resourceinputstream.java

有关j2me的很好的例子可以研究一下

/*
 * @(#)ResourceInputStream.java	1.6 01/08/21
 * Copyright (c) 1999-2001 Sun Microsystems, Inc. All Rights Reserved.
 *
 * This software is the confidential and proprietary information of Sun
 * Microsystems, Inc. ("Confidential Information").  You shall not
 * disclose such Confidential Information and shall use it only in
 * accordance with the terms of the license agreement you entered into
 * with Sun.
 *
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
 * SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES
 * SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING
 * THIS SOFTWARE OR ITS DERIVATIVES.
 */

package com.sun.midp.io;

import java.io.*;
import java.util.*;

/**
 * Input stream class for accessing resource files in classpath.
 */
public class ResourceInputStream extends InputStream {

    /**
     * instance handle to hold the native reference to the
     * underlying stream.
     * This field must be an Object, since it will point to something
     * that needs to be protected from the garbage collector.
     */
    private Object handle;

    /**
     * Construct a resource input stream for accessing objects in the jar file.
     *
     * @param name the name of the resource in classpath to access.
     * @exception  IOException  if an I/O error occurs.
     */
    public ResourceInputStream(String name) throws IOException {
	if (handle != null) { 
	    throw new IOException();
	}  
	handle = open(name);
    }

    /**
     * Reads the next byte of data from the input stream.
     *
     * @return     the next byte of data, or <code>-1</code> if the end of the
     *             stream is reached.
     * @exception  IOException  if an I/O error occurs.
     */

    public int read() throws IOException { 
	return read(handle);
    }

    /**
     * closes the open resource stream.
     * @exception  IOException  if an I/O error occurs.
     */
    public void close() throws IOException { 
	close(handle);
	handle = null;
    }

    /**
     * native interface to open resource as stream.
     * @param name name of the resource in CLASSPATH
     * @return the Object reference to the located resource.
     * @exception IOException if I/O error occurs.
     */
    private static native Object open(String name) throws IOException;

    /**
     * native interface to read a byte from the opened resource.
     * @param handle for the opened resource
     * @return a character read from the opened resource.
     * @exception IOException if I/O error occurs.
     */
    private static native int read(Object handle) throws IOException;

    /**
     * native interface to close the opened resource.
     * @param handle for the opened resource
     * @exception IOException if I/O error occurs.
     */
    private static native void close(Object handle) throws IOException;
}