Gson - Null Object Support


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Gson by default generates optimized Json content ignoring the NULL values. But GsonBuilder provides flags to show NULL values in the Json output using the GsonBuilder.serializeNulls() method.

GsonBuilder builder = new GsonBuilder(); 
builder.serializeNulls(); 
Gson gson = builder.create(); 

Example without serializeNulls Call

Create a Java class file named GsonTester in C:\>GSON_WORKSPACE.

File: GsonTester.java

import com.google.gson.Gson;  

public class GsonTester { 
   public static void main(String args[]) { 
      Gson gson = new Gson();  
      
      Student student = new Student(); 
      student.setRollNo(1);  
      String jsonString = gson.toJson(student); 
      
      System.out.println(jsonString);  
      student = gson.fromJson(jsonString, Student.class); 
      System.out.println(student); 
   }      
} 
class Student { 
   private int rollNo; 
   private String name;  
   
   public int getRollNo() { 
      return rollNo; 
   }  
   public void setRollNo(int rollNo) { 
      this.rollNo = rollNo; 
   }  
   public String getName() { 
      return name; 
   }  
   public void setName(String name) { 
      this.name = name; 
   }   
   public String toString() { 
      return "Student[ name = "+name+", roll no: "+rollNo+ "]"; 
   } 
}

Verify the result

Compile the classes using javac compiler as follows −

C:\GSON_WORKSPACE>javac GsonTester.java

Now run the GsonTester to see the result −

C:\GSON_WORKSPACE>java GsonTester

Verify the output.

{"rollNo": 1} 
Student[ name = null, roll no: 1] 

Example with serializeNulls call

Create a Java class file named GsonTester in C:\>GSON_WORKSPACE.

File: GsonTester.java

import com.google.gson.Gson; 
import com.google.gson.GsonBuilder;  

public class GsonTester { 
   public static void main(String args[]) { 
      GsonBuilder builder = new GsonBuilder(); 
      builder.serializeNulls(); 
      builder.setPrettyPrinting(); 
      Gson gson = builder.create();  
      
      Student student = new Student(); 
      student.setRollNo(1);  
      String jsonString = gson.toJson(student); 
      
      System.out.println(jsonString);  
      student = gson.fromJson(jsonString, Student.class); 
      System.out.println(student); 
   }      
} 
class Student { 
   private int rollNo; 
   private String name;  
   
   public int getRollNo() { 
      return rollNo; 
   }  
   public void setRollNo(int rollNo) { 
      this.rollNo = rollNo; 
   }  
   public String getName() { 
      return name; 
   }  
   public void setName(String name) { 
      this.name = name; 
   }   
   public String toString() { 
      return "Student[ name = "+name+", roll no: "+rollNo+ "]"; 
   } 
}

Verify the result

Compile the classes using javac compiler as follows −

C:\GSON_WORKSPACE>javac GsonTester.java

Now run the GsonTester to see the result −

C:\GSON_WORKSPACE>java GsonTester

Verify the output.

{ 
   "rollNo": 1, 
   "name": null 
} 
Student[ name = null, roll no: 1] 


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