Jackson 中的类型处理注解

17 Mar 2025 | 5 分钟阅读

类型处理注解用于处理属性的类型。 Jackson 提供了多个类型处理注解，例如 JsonTypeInfo、JsonSubTypes 和 JsonTypeName。类型处理注解可以在序列化对象或反序列化 Json 字符串时使用。

让我们通过一个例子来逐个了解它们，以理解这些注解是如何用于类型处理的。

@JsonTypeInfo

它是最常用的类型处理注解之一，我们在序列化对象时使用它。它用于指示在序列化和反序列化中包含哪种类型的信息的详细信息。

让我们举个例子来理解该注解是如何用于获取信息的详细信息的。

JsonTypeInfoExample.java

// import required classes and package if any
import java.io.IOException;
import java.util.Scanner;

import com.fasterxml.jackson.annotation.JsonSubTypes;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.annotation.JsonTypeInfo.As;
import com.fasterxml.jackson.annotation.JsonTypeName;
import com.fasterxml.jackson.databind.ObjectMapper;

// create class JsonTypeInfoExample to understand the use of @JsonTypeInfo
public class JsonTypeInfoExample {
    
    // main() method start
    public static void main(String args[]) throws IOException {
        
        // create Scanner class object
        Scanner sc= new Scanner(System.in);		
        
        ShapeInfo shapeObj;
        
        String name;
        Double radious;
        
        System.out.println("Enter name of Circle:");
        name = sc.nextLine();
        
        System.out.println("Enter radious of Circle:");
        radious = sc.nextDouble();
        
        // create an instance of Shape class
        shapeObj = new JsonTypeInfoExample.CircleInfo(name, radious);
        
        // Serialize CircleInfo
        String result = new ObjectMapper()
            .writerWithDefaultPrettyPrinter()
            .writeValueAsString(shapeObj);
        System.out.println(result); 
        
        // json string to de-serialize
        String jsonString = "{\"name\":\"squareTest\",\"length\":0.5, \"type\":\"square\"}";
        System.out.println("Json data to deserialize: "+jsonString);
        
        // use ObjectMapper class for deserializing json
        SquareInfo square = new ObjectMapper().readerFor(ShapeInfo.class).readValue(jsonString);
        System.out.println(square.name);
        
        // close Scanner class object
        sc.close();
        
    }
    
    // create class ShapeInfo by using @JsonTypeInfo and @JsonSubTypes
    @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = As.PROPERTY, property = "type") @JsonSubTypes({
        @JsonSubTypes.Type(value = SquareInfo.class, name = "square"),
            @JsonSubTypes.Type(value = CircleInfo.class, name = "circle")
            })
    static class ShapeInfo {
        public String name; 
        
        // parameterized constructor
        ShapeInfo(String name){
            this.name = name;
        }
    }
    
    // create class CircleInfo that extend ShapeInfo
    @JsonTypeName("square")
    static class SquareInfo extends ShapeInfo {
        public double length;
        
        // default constructor for setting default values
        SquareInfo(){
            this(null,0.0);
        }
        
        // parameterized constructor to set user define values
        SquareInfo(String name, double length){
            super(name);
            this.length = length;
        }
    }
    
    // create class CircleInfo that extend Shape
    @JsonTypeName("circle")
    static class CircleInfo extends ShapeInfo {
        public double circleRadius;  
        
        // default constructor for setting default values
        CircleInfo(){
            this(null,0.0);
        }
        
        // parameterized constructor to set user define values
        CircleInfo(String circleName, double circleRadius) {
            super(circleName);
            this.circleRadius = circleRadius;
        }
    }
}

输出

@JsonSubTypes

这是另一个最常用的 THandling 注解，我们也在序列化和反序列化对象时使用它。它用于指示被注解类型的子类型。 @JsonSubTypes 注解与 @JsonTypeInfo 注解一起使用。

让我们举个例子来理解该注解的用法。

JsonSubTypesExample.java

//import required classes and package if any
import java.io.IOException;
import java.util.Scanner;

import com.fasterxml.jackson.annotation.JsonSubTypes;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.annotation.JsonTypeInfo.As;
import com.fasterxml.jackson.annotation.JsonTypeName;
import com.fasterxml.jackson.databind.ObjectMapper;

//create class JsonSubTypesExample to understand the use of @JsonSubTypes
public class JsonSubTypesExample {
    
    // main() method start
    public static void main(String args[]) throws IOException {
        
        // create Scanner class object
        Scanner sc= new Scanner(System.in);		
        
        PersonInfo personObj;
        
        String name;
        String id;
        
        System.out.println("Enter Name of Student:");
        name = sc.nextLine();
        
        System.out.println("Enter Student Id:");
        id = sc.nextLine();
        
        // create an instance of Person class
        personObj = new JsonSubTypesExample.StudentInfo(name, id);
        
        // Serialize CircleInfo
        String result = new ObjectMapper()
            .writerWithDefaultPrettyPrinter()
            .writeValueAsString(personObj);
        System.out.println(result); 
        
        // json string to de-serialize
        String jsonString = "{\"name\":\"Sharon Lorenz\",\"id\":\"0121\", \"type\":\"faculty\"}";
        System.out.println("Json data to deserialize: "+jsonString);
        
        // use ObjectMapper class for deserializing json
        FacultyInfo faculty = new ObjectMapper().readerFor(PersonInfo.class).readValue(jsonString);
        System.out.println(faculty.name);
        
        // close Scanner class object
        sc.close();
        
    }
    
    // create class PersonInfo by using @JsonTypeInfo and @JsonSubTypes
    @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = As.PROPERTY, property = "type") @JsonSubTypes({
        @JsonSubTypes.Type(value = StudentInfo.class, name = "student"),
            @JsonSubTypes.Type(value = FacultyInfo.class, name = "faculty")
            })
    static class PersonInfo {
        public String name; 
        
        // parameterized constructor
        PersonInfo(String name){
            this.name = name;
        }
    }
    
    // create class StudentInfo that extend PersonInfo
    @JsonTypeName("student")
    static class StudentInfo extends PersonInfo {
        public String id;
        
        // default constructor for setting default values
        StudentInfo(){
            this(null, "");
        }
        
        // parameterized constructor to set user define values
        StudentInfo(String name, String id){
            super(name);
            this.id = id;
        }
    }
    
    // create class FacultyInfo that extend PersonInfo
    @JsonTypeName("faculty")
    static class FacultyInfo extends PersonInfo {
        public String id;  
        
        // default constructor for setting default values
        FacultyInfo(){
            this(null,"");
        }
        
        // parameterized constructor to set user define values
        FacultyInfo(String name, String id) {
            super(name);
            this.id = id;
        }
    }
}

输出

@JsonTypeName

这是另一个重要的**类型处理**注解，用于设置要用于注解类的类型名称。

让我们举个例子来理解该注解在 Java 中的工作方式

JsonTypeNameExample.java

// import required classes and package if any 
import java.io.IOException;
import java.util.Scanner;

import com.fasterxml.jackson.annotation.JsonSubTypes;
import com.fasterxml.jackson.annotation.JsonTypeInfo;
import com.fasterxml.jackson.annotation.JsonTypeInfo.As;
import com.fasterxml.jackson.annotation.JsonTypeName;
import com.fasterxml.jackson.databind.ObjectMapper;

// create class JsonTypeNameExample to understand the use of @JsonTypeName
public class JsonTypeNameExample {
    
    // main() method start
    public static void main(String args[]) throws IOException {
        
        // create Scanner class object
        Scanner sc= new Scanner(System.in);		
        
        ShapeInfo shapeObj;
        
        String name;
        Double radious;
        
        System.out.println("Enter name of Circle:");
        name = sc.nextLine();
        
        System.out.println("Enter radious of Circle:");
        radious = sc.nextDouble();
        
        // create an instance of Shape class
        shapeObj = new JsonTypeNameExample.CircleInfo(name, radious);
        
        // Serialize CircleInfo
        String result = new ObjectMapper()
            .writerWithDefaultPrettyPrinter()
            .writeValueAsString(shapeObj);
        System.out.println(result); 
        
        // json string to de-serialize
        String jsonString = "{\"name\":\"squareTest\",\"length\":0.5, \"type\":\"square\"}";
        System.out.println("Json data to deserialize: "+jsonString);
        
        // use ObjectMapper class for deserializing json
        SquareInfo square = new ObjectMapper().readerFor(ShapeInfo.class).readValue(jsonString);
        System.out.println(square.name);
        
        // close Scanner class object
        sc.close();
        
    }
    
    // create class ShapeInfo by using @JsonTypeInfo and @JsonSubTypes
    @JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = As.PROPERTY, property = "type") @JsonSubTypes({
        @JsonSubTypes.Type(value = SquareInfo.class, name = "square"),
            @JsonSubTypes.Type(value = CircleInfo.class, name = "circle")
            })
    static class ShapeInfo {
        public String name; 
        
        // parameterized constructor
        ShapeInfo(String name){
            this.name = name;
        }
    }
    
    // create class CircleInfo that extend ShapeInfo
    @JsonTypeName("square")
    static class SquareInfo extends ShapeInfo {
        public double length;
        
        // default constructor for setting default values
        SquareInfo(){
            this(null,0.0);
        }
        
        // parameterized constructor to set user define values
        SquareInfo(String name, double length){
            super(name);
            this.length = length;
        }
    }
    
    // create class CircleInfo that extend Shape
    @JsonTypeName("circle")
    static class CircleInfo extends ShapeInfo {
        public double circleRadius;  
        
        // default constructor for setting default values
        CircleInfo(){
            this(null,0.0);
        }
        
        // parameterized constructor to set user define values
        CircleInfo(String circleName, double circleRadius) {
            super(circleName);
            this.circleRadius = circleRadius;
        }
    }
}

输出