Java Tech - Chapter 14 : Web Servers

Our Worker communicates with the client via the I/O streams created with the Socket object. From Chapter 9: Java I/O we learned about streams and how you can obtained inhanced functionality by wrapping higher level streams around a basic level stream.

We first create out input stream and then wrap it with an InputStreamReader using the 8859_1 character encoding and then wrap that with a BufferedReader. (See Chapter 9 for information about character encodings such as 8859_1.)

/** Threaded process to serve the client connected to the socket.**/
class Worker extends Thread {

  Socket fClient;
      ...
}
public void run () {
    try {
      // Use the client socket to obtain an input stream from it.
      InputStream socket_in = fClient.getInputStream ();
      // For text input we wrap an InputStreamReader around
      // the raw input stream and set ASCII character encoding.
      InputStreamReader isr =
         new InputStreamReader (socket_in, "8859_1");
      // Finally, use a BufferReader wrapper to obtain
      // buffering and higher order read methods.
      BufferedReader client_in = new BufferedReader (isr);
      ...

We then obtain an OutputStream from the socket as shown in the next code snippet. We wrap this with an OutputStreamWriter and then with a PrintWriter.

            ...
      // Now get an output stream to the client.
      OutputStream client_out = fClient.getOutputStream ();

      // For text output we wrap an OutputStreamWriter around
      // the raw output stream and set ASCII character encoding.
      OutputStreamWriter osr =
        new OutputStreamWriter (client_out, "8859_1");
      // Finally, we use a PrintWriter wrapper to obtain its
      // higher level output methods.
      // Open in append mode.
      PrintWriter pw_client_out = new PrintWriter (osr, true);

      ....

At this point in the code we have streams for both input and output communications with the client, but we yet discussed what exactly it is that they they will communicate. The client can place arbitrary bytes on the stream and the server will see them, but unless some agreement is made about what form those bytes should take and what they mean, the communication that happens is rather meaningless.

In other words, we need to develop some sort of protocol so that the server and the client can understand each other. We next discuss the appropriate HTTP protocol.

References & Web Resources

Specifications:
Niemeyer & Knudson, Learning Java... - presents a Web server demo similar to the one here..
Writing a Client/Server Pair - Java Tutorial
All About Sockets - Java Tutorial

Latest update: Dec. 9, 2004