Java example source code file (CheckClassFileVersion.java)

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Java - Java tags/keywords

bytebuffer, checkclassfileversion, could, filechannel, ioexception, nio, string

The CheckClassFileVersion.java Java example source code

/*
 * Copyright (c) 2004, 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.
 *
 * 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.
 */

import java.io.*;
import java.nio.*;
import java.nio.channels.*;


public class CheckClassFileVersion {

    static String get(String fn) throws IOException {
        ByteBuffer bb = ByteBuffer.allocate(1024);
        FileChannel fc = new FileInputStream(fn).getChannel();
        try {
            bb.clear();
            if (fc.read(bb) < 0)
                throw new IOException("Could not read any bytes");
            bb.flip();
            int minor = bb.getShort(4);
            int major = bb.getShort(6);
            return major + "." + minor;
        } finally {
            fc.close();
        }
    }

    public static void main(String[] args) throws IOException {
        String cfv = get(args[0]);
        if (args.length == 1) {
            System.out.println(cfv);
            return;
        }
        if (!cfv.equals(args[1])) {
            System.err.println("Class-file version mismatch: Expected "
                               + args[1] + ", got " + cfv);
            System.exit(1);
        }
    }

}