjectMapper();
Person person = new Person("jackson",20,175);
System.out.println(mapper.writeValueAsString(person));

运行结果为：{"userHeight":175}

{"userHeight":175}

2.3.2、@JsonIgnoreProperties(ignoreUnknown = true)用于忽略字段不匹配情况，相当于mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);

备注：反序列化需要有无参构造器

ObjectMapper mapper = new ObjectMapper();
Person person = new Person("jackson",20,175);
System.out.println(mapper.writeValueAsString(person));
//mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
System.out.println(mapper.readValue("{\"sheight\":172}", Person.class).getHeight());

2.4、@JsonTypeName @JsonTypeInfo

@JsonTypeName(value = "user")
@JsonTypeInfo(include = JsonTypeInfo.As.WRAPPER_OBJECT, use = JsonTypeInfo.Id.NAME)

在序列化是增加一层

序列化结果为：{"user":{"height":175}}

{"user":{"height":175}}

2.5、@JsonRootName注解

　　2.4组合等于类上注解@JsonRootName("user") 和 mapper.enable(SerializationFeature.WRAP_ROOT_VALUE);

2.6、@JsonFormat注解格式化日期格式

@JsonFormat(pattern="yyyy-MM-dd HH:mm:ss:SSS",timezone="GMT+8")
    private Date date;