Java tutorial
/* File: $Id$ * Revision: $Revision$ * Author: $Author$ * Date: $Date$ * * The Netarchive Suite - Software to harvest and preserve websites * Copyright 2004-2012 The Royal Danish Library, the Danish State and * University Library, the National Library of France and the Austrian * National Library. * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * This library is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this library; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ package dk.netarkivet.harvester.distribute; import javax.jms.Message; import javax.jms.MessageListener; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import dk.netarkivet.common.distribute.JMSConnection; import dk.netarkivet.common.distribute.NetarkivetMessage; import dk.netarkivet.common.exceptions.ArgumentNotValid; import dk.netarkivet.common.exceptions.PermissionDenied; import dk.netarkivet.harvester.harvesting.distribute.CrawlProgressMessage; import dk.netarkivet.harvester.harvesting.distribute.CrawlStatusMessage; import dk.netarkivet.harvester.harvesting.distribute.DoOneCrawlMessage; import dk.netarkivet.harvester.harvesting.distribute.FrontierReportMessage; import dk.netarkivet.harvester.harvesting.distribute.HarvesterRegistrationRequest; import dk.netarkivet.harvester.harvesting.distribute.HarvesterRegistrationResponse; import dk.netarkivet.harvester.harvesting.distribute.HarvesterReadyMessage; import dk.netarkivet.harvester.harvesting.distribute.JobEndedMessage; import dk.netarkivet.harvester.indexserver.distribute.IndexRequestMessage; /** * This default message handler shields of all unimplemented methods from the * HarvesterMessageVisitor interface. * * Classes should not implement HarvesterMessageVisitor but extend this class. * * @see HarvesterMessageVisitor * */ public abstract class HarvesterMessageHandler implements HarvesterMessageVisitor, MessageListener { private final Log log = LogFactory.getLog(getClass().getName()); /** * Creates a HarvesterMessageHandler object. */ public HarvesterMessageHandler() { } /** * Unpacks and calls accept() on the message object. * * This method catches <b>all</b> exceptions and logs them. * * @param msg an ObjectMessage */ @Override public void onMessage(Message msg) { ArgumentNotValid.checkNotNull(msg, "msg"); log.trace("Message received:\n" + msg.toString()); try { NetarkivetMessage unpackedMsg = JMSConnection.unpack(msg); ((HarvesterMessage) unpackedMsg).accept(this); } catch (Throwable e) { log.warn("Error processing message '" + msg + "'", e); } } /** Handles when a handler receives a message it is not prepare to handle. * * @param msg The received message. * @throws PermissionDenied Always */ private void deny(HarvesterMessage msg) { throw new PermissionDenied("'" + this + "' provides no handling for " + msg + " of type " + msg.getClass().getName() + " and should not be invoked!"); } /** * This method should be overridden and implemented by a sub class if * message handling is wanted. * @param msg a CrawlStatusMessage * @throws PermissionDenied when invoked */ @Override public void visit(CrawlStatusMessage msg) throws PermissionDenied { ArgumentNotValid.checkNotNull(msg, "msg"); deny(msg); } /** * This method should be overridden and implemented by a sub class if * message handling is wanted. * @param msg a DoOneCrawlMessage * @throws PermissionDenied when invoked */ @Override public void visit(DoOneCrawlMessage msg) throws PermissionDenied { ArgumentNotValid.checkNotNull(msg, "msg"); deny(msg); } /** * This method should be overridden and implemented by a sub class if * message handling is wanted. * @param msg a {@link CrawlProgressMessage} * @throws PermissionDenied when invoked */ @Override public void visit(CrawlProgressMessage msg) { ArgumentNotValid.checkNotNull(msg, "msg"); deny(msg); } /** * This method should be overridden and implemented by a sub class if * message handling is wanted. * @param msg a {@link FrontierReportMessage} * @throws PermissionDenied when invoked */ @Override public void visit(FrontierReportMessage msg) { ArgumentNotValid.checkNotNull(msg, "msg"); deny(msg); } /** * This method should be overridden and implemented by a sub class if * message handling is wanted. * @param msg a {@link JobEndedMessage} * @throws PermissionDenied when invoked */ @Override public void visit(JobEndedMessage msg) { ArgumentNotValid.checkNotNull(msg, "msg"); deny(msg); } /** * This method should be overridden and implemented by a sub class if * message handling is wanted. * @param msg a {@link HarvesterReadyMessage} * @throws PermissionDenied when invoked */ @Override public void visit(HarvesterReadyMessage msg) { ArgumentNotValid.checkNotNull(msg, "msg"); deny(msg); } /** * This method should be overridden and implemented by a sub class if * message handling is wanted. * @param msg a {@link IndexReadyMessage} * @throws PermissionDenied when invoked */ @Override public void visit(IndexReadyMessage msg) { ArgumentNotValid.checkNotNull(msg, "msg"); deny(msg); } /** * This method should be overridden and implemented by a sub class if * message handling is wanted. * @param msg a {@link IndexRequestMessage} * @throws PermissionDenied when invoked */ @Override public void visit(IndexRequestMessage msg) { ArgumentNotValid.checkNotNull(msg, "msg"); deny(msg); } /** * This method should be overridden and implemented by a sub class if * message handling is wanted. * @param msg a {@link HarvesterRegistrationRequest} */ @Override public void visit(HarvesterRegistrationRequest msg) { ArgumentNotValid.checkNotNull(msg, "msg"); deny(msg); } /** * This method should be overridden and implemented by a sub class if * message handling is wanted. * @param msg a {@link HarvesterRegistrationResponse} */ @Override public void visit(HarvesterRegistrationResponse msg) { ArgumentNotValid.checkNotNull(msg, "msg"); deny(msg); } }