ObjectOutputStream | Java In A Nutshell, 5th Edition

ObjectOutputStream

java.io

Java 1.1

closeable flushable

The ObjectOutputStream serializes objects, arrays, and other values to a stream. The writeObject( ) method serializes an object or array, and various other methods write primitive data values to the stream. Note that only objects that implement the Serializable or Externalizable interface can be serialized.

A class that wants to customize the way instances are serialized should declare a private writeObject(ObjectOutputStream) method. This method is invoked when an object is being serialized and can use several additional methods of ObjectOutputStream . defaultWriteObject( ) performs the same serialization that would happen if no writeObject( ) method existed. An object can call this method to serialize itself and then use other methods of ObjectOutputStream to write additional data to the serialization stream. The class must define a matching readObject( ) method to read that additional data, of course. When working with multiple versions or implementations of a class, you may have to serialize a set of fields that do not precisely match the fields of your class. In this case, give your class a static field named serialPersistentFields whose value is an array of ObjectStreamField objects that describe the fields to be serialized. In your writeObject( ) method, call putFields( ) to obtain an ObjectOutputStream.PutField object. Store field names and values into this object, and then call writeFields( ) to write them out to the serialization stream. See ObjectStreamField and ObjectOutputStream.PutField for further details.

The remaining methods of ObjectOutputStream are miscellaneous stream-manipulation methods and protected methods for use by subclasses that want to customize its serialization behavior.

Figure 9-38. java.io.ObjectOutputStream

 public class  ObjectOutputStream  extends OutputStream implements ObjectOutput,       ObjectStreamConstants {  // Public Constructors  public  ObjectOutputStream  (OutputStream  out  ) throws IOException;  // Protected Constructors   1.2  protected  ObjectOutputStream  ( ) throws IOException, SecurityException;  // Nested Types   1.2  public abstract static class  PutField  ;  // Public Instance Methods  public void  defaultWriteObject  ( ) throws IOException;  1.2  public ObjectOutputStream.PutField  putFields  ( ) throws IOException;        public void  reset  ( ) throws IOException;  1.2  public void  useProtocolVersion  (int  version  ) throws IOException;  1.2  public void  writeFields  ( ) throws IOException;  1.4  public void  writeUnshared  (Object  obj  ) throws IOException;  // Methods Implementing DataOutput  public void  writeBoolean  (boolean  val  ) throws IOException;        public void  writeByte  (int  val  ) throws IOException;        public void  writeBytes  (String  str  ) throws IOException;        public void  writeChar  (int  val  ) throws IOException;        public void  writeChars  (String  str  ) throws IOException;        public void  writeDouble  (double  val  ) throws IOException;        public void  writeFloat  (float  val  ) throws IOException;        public void  writeInt  (int  val  ) throws IOException;        public void  writeLong  (long  val  ) throws IOException;        public void  writeShort  (int  val  ) throws IOException;        public void  writeUTF  (String  str  ) throws IOException;  // Methods Implementing ObjectOutput  public void  close  ( ) throws IOException;        public void  flush  ( ) throws IOException;        public void  write  (int  val  ) throws IOException;        public void  write  (byte[ ]  buf  ) throws IOException;        public void  write  (byte[ ]  buf  , int  off  , int  len  ) throws IOException;        public final void  writeObject  (Object  obj  ) throws IOException;  // Protected Instance Methods  protected void  annotateClass  (Class<?>  cl  ) throws IOException;  empty   1.3  protected void  annotateProxyClass  (Class<?>  cl  ) throws IOException;  empty  protected void  drain  ( ) throws IOException;        protected boolean  enableReplaceObject  (boolean  enable  ) throws SecurityException;        protected Object  replaceObject  (Object  obj  ) throws IOException;  1.3  protected void  writeClassDescriptor  (ObjectStreamClass  desc  ) throws IOException;  1.2  protected void  writeObjectOverride  (Object  obj  ) throws IOException;  empty  protected void  writeStreamHeader  ( ) throws IOException;   }