How to determine the Java byte code version of the current class programatically? [duplicate]

Question

I have a situation where the deployment platform is Java 5 and the development happens with Eclipse under Java 6 where we have established a procedure of having a new workspace created when beginning work on a given project. One of the required steps is therefore setting the compiler level to Java 5, which is frequently forgotten.

We have a test machine running the deployment platform where we can run the code we build and do initial testing on our PC's, but if we forget to switch the compiler level the program cannot run. We have a build server for creating what goes to the customer, which works well, but this is for development where the build server is not needed and would add unnecessary waits.

The question is: CAN I programmatically determine the byte code version of the current class, so my code can print out a warning already while testing on my local PC?

---

EDIT: Please note the requirement was for the current class. Is this available through the classloadeer? Or must I locate the class file for the current class, and then investigate that?

Answer 1

Easy way to find this to run javap on class

For more details goto http://download.oracle.com/javase/1,5.0/docs/tooldocs/windows/javap.html

Example:

M:\Projects\Project-1\ant\javap -classpath M:\Projects\Project-1\build\WEB-INF\classes -verbose com.company.action.BaseAction

and look for following lines

minor version: 0
major version: 50

Answer 2

You could load the class file as a resource and parse the first eight bytes.

//TODO: error handling, stream closing, etc.
InputStream in = getClass().getClassLoader().getResourceAsStream(
    getClass().getName().replace('.', '/') + ".class");
DataInputStream data = new DataInputStream(in);
int magic = data.readInt();
if (magic != 0xCAFEBABE) {
  throw new IOException("Invalid Java class");
}
int minor = 0xFFFF & data.readShort();
int major = 0xFFFF & data.readShort();
System.out.println(major + "." + minor);

Answer 3

Take a look at question: Java API to find out the JDK version a class file is compiled for?