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Posted 17 Jan 2012

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A quick and easy way to direct Java System.out to File and to Console

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17 Jan 2012CPOL
A quick and easy way to direct Java System.out to File and to Console.

The following code demonstrates a very easy and simple way to redirect Java System.out and System.err streams to both a File and Console.

For some reason, Googling for "Java stdout redirect to File and Console" does not result in any easy answers on the first few pages. The answer being so insanely simple, I decided to quickly write the method here, in the hopes that future programmers won't have to spend more than a few minutes on such an issue.

The issue being, of course, how does one use the methods in System.out or System.err to print to both a file and the console without having to resort to ridiculous extremes? In short, the answer is to wrap multiple OutputStreams into a single OutputStream class implementation and construct a PrintStream instance on this implementation, and then set this PrintStream implementation on System.

So first define your MultiOutputStream class:

public class MultiOutputStream extends OutputStream
	OutputStream[] outputStreams;
	public MultiOutputStream(OutputStream... outputStreams)
		this.outputStreams= outputStreams; 
	public void write(int b) throws IOException
		for (OutputStream out: outputStreams)
	public void write(byte[] b) throws IOException
		for (OutputStream out: outputStreams)

	public void write(byte[] b, int off, int len) throws IOException
		for (OutputStream out: outputStreams)
			out.write(b, off, len);

	public void flush() throws IOException
		for (OutputStream out: outputStreams)

	public void close() throws IOException
		for (OutputStream out: outputStreams)

Next construct your PrintStream instance and set it on System:

	FileOutputStream fout= new FileOutputStream("stdout.log");
	FileOutputStream ferr= new FileOutputStream("stderr.log");
	MultiOutputStream multiOut= new MultiOutputStream(System.out, fout);
	MultiOutputStream multiErr= new MultiOutputStream(System.err, ferr);
	PrintStream stdout= new PrintStream(multiOut);
	PrintStream stderr= new PrintStream(multiErr);
catch (FileNotFoundException ex)
	//Could not create/open the file

Now you can go bananas and use System.out or System.err to write whatever you like, and it will be written to both the console and a file:

System.out.println("Holy Rusty Metal Batman! I can't believe this was so simple!");
System.err.println("God I hate you Robin.");

Goodbye, have a nice time!


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Written By
Software Developer (Senior) Nokia
Germany Germany
Writing C++ and Java Software like its 1999.

Comments and Discussions

QuestionGreat article, just what I was looking for Pin
GeVanCo13-Jul-18 19:08
MemberGeVanCo13-Jul-18 19:08 
GeneralMy vote of 3 Pin
family5215-Feb-13 15:34
Memberfamily5215-Feb-13 15:34 
GeneralReason for my vote of 5 Very simple and straight forward sol... Pin
All Time Programming6-Feb-12 19:07
MemberAll Time Programming6-Feb-12 19:07 
General@Member 3896609, If we use TeeOutputStream then our applicat... Pin
All Time Programming6-Feb-12 19:05
MemberAll Time Programming6-Feb-12 19:05 
GeneralRe: Agreed. If you are using the Commons IO library then, by all... Pin
Lodewijk Pool7-Feb-12 0:47
MemberLodewijk Pool7-Feb-12 0:47 
GeneralThe implementation of MultiOutputStream is unnecessary in yo... Pin
Member 38966092-Feb-12 1:23
MemberMember 38966092-Feb-12 1:23 
QuestionNice article Pin
devcovato17-Jan-12 5:49
Memberdevcovato17-Jan-12 5:49 

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