Redirect System.out.println

My application has many System.out.println() statements.

I want to catch messages from println and send them to the standard logger (Log4j, JUL etc).

How to do that ?

The System class has a setOut and setErr that can be used to change the output stream to, for example, a new PrintStream with a backing File or, in this case, probably another stream which uses your logging subsystem of choice.

Keep in mind you may well get yourself into trouble if you ever configure your logging library to output to standard output or error (of the infinite recursion type, possibly).

If that's the case, you may want to just go and replace your System.out.print-type statements with real logging calls.

I had a similar need once. I needed to intercept the output of some 3rd party component and react on a error message. The concept looks like this:

private class Interceptor extends PrintStream
{
    public Interceptor(OutputStream out)
    {
        super(out, true);
    }
    @Override
    public void print(String s)
    {//do what ever you like
        super.print(s);
    }
}
public static void main(String[] args)
{
    PrintStream origOut = System.out;
    PrintStream interceptor = new Interceptor(origOut);
    System.setOut(interceptor);// just add the interceptor
}

The better solution is to go through and change all the println statements to use a proper logging library. What you're trying to do is a big hack.