How to write data to two java.io.OutputStream objects at once?

Question

I'm looking for magical Java class that will allow me to do something like this:

ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
FileOutputStream fileStream = new FileOutputStream(new File("/tmp/somefile"));

MultiOutputStream outStream = new MultiOutputStream(byteStream, fileStream);

outStream.write("Hello world".getBytes());

Basically, I want tee for OutputStreams in Java. Any ideas?

Thanks!

Answer 1

Try the Apache Commons TeeOutputStream.

Answer 2

Just roll your own. There isn't any magic at all. Using Apache's TeeOutputStream you would basically use the code below. Of course using the Apache Commons I/O library you can leverage other classes, but sometimes it is nice to actually write something for yourself. :)

public final class TeeOutputStream extends OutputStream {

  private final OutputStream out;
  private final OutputStream tee;

  public TeeOutputStream(OutputStream out, OutputStream tee) {
    if (out == null)
      throw new NullPointerException();
    else if (tee == null)
      throw new NullPointerException();

    this.out = out;
    this.tee = tee;
  }

  @Override
  public void write(int b) throws IOException {
    out.write(b);
    tee.write(b);
  }

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

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

  @Override
  public void flush() throws IOException {
    out.flush();
    tee.flush();
  }

  @Override
  public void close() throws IOException {
    try {
      out.close();
    } finally {
      tee.close();
    }
  }
}

Testing with the above class with the following

public static void main(String[] args) throws IOException {
  TeeOutputStream out = new TeeOutputStream(System.out, System.out);
  out.write("Hello world!".getBytes());
  out.flush();
  out.close();
}

would print Hello World!Hello World!.

(Note: the overridden close() could use some care tho' :)

Answer 3

final ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
final FileOutputStream fileStream = new FileOutputStream(new File("/tmp/somefile"));
OutputStream outStream = new OutputStream() {

    public void write(int b) throws IOException {
        byteStream.write(b);
        fileStream.write(b);
    }
};
outStream.write("Hello world".getBytes());

Answer 4

Just found this thread beacause I had to face the same problem. If someone wants to see my solution (java7 code):

package Core;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;

public class MultiOutputStream extends OutputStream {

private List<OutputStream> out;

public MultiOutputStream(List<OutputStream> outStreams) {

    this.out = new LinkedList<OutputStream>();

    for (Iterator<OutputStream> i = outStreams.iterator(); i.hasNext();) {
        OutputStream outputStream = (OutputStream) i.next();

        if(outputStream == null){
            throw new NullPointerException();
        }
        this.out.add(outputStream);
    }
}

@Override
public void write(int arg0) throws IOException {

    for (Iterator<OutputStream> i = out.iterator(); i.hasNext();) {
        OutputStream var = (OutputStream) i.next();

        var.write(arg0);
    }
}

@Override
public void write(byte[] b) throws IOException{

    for (Iterator<OutputStream> i = out.iterator(); i.hasNext();) {
        OutputStream var = (OutputStream) i.next();

        var.write(b);
    }
}

@Override
public void write(byte[] b, int off, int len) throws IOException{

    for (Iterator<OutputStream> i = out.iterator(); i.hasNext();) {
        OutputStream var = (OutputStream) i.next();

        var.write(b, off, len);
    }
}

@Override
public void close() throws IOException{

    for (Iterator<OutputStream> i = out.iterator(); i.hasNext();) {
        OutputStream var = (OutputStream) i.next();

        var.close();
    }
}

@Override
public void flush() throws IOException{

    for (Iterator<OutputStream> i = out.iterator(); i.hasNext();) {
        OutputStream var = (OutputStream) i.next();

        var.flush();
    }
}

}

Works fine so far, just tested some basic operation, e.g. setting up a MultiOutputStream from the System.out Stream and 2 PrintStreams each writing into a seperate log. I used

System.setOut(multiOutputStream);

to write to my terminal screen and two logs which worked without any problems.

Answer 5

Roll your own, it's basically trivial. Use an ArrayList<OutputStream> or whatever's popular nowadays to store all the streams you want and write the write method to loop over all of them, writing to each.

Answer 6

Here's an example of TeeOutputStream usage (keep outputting stdout & stderr) and printing it to file:

public static void main(String[] args) throws IOException {

    System.setOut(new PrintStream(new TeeOutputStream(System.out, new PrintStream("out.log"))));
    System.setErr(new PrintStream(new TeeOutputStream(System.err, new PrintStream("err.log"))));
...