Getting transient variable values while deserializing

[Dinakar Kas]

Hi all,

I have the following code:

  

package ioexamples;

import java.io.Serializable;

public class Employee implements Serializable{

	private static final long serialVersionUID = 2888019250806468706L;
	private long empId;
	private String empName;
	private transient String dept;
	
	public String getDept() {
		return dept;
	}
	public void setDept(String dept) {
		this.dept = dept;
	}
	
	public long getEmpId() {
		return empId;
	}
	public void setEmpId(long empId) {
		this.empId = empId;
	}
	public String getEmpName() {
		return empName;
	}
	public void setEmpName(String empName) {
		this.empName = empName;
	}
	
	public Object clone()
	throws CloneNotSupportedException
  {
    throw new CloneNotSupportedException(); 
  
  }

}

  

  

package ioexamples;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class ObjectInputOutputStreamExample {

	/**
	 * @param args
	 */
	public static void main(String[] args) throws Exception{
	ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("E:\\objects\\obj.dat"));
	Employee emp = new Employee();
	emp.setEmpId(2);
	emp.setEmpName("Dinakar");
	emp.setDept("IT");
	oos.writeObject(emp);
	oos.flush();
	oos.close();
	ObjectInputStream ois = new ObjectInputStream(new FileInputStream("E:\\objects\\obj.dat"));
	Employee emp2 = (Employee)ois.readObject();
	System.out.println("Employee Id: "+emp2.getEmpId());
	System.out.println("Employee Id: "+emp2.getEmpName());
	System.out.println("Dept Name "+emp2.getDept());
	}

}

  

It works fine.

Now, I made Employee as Singleton, and serializing and deserializing it.

  
package javaranch;

import java.io.Serializable;

public class Employee implements Serializable{

	private static final long serialVersionUID = -5359502671506171397L;
	static  Employee emp;
	public static Employee getInstance(){
		synchronized (Employee.class) {
		if(emp == null){
		emp = new Employee();
		}
		}
		return emp;
	}
	
	private Employee(){
		
	}
	protected Object readResolve(){
		return emp;
	}
	
	private long empId;
	private String empName;
	private transient String dept;
	
	public String getDept() {
		return dept;
	}
	public void setDept(String dept) {
		this.dept = dept;
	}
	
	public long getEmpId() {
		return empId;
	}
	public void setEmpId(long empId) {
		this.empId = empId;
	}
	public String getEmpName() {
		return empName;
	}
	public void setEmpName(String empName) {
		this.empName = empName;
	}
	public Object clone()
	throws CloneNotSupportedException
  {
    throw new CloneNotSupportedException(); 
  
  }
	
}

  

 
package javaranch;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class ObjectInputOutputStreamExample {

	public static void main(String[] args) throws Exception{
	ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("E:\\objects\\obj.dat"));
	Employee emp = Employee.getInstance();
	emp.setEmpId(2);
	emp.setEmpName("Dinakar");
	emp.setDept("IT");
	oos.writeObject(emp);
	oos.flush();
	oos.close();
	ObjectInputStream ois = new ObjectInputStream(new FileInputStream("E:\\objects\\obj.dat"));
	Employee emp2 = (Employee)ois.readObject();
	System.out.println("Employee Id: "+emp2.getEmpId());
	System.out.println("Employee Name: "+emp2.getEmpName());
	System.out.println("Dept Name: "+emp2.getDept());
	}

}

   

When I made Employee as Singleton, while de-serialization, I was able to print the department name which is a transient variable(dept in Employee).

Am I going wrong anywhere?

Thanks
Dinakar

[Christophe Verré]

Transient variables are not initialized after unmarshalling.

EDIT: I mean if you use a singleton. Transient variables would be implicitly initialized to their default values if a new instance was created.

[Dinakar Kas]

Transient variables would be implicitly initialized to their default values if a new instance was created.

But, I am not creating any new Employee object here. I am only unmarshalling it.

Also, even if I create a new Object(Employee here), as I did not specify any default value in it, it should still return null.

so where can be the problem?

Thanks,
Dinakar

[Rob Spoor]

One hint: return getInstance() from readResolve(), not emp. What if emp is still null?

[Dinakar Kas]

return getInstance() from readResolve(), not emp. What if emp is still null?

Done it. Still Nope.

[Rob Spoor]

I didn't say it would solve this issue. It's just very important because it will solve future errors.

readResolve means that the de-serialization process will not return the serialized object but the object returned by the method. This means that the non-serialized singleton instance will be returned, which still has its department set.