JavaLayerUtils.java

/*
 * 11/19/04		1.0 moved to LGPL.
 * 12/12/99		Initial version.	mdm@techie.com
 *-----------------------------------------------------------------------
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU Library General Public License as published
 *   by the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU Library General Public License for more details.
 *
 *   You should have received a copy of the GNU Library General Public
 *   License along with this program; if not, write to the Free Software
 *   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 *----------------------------------------------------------------------
 */

package audio.javazoom.jl.decoder;

import java.io.IOException;
import java.io.InputStream;
import java.io.InvalidClassException;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.OutputStream;
import java.lang.reflect.Array;

/**
 * The JavaLayerUtils class is not strictly part of the JavaLayer API.
 * It serves to provide useful methods and system-wide hooks.
 * 
 * @author MDM
 */
public class JavaLayerUtils
{
	static private JavaLayerHook	hook = null;
	
	/**
	 * Deserializes the object contained in the given input stream.
	 * @param in	The input stream to deserialize an object from.
	 * @param cls	The expected class of the deserialized object. 
	 */
	static public Object deserialize(InputStream in, Class cls)
		throws IOException
	{
		if (cls==null)
			throw new NullPointerException("cls");
		
		Object obj = deserialize(in, cls);
		if (!cls.isInstance(obj))
		{
			throw new InvalidObjectException("type of deserialized instance not of required class.");
		}
		
		return obj;
	}
	
	/**
	 * Deserializes an object from the given <code>InputStream</code>.
	 * The deserialization is delegated to an <code>
	 * ObjectInputStream</code> instance. 
	 * 
	 * @param in	The <code>InputStream</code> to deserialize an object
	 *				from.
	 * 
	 * @return The object deserialized from the stream. 
	 * @exception IOException is thrown if there was a problem reading
	 *		the underlying stream, or an object could not be deserialized
	 *		from the stream.
	 * 
	 * @see java.io.ObjectInputStream
	 */
	static public Object deserialize(InputStream in)
		throws IOException
	{
		if (in==null)
			throw new NullPointerException("in");
		
		ObjectInputStream objIn = new ObjectInputStream(in);
		
		Object obj;
		
		try
		{
			obj = objIn.readObject();
		}
		catch (ClassNotFoundException ex)
		{
			throw new InvalidClassException(ex.toString());
		}
		
		return obj;
	}

	/**
	 * Deserializes an array from a given <code>InputStream</code>.
	 * 
	 * @param in		The <code>InputStream</code> to 
	 *					deserialize an object from.
	 *				
	 * @param elemType	The class denoting the type of the array
	 *					elements.
	 * @param length	The expected length of the array, or -1 if
	 *					any length is expected.
	 */
	static public Object deserializeArray(InputStream in, Class elemType, int length)
		throws IOException
	{
		if (elemType==null)
			throw new NullPointerException("elemType");
		
		if (length<-1)
			throw new IllegalArgumentException("length");
		
		Object obj = deserialize(in);
		
		Class cls = obj.getClass();
		
		
		if (!cls.isArray())
			throw new InvalidObjectException("object is not an array");
		
		Class arrayElemType = cls.getComponentType();
		if (arrayElemType!=elemType)
			throw new InvalidObjectException("unexpected array component type");
				
		if (length != -1)
		{
			int arrayLength = Array.getLength(obj);
			if (arrayLength!=length)
				throw new InvalidObjectException("array length mismatch");
		}
		
		return obj;
	}

	static public Object deserializeArrayResource(String name, Class elemType, int length)
		throws IOException
	{		
		InputStream str = getResourceAsStream(name);
		if (str==null)
			throw new IOException("unable to load resource '"+name+"'");
		
		Object obj = deserializeArray(str, elemType, length);
		
		return obj;
	}	
	
	static public void serialize(OutputStream out, Object obj)
		throws IOException
	{
		if (out==null)
			throw new NullPointerException("out");
		
		if (obj==null)
			throw new NullPointerException("obj");
		
		ObjectOutputStream objOut = new ObjectOutputStream(out);
		objOut.writeObject(obj);
				
	}

	/**
	 * Sets the system-wide JavaLayer hook.
	 */
	static synchronized public void setHook(JavaLayerHook hook0)		
	{
		hook = hook0;
	}
	
	static synchronized public JavaLayerHook getHook()
	{
		return hook;	
	}
	
	/**
	 * Retrieves an InputStream for a named resource. 
	 * 
	 * @param name	The name of the resource. This must be a simple
	 *				name, and not a qualified package name.
	 * 
	 * @return		The InputStream for the named resource, or null if
	 *				the resource has not been found. If a hook has been 
	 *				provided, its getResourceAsStream() method is called
	 *				to retrieve the resource. 
	 */
	static synchronized public InputStream getResourceAsStream(String name)
	{
		InputStream is = null;
		
		if (hook!=null)
		{
			is = hook.getResourceAsStream(name);	
		}
		else
		{
			Class cls = JavaLayerUtils.class;
			is = cls.getResourceAsStream(name);
		}
		
		return is;		
	}
}