1 /*

     2  * Copyright (c) 2004, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.

     8  *

     9  * This code is distributed in the hope that it will be useful, but WITHOUT

    10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    12  * version 2 for more details (a copy is included in the LICENSE file that

    13  * accompanied this code).

    14  *

    15  * You should have received a copy of the GNU General Public License version

    16  * 2 along with this work; if not, write to the Free Software Foundation,

    17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    18  *

    19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    20  * or visit www.oracle.com if you need additional information or have any

    21  * questions.

    22  */

    23 

    24 import java.io.*;

    25 import java.nio.*;

    26 import java.nio.channels.*;

    27 

    28 

    29 public class CheckClassFileVersion {

    30 

    31     static String get(String fn) throws IOException {

    32         ByteBuffer bb = ByteBuffer.allocate(1024);

    33         FileChannel fc = new FileInputStream(fn).getChannel();

    34         try {

    35             bb.clear();

    36             if (fc.read(bb) < 0)

    37                 throw new IOException("Could not read any bytes");

    38             bb.flip();

    39             int minor = bb.getShort(4);

    40             int major = bb.getShort(6);

    41             return major + "." + minor;

    42         } finally {

    43             fc.close();

    44         }

    45     }

    46 

    47     public static void main(String[] args) throws IOException {

    48         String cfv = get(args[0]);

    49         if (args.length == 1) {

    50             System.out.println(cfv);

    51             return;

    52         }

    53         if (!cfv.equals(args[1])) {

    54             System.err.println("Class-file version mismatch: Expected "

    55                                + args[1] + ", got " + cfv);

    56             System.exit(1);

    57         }

    58     }

    59 

    60 }