gov.lbl.dsd.sea.nio
Class AgentEventHandler

java.lang.Object
  gov.lbl.dsd.sea.EventHandler
      gov.lbl.dsd.sea.nio.AgentEventHandler

Direct Known Subclasses:

EchoServer, HttpClient, PingPong, PingPongBench, StreamingBench, TimeServer

public abstract class AgentEventHandler

extends EventHandler

Abstract base class simplifying the implementation of event handlers sending requests to an agent, and receiving responses from the agent.

Override protected onXYZ event handling methods for application specific behaviour.

For example, a typical non-blocking agent event handler accumulates partial reads along the following lines:

public class MyAgentEventHandler extends AgentEventHandler {
        // simple variable msg size protocol: MESSAGE = [payLoadLength(4 bytes) payLoad]
        private static final Charset CHARSET = Charset.forName("UTF-8");

        protected void onAccepted(ChannelResponse.Accepted rsp) {
                // prepare read buffer and register READ interest
                rsp.getKey().attach(new gov.lbl.dsd.sea.nio.util.ArrayByteList());
                rsp.getAgent().enqueue(
                                new ChannelRequest.Register(this.getStage(), rsp.getKey()
                                                .channel(), SelectionKey.OP_READ));
        }


        protected void onRead(ChannelResponse.Read rsp) {
                ArrayByteList readBuffer = (ArrayByteList) rsp.getKey().attachment();
                readBuffer.add(rsp.getBuffer());
                rsp.getAgent().getReadBufferPool().put(rsp.getBuffer()); // recycle buffer
                while (readBuffer.size() >= 4) {
                        // message header containing payload length has arrived
                        int payloadLength = readBuffer.asByteBuffer().getInt(0);
                        if (4 + payloadLength > readBuffer.size()) {
                                break; // payload not yet fully received, wait for more data
                        }
                        else {
                                // we have received the entire variable length payload
                                String payload = readBuffer.toString(4, 4 + payloadLength, CHARSET);
                                readBuffer.remove(0, 4 + payloadLength); // remove header and payload

                                // do something useful with payload, here we just print it
                                System.out.println("payload=" + payload);
                        }
                }
        }

        // A more efficient but less readable/understandable alternative:
        protected void onRead(ChannelResponse.Read rsp) {
                ArrayByteList readBuffer = (ArrayByteList) rsp.getKey().attachment();
                readBuffer.add(rsp.getBuffer());
                rsp.getAgent().getReadBufferPool().put(rsp.getBuffer()); // recycle buffer
                int i = 0;
                while (i + 4 <= readBuffer.size()) {
                        // message header containing payload length has arrived
                        int payloadLength = readBuffer.asByteBuffer().getInt(i);
                        if (i + 4 + payloadLength > readBuffer.size()) {
                                // payload not yet fully received - wait for more data
                                break; 
                        }
                        else {
                                i += 4;
                                // we have received the entire variable length payload
                                String payload = readBuffer.toString(i, i + payloadLength, CHARSET);
                                i += payLoadLength;

                                // do something useful with payload, here we just print it
                                System.out.println("payload=" + payload);
                        }
                }
                // remove fully processed headers and payloads, if any
                readBuffer.remove(0, i); 
        }

        ...
}

Version:

$Revision: 1.12 $, $Date: 2004/08/04 23:24:56 $

Method Summary

void	handle(Object event) Called when an event has been received

Methods inherited from class gov.lbl.dsd.sea.EventHandler

onStart, onStop

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

handle

public void handle(Object event)

Called when an event has been received

Specified by:

handle in class EventHandler