Java example source code file (JarOutputStream.java)

This example Java source code file (JarOutputStream.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

arrayindexoutofboundsexception, bufferedoutputstream, ioexception, jar_magic, jaroutputstream, manifest, nullpointerexception, zip, zipentry, zipoutputstream

The JarOutputStream.java Java example source code

/*
 * Copyright (c) 1997, 2012, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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 General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.util.jar;

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

/**
 * The <code>JarOutputStream class is used to write the contents
 * of a JAR file to any output stream. It extends the class
 * <code>java.util.zip.ZipOutputStream with support
 * for writing an optional <code>Manifest entry. The
 * <code>Manifest can be used to specify meta-information about
 * the JAR file and its entries.
 *
 * @author  David Connelly
 * @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 with the specified
     * <code>Manifest. The manifest is written as the first
     * entry to the output stream.
     *
     * @param out the actual output stream
     * @param man the optional <code>Manifest
     * @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 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)) {
                if (edata == null) {
                    edata = new byte[4];
                } else {
                    // Prepend magic to existing extra data
                    byte[] tmp = new byte[edata.length + 4];
                    System.arraycopy(edata, 0, tmp, 4, edata.length);
                    edata = tmp;
                }
                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 Byte.toUnsignedInt(b[off]) | ( Byte.toUnsignedInt(b[off+1]) << 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);
    }
}