Re: Is there a DataOutput buffer in Java?

Thomas Hawtin <>
Fri, 15 Dec 2006 14:21:13 +0000
Bryan wrote:

I'm using a DataOutputStream to write primitive values to a network
socket. Is there some sort of DataOutput buffer I can use to write to
so I can print what I'm sending over the socket to the screen?

I suggest two classes.

First a class the forks the stream into two:

class ForkOutputStream extends OutputStream {
     private final OutputStream out0;
     private final OutputStream out1;
     public ForkOutputStream(OutputStream out0, OutputStream out1) {
         this.out0 = out0;
         this.out1 = out1;
     public synchronized void write(int b) throws IOException {
         // This way around because:
         // Assume out1 is some kind of monitoring stream.
         // If out0 throws, we want the data already monitored.
         // out0 exceptions are more important.
         try {
         } finally {

Then a class for dumbing output:

class DumpOutputSteam extends OutputStream {
     private final byte[] buff = { 0, 0, ' ' };
     private final OutputStream out;

     public ForkOutputStream(OutputStream out) {
         this.out = out;
     private static byte toHexDigit(int b) {
         b &= 0xf;
         return b<10 ? (byte)('0'+b) : (byte)('a'-10+b);
     public synchronized void write(int b) throws IOException {
         buff[0] = toHexDigit(b>>4);
         buff[1] = toHexDigit(b);
         out.write(buff, 0, 3);

Put it together:

      DataOutputStream out = new DataOutputStream(
          new BufferedOutputStream(new ForkOutputStream(
                  rawOut, new DumpOutputStream(System.err)

(Disclaimer: I have not attempted to compile or test this code.)

Tom Hawtin

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