jaroutputstream.java

JAVA基本类源代码,大家可以学习学习!

/*
 * @(#)JarOutputStream.java	1.21 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.util.jar;

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

/**
 * The <code>JarOutputStream</code> class is used to write the contents
 * of a JAR file to any output stream. It extends the class
 * <code>java.util.zip.ZipOutputStream</code> with support
 * for writing an optional <code>Manifest</code> entry. The
 * <code>Manifest</code> can be used to specify meta-information about
 * the JAR file and its entries.
 *
 * @author  David Connelly
 * @version 1.21, 01/23/03
 * @see	    Manifest
 * @see	    java.util.zip.ZipOutputStream
 * @since   1.2
 */
public
class JarOutputStream extends ZipOutputStream {
    private static final int JAR_MAGIC = 0xCAFE;

    /**
     * Creates a new <code>JarOutputStream</code> with the specified
     * <code>Manifest</code>. The manifest is written as the first
     * entry to the output stream.
     *
     * @param out the actual output stream
     * @param man the optional <code>Manifest</code>
     * @exception IOException if an I/O error has occurred
     */
    public JarOutputStream(OutputStream out, Manifest man) throws IOException {
	super(out);
	if (man == null) {
	    throw new NullPointerException("man");
	}
	ZipEntry e = new ZipEntry(JarFile.MANIFEST_NAME);
	putNextEntry(e);
	man.write(new BufferedOutputStream(this));
	closeEntry();
    }

    /**
     * Creates a new <code>JarOutputStream</code> with no manifest.
     * @param out the actual output stream
     * @exception IOException if an I/O error has occurred
     */
    public JarOutputStream(OutputStream out) throws IOException {
	super(out);
    }

    /**
     * Begins writing a new JAR file entry and positions the stream
     * to the start of the entry data. This method will also close
     * any previous entry. The default compression method will be
     * used if no compression method was specified for the entry.
     * The current time will be used if the entry has no set modification
     * time.
     *
     * @param ze the ZIP/JAR entry to be written
     * @exception ZipException if a ZIP error has occurred
     * @exception IOException if an I/O error has occurred
     */
    public void putNextEntry(ZipEntry ze) throws IOException {
	if (firstEntry) {
	    // Make sure that extra field data for first JAR
	    // entry includes JAR magic number id.
	    byte[] edata = ze.getExtra();
	    if (edata != null && !hasMagic(edata)) {
		// Prepend magic to existing extra data
		byte[] tmp = new byte[edata.length + 4];
		System.arraycopy(tmp, 4, edata, 0, edata.length);
		edata = tmp;
	    } else {
		edata = new byte[4];
	    }
	    set16(edata, 0, JAR_MAGIC); // extra field id
	    set16(edata, 2, 0);         // extra field size
	    ze.setExtra(edata);
	    firstEntry = false;
	}
	super.putNextEntry(ze);
    }

    private boolean firstEntry = true;

    /*
     * Returns true if specified byte array contains the
     * jar magic extra field id.
     */
    private static boolean hasMagic(byte[] edata) {
	try {
	    int i = 0;
	    while (i < edata.length) {
		if (get16(edata, i) == JAR_MAGIC) {
		    return true;
		}
		i += get16(edata, i + 2) + 4;
	    }
	} catch (ArrayIndexOutOfBoundsException e) {
	    // Invalid extra field data
	}
	return false;
    }

    /*
     * Fetches unsigned 16-bit value from byte array at specified offset.
     * The bytes are assumed to be in Intel (little-endian) byte order.
     */
    private static int get16(byte[] b, int off) {
	return (b[off] & 0xff) | ((b[off+1] & 0xff) << 8);
    }

    /*
     * Sets 16-bit value at specified offset. The bytes are assumed to
     * be in Intel (little-endian) byte order.
     */
    private static void set16(byte[] b, int off, int value) {
	b[off+0] = (byte)value;
	b[off+1] = (byte)(value >> 8);
    }
}