How to get output stream name (i.e. stderr or stdout) in java?

Question

In Java, how can I find the name of the stream that is passed as an argument if 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 tried arg0.toString() , but this does not seem useful, since the return name is something like java.io.PrintStream@71cb25 and changes every time it starts. If the name was fixed, I could just compare it with the famous names for stdout and stderr.

Answer 1

Try the following:

 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); } 

Answer 2

System.out and System.err are both instances of PrintStream. Print streams and output streams do not have properties that you could use to differentiate them.

API docs show what is available:

http://docs.oracle.com/javase/6/docs/api/java/io/PrintStream.html

http://docs.oracle.com/javase/6/docs/api/java/io/OutputStream.html

In this case, you can simply check if this == is either System.out or System.err:

 if (arg0 == System.out) { } else if (arg0 == System.err) { } else { // it is another output stream } 

Answer 3

This may not be the best solution, but it works.

 public String getStreamName(OutputStream arg0) { boolean lol = arg0.equals(System.err); String streamName; if(lol) streamName = "System.err"; else streamName = "System.out"; return "This is stream: " + streamName; } 

Edit:

 public String getStreamName(OutputStream arg0) { return "This is stream: " + ((arg0.equals(System.err)) ? "System.err" : "System.out"); }