Websocket

Resin's WebSocket API follows the Servlet API's stream model, using InputStream/OutputStream for binary messages and a Reader/PrintWriter for text messages. HTTP browsers will use text messages, while custom clients like phone/pad applications may use binary messages for efficiency.

The servlet resin-web.xml configuration is the same as for a normal servlet. On the initial request, the servlet will dispatch to a websocket listener.

WebSocketServletRequest

The servlet is responsible for detecting websocket requests and attaching a listener to that connection.

package example;

import com.caucho.websocket.WebSocketListener;
import com.caucho.websocket.WebSocketServletRequest;

import java.io.IOException;
import javax.servlet.*;
import javax.servlet.http.*;

public class MyServlet extends HttpServlet {

  public void service(HttpServletRequest req, HttpServletResponse res)
    throws IOException, ServletException
  {
    String protocol = req.getHeader("Sec-WebSocket-Protocol");

    WebSocketListener listener;

    if (! "my-protocol".equals(protocol)) {
      res.sendError(404);
      return;
    }

    listener = new MyListener();
    res.setHeader("Sec-WebSocket-Protocol", "my-protocol");
    
    WebSocketServletRequest wsReq = (WebSocketServletRequest) req;

    wsReq.startWebSocket(listener);
  }
}

WebSocketListener

The listener is responsible for the communcation and stateful data.

package example;

import com.caucho.websocket.WebSocketListener

import java.io.*;

import java.util.logging.Logger;

public class MyListener implements WebSocketListener
{
  private static final Logger log
    = Logger.getLogger(MyListener.class.getName());

  public void onStart(WebSocketContext context)
    throws IOException
  {
    log.info("onStart");
  }

  public void onReadBinary(WebSocketContext context, InputStream is)
    throws IOException
  {
    StringBuilder sb = new StringBuilder();
    int ch;
    
    while ((ch = is.read()) >= 0) {
      sb.append((char) ch);
    }
    
    log.info("onReadBinary: " + sb);
  }

  public void onReadText(WebSocketContext context, Reader is)
    throws IOException
  {
    StringBuilder sb = new StringBuilder();
    int ch;
    
    while ((ch = is.read()) >= 0) {
      sb.append((char) ch);
    }
    
    log.info("onReadText: " + sb);
  }

  public void onClose(WebSocketContext context)
    throws IOException
  {
    log.info("onClose");
  }

  public void onDisconnect(WebSocketContext context)
    throws IOException
  {
    log.info("onDisconnect");
  }

  public void onTimeout(WebSocketContext context)
    throws IOException
  {
    log.info("onTimeout");
  }
}

See com.caucho.websocket.WebSocketListener.

Resin Documentation

websocket

WebSocket

WebSocketServletRequest

WebSocketListener