Java in a Nutshell, 5th Edition

Object Persistence

The Java platform provides two mechanisms for object persistence: the ability to save object state so that the object can later be recreated. Both mechanisms involve serialization; the second is aimed particularly at JavaBeans.

Serialization

One of the most important features of the java.io package is the ability to serialize objects: to convert an object into a stream of bytes that can later be deserialized back into a copy of the original object. The following code shows how to use serialization to save an object to a file and later read it back:

Object o;  // The object we are serializing; it must implement Serializable
File f;    // The file we are saving it to

try {
  // Serialize the object
  ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(f));
  oos.writeObject(o);
  oos.close();

  // Read the object back in
  ObjectInputStream ois = new ObjectInputStream(new FileInputStream(f));
  Object copy = ois.readObject();
  ois.close();
} 
catch (IOException e) { /* Handle input/output exceptions */ }
catch (ClassNotFoundException cnfe) { /* readObject() can throw this */ }

The previous example serializes to a file, but remember, you can write serialized objects to any type of stream. Thus, you can write an object to a byte array, then read it back from the byte array, creating a deep copy of the object. You can write the object’s bytes to a compression stream or even write the bytes to a stream connected across a network to another program!

JavaBeans Persistence ...