In this post, I am going to explain how to replicate an output stream into two separate streams.

We can do this by extending OutputStream class.

public class BiOutputStream extends OutputStream {
	private OutputStream first;
	private OutputStream second;

	public BiOutputStream(OutputStream first, OutputStream second) {
		this.first = first;
		this.second = second;
	}

	.........
	.........
}

Apart from extending, we need to override below methods.

a.   public Void close() throws IOException

b.   public void flush() throws IOException

c.    write method

1.   public void write(byte[] b) throws IOException

2.   public void write(byte[] b, int off, int len) throws IOException

3.   public void write(int b) throws IOException

Close both output streams

@Override
public void close() throws IOException {
	closeStream(first);
	closeStream(second);
}

Flush the streams

@Override
public void flush() throws IOException {
	first.flush();
	second.flush();
}

Write the data to streams

@Override
public void write(byte[] b) throws IOException {
	first.write(b);
	second.write(b);
}

@Override
public void write(byte[] b, int off, int len) throws IOException {
	first.write(b, off, len);
	second.write(b, off, len);
}

@Override
public void write(int b) throws IOException {
	first.write(b);
	second.write(b);
}

Find the below working application.

package com.sample.app.streams;

import java.io.IOException;
import java.io.OutputStream;

public class BiOutputStream extends OutputStream {
	private OutputStream first;
	private OutputStream second;

	public BiOutputStream(OutputStream first, OutputStream second) {
		if (first == null) {
			throw new IllegalArgumentException("first stream is null");
		}

		if (second == null) {
			throw new IllegalArgumentException("first stream is null");
		}

		this.first = first;
		this.second = second;
	}

	@Override
	public void close() throws IOException {
		closeStream(first);
		closeStream(second);
	}

	@Override
	public void flush() throws IOException {
		first.flush();
		second.flush();
	}

	@Override
	public void write(byte[] b) throws IOException {
		first.write(b);
		second.write(b);
	}

	@Override
	public void write(byte[] b, int off, int len) throws IOException {
		first.write(b, off, len);
		second.write(b, off, len);
	}

	@Override
	public void write(int b) throws IOException {
		first.write(b);
		second.write(b);
	}

	private static void closeStream(OutputStream outputStream) {
		if (outputStream == null) {
			return;
		}

		try {
			outputStream.close();
		} catch (Throwable t) {
			t.printStackTrace(System.err);
		}

	}
}

BiOutputStreamDemo.java

package com.sample.app.streams;

import java.io.IOException;

public class BiOutputStreamDemo {

	public static void main(String[] args) throws IOException {
		BiOutputStream bos = new BiOutputStream(System.out, System.err);

		bos.write(new String("This message is published to both\n\t1. System.out and\n\t2. System.err\n").getBytes());

		bos.close();
	}

}

Output in Eclipse IDE

You may like

file and stream programs in Java

Check given path is a file and not a symbolic link in Java

Check given path is a directory and not a symbolic link in Java

Convert InputStream to string

Write InputStream to a file in Java

File separator, separatorChar, pathSeparator, pathSeparatorChar in Java