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A Serialization Question

Posted on 2001-06-20
8
Medium Priority
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Last Modified: 2011-09-20
Experts,

I have a class named Address which has NOT implemented the Serializable interface. Then I have another class Employee which has implemented the Serializable interface. This Employee class HAS-A Address object embedded as a data member. I do the serialization. I can see the file employee1.dat is created but no data. Why the serialization is not happenning?. Here is the sample program.

prain.


import java.io.*;

class Address
{
     private String address;

     public Address(){}

     public Address( String a )
     {
          setAddress( a );
     }

     public void setAddress( String a )
     {
          address = a ;
     }

     public String getAddress()
     {
          return address;
     }

     public String toString()
     {
          return address;
     }
}

class Employee implements Serializable
{
     String name;
     Address addr;

     public Employee( String a, String b )
     {
          name = a;
          addr = new Address( b );
     }

     public String toString()
     {
          return "Employee: " + name + addr.toString();
     }

     private void writeObject( ObjectOutputStream objout ) throws IOException
     {
          try
          {
               objout.writeObject( addr.getAddress() );
               objout.defaultWriteObject();
          }

          catch( Throwable ex ){}
     }

     private void readObject( ObjectInputStream objin ) throws IOException
     {
          try
          {
               addr.setAddress( (String)objin.readObject() );
               objin.defaultReadObject();
          }

          catch( Throwable ex ){}
     }

     public static void main( String[] args )
     {
          Employee emp = new Employee( "Jack", "Bay Area" );

          try
          {
               ObjectOutputStream out = new ObjectOutputStream( new
BufferedOutputStream( new FileOutputStream( "employee.dat" )));
               out.writeObject( emp );

               out.close();

          }

          catch( Exception e ){}

          try
          {
               ObjectInputStream in = new ObjectInputStream( new
BufferedInputStream( new FileInputStream( "employee.dat" )));

               Employee emp1 = (Employee)in.readObject();
               System.out.println( emp1 );

          }

          catch( Exception e ){}

     }
}



0
Comment
Question by:prain
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8 Comments
 
LVL 3

Accepted Solution

by:
rjackman earned 150 total points
ID: 6210346
hi
The reason is u can't serailise the object which does not implements the Serializable interface
u are getting the exception here but since u have nothing in cath u are not able to c the exception
pls try following
try
{
//ur code goes here
}
catch(Exception ee)
{
  ee.printStackTrace();
}

Soln to the problem is Address shold implement the Serializable interface,
cheers
RJ
0
 
LVL 9

Assisted Solution

by:Ovi
Ovi earned 150 total points
ID: 6210419
Here is an simple example of mine which save the state of an JFrame :


import java.awt.*;
import java.awt.event.*;
import java.io.*;
import javax.swing.*;

public class Serialization extends JFrame {
     protected String title;
     protected Dimension size;
     protected transient JButton sizer = new JButton("HalfSize");
     protected transient JButton titler = new JButton("Title reducer");    
     
     public Serialization(String t, Dimension d) {
          if(!loadState()) {
               setTitle(t);
               setSize(d);              
          }
         
          sizer.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e) {
                    Serialization.this.setSize(new Dimension(size.width/2, size.height/2));
               }
          });
          titler.addActionListener(new ActionListener() {
               public void actionPerformed(ActionEvent e) {
                    Serialization.this.setTitle(title.substring(0, title.length() - 1));
               }
          });
          getContentPane().setLayout(new BorderLayout());
          getContentPane().add(sizer, BorderLayout.NORTH);
          getContentPane().add(titler, BorderLayout.SOUTH);
          addWindowListener(new WindowAdapter() {
               public void windowClosing(WindowEvent w) {
                    saveState();
                    System.exit(0);
               }
          });
     }
     
     public void setTitle(String t) {
          title = t;
          super.setTitle(t);
     }
     
     public String getTitle() {
          return(title);
     }
     
     public void setSize(Dimension d) {
          size = d;
          super.setSize(d);
     }
     
     public Dimension getSize() {
          return(size);
     }
     
     private void saveState() {
         try {
           FileOutputStream fos = new FileOutputStream ("obj.ser");
           ObjectOutputStream oos = new ObjectOutputStream (fos);
           oos.writeObject (this);
           oos.flush();
           oos.close();
           System.out.println("Saved to disk");
         } catch (IOException e) {
           System.out.println("Unable to save");
           e.printStackTrace();
         }          
     }
     
     private boolean loadState() {
          try {
               FileInputStream fis = new FileInputStream("obj.ser");
               ObjectInputStream ois = new ObjectInputStream(fis);
               Object o = ois.readObject();
               ois.close();
               if(o != null)  {
                    setSize(((Serialization) o).getSize());
                    setTitle(((Serialization) o).getTitle());
                    return(true);
               }
          } catch(FileNotFoundException e1) {
               System.out.println("Nu exista fisierul");
          } catch(IOException e2) {
               System.out.println("IOException...");
          } catch(ClassNotFoundException e3) {
               System.out.println("Nu gasesc clasa ");
          }
          return(false);
     }    

     public static void main(String args[]) {
          Serialization s = new Serialization("Serialization example", new Dimension(600, 600));
          s.setLocation(200, 200);
          s.setVisible(true);
     }    
}
0
 
LVL 3

Expert Comment

by:superschlonz
ID: 6210434
There are several bugs in class Emplyeee:

1. make the fields transient which should not be serialized:

transient Address addr;

2. call defaultWriteObject() and defaultReadObject() before writing/reading
other data.

3. In readObject) method the address is null when you want to call setAddress(),
you have to allocate a new object.

addr = new Address( (String)objin.readObject() );

4. why do you make this tray {} catch( Throwable 9 {} without doing something when
it fails. This way you won't find out that something failed reading or writing.
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LVL 9

Expert Comment

by:Ovi
ID: 6210490
My code is not supposed to be a Java bean, but if your read the specification of the Java Bean components there are some restrictions for working with the default serialization process like :
in order to be serializable an java Bean must provide :
- implements Serializable or Externalizable (this only if you implement yourself the serialization) interfaces
- an default constructor which takes no parameters.
- pairs of methods getFoo...&setFoo... for the serializable fields;
- static and final members are not serializable;
- all nonserializable fields must be declared as transient.
0
 
LVL 9

Expert Comment

by:Ovi
ID: 6210496
My code is not supposed to be a Java bean, but if your read the specification of the Java Bean components there are some restrictions for working with the default serialization process like :
in order to be serializable an java Bean must provide :
- implements Serializable or Externalizable (this only if you implement yourself the serialization) interfaces
- an default constructor which takes no parameters.
- pairs of methods getFoo...&setFoo... for the serializable fields;
- static and final members are not serializable;
- all nonserializable fields must be declared as transient.
0
 

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by:Tuvok
ID: 6828809
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Expert Comment

by:CleanupPing
ID: 9062034
prain:
This old question needs to be finalized -- accept an answer, split points, or get a refund.  For information on your options, please click here-> http:/help/closing.jsp#1 
EXPERTS:
Post your closing recommendations!  No comment means you don't care.
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LVL 14

Expert Comment

by:sudhakar_koundinya
ID: 9253853
No comment has been added lately, so it's time to clean up this TA.
I will leave a recommendation in the Cleanup topic area that this question is:


[points to Ovi]


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