Redirect System.out and System.err

Question

I have some legacy code (or rather some code we don\'t control but we have to use) that writes a lot of statements to system.out/err.

At the same time, we are using

Answer 1

Take a look at the constructors provided by PrintStream. You can pass the logging framework OutputStream directly to PrintStream, then set the System.out and System.err to use the PrintStream.

Edit: Here's a simple test case:

public class StreamTest
{
    public static class MyOutputStream extends FilterOutputStream
    {
        public MyOutputStream(OutputStream out)
        {
            super(out);
        }

        @Override
        public void write(byte[] b, int off, int len) throws IOException
        {
            byte[] text = "MyOutputStream called: ".getBytes();         
            super.write(text, 0, text.length);
            super.write(b, off, len);
        }
    }

    @Test   
    public void test()
    {       
        //Any OutputStream-implementation will do for PrintStream, probably
        //you'll want to use the one from the logging framework
        PrintStream outStream = new PrintStream(new MyOutputStream(System.out), true);  //Direct to MyOutputStream, autoflush
        System.setOut(outStream); 

        System.out.println("");
        System.out.print("TEST");
        System.out.println("Another test");
    }
}

The output is:

MyOutputStream called: 
MyOutputStream called: TESTMyOutputStream called: Another testMyOutputStream called: 

The second line has an "empty" call (MyOutputStream called: -output and then nothing after it), because println will first pass the Another test -string to the write-method, and then calls it again with a line feed.