Question

In Java, how can I find the name of the stream which is passed as an argument, provided the given stream is either System.err or System.out?

public String getStreamName(OutputStream arg0) {
    String streamName = ????;
    return "This is stream: " + streamName;
}

should return something like:

This is stream: System.err

I’ve tried arg0.toString(), but that doesn’t seem useful, as the name returned is something like java.io.PrintStream@71cb25 and changes with each run. If the name was fixed, I could just compare it with the known names for stdout and stderr.

Answer 1

Try this:

public void printStreamName(OutputStream stream) {
    String streamName = "Other";

    if(stream instanceof PrintStream) {
        streamName = stream == System.err ? "System.err" : (stream == System.out ? "System.out" : "Other");
    }

    System.out.println("This is stream: " + streamName);
}