// $Id: Marshaller.java,v 1.6 2007/05/01 09:15:17 belaban Exp $
package org.jgroups.util;
import org.jgroups.conf.ClassConfigurator;
import org.jgroups.ChannelException;
import java.io.Externalizable;
import java.io.IOException;
import java.io.ObjectInput;
import java.io.ObjectOutput;
/**
* Title: JGroups Communications
* Description: Contact me at <a href="mailto:mail@filip.net">mail@filip.net</a>
* Copyright: Copyright (c) 2002
* Company: www.filip.net
* @author Filip Hanik
* @author Bela Ban
* @version 1.0
*
* This class marshalls classes, in other words it serializes and deserializes classes
* to and from object streams.
* It performs a magic number matching to decrease the number of bytes that are being sent
* over the wire.
* If no magic number is available for the class, the classname is sent over instead
*/
public class Marshaller {
/**
* The class configurator maps classes to magic numbers
*/
private static final ClassConfigurator mConfigurator;
static {
try {
mConfigurator=ClassConfigurator.getInstance(true);
}
catch(ChannelException e) {
throw new ExceptionInInitializerError(e.toString());
}
}
public Marshaller() {
}
/**
* reads the magic number, instantiates the class (from the
* configurator) and invokes the readExternal method on the object.
* If no magic number is present, the method will read the
* string and then get the class from the configurator.
* @param in an ObjectInput stream - the stream should be composed as follows:<BR>
* [boolean -> int|string -> object data]
* <BR>
* If the boolean is true, then the next value is an int, the magic number.<BR>
* If the boolean is false, then the next value is a string (the class name)<BR>
* The object data is what the object instance uses to populate its fields<BR>
*/
public static Externalizable read(ObjectInput in) throws IOException {
try {
boolean is_null=in.readBoolean();
if(is_null)
return null;
//see if we want to use a magic number
boolean usemagic=in.readBoolean();
//the class that we will use to instantiate the object with
Class extclass=null;
if(usemagic) {
//read the magic number
short magic=in.readShort();
//from the magic number, get the class
extclass=mConfigurator.get(magic);
}
else {
//we don't have a magic number, read the class name
String magic=in.readUTF();
//get the class, ie let the configurator load it
extclass=mConfigurator.get(magic);
}//end if
//instantiate the object
Externalizable newinstance=(Externalizable)extclass.newInstance();
//populate the object with its data
newinstance.readExternal(in);
//return the instance
return newinstance;
}
catch(Throwable x) {
if(x instanceof IOException)
throw (IOException)x;
else
throw new IOException(x.toString());
}
}
/**
* Writes an object to the ObjectOutput stream.
* If possible, we will send over a magic number instead of the class name
* so that we transfer less amount of data.
* @param inst - an object instance to be serialized, can not be null
* @param out - the ObjectOutput stream we will write the serialized data to
*/
public static void write(Externalizable inst, ObjectOutput out) throws IOException {
boolean is_null=(inst == null);
try {
// if inst is a null value we write this first
out.writeBoolean(is_null);
if(is_null)
return;
//find out if we have a magic number for this class
short magic=mConfigurator.getMagicNumber(inst.getClass());
//-1 means no magic number otherwise we have one
if(magic != -1) {
//true means we use a magic number
out.writeBoolean(true);
//write the magic number
out.writeShort(magic);
}
else {
//we don't have a magic number
out.writeBoolean(false);
//write the classname instead
out.writeUTF(inst.getClass().getName());
}//end if
//write the object data
inst.writeExternal(out);
}
catch(Exception x) {
if(x instanceof IOException)
throw (IOException)x;
else
throw new java.io.IOException(x.toString());
}
}
}