agletinputstream.java

aglet的部分源码

package com.ibm.aglets;

/*
 * @(#)AgletInputStream.java
 * 
 * IBM Confidential-Restricted
 * 
 * OCO Source Materials
 * 
 * 03L7246 (c) Copyright IBM Corp. 1996, 1998
 * 
 * The source code for this program is not published or otherwise
 * divested of its trade secrets, irrespective of what has been
 * deposited with the U.S. Copyright Office.
 */

import java.io.*;

/**
 * An instance of this class reads objects from an input stream which contains
 * class data with objects. The input stream contains objects, class data of
 * these objects and class data of all super classes of these classes. Data in
 * the input stream must be written by an instance of the AgletOutputStream.<p>
 * 
 * This aglet input stream looks into the class loader cache of the AgletLoader
 * and gets a class loader corresponding to the URL of an origin of the
 * received class. If the class loader is not found in the cache, this stream
 * will creates a new class loader and put it into the cache. After getting the
 * class loader, this stream gets a class of the received object from the class
 * cache of the class loader. If the class is not found in the class cache, the
 * class loader will create the class.
 * 
 * @see AgletOutputStream
 * @see AgletLoader
 * @version     1.00    96/06/28
 * @author      Gaku Yamamoto
 * @author	Mitsuru Oshima
 */

final class AgletInputStream extends ObjectInputStream {

	private ResourceManager rm = null;

	/**
	 * Create a new instance of this class.
	 * @param in an input stream containing objests and class data.
	 * @exception IOException if can not read data from the input stream.
	 * @exception StreamCorruptedException if data in the input stream is
	 * invalid.
	 */
	public AgletInputStream(InputStream in, 
							ResourceManager rm) throws IOException {
		super(in);
		this.rm = rm;
	}
	/*
	 * Verify and check whether the stream contains the aglet
	 */
	protected void readStreamHeader() 
			throws IOException, StreamCorruptedException {
		int incoming_magic = readInt();

		if (incoming_magic != AgletRuntime.AGLET_MAGIC) {
			throw new StreamCorruptedException("InputStream does not contain an aglet");
		} 

		byte stream_version = readByte();

		if (stream_version != AgletRuntime.AGLET_STREAM_VERSION) {
			throw new StreamCorruptedException("Stream Version Mismatch: " 
											   + stream_version);
		} 
	}
	/**
	 * Resolve a class specified by classname. This method reads class data
	 * from the input stream and resolves the class by using a class loader
	 * corresponding to the origin of the class. If the class is common class,
	 * the class will be resolved by super.resolveClass. This method reads
	 * class data of all super classes of the class in the input stream and
	 * put them into the class data cache of the class loader. These super
	 * classes will be  resolved on demand.
	 * @param classname class name.
	 * @return the resolved class.
	 * @exception IOException if can not read data from the input stream.
	 * @exception ClassNotFoundException if can not resolve the class.
	 */
	public Class resolveClass(ObjectStreamClass classinfo) 
			throws IOException, ClassNotFoundException {
		return rm.loadClass(classinfo.getName());
	}
}