Gustavo.cabral: /* Write a JMS Listener */

2010-06-03T17:14:34Z

‎Write a JMS Listener

Kyle at 22:38, 24 November 2009

2009-11-24T22:38:51Z

Kyle: New page: ==Write at TagLocation Service== Now that we have all the MVC plumbing working, we need to hook up the RFID application with the web application. We will do this by creating a service tha...

2009-11-24T19:22:07Z

New page: ==Write at TagLocation Service== Now that we have all the MVC plumbing working, we need to hook up the RFID application with the web application. We will do this by creating a service tha...

New page

==Write at TagLocation Service==
Now that we have all the MVC plumbing working, we need to hook up the RFID application with the web application. We will do this by creating a service that the controller can use to find out the list of tags at each stage. Then we will write a JMS listener who will update the service with the latest information. Finally we will inject the service into the contoller.
===Write a Service Interface===
* Create a new package called <tt>com.northwind.rfid.shipping.war.service</tt>
* Create a new Interface called <tt>TagLocationService</tt>
<pre>
package com.northwind.rfid.shipping.war.service;

import java.util.List;
import com.northwind.rfid.shipping.notifications.AlertNotification;

/**
* This service provides the current list of tags at the Dock Door and the Weigh
* Station, as well as all the alerts that have happened so far
*
* @author Kyle Neumeier - kyle@pramari.com
*
*/
public interface TagLocationService {
/**
* Get a list of all packages at the dock door
*
* @return
*/
List<String> getDockDoorItems();

/**
* Get a list of all packages at the Weigh Station
*
* @return
*/
List<String> getWeighStationItems();

/**
* Get a list of all the alerts
*
* @return
*/
List<AlertNotification> getAlerts();
}

</pre>

===Write a Manager Interface===
The <tt>TagLocationService</tt> interface allows a component to consume information. We also need the ability to add data to the service as it arrives. As such, let's create a second interface with the required methods.
* Create a new package called <tt>com.northwind.rfid.shipping.war.service.impl</tt>
* Create a new Interface called <tt>TagLocationServiceManager</tt>
<pre>
package com.northwind.rfid.shipping.war.service.impl;

import com.northwind.rfid.shipping.notifications.AlertNotification;

/**
* The manager of the TagLocationService. It allows a component to add data.
*
* @author Kyle Neumeier - kyle@pramari.com
*
*/
public interface TagLocationServiceManager {

/**
* Called when a new package has arrived at the dockdoor
*
* @param item
*/
void PackageArrivedAtDockDoor(String item);

/**
* Called when a package departs from the dock door
*
* @param item
*/
void PackageDepartedFromDockDoor(String item);

/**
* Called when an item arrives at the weigh station
*
* @param item
*/
void PackageArrivedAtWeighStation(String item);

/**
* Called when an item departs from the weigh station
*
* @param item
*/
void PackageDepartedFromWeighStation(String item);

/**
* Called when a new alert happens
*
* @param notification
*/
void Alert(AlertNotification notification);
}

</pre>

===Implement the Service===
Create a class called <tt>TagLocationServiceImpl</tt> in the <tt>com.northwind.rfid.shipping.war.service.impl</tt> package.
There are a few considerations to take into account:
# The class needs to be thread-safe, since multiple threads might access the class. In our case, there are two: The JMS thread will call the manager methods, while the servlet thread will call the service methods. In order to prevent any race conditions, I wrapped the three data structures in synchronized collections. I also made sure to copy the collections before I returned them.
# We probably want to preserve the ordering that tags were inserted into the lists, however we don't want to store one tag more than once in each data structure. Therefore, I used a LinkedHashSet.
<pre>
package com.northwind.rfid.shipping.war.service.impl;

import java.util.Collections;
import java.util.LinkedHashSet;
import java.util.LinkedList;
import java.util.List;
import java.util.Set;

import com.northwind.rfid.shipping.notifications.AlertNotification;
import com.northwind.rfid.shipping.war.service.TagLocationService;

/**
* Thread-safe implementation of TagLocationService and TagLocationServiceManager
* interfaces.
*
* @author Kyle Neumeier - kyle@pramari.com
*
*/
public class TagLocationServiceImpl implements TagLocationService,
TagLocationServiceManager {

/** All the items that can be seen at dock door */
private final Set<String> dockDoor = Collections
.synchronizedSet(new LinkedHashSet<String>());
/** All the items that can be seen at the weigh station */
private final Set<String> weighstation = Collections
.synchronizedSet(new LinkedHashSet<String>());
/** All the alerts that have been created */
private final List<AlertNotification> alerts = Collections
.synchronizedList(new LinkedList<AlertNotification>());

/*
* (non-Javadoc)
*
* @see
* com.northwind.rfid.shipping.war.service.TagLocationService#getAlerts()
*/
@Override
public List<AlertNotification> getAlerts() {
return new LinkedList<AlertNotification>(alerts);
}

/*
* (non-Javadoc)
*
* @see
* com.northwind.rfid.shipping.war.service.TagLocationService#getDockDoorItems
* ()
*/
@Override
public List<String> getDockDoorItems() {
return new LinkedList<String>(dockDoor);
}

/*
* (non-Javadoc)
*
* @seecom.northwind.rfid.shipping.war.service.TagLocationService#
* getWeighStationItems()
*/
@Override
public List<String> getWeighStationItems() {
return new LinkedList<String>(weighstation);
}

/*
* (non-Javadoc)
*
* @see
* com.northwind.rfid.shipping.war.service.impl.TagLocationServiceManager
* #Alert(com.northwind.rfid.shipping.notifications.AlertNotification)
*/
@Override
public void Alert(AlertNotification notification) {
this.alerts.add(notification);
}

/*
* (non-Javadoc)
*
* @see
* com.northwind.rfid.shipping.war.service.impl.TagLocationServiceManager
* #PackageArrivedAtDockDoor(java.lang.String)
*/
@Override
public void PackageArrivedAtDockDoor(String item) {
this.dockDoor.add(item);
}

/*
* (non-Javadoc)
*
* @see
* com.northwind.rfid.shipping.war.service.impl.TagLocationServiceManager
* #PackageArrivedAtWeighStation(java.lang.String)
*/
@Override
public void PackageArrivedAtWeighStation(String item) {
this.weighstation.add(item);
}

/*
* (non-Javadoc)
*
* @see
* com.northwind.rfid.shipping.war.service.impl.TagLocationServiceManager
* #PackageDepartedFromDockDoor(java.lang.String)
*/
@Override
public void PackageDepartedFromDockDoor(String item) {
this.dockDoor.remove(item);
}

/*
* (non-Javadoc)
*
* @see
* com.northwind.rfid.shipping.war.service.impl.TagLocationServiceManager
* #PackageDepartedFromWeighStation(java.lang.String)
*/
@Override
public void PackageDepartedFromWeighStation(String item) {
this.weighstation.remove(item);
}
}
</pre>

===Write a JMS Listener===
Create a new class called <tt>MessageReceiever</tt> in the <tt>com.northwind.rfid.shipping.war</tt> pacakge.
<pre>
package com.northwind.rfid.shipping.war;

import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.ObjectInputStream;

import javax.jms.BytesMessage;
import javax.jms.JMSException;
import javax.jms.Message;
import javax.jms.MessageListener;

import com.northwind.rfid.shipping.notifications.AlertNotification;
import com.northwind.rfid.shipping.notifications.EZone;
import com.northwind.rfid.shipping.notifications.ItemArrivalNotification;
import com.northwind.rfid.shipping.notifications.ItemDepartureNotification;
import com.northwind.rfid.shipping.war.service.impl.TagLocationServiceManager;

/**
* The class that implements the logic of receiving a notification from JMS
* using the TagLocationServiceManager to update the TagLocationService
*
* @author Kyle Neumeier - kyle@pramari.com
*
*/
public class MessageReceiver implements MessageListener {

/** The TagLocationServiceManager to use */
private volatile TagLocationServiceManager TLSManager;

/**
* Called by spring
*
* @param TLSManager
* The TagLocationServiceManager
*/
public void setTLSManager(TagLocationServiceManager TLSManager) {
this.TLSManager = TLSManager;
}

/*
* (non-Javadoc)
*
* @see javax.jms.MessageListener#onMessage(javax.jms.Message)
*/
@Override
public void onMessage(Message arg0) {
if (arg0 instanceof BytesMessage) {
try {
// deserialize the message
Object message = deserialize((BytesMessage) arg0);
if (message instanceof ItemArrivalNotification) {
// If the message is an ItemArrival
ItemArrivalNotification notification = (ItemArrivalNotification) message;
if (notification.getZone() == EZone.DOCK_DOOR) {
// If it arrived at the dock door
TLSManager.PackageArrivedAtDockDoor(notification
.getTag_Id());
} else {
// otherwise it arrived at the weigh station
TLSManager.PackageArrivedAtWeighStation(notification
.getTag_Id());
}
} else if (message instanceof ItemDepartureNotification) {
// if the message is an Item Departure
ItemDepartureNotification notification = (ItemDepartureNotification) message;
if (notification.getZone() == EZone.DOCK_DOOR) {
// If it departed from the dock door
TLSManager.PackageDepartedFromDockDoor(notification
.getTag_Id());
} else {
// otherwise it departed from the weigh station
TLSManager.PackageDepartedFromWeighStation(notification
.getTag_Id());
}
} else if (message instanceof AlertNotification) {
// if the message is an alert
TLSManager.Alert((AlertNotification) message);
} else {
System.out.println("Notification type not recognized");
}
} catch (JMSException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
}

/***
* A private helper method that deserializes the incoming JMS notifications
*
* @param message
* The message to deserialize
* @return
* @throws JMSException
* @throws IOException
* @throws ClassNotFoundException
*/
private Object deserialize(BytesMessage message) throws JMSException,
IOException, ClassNotFoundException {
int length = (int) message.getBodyLength();
byte[] bytes = new byte[length];
message.readBytes(bytes);
ObjectInputStream in = new ObjectInputStream(new ByteArrayInputStream(
bytes));
return in.readObject();
}
}
</pre>

@@ Line 237: / Line 237: @@
 ===Write a JMS Listener===
-Create a new class called <tt>MessageReceiever</tt> in the <tt>com.northwind.rfid.shipping.war</tt> pacakge.
+Create a new class called <tt>MessageReceiver</tt> in the <tt>com.northwind.rfid.shipping.war</tt> package.
 <pre>
 package com.northwind.rfid.shipping.war;

@@ Line 1: / Line 1: @@
-==Write at TagLocation Service==
+This is Step 8 in the [[Northwind Tutorial|Northwind Application Tutorial]]<br>
 Now that we have all the MVC plumbing working, we need to hook up the RFID application with the web application.  We will do this by creating a service that the controller can use to find out the list of tags at each stage.  Then we will write a JMS listener who will update the service with the latest information.  Finally we will inject the service into the contoller.
 ===Write a Service Interface===

Northwind TagLocationService - Revision history

Gustavo.cabral: /* Write a JMS Listener */

Kyle at 22:38, 24 November 2009

Kyle: New page: ==Write at TagLocation Service== Now that we have all the MVC plumbing working, we need to hook up the RFID application with the web application. We will do this by creating a service tha...