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Friday, 6 July 2018

Gson - Excluding fields from Serialization



Gson - Excluding fields from Serialization

By default, GSON excludes transient and static fields from the serialization/deserialization process. Let’s take a look at the following example.

Example

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();     
      Gson gson = builder.create();  
      
      Student student = new Student(); 
      student.setRollNo(1); 
      student.setName("Mahesh Kumar"); 
      student.setVerified(true); 
      student.setId(1); 
      student.className = "VI";  
      
      String jsonString = gson.toJson(student); 
      System.out.println(jsonString);    
   }      
} 
class Student { 
   private int rollNo; 
   private String name; 
   private boolean verified;  
   private transient int id; 
   public static String className;  
   
   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 void setVerified(boolean verified) { 
      this.verified = verified; 
   }  
   public boolean isVerified() { 
      return verified; 
   }  
   public int getId() { 
      return id; 
   }  
   public void setId(int id) { 
      this.id = id; 
   } 
}   

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":"Mahesh Kumar","verified":true}

Using excludeFieldsWithModifiers

GsonBuilder provides control over excluding fields with particular modifier using excludeFieldsWithModifiers() method from serialization/deserialization process. See the following example.

Example

Create a Java class file named GsonTester in C:\>GSON_WORKSPACE.
File: GsonTester.java
import java.lang.reflect.Modifier; 

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

public class GsonTester { 
   public static void main(String args[]) { 
      GsonBuilder builder = new GsonBuilder(); 
      builder.excludeFieldsWithModifiers(Modifier.TRANSIENT);    
      Gson gson = builder.create();  
      
      Student student = new Student(); 
      student.setRollNo(1); 
      student.setName("Mahesh Kumar"); 
      student.setVerified(true); 
      student.setId(1); 
      student.className = "VI";  
      
      String jsonString = gson.toJson(student); 
      System.out.println(jsonString);    
   }      
} 
class Student { 
   private int rollNo; 
   private String name;
   private boolean verified;  
   private transient int id; 
   public static String className;  
   
   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 void setVerified(boolean verified) { 
      this.verified = verified; 
   }  
   public boolean isVerified() { 
      return verified; 
   }  
   public int getId() { 
      return id; 
   }  
   public void setId(int id) { 
      this.id = id; 
   } 
} 

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":"Mahesh Kumar","verified":true,"className":"VI"}

Using @Expose Annotation

Gson provides @Expose annotation to control the Json serialization/deserialization of a class based on its scope. Consider the following class with a variable having @Expose support. In this class, nameand rollno variables are to be exposed for serialization. Then we've used the GsonBuilder.excludeFieldsWithoutExposeAnnotation() method to indicate that only exposed variables are to be serialized/deserialized. See the following example.

Example

Create a Java class file named GsonTester in C:\>GSON_WORKSPACE.
File: GsonTester.java
import com.google.gson.Gson; 
import com.google.gson.GsonBuilder; 
import com.google.gson.annotations.Expose;  

public class GsonTester { 
   public static void main(String args[]) { 
      GsonBuilder builder = new GsonBuilder();     
      builder.excludeFieldsWithoutExposeAnnotation(); 
      Gson gson = builder.create();  
      
      Student student = new Student(); 
      student.setRollNo(1); 
      student.setName("Mahesh Kumar"); 
      student.setVerified(true); 
      student.setId(1); 
      student.className = "VI"; 
      
      String jsonString = gson.toJson(student); 
      System.out.println(jsonString);    
   }      
} 
class Student { 
   @Expose 
   private int rollNo; 
   
   @Expose 
   private String name; 
   private boolean verified;  
   private int id; 
   public static String className;  
   
   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 void setVerified(boolean verified) { 
      this.verified = verified; 
   }  
   public boolean isVerified() { 
      return verified; 
   }  
   public int getId() { 
      return id; 
   }  
   public void setId(int id) { 
      this.id = id; 
   } 
}

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":"Mahesh Kumar"} 

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