Message Driven Bean Example 2

1
Message Driven Bean Example 2

• A DealerBean for Bridge
• Group 4

2
What a Card Dealer Should Do

• Shuffle cards
• Deal cards
• Be Fair

3
The Model MDB JMS Topic
4
Shuffle Cards Session Bean PublisherBean.java

• A card a java.net.URL or URI object represents
  the path of a cards images. (http//www.server,
  ldap//ldapserver)
• A deck of cards a URLs52
• A shuffled/deal card a Vector contains the 52
  cards image URL objects, which will be randomly
  selected to be removed and sent to the topic.
• -- why sending the URL objects, not the image
  files?
• (source code http//www.ecst.csuchico.edu/pc/M
  DB/MDB.htm)

5
Why not just sending image files as messages?

• The java.io package is prohibited
• An enterprise bean must not use the java.io
  package to attempt to access files and
  directories in the file system.
• - EJB 2.0 Specification, Section 24.1.2
  Programming restriction
• - Portability J2EE Application might not
  be platform depended.
• - Performance I/O Overhead increased,
  performance decreased.
• - Security Required security policy
  cannot be enforced.
• How should an EJB gets/sets its resource
• - JDBC - URL - JavaMail
  - JMS
• (Ref EJB 2.0 spec http//java.sun.com/products/ej
  b/docs.html )

6
More on Message Objectcard

• 3 types of message are suitable for this example
• TextMessage Send text (java.lang.String) as
  message.
• textMessage.setText(http//www.myCardServer.edu
  )
• MapMessage name-value pair message (String,
  Object)
• mapMessage.setObject(heartA,heartAUrl)
  MessageFormatExcption
• ObjectMessage Send an object (Serializable) as
  Message.
• textMessage.setObject(new URL(http//example.e
  du/)

7
Deal Cards Message Driven Bean

• Displaying cards on a web page (JSP vs. Applet)
• JSP seems cannot really instantly retrieve the
  message because of the nature of http even with
  auto-reload web page every 5 secs.
• Applet able to accomplish dynamic/instant
  updating, but must use JApplet, which is not very
  well supported by some browsers. (can be
  overcome, though)
• An enterprise Bean must not use the AWT
  functionality to attempt to output information to
  display
• - EJB 2.0 Specification, Section C.1.2
  Programming restrictions

8
How to implement Be Fair

• While shuffling cards
• Randomizing by generating java.util.Random or
  java.lang.Math.
• While dealing card -- Message Delivery Mode
  PERSISTENT
• Using persistent mode, Once and only once
  delivery guaranteed
• A JMS provider must deliver a PERSISTENT message
  once-and-only-once. This means a JMS provider
  failure must not cause it to be lost and it must
  not deliver it twice.
  JMS SPEC.
• (reference http//docs.sun.com/db/doc/816-5904-1
  0)

9
Deployment

• Add connection Factory and Destination-j2eeadmin
  -addJmsFactory jms/DurableTopicCF topic -props
  clientIDMyID-j2eeadmin -addJmsDestination
  jms/MyTopic topic
• .ear file source code
• http//www.ecst.csuchico.edu/pc/BMD/BMD.htmTh
  ank you.