Jackson Ignore Properties on Marshalling

In this section, we will understand how we can ignore the fields at the time of serializing an object into JSON. There are various ways to ignore the properties which we use when Jackson defaults are not enough to control what gets serialized to JSON.

Ignore fields at the class level

At the class level, we can easily ignore the specific fields by using the @JsonIgnoreProperties and specifying the fields by name. Let's take an example to understand how we use this annotation to ignore fields at the class level.

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;  
	}  
   
}  

Output:

Jackson Ignore Properties on Marshalling

Ignore fields at the field level

At the field level, we can directly ignore the field with the help of the @JsonIgnore. Let's take an example to understand how we use this annotation to ignore fields at the field level.

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;  
	}  
}   

Output:

Ignore all fields by type

In this way, we ignore all the fields of a specified type. We can directly annotate the class if we can control the type.

@JsonIgnoreType
public class SomeType { ? }

All the time, however, we don't have control of the class itself, so we can use Jackson mixins too. We use the following steps to use mixins:

1. Define mixin for the type we would like to ignore.

2. Annotate mixin with @JsonIgnoreType annotation.

@JsonIgnoreType
public class MyMixInForIgnoreType {}

3. Register mixin for ignoring all Address types during marshalling.

Let's take an example to understand how we can use mixin to ignore fields of Address type.

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 {}  

Output:

Ignore fields by using filters

By using the filters, we can also ignore the specific fields in Jackson. In order to use the filter, we need to define it on the Java object in the following way:

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

After that, we define a simple filter to ignore the intValue field:

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

Let's take an example to understand how we can use a filter to ignore the intValue field.

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;  
	}         
}

Output: