Getting local variables

Question

When getting a stacktrace as error report from an application that is already deployed, it would be helpful to also get the actual variable values to reconstruct the system's state at the point before the exception was thrown.

Is anything like that feasible in Java and how could one do that?

Cheers, Max

Answer 1

I'm pretty sure you cannot get the local variables in the stacktrace as the output is built from instance of StackTraceElement which only contains, the class, the file, the method and the line number (see http://download.oracle.com/javase/6/docs/api/java/lang/StackTraceElement.html).

Answer 2

Have a look at this tool:

http://www.chrononsystems.com/

It allows you to keep track of the stack trace with the option to go back in time in the application's timeline. I haven't tried it myself but it looks really promising for the type of situation you are referring to (unexpected Exceptions).

It will be good to hear if it helped :)

Answer 3

If you use an IDE such as Eclipse - you can use debugging tools to view this through the entire execution of the program.

Answer 4

The only way that's going to happen is if the system state in question is reachable through either variables available higher up in the exception-catching chain, or via the exception object itself (in the case of a custom exception):

public class MySpiffyException extends RuntimeException
{
    final private int foo;
    final private String bar;

    public MySpiffyException(String message, int foo, String bar) { 
       super(message); this.foo = foo; this.bar = bar; 
    }
    public MySpiffyException(Throwable cause, int foo, String bar) { 
       super(cause); this.foo = foo; this.bar = bar; 
    }
    public int getFoo() { return this.foo; }
    public String getBar() { return this.bar; }
}

...

public void someCode() {
   ...

   int foo = ...;
   String bar = ...;

   if (foo > 0)
      throw new MySpiffyException(foo, bar);
}