Multitarget Output Streams

As a final example, I present two slightly unusual filter output streams that direct their data to multiple underlying streams. The TeeOutputStream class in Example 6-6 has not one but two underlying streams. It does not modify the data that's written in any way; it merely writes that data on both of its underlying streams.

Example 6-6. The TeeOutputStream class

package com.elharo.io;
import java.io.*;
public class TeeOutputStream extends FilterOutputStream {
 private OutputStream out1;
 private OutputStream out2;
 public TeeOutputStream(OutputStream stream1, OutputStream stream2) {
 super(stream1);
 out1 = stream1;
 out2 = stream2;
 }
 public void write(int b) throws IOException {
 out1.write(b);
 out2.write(b);
 }
 public void write(byte[] data, int offset, int length)
 throws IOException {
 out1.write(data, offset, length);
 out2.write(data, offset, length);
 }
 public void flush( ) throws IOException {
 out1.flush( );
 out2.flush( );
 }
 public void close( ) throws IOException {
 out1.close( );
 out2.close( );
 }
}

It would be possible to store one of the output streams in FilterOutputStream's protected out field and the other in a field in this class. However, it's simpler and cleaner to maintain the parallelism between the two streams by storing them both in the TeeOutputStream class.

Example 6-7 demonstrates how one might use this class to write a TeeCopier program that copies a file into two separate, new files.

Example 6-7. The TeeCopier program

import java.io.*;
import com.elharo.io.*;
public class TeeCopier {
 public static void main(String[] args) throws IOException {
 if (args.length != 3) {
 System.out.println("Usage: java TeeCopier infile outfile1 outfile2");
 return;
 }
 FileInputStream fin = new FileInputStream(args[0]);
 FileOutputStream fout1 = new FileOutputStream(args[1]);
 FileOutputStream fout2 = new FileOutputStream(args[2]);
 TeeOutputStream tout = new TeeOutputStream(fout1, fout2);
 BufferedStreamCopier.copy(fin, tout);
 fin.close( );
 tout.close( );
 }
}