Home » Tip Bank » Java » Object Serialization

Language: Java
Expertise: Beginner

Sep 23, 1997

Some applications must keep small amounts of information between the times they are run. For example a personal calendar or personal information system, will store information after each session. Instead of using a Random access file or even a database to store this information, use Java Object Serialization. Object serialization is fast and reliable, and it restores the complete state of all of your objects. To use Object Serialization, use the following code (JDK 1.1):

 FileOutputStream   fos = new FileOutputStream(
"c:\\store\\objects.ser");
ObjectOutputStream oos = new ObjectOutputStream( fos );

// Write out the root Object of your in-memory object structure.
// Object Serialization will write out all of the objects to the disk
file.

fos.writeObject( rootObject );

To read them back in, reverse the process with:

 FileInputStream fis = new FileInputStream( "c:\\store\\object.ser");
ObjectInputStream oos = new ObjectInputStream( fis );

Object root = oos.readObject();

You must remember to "implement" the interface java.io.Serializable in all of the classes that are to be written to disk:

 public class Person implements java.io.Serializable
{
   . . .
}

This technique works when you want to save the entire state of your memory to disk at one time. If you need to store single objects, then you will need a different architecture.