Check Java Class Version

There is always a situation in a java developers life, when he needs to deal with various versions of java and incompatibilites which might arise with them.In my regular googling exercise, i found a very good solution given by Real Gagnon.So, to identify the version of java class file, is to extract the class file from the jar/war and just run the below program:

import java.io.*;

public class ClassVersionChecker {
    public static void main(String[] args) throws IOException {
        for (int i = 0; i < args.length; i++)
            checkClassVersion(args[i]);
    }

    private static void checkClassVersion(String filename)
        throws IOException
    {
        DataInputStream in = new DataInputStream
         (new FileInputStream(filename));

        int magic = in.readInt();
        if(magic != 0xcafebabe) {
          System.out.println(filename + " is not a valid class!");;
        }
        int minor = in.readUnsignedShort();
        int major = in.readUnsignedShort();
        System.out.println(filename + ": " + major + " . " + minor);
        in.close();
    }
}

> java ClassVersionChecker ClassVersionChecker.class
ClassVersionChecker.class: 49 . 0

Comparison Chart:

major  minor Java platform version 
45       3           1.0
45       3           1.1
46       0           1.2
47       0           1.3
48       0           1.4
49       0           1.5
50       0           1.6

Courtesy: Real Gagnon(Click Here for actual post)

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