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Generic message consumer for event handling in KIT Data Manager 2.0 services
/*
* Copyright 2018 Karlsruhe Institute of Technology.
*
* 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 edu.kit.datamanager.messaging.client;
import edu.kit.datamanager.entities.messaging.BasicMessage;
import edu.kit.datamanager.messaging.client.configuration.RabbitMQConsumerConfiguration;
import edu.kit.datamanager.messaging.client.handler.IMessageHandler;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.amqp.core.Message;
import org.springframework.amqp.rabbit.core.RabbitTemplate;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.scheduling.annotation.Scheduled;
import org.springframework.stereotype.Component;
/**
*
* @author jejkal
*/
@Component
public class ScheduledMessageReceiver{
private static final Logger LOGGER = LoggerFactory.getLogger(ScheduledMessageReceiver.class);
private final RabbitTemplate rabbitTemplate;
private IMessageHandler[] messageHandlers;
private final List endorsedHandlers = new ArrayList<>();
private boolean INITIALIZED = false;
private boolean NO_HANDLER_WARNING_EMITTED = false;
@Autowired
public ScheduledMessageReceiver(Optional messageHandlers, RabbitTemplate rabbitTemplate){
this.rabbitTemplate = rabbitTemplate;
if(messageHandlers.isPresent()){
this.messageHandlers = messageHandlers.get();
} else{
this.messageHandlers = null;
}
}
@Autowired
private RabbitMQConsumerConfiguration config;
@Scheduled(fixedRateString = "${repo.schedule.rate}")
public void receiveNextMessage(){
if(messageHandlers == null){
if(!NO_HANDLER_WARNING_EMITTED){
LOGGER.warn("No message handlers registered. Skip receiving all messages.");
NO_HANDLER_WARNING_EMITTED = true;
}
return;
}
if(!INITIALIZED){
//if not initialized, check all handlers for endorsement
//this is done before handling the first message as at this point, the repository is running in any case, also if the receiver is part of the repository
//this allows the handler to check for the repository
for(IMessageHandler handler : messageHandlers){
LOGGER.trace("Trying to configure handler {}.", handler.getHandlerIdentifier());
if(handler.configure()){
LOGGER.trace("Adding handler {} to list of endorsed handlers.", handler.getHandlerIdentifier());
endorsedHandlers.add(handler);
} else{
LOGGER.warn("Dropping handler {} due to misconfiguration.", handler.getHandlerIdentifier());
}
}
INITIALIZED = true;
}
LOGGER.trace("Performing receiveNextMessage() from queue {}.", config.queue().getName());
Message msg = rabbitTemplate.receive(config.queue().getName(), 1000);
if(msg != null){
try{
BasicMessage message = BasicMessage.fromJson(new String(msg.getBody()));
LOGGER.trace("Processing received message using {} registered handler(s).", messageHandlers.length);
boolean messageHandledByOne = false;
for(IMessageHandler handler : endorsedHandlers){
LOGGER.trace("Processing message by handler {}.", handler.getClass());
IMessageHandler.RESULT result = handler.handle(message);
switch(result){
case SUCCEEDED:
LOGGER.trace("Message {} has been successfully processed by handler {}.", message, handler.getHandlerIdentifier());
messageHandledByOne = true;
break;
case FAILED:
LOGGER.trace("Processing message {} by handler {} has been failed.", message, handler.getHandlerIdentifier());
if(preserveUnhandledMessage(handler.getHandlerIdentifier(), message)){
//preservation done, message handled and must not be preserved at the end again
messageHandledByOne = true;
}
break;
case REJECTED:
LOGGER.trace("Message {} has been rejected by handler {}.", message, handler.getHandlerIdentifier());
}
}
if(!messageHandledByOne){
LOGGER.debug("Message {} has been rejected by all configured handlers. Message will be discarded.", message);
}
} catch(IOException ex){
LOGGER.error("Failed to deserialize message " + msg + ".", ex);
}
}
}
/**
* Preserve messages that could not be processed by a certain handler. The
* messages are written into a textfile in the current folder and can be
* processed later separately.
*
* @param handlerIdentifier The handler which failed to process the message.
* @param message The message failed to be processed.
*
* @return TRUE if the message could be preserved (and can be assumed as
* 'handled' in some sense), FALSE otherwise.
*/
private boolean preserveUnhandledMessage(String handlerIdentifier, BasicMessage message){
boolean result = false;
LOGGER.warn("Preserving message {} for handler {}. Writing new entry to failed_message_handles.csv.", message, handlerIdentifier);
String entry = handlerIdentifier + ", " + message + "\n";
try{
Path logfile = Paths.get("failed_message_handles.csv");
if(!Files.exists(logfile)){
Files.write(logfile, "message handler, message\n".getBytes(), StandardOpenOption.CREATE);
}
Files.write(logfile, entry.getBytes(), StandardOpenOption.APPEND);
result = true;
} catch(IOException ex){
LOGGER.error("Failed to write entry " + entry + " to message error log 'failed_message_handles.csv'.", ex);
}
return result;
}
}