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; 
	}
	
	@Override
	public void write(int b) throws IOException
	{
		for (OutputStream out: outputStreams)
			out.write(b);			
	}
	
	@Override
	public void write(byte[] b) throws IOException
	{
		for (OutputStream out: outputStreams)
			out.write(b);
	}

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

	@Override
	public void flush() throws IOException
	{
		for (OutputStream out: outputStreams)
			out.flush();
	}

	@Override
	public void close() throws IOException
	{
		for (OutputStream out: outputStreams)
			out.close();
	}
}

Next construct your PrintStream instance and set it on System:

try
{
	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);
	
	System.setOut(stdout);
	System.setErr(stderr);
}
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!