Jackson的使用

一引入依赖

<!--Jackson是spring-boot-starter-json的一个依赖（spring-boot-starter-web中包含spring-boot-starter-json）。也就是说，当项目中引入spring-boot-starter-web后会自动引入spring-boot-starter-json -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>
<!-- 简洁代码和方便打印 -->
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.24</version> 
</dependency>

二测试的实体

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Student implements Serializable,Cloneable {

    private static final long serialVersionUID = 6447932156561222739L;
    private Integer sNo;
    private String name;
    @JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss",timezone="GMT+8")
    private Date birthday;
    private Integer classNo;
    private String grade;

    /**
     * 方便对象复制
     * @return
     * @throws CloneNotSupportedException
     */
    @Override
    protected Student clone() throws CloneNotSupportedException {
        return (Student) super.clone();
    }
}

三转json(序列化）

先声明一个类的全局变量

private static ObjectMapper objectMapper = new ObjectMapper();

实体(JavaBean)转json

Student s1 = new Student(1,"张三",new Date(),1001,"一年级");
String s1Json = objectMapper.writeValueAsString(s1);
log.info("jackson将Student转的json为{}",s1Json);

测试结果：
jackson将Student转的json为{“name”:“张三”,“birthday”:“2024-06-16 16:42:07”,“classNo”:1001,“grade”:“一年级”,“sno”:1}
2. Map转json

Student s1 = new Student(1,"张三",new Date(),1001,"一年级");
Student s2 = s1.clone();
s2.setSNo(2);
Student s3 = s1.clone();
s3.setSNo(3);
Student s4 = s1.clone();
s4.setSNo(4);
Map<String,Student> data = new LinkedHashMap();
data.put("s1",s1);
data.put("s2",s2);
data.put("s3",s3);
data.put("s4",s4);

String mapJson = objectMapper.writeValueAsString(data);
log.info("jackson将map转的json为{}",mapJson);

测试结果：
jackson将map转的json为{“s1”:{“name”:“张三”,“birthday”:“2024-06-16 16:42:07”,“classNo”:1001,“grade”:“一年级”,“sno”:1},“s2”:{“name”:“张三”,“birthday”:“2024-06-16 16:42:07”,“classNo”:1001,“grade”:“一年级”,“sno”:2},“s3”:{“name”:“张三”,“birthday”:“2024-06-16 16:42:07”,“classNo”:1001,“grade”:“一年级”,“sno”:3},“s4”:{“name”:“张三”,“birthday”:“2024-06-16 16:42:07”,“classNo”:1001,“grade”:“一年级”,“sno”:4}}
3. List转json

Student s1 = new Student(1,"张三",new Date(),1001,"一年级");
Student s2 = s1.clone();
s2.setSNo(2);
Student s3 = s1.clone();
s3.setSNo(3);
Student s4 = s1.clone();
s4.setSNo(4);

List<Student> studentList = new ArrayList<>(Arrays.asList(s1,s2,s3,s4));
String listJson = objectMapper.writeValueAsString(studentList);
log.info("jackson将List转的json为{}",listJson);

测试结果：
jackson将List转的json为[{“name”:“张三”,“birthday”:“2024-06-16 16:42:07”,“classNo”:1001,“grade”:“一年级”,“sno”:1},{“name”:“张三”,“birthday”:“2024-06-16 16:42:07”,“classNo”:1001,“grade”:“一年级”,“sno”:2},{“name”:“张三”,“birthday”:“2024-06-16 16:42:07”,“classNo”:1001,“grade”:“一年级”,“sno”:3},{“name”:“张三”,“birthday”:“2024-06-16 16:42:07”,“classNo”:1001,“grade”:“一年级”,“sno”:4}]

四转java对象(反序列化)

转实体(JavaBean)

Student s1 = new Student(1,"张三",new Date(),1001,"一年级");
String s1Json = objectMapper.writeValueAsString(s1);
log.info("jackson将Student转的json为{}",s1Json);

Student json1Student1 = objectMapper.readValue(s1Json,Student.class);
log.info("jackson转实体Student结果：{}",json1Student1);

JavaType studentType1 = objectMapper.getTypeFactory().constructType(Student.class);
Student json1Student2 = objectMapper.readValue(s1Json,studentType1);
log.info("jackson转实体Student结果：{}",json1Student2);

Student json1Student3 = objectMapper.readValue(s1Json, new TypeReference<Student>() {});
log.info("jackson转实体Student结果：{}",json1Student3);

测试结果：
jackson转实体Student结果：Student(sNo=1, name=张三, birthday=Sun Jun 16 16:42:07 CST 2024, classNo=1001, grade=一年级)
2. 转Map

Student s1 = new Student(1,"张三",new Date(),1001,"一年级");
Student s2 = s1.clone();
s2.setSNo(2);
Student s3 = s1.clone();
s3.setSNo(3);
Student s4 = s1.clone();
s4.setSNo(4);
Map<String,Student> data = new LinkedHashMap();
data.put("s1",s1);
data.put("s2",s2);
data.put("s3",s3);
data.put("s4",s4);

String mapJson = objectMapper.writeValueAsString(data);
log.info("jackson将map转的json为{}",mapJson);

Map<String,Student> json2map = objectMapper.readValue(mapJson,Map.class);
log.info("jackson转Map结果：{}",json2map);

测试结果：
jackson转Map结果：{s1={name=张三, birthday=2024-06-16 16:42:07, classNo=1001, grade=一年级, sno=1}, s2={name=张三, birthday=2024-06-16 16:42:07, classNo=1001, grade=一年级, sno=2}, s3={name=张三, birthday=2024-06-16 16:42:07, classNo=1001, grade=一年级, sno=3}, s4={name=张三, birthday=2024-06-16 16:42:07, classNo=1001, grade=一年级, sno=4}}
3. 转List

Student s1 = new Student(1,"张三",new Date(),1001,"一年级");
Student s2 = s1.clone();
s2.setSNo(2);
Student s3 = s1.clone();
s3.setSNo(3);
Student s4 = s1.clone();
s4.setSNo(4);
List<Student> studentList = new ArrayList<>(Arrays.asList(s1,s2,s3,s4));

String listJson = objectMapper.writeValueAsString(studentList);
log.info("jackson将List转的json为{}",listJson);

JavaType listType = objectMapper.getTypeFactory().constructCollectionType(List.class,Student.class);
List<Student> json2List = objectMapper.readValue(listJson,listType);
log.info("jackson转List结果：{}",json2List);

测试结果：
jackson转List结果：[Student(sNo=1, name=张三, birthday=Sun Jun 16 16:42:07 CST 2024, classNo=1001, grade=一年级), Student(sNo=2, name=张三, birthday=Sun Jun 16 16:42:07 CST 2024, classNo=1001, grade=一年级), Student(sNo=3, name=张三, birthday=Sun Jun 16 16:42:07 CST 2024, classNo=1001, grade=一年级), Student(sNo=4, name=张三, birthday=Sun Jun 16 16:42:07 CST 2024, classNo=1001, grade=一年级)]