Jackson 在编组时忽略属性

17 Mar 2025 | 5 分钟阅读

在本节中，我们将了解在将对象序列化为 JSON 时，如何忽略字段。有多种方法可以忽略属性，当我们使用 Jackson 默认值不足以控制序列化到 JSON 的内容时，可以使用这些方法。

在类级别忽略字段

在类级别，我们可以通过使用 @JsonIgnoreProperties 和 按名称指定字段 来轻松地忽略特定字段。让我们举个例子来了解如何使用此注解在类级别忽略字段。

IgnoreFieldExample1.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 IgnoreFieldExample1 to understand how we can ignore properties on marshalling
public class IgnoreFieldExample1 {  
   
	//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
		try {  
           
			College colg;  
           
			String name, university, address, rank;  
           
			System.out.println("Enter College Name:");  
			name = sc.nextLine();  
           
			System.out.println("Enter University Name:");  
			university = sc.nextLine();  
           
			System.out.println("Enter College Address:");  
			address = sc.nextLine();  
           
			System.out.println("Enter College Rank:");  
			rank = sc.nextLine();  
           
			// set values to College object by using constructor  
			colg = new College(name, university, address, rank);     
           
			// serialize College using mapper  
			String jsonString = mapper  
					.writerWithDefaultPrettyPrinter()  
					.writeValueAsString(colg);  
			System.out.println(jsonString);  
		} catch (IOException e) {   
			e.printStackTrace();  
		}  
       
		//close Scanner class object  
		sc.close();  
       
	}  
}  

//create class College by using @JsonIgnoreProperties  
@JsonIgnoreProperties({ "address", "rank" })  
class College {    
	//Creating properties of College class    
	public String name;      
	public String university;      
	public String address;  
	public String rank;   
   
	// constructor  
	College(String name, String university, String address, String rank){  
		this.name = name;  
		this.university = university;  
		this.address = address;  
		this.rank = rank;  
	}  
   
}  

输出

Jackson Ignore Properties on Marshalling

在字段级别忽略字段

在字段级别，我们可以借助 @JsonIgnore 直接忽略该字段。让我们举个例子来了解如何使用此注解在字段级别忽略字段。

IgnoreFieldExample2.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 IgnoreFieldExample2 to understand how we can ignore properties on marshalling
public class IgnoreFieldExample2 {  
 
	//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
		try {  
         
			College colg;  
         
			String name, university, address, rank;  
         
			System.out.println("Enter College Name:");  
			name = sc.nextLine();  
         
			System.out.println("Enter University Name:");  
			university = sc.nextLine();  
         
			System.out.println("Enter College Address:");  
			address = sc.nextLine();  
         
			System.out.println("Enter College Rank:");  
			rank = sc.nextLine();  
         
			// set values to College object by using constructor  
			colg = new College(name, university, address, rank);     
         
			// serialize College using mapper  
			String jsonString = mapper  
					.writerWithDefaultPrettyPrinter()  
					.writeValueAsString(colg);  
			System.out.println(jsonString);  
		} catch (IOException e) {   
			e.printStackTrace();  
		}  
     
		//close Scanner class object  
		sc.close();  
     
	}  
}  

//create class College by using @JsonIgnore
class College {    
 
	//Creating properties of College class    
	public String name;      
	public String university;   
	
	@JsonIgnore
	public String address;  
	
	@JsonIgnore
	public String rank;   
 
	// constructor  
	College(String name, String university, String address, String rank){  
		this.name = name;  
		this.university = university;  
		this.address = address;  
		this.rank = rank;  
	}  
}   

输出

按类型忽略所有字段

通过这种方式，我们忽略了指定类型的所有字段。如果我们可以控制类型，则可以直接注释该类。

@JsonIgnoreType
public class SomeType { ? }

然而，我们并不总是可以控制类本身，因此我们也可以使用 Jackson mixins。我们使用以下步骤来使用 mixins

1. 为我们想要忽略的类型定义 mixin。

2. 使用 @JsonIgnoreType 注解注释 mixin。

@JsonIgnoreType
public class MyMixInForIgnoreType {}

3. 注册 mixin 以在编组期间忽略所有 Address 类型。

让我们举个例子来了解如何使用 mixin 来忽略 Address 类型的字段。

IgnoreFieldExample3.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 IgnoreFieldExample3 to understand how we can ignore properties on marshalling using mixin
public class IgnoreFieldExample3 {  

	//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
		try {  
       
			College colg;  
       
			String name, university, street, state, city, rank;  
       
			System.out.println("Enter College Name:");  
			name = sc.nextLine();  
       
			System.out.println("Enter University Name:");  
			university = sc.nextLine();  
       
			System.out.println("Enter Street:");  
			street = sc.nextLine();  
			
			System.out.println("Enter City:");  
			city = sc.nextLine();
			
			System.out.println("Enter State:");  
			state = sc.nextLine();
			
			System.out.println("Enter College Rank:");  
			rank = sc.nextLine();  
       
			// set values to College object by using constructor  
			colg = new College(name, university, new Address(street, state, city), rank);
			
			//  register mixin to ignore field of Address type
			mapper.addMixIn(Address.class, MixInForIgnoreType.class);  
			
			String jsonStr = mapper
					.writerWithDefaultPrettyPrinter()  
	                .writeValueAsString(colg);
			System.out.println(jsonStr);  
	            
		} catch (IOException e) {   
			e.printStackTrace();  
		}  
   
		//close Scanner class object  
		sc.close();  
   
	}  
}  

//create class College by using @JsonIgnore
class College {    

	//Creating properties of College class    
	public String name;      
	public String university;   
	public Address address;  
	public String rank;   

	// constructor  
	College(String name, String university, Address address, String rank){  
		this.name = name;  
		this.university = university;  
		this.address = address;  
		this.rank = rank;  
	}  

} 
//create class Address  
class Address {  
	public String address;
	
	Address(String street, String state, String city){  
		address = street+", "+city+", "+state;  
	}         
}  
@JsonIgnoreType  
class MixInForIgnoreType {}  

输出

通过使用过滤器忽略字段

通过使用过滤器，我们还可以在 Jackson 中忽略特定字段。为了使用过滤器，我们需要以下列方式在 Java 对象上定义它

@JsonFilter("myFilter")
public class MyDtoWithFilter { ... }

之后，我们定义一个简单的过滤器来忽略 intValue 字段

SimpleBeanPropertyFilter filter = SimpleBeanPropertyFilter
  .serializeAllExcept("intValue");
FilterProvider filters = new SimpleFilterProvider()
  .addFilter("myFilter", filter);

让我们举个例子来了解如何使用过滤器来忽略 intValue 字段。

IgnoreFieldExample4.java

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

import com.fasterxml.jackson.annotation.JsonFilter;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.ser.FilterProvider;
import com.fasterxml.jackson.databind.ser.impl.SimpleBeanPropertyFilter;
import com.fasterxml.jackson.databind.ser.impl.SimpleFilterProvider;  

//create class IgnoreFieldExample4 to understand how we can ignore properties on marshalling using filter
public class IgnoreFieldExample4 {  

	//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
		try {  
       
			College colg;  
       
			String name, university, street, state, city, rank;  
       
			System.out.println("Enter College Name:");  
			name = sc.nextLine();  
       
			System.out.println("Enter University Name:");  
			university = sc.nextLine();  
       
			System.out.println("Enter Street:");  
			street = sc.nextLine();  
			
			System.out.println("Enter City:");  
			city = sc.nextLine();
			
			System.out.println("Enter State:");  
			state = sc.nextLine();
			
			System.out.println("Enter College Rank:");  
			rank = sc.nextLine();  
       
			// set values to College  object by using constructor  
			colg = new College(name, university, new Address(street, state, city), rank);
			
			SimpleBeanPropertyFilter filter = SimpleBeanPropertyFilter
					.serializeAllExcept("rank");
			FilterProvider filters = new SimpleFilterProvider()
					.addFilter("myFilter", filter);
			
			String dtoAsString = mapper.writer(filters).writeValueAsString(colg);
			System.out.println(dtoAsString);
	            
		} catch (IOException e) {   
			e.printStackTrace();  
		}  
   
		//close Scanner class object  
		sc.close();  
   
	}  
}  
//create class College by using @JsonFilter("myFilter")
@JsonFilter("myFilter")
class College {    

	//Creating properties of College class    
	public String name;      
	public String university;   
	public Address address;  
	public String rank;   

	// constructor  
	College(String name, String university, Address address, String rank){  
		this.name = name;  
		this.university = university;  
		this.address = address;  
		this.rank = rank;  
	}  

}
//create class Address  
class Address {  
	public String address;
	
	Address(String street, String state, String city){  
		address = street+", "+city+", "+state;  
	}         
}

输出