org.cometd.server.AbstractService Maven / Gradle / Ivy
/*
* Copyright (c) 2008-2022 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.cometd.server;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import org.cometd.bayeux.Promise;
import org.cometd.bayeux.Session;
import org.cometd.bayeux.server.BayeuxServer;
import org.cometd.bayeux.server.LocalSession;
import org.cometd.bayeux.server.ServerChannel;
import org.cometd.bayeux.server.ServerMessage;
import org.cometd.bayeux.server.ServerSession;
import org.eclipse.jetty.util.component.LifeCycle;
import org.eclipse.jetty.util.thread.QueuedThreadPool;
import org.eclipse.jetty.util.thread.ThreadPool;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* {@link AbstractService} provides convenience methods to assist with the
* creation of a CometD services.
* A CometD service runs application code whenever a message is received on
* a particular channel.
* Specifically it provides:
*
* - Mapping of channel subscriptions to method invocation on the derived
* service class.
* - Optional use of a thread pool used for method invocation if handling
* can take considerable time and it is desired not to hold up the delivering
* thread (typically a HTTP request handling thread).
* - The objects returned from method invocation are delivered back to the
* calling client in a private message.
*
* Subclasses should call {@link #addService(String, String)} in order to
* map channel subscriptions to method invocations, usually in the subclass
* constructor.
* Each CometD service has an associated {@link LocalSession} that can be
* used as the source for messages published via
* {@link ServerChannel#publish(Session, ServerMessage.Mutable, Promise)} or
* {@link ServerSession#deliver(Session, ServerMessage.Mutable, Promise)}.
*
* @see BayeuxServer#newLocalSession(String)
*/
public abstract class AbstractService {
private static final Logger LOGGER = LoggerFactory.getLogger(AbstractService.class);
private final Map invokers = new ConcurrentHashMap<>();
private final String _name;
private final BayeuxServerImpl _bayeux;
private final LocalSession _session;
private ThreadPool _threadPool;
private boolean _seeOwn = false;
/**
* Instantiates a CometD service with the given name.
*
* @param bayeux The BayeuxServer instance.
* @param name The name of the service (used as client ID prefix).
*/
public AbstractService(BayeuxServer bayeux, String name) {
this(bayeux, name, 0);
}
/**
* Instantiate a CometD service with the given name and max number of pooled threads.
*
* @param bayeux The BayeuxServer instance.
* @param name The name of the service (used as client ID prefix).
* @param maxThreads The max size of a ThreadPool to create to handle messages.
*/
public AbstractService(BayeuxServer bayeux, String name, int maxThreads) {
_name = name;
_bayeux = (BayeuxServerImpl)bayeux;
_session = _bayeux.newLocalSession(name);
_session.handshake();
if (maxThreads > 0) {
setThreadPool(new QueuedThreadPool(maxThreads));
}
if (!Modifier.isPublic(getClass().getModifiers())) {
throw new IllegalArgumentException("Service class '" + getClass().getName() + "' must be public");
}
}
public BayeuxServer getBayeux() {
return _bayeux;
}
public String getName() {
return _name;
}
/**
* @return The {@link LocalSession} associated with this CometD service
*/
public LocalSession getLocalSession() {
return _session;
}
/**
* @return The {@link ServerSession} of the {@link LocalSession} associated
* with this CometD service
*/
public ServerSession getServerSession() {
return _session.getServerSession();
}
/**
* @return The thread pool associated with this CometD service, or null
* @see #AbstractService(BayeuxServer, String, int)
*/
public ThreadPool getThreadPool() {
return _threadPool;
}
/**
* Sets the thread pool associated to this CometD service.
* If the {@link ThreadPool} is a {@link LifeCycle} instance,
* and it is not already started, then it will started.
*
* @param pool The ThreadPool
*/
public void setThreadPool(ThreadPool pool) {
try {
if (pool instanceof LifeCycle) {
if (!((LifeCycle)pool).isStarted()) {
((LifeCycle)pool).start();
}
}
} catch (Exception e) {
throw new IllegalStateException(e);
}
_threadPool = pool;
}
/**
* @return whether this CometD service receives messages published by itself
* on channels it is subscribed to (defaults to false).
* @see #setSeeOwnPublishes(boolean)
*/
public boolean isSeeOwnPublishes() {
return _seeOwn;
}
/**
* @param seeOwnPublishes whether this CometD service receives messages published by itself
* on channels it is subscribed to (defaults to false).
* @see #isSeeOwnPublishes()
*/
public void setSeeOwnPublishes(boolean seeOwnPublishes) {
_seeOwn = seeOwnPublishes;
}
/**
* Maps the method of a subclass with the given name to a
* {@link ServerChannel.MessageListener} on the given channel, so that the method
* is invoked for each message received on the channel.
* The channel name may be a {@link ServerChannel#isWild() wildcard channel name}.
* The method must have a unique name and the following signature:
*
* - {@code myMethod(ServerSession from, ServerMessage message)}
*
* Typically a service will be used to a channel in the {@code /service/**}
* space which is not a broadcast channel.
* Any object returned by a mapped method is delivered back to the
* client that sent the message and not broadcast. If the method returns void or null,
* then no response is sent.
* A mapped method may also call {@link #send(org.cometd.bayeux.server.ServerSession, String, Object)}
* to deliver message(s) to specific clients and/or channels.
* A mapped method may also publish to different channels via
* {@link ServerChannel#publish(Session, ServerMessage.Mutable, Promise)}.
*
* @param channelName The channel to listen to
* @param methodName The name of the method on this subclass to call when messages
* are received on the channel
* @see #removeService(String, String)
*/
public void addService(String channelName, String methodName) {
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Mapping {}#{} to {}", _name, methodName, channelName);
}
Method candidate = null;
Class c = this.getClass();
while (c != null && c != AbstractService.class) {
Method[] methods = c.getDeclaredMethods();
for (int i = methods.length; i-- > 0; ) {
Method method = methods[i];
if (methodName.equals(method.getName()) && Modifier.isPublic(method.getModifiers())) {
if (candidate != null) {
throw new IllegalArgumentException("Multiple service methods called '" + methodName + "'");
}
candidate = method;
}
}
c = c.getSuperclass();
}
if (candidate == null) {
throw new NoSuchMethodError("Cannot find public service method '" + methodName + "'");
}
int params = candidate.getParameterTypes().length;
if (params != 2) {
throw new IllegalArgumentException("Service method '" + methodName + "' must have 2 parameters");
}
if (!ServerSession.class.isAssignableFrom(candidate.getParameterTypes()[0])) {
throw new IllegalArgumentException("Service method '" + methodName + "' does not have " + ServerSession.class.getName() + " as first parameter");
}
if (!ServerMessage.class.isAssignableFrom(candidate.getParameterTypes()[1])) {
throw new IllegalArgumentException("Service method '" + methodName + "' does not have " + ServerMessage.class.getName() + " as second parameter");
}
ServerChannel channel = _bayeux.createChannelIfAbsent(channelName).getReference();
Invoker invoker = new Invoker(channelName, candidate);
channel.addListener(invoker);
invokers.put(methodName, invoker);
}
/**
* Unmaps the method with the given name that has been mapped to the given channel.
*
* @param channelName The channel name
* @param methodName The name of the method to unmap
* @see #addService(String, String)
* @see #removeService(String)
*/
public void removeService(String channelName, String methodName) {
ServerChannel channel = _bayeux.getChannel(channelName);
if (channel != null) {
Invoker invoker = invokers.remove(methodName);
channel.removeListener(invoker);
}
}
/**
* Unmaps all the methods that have been mapped to the given channel.
*
* @param channelName The channel name
* @see #addService(String, String)
* @see #removeService(String, String)
*/
public void removeService(String channelName) {
ServerChannel channel = _bayeux.getChannel(channelName);
if (channel != null) {
for (Invoker invoker : invokers.values()) {
if (invoker.channelName.equals(channelName)) {
channel.removeListener(invoker);
}
}
}
}
/**
* Sends data to an individual remote client.
* The data passed is sent to the client
* as the "data" member of a message with the given channel. The
* message is not published on the channel and is thus not broadcast to all
* channel subscribers, but instead delivered directly to the target client.
* Typically this method is only required if a service method sends
* response(s) to clients other than the sender, or on different channels.
* If the response is to be sent to the sender on the same channel,
* then the data can simply be the return value of the method.
*
* @param toClient The target client
* @param onChannel The channel of the message
* @param data The data of the message
*/
protected void send(ServerSession toClient, String onChannel, Object data) {
toClient.deliver(_session.getServerSession(), onChannel, data, Promise.noop());
}
/**
* Handles exceptions during the invocation of a mapped method.
* This method is called when a mapped method throws and exception while handling a message.
*
* @param method the name of the method invoked that threw an exception
* @param session the remote session that sent the message
* @param local the local session associated to this service
* @param message the message sent by the remote session
* @param x the exception thrown
*/
protected void exception(String method, ServerSession session, LocalSession local, ServerMessage message, Throwable x) {
LOGGER.info("Exception while invoking " + _name + "#" + method + " from " + session + " with " + message, x);
}
private void invoke(Method method, ServerSession fromClient, ServerMessage msg) {
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Invoking {}#{} from {} with {}", _name, method.getName(), fromClient, msg);
}
ThreadPool threadPool = getThreadPool();
if (threadPool == null) {
doInvoke(method, fromClient, msg);
} else {
threadPool.execute(() -> doInvoke(method, fromClient, msg));
}
}
protected void doInvoke(Method method, ServerSession session, ServerMessage message) {
try {
Object reply = method.invoke(this, session, message);
if (reply != null) {
send(session, message.getChannel(), reply);
}
} catch (Throwable x) {
exception(method.toString(), session, _session, message, x);
}
}
private class Invoker implements ServerChannel.MessageListener {
private final String channelName;
private final Method method;
public Invoker(String channelName, Method method) {
this.channelName = channelName;
this.method = method;
}
@Override
public boolean onMessage(ServerSession from, ServerChannel channel, ServerMessage.Mutable message) {
if (isSeeOwnPublishes() || from != getServerSession()) {
invoke(method, from, message);
}
return true;
}
}
}