Jackson使用手册

迈不过友情╰ 2021-11-05 13:00 456阅读 0赞

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-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][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组合在序列化上等于类上注解@JsonRootName("user") 和 mapper.enable(SerializationFeature.WRAP\_ROOT\_VALUE),反序列化无用;

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;

2.7、@JsonAnyGetter注解  
@JsonAnyGetter注解主要用在序列化：  
1.方法是非静态，没有参数的,方法名随意  
2.方法返回值必须是Map类型  
3.在一个实体类中仅仅用在一个方法上  
4.序列化的时候json字段的key就是返回Map的key,value就是Map的value

//@JsonAnyGetter
        public Map<String,Object> getMap(){
            return map;
        }

序列化结果为：\{"height":175,"map":\{"1":"1","key":"value"\},"date":"2019-05-29 10:37:55:759"\}

取消注释后序列化结果为：\{"height":175,"date":"2019-05-29 10:39:14:685","1":"1","key":"value"\}

2.8、@JsonAnySetter注解  
@JsonAnySetter注解主要作用于反序列化上：  
1.用在非静态方法上，注解的方法必须有两个参数，第一个是json字段中的key，第二个是value，方法名随意  
2.反序列化的时候将对应不上的字段全部放到Map里面

2.9、JavaType

list反序列化为LinkedHashMap如果要转换为原来对象类型

如果为Map类型 mapper.getTypeFactory().constructParametricType(Map.class,String.class,Student.class);// 第二个参数是Map的key，第三个参数是Map的value
    如果为List类型 personList  =  mapper.readValue(mapper.writeValueAsString(personList),mapper.getTypeFactory().constructParametricType(List.class,Person.class));

2.10、TypeReference

TypeReference比javaType模式更加方便，代码也更加简洁

mapper.readValue(json, new TypeReference<List<Person>>(){});

3、序列化(SerializationFeature)与反序列化(DeserializationFeature)自定义规则

转载于:https://www.cnblogs.com/miaosj/p/10936451.html

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