Jackson 的属性包含注解

17 Mar 2025 | 5 分钟阅读

Jackson 提供了不止一个属性包含注解，例如 JsonIgnoreProperties, JsonIgnore, JsonIgnoreType 等。这些注解用于序列化和反序列化。每个注解用于不同的用例。

Property Inclusion Annotations in Jackson

让我们通过示例逐一理解它们。

@JsonIgnoreProperties

@JsonIgnoreProperties 注解是一个重要的属性包含注解，我们主要使用它来标记要忽略的属性或属性列表。它主要在类级别使用。

让我们举个例子来了解它是如何工作的。

JsonIgnorePropertiesExample.java

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

import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
import com.fasterxml.jackson.databind.ObjectMapper;

// create class JsonIgnorePropertiesExample to understand the working of annotation
public class JsonIgnorePropertiesExample {
    
    //main() methods start
    public static void main(String args[]) {
        
        // create an instance of ObjectMapper class
        ObjectMapper mapper = new ObjectMapper();
        
        // create Scanner class object
        Scanner sc= new Scanner(System.in);		
        
        // using try-catch for serializing Product
        try {
            
            Product product;
            
            String proId, proName, proPrice, proExpiry;
            
            System.out.println("Enter Product Id:");
            proId = sc.nextLine();
            
            System.out.println("Enter Product Name");
            proName = sc.nextLine();
            
            System.out.println("Enter Product Price");
            proPrice = sc.nextLine();
            
            System.out.println("Enter Product Expiry");
            proExpiry = sc.nextLine();
            
            // set values to Student object by using constructor
            product = new Product(proId, proName, proPrice, proExpiry);   
            
            // serialize Product using mapper
            String jsonString = mapper
                .writerWithDefaultPrettyPrinter()
                .writeValueAsString(product);
            System.out.println(jsonString);
        }
        catch (IOException e) { 
            e.printStackTrace();
        }
        
        //close Scanner class object
        sc.close();
        
    }
}

//create class Product by using @JsonIgnoreProperties
@JsonIgnoreProperties({ "proId", "expire" })
class Product {  
    
    //Creating properties of Product class  
    public String proId;    
    public String name;    
    public String price;
    public String expire; 
    
    // constructor
    Product(String proId, String name, String price, String expire){
        this.proId = proId;
        this.name = name;
        this.price = price;
        this.expire = expire;
    }
    
}

输出

@JsonIgnore

@JsonIgnore 注解是另一个属性包含注解，用于标记要忽略的属性或属性列表。 @JsonIgnoreProperties 和 @JsonIgnore 之间唯一的区别是 @JsonIgnore 在字段级别使用，而 @JsonIgnoreProperties 在类级别使用。

让我们举个例子来了解它是如何工作的。

JsonIgnoreExample.java

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

import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.databind.ObjectMapper;

//create class JsonIgnorePropertiesExample to understand the working of annotation
public class JsonIgnoreExample {
    
    //main() methods start
    public static void main(String args[]) {
        
        // create an instance of ObjectMapper class
        ObjectMapper mapper = new ObjectMapper();
        
        // create Scanner class object
        Scanner sc= new Scanner(System.in);
        
        // using try-catch for serializing Product
        try {
            
            Product product;
            
            String proId, proName, proPrice, proExpiry;
            
            System.out.println("Enter Product Id:");
            proId = sc.nextLine();
            
            System.out.println("Enter Product Name");
            proName = sc.nextLine();
            
            System.out.println("Enter Product Price");
            proPrice = sc.nextLine();
            
            System.out.println("Enter Product Expiry");
            proExpiry = sc.nextLine();
            
            // set values to Student object by using constructor
            product = new Product(proId, proName, proPrice, proExpiry);   
            
            // serialize Product using mapper
            String jsonString = mapper
                .writerWithDefaultPrettyPrinter()
                .writeValueAsString(product);
            System.out.println(jsonString);
        }
        catch (IOException e) { 
            e.printStackTrace();
        }   
        
        // close Scanner class object
        sc.close();
    }
}

//create class Product by using @JsonIgnore
class Product {  
    
    //Creating properties of Product class  
    public String proId;    
    public String name;    
    public String price;
    @JsonIgnore
    public String expire; 
    
    // constructor
    Product(String proId, String name, String price, String expire){
        this.proId = proId;
        this.name = name;
        this.price = price;
        this.expire = expire;
    }
    
}

输出

@JsonIgnoreType

@JsonIgnoreType 是另一个注解，我们还用它来标记要忽略的特殊类型属性。让我们以 @JsonIgnoreType 注解为例来了解它是如何工作的。

JsonIgnoreTypeExample.java

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

import com.fasterxml.jackson.annotation.JsonIgnoreType;
import com.fasterxml.jackson.databind.ObjectMapper;

//create class JsonIgnoreTypeExample to understand the working of annotation
public class JsonIgnoreTypeExample {
    
    //main() methods start
    public static void main(String args[]) {
        
        // create an instance of ObjectMapper class
        ObjectMapper mapper = new ObjectMapper();
        
        // create Scanner class object
        Scanner sc= new Scanner(System.in);
        
        // using try-catch for serializing Product
        try {
            
            Product product;
            
            String proId, proName, proPrice, proExpiry;
            
            System.out.println("Enter Product Id:");
            proId = sc.nextLine();
            
            System.out.println("Enter Product Name");
            proName = sc.nextLine();
            
            System.out.println("Enter Product Price");
            proPrice = sc.nextLine();
            
            System.out.println("Enter Product Expiry");
            proExpiry = sc.nextLine();
            
            // set values to Student object by using constructor
            product = new Product(proId, proName, proPrice, proExpiry);   
            
            // serialize Product using mapper
            String jsonString = mapper
                .writerWithDefaultPrettyPrinter()
                .writeValueAsString(product);
            System.out.println(jsonString);
        }
        catch (IOException e) { 
            e.printStackTrace();
        }   
        
        //close Scanner class object
        sc.close();
        
    }
}

//create class Product by using @JsonIgnore
class Product {  
    
    //Creating properties of Product class  
    public String proId;    
    public Name name;    
    public String price;
    public String expire; 
    
    // constructor
    Product(String proId, String name, String price, String expire){
        this.proId = proId;
        this.name = new Name(name);
        this.price = price;
        this.expire = expire;
    }
    
    @JsonIgnoreType
    class Name {
        public String name;
        Name(String name){
            this.name = name;
        }       
    }
}

输出

@JsonInclude

@JsonInclude 是另一个重要的属性包含注解，用于排除具有默认值、空值或空值的属性。让我们举个例子来了解如何使用该注解从序列化中排除 null 值。

JsonIncludeExample.java

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

import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.databind.ObjectMapper;

//create class JsonIncludeExample to understand the working of annotation
public class JsonIncludeExample {
    
    //main() methods start
    public static void main(String args[]) {
        
        // create an instance of ObjectMapper class
        ObjectMapper mapper = new ObjectMapper();
        
        // create Scanner class object
        Scanner sc= new Scanner(System.in);		
        
        // using try-catch for serializing Product
        try {
            
            Product product;
            
            String proId, proName, proPrice, proExpiry;
            
            System.out.println("Enter Product Id:");
            proId = sc.nextLine();
            
            System.out.println("Enter Product Name");
            proName = sc.nextLine();
            
            System.out.println("Enter Product Price");
            proPrice = sc.nextLine();
            
            // set values to Student object by using constructor
            product = new Product(proId, proName, proPrice, null);   
            
            // serialize Product using mapper
            String jsonString = mapper
                .writerWithDefaultPrettyPrinter()
                .writeValueAsString(product);
            System.out.println(jsonString);
        }
        catch (IOException exception) { 
            exception.printStackTrace();
        }
        
        //close Scanner class object
        sc.close();
        
    }
}

//create class Product by using @JsonInclude
@JsonInclude(JsonInclude.Include.NON_NULL)
class Product {  
    
    //Creating properties of Product class  
    public String proId;    
    public String name;    
    public String price;
    public String expire; 
    
    // constructor
    Product(String proId, String name, String price, String expire){
        this.proId = proId;
        this.name = name;
        this.price = price;
        this.expire = expire;
    }
}

输出

@JsonAutoDetect

@JsonAutoDetect 是另一个重要的属性包含注解，用于包含否则无法访问的属性。让我们了解如何使用该注解来包含不可访问的属性。

JsonAutoDetectExample.java

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

import com.fasterxml.jackson.annotation.JsonAutoDetect;
import com.fasterxml.jackson.databind.ObjectMapper;

//create class JsonAutoDetectExample to understand the working of annotation
public class JsonAutoDetectExample {
    
    //main() methods start
    public static void main(String args[]) {
        
        // create an instance of ObjectMapper class
        ObjectMapper mapper = new ObjectMapper();
        
        // create Scanner class object
        Scanner sc= new Scanner(System.in);		
        
        // using try-catch for serializing Product
        try {
            
            Product product;
            
            String proId, proName, proPrice, proExpiry;
            
            System.out.println("Enter Product Id:");
            proId = sc.nextLine();
            
            System.out.println("Enter Product Name");
            proName = sc.nextLine();
            
            System.out.println("Enter Product Price");
            proPrice = sc.nextLine();
            
            System.out.println("Enter Product Expiry");
            proExpiry = sc.nextLine();
            
            // set values to Student object by using constructor
            product = new Product(proId, proName, proPrice, proExpiry);   
            
            // serialize Product using mapper
            String jsonString = mapper
                .writerWithDefaultPrettyPrinter()
                .writeValueAsString(product);
            System.out.println(jsonString);
        }
        catch (IOException e) { 
            e.printStackTrace();
        }
        
        //close Scanner class object
        sc.close();
        
    }
}

//create class Product by using @JsonAutoDetect
@JsonAutoDetect(fieldVisibility = JsonAutoDetect.Visibility.ANY)
class Product {  
    
    //Creating properties of Product class  
    private String proId;    
    private String name;    
    private String price;
    private String expire; 
    
    // constructor
    Product(String proId, String name, String price, String expire){
        this.proId = proId;
        this.name = name;
        this.price = price;
        this.expire = expire;
    } 
}

输出