How can I find the target Java version for a compiled class?

Duplicate:

Tool to read and display Java .class versions

If I have a compiled Java class, is there a way to tell from just the class file what its target version compatibility is? Specifically, I have a number of class files, compiled to Java 6, which are running under Java 5 and giving the the "Unrecognized version" error. I want to be able to look at a class file and find what its target version compatibility is without running the JVM. Any ideas?

From stackoverflow

• I've found this on the net and it works.

  Every '.class' file starts off with the following:

  • Magic Number [4 bytes]
  • Version Information [4 bytes]

  A hexdump of a '.class' file compiled with each of the following options reveals:

  javac -target 1.1 ==> CA FE BA BE 00 03 00 2D
javac -target 1.2 ==> CA FE BA BE 00 00 00 2E
javac -target 1.3 ==> CA FE BA BE 00 00 00 2F
javac -target 1.4 ==> CA FE BA BE 00 00 00 30

  Perhaps you could use this information to write your own '.class' file version checking utility, using Java, or perhaps a scripting or shell language ;) !

  I hope this helps.

  Anthony Borla

  From: http://bytes.com/groups/java/16603-how-determine-java-bytecode-version

  Mike Pone : Great, but what about versions 1.5 and 1.6, which are the ones I care about?

  Mike Pone : Seems like the last number represents the final version hex 31 = dec 49 hex 32 = dec 50. That's what I need. Thanks.

  Kalecser : Version 1.6 = 32 and 1.5 is 31

• You can look at the byte offset 6 and 7 in the file (in a hex dump probably), which tells you which version is used. I think the Bytecode Visualizer (eclipse plugin) can see which version a class file is made for.

  Further reading

• You can use the javap utility that comes with the standard JDK.

  javap -verbose MyClass
  
  Compiled from “MyClass.java”
  public class MyClass extends java.lang.Object
  SourceFile: “MyClass.java”
  minor version: 3
  major version: 45
  

  Mike Pone : while it may be considered "better" it is not exactly what I was looking for.

• Taken from: http://twit88.com/blog/2008/09/22/java-check-class-version/

  try {
      String filename = “C:\\MyClass.class”;
      DataInputStream in = new DataInputStream(new FileInputStream(filename));
      int magic = in.readInt();
      if (magic != 0xcafebabe) {
          log.info(filename + ” is not a valid class!”);
      }
      int minor = in.readUnsignedShort();
      int major = in.readUnsignedShort();
      log.info(filename + “: “ + major + ” . “ + minor);
      in.close();
  } catch (IOException e) {
      log.info(“Exception: “ + e.getMessage(), e);
  }