Lab 3 - JMS

The tasks for the labs are:

• Download a JMS provider
• Download source code of an example and the task
• Explore the source code of the example
• Run the example on your local computer
• Edit the example to exchange messages with our server
• Run it and obtain a hash of your nickname (counts as lab attendance)
• Read the homework assignment
• Explore the source of the homework assignment

Download a JMS Provider

Download and unpack either ActiveMQ 5.17 or ActiveMQ Artemis 2.21.

JMS

Specification of message passing API for Java.

• JMS 1.1
  • Classic API
  • Specification: https://jcp.org/aboutJava/communityprocess/final/jsr914/index.html
• JMS 2.0
  • Simplified API
  • Specification: https://jcp.org/aboutJava/communityprocess/mrel/jsr343/index.html

JMS Provider

Multiple commercial or open source implementations of JMS exist. Use one of these implementations:

• Artemis 2.21
  • https://activemq.apache.org/components/artemis/download/
  • Classic and Simplified API
  • preferred (the examples given in this lab use the Classic API and Maven)
• ActiveMQ 5.17
  • https://activemq.apache.org/components/classic/download/
  • Classic API only
  • (the examples given in this lab use shell scripts, not Maven)

The differences for the purpose of these labs is very small:

• If you want to (optionally) use the JMS 2.0 Simplified API, choose Artemis.
• In the example code provided for the labs and the task, Artemis examples use Maven, while ActiveMQ classic examples use simple shell scripts.

If using Java 8, then use ActiveMQ Classic 5.16.4 or ActiveMQ Artemis 2.19.1.

Download source code

Download and unpack https://d3s.mff.cuni.cz/files/teaching/nswi080/labs/Files/sources-3.zip .

• Example-Classic is a simple producer-consumer example
• Example-Artemis version for the Artemis provider
• Input-Classic base for implementing the homework assignment
• Input-Artemis version for the Artemis provider

Materials from lectures

For more examples, you can also look at:

• Lecture notes
  • https://d3s.mff.cuni.cz/files/teaching/nswi080/lectures/notes/ch02s08.html
• Examples
  • Classic API
    https://github.com/D-iii-S/teaching-middleware/tree/master/src/activemq-basic-client
  • Simplified API
    https://github.com/D-iii-S/teaching-middleware/tree/master/src/activemq-simplified-client/java

Explore example source codes

The example shows how to send and receive messages to and from queues (producer-consumer)

Java Sources

• ExampleProducer.java
  • connects to the ActiveMQ message broker and sends a text message to queues ExampleQueue1 and ExampleQueue2
• ExampleConsumer.java
  • connects to the ActiveMQ message broker and receives messages from queues ExampleQueue1 and ExampleQueue2
  • shows how to receive a message synchronously and asynchronously
    • synchronous: method call blocks the thread until a message is received
    • asynchronous: by setMessageListener, tell the consumer to call MessageListener of the specified object whenever a message is received
  • note the use of sessions:
    • each session used from one thread
    • setting a message listener in session1 binds this session to a different thread
    • so to receive a message synchronously in the main thread, we use session2

Build / run scripts

• ActiveMQ Classic
  • activemq starts the broker
  • make compile sources
  • producer, consumer run applications
• ActiveMQ Artemis
  • install script configures the broker
  • activemq starts the broker
  • make compile sources using Maven
  • producer, consumer run applications using Maven

Run the example

• Edit the setenv scripts to point to the extracted ActiveMQ implementation directory.

ActiveMQ Classic

• Start message broker

  • The broker must be running prior to the execution of the clients
  • Run in background
    • bash activemq start
    • when finished, bash activemq stop
  • Or run in foreground
    • bash activemq console

• Running the example

  • bash make to compile java code
  • bash consumer to run the consumer (will be blocked until a message arrives to ExampleQueue1)
  • bash producer to run the producer

ActiveMQ Artemis

• Configure message broker

  • bash install

• Start message broker

  • The broker must be running prior to the execution of the clients
  • Run
    • bash activemq run
    • when finished, bash activemq stop

• Running the example

  • bash make to compile java code
  • bash consumer to run the consumer (will be blocked until a message arrives to ExampleQueue1)
  • bash producer to run the producer

Note

You may encounter a warning WARNING: An illegal reflective access operation has occurred, or SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".. These warnings should not affect the working of the programs and can be ignored.

Network configuration

The message broker by default listens on tcp://0.0.0.0:61616 and running the examples and solving the tasks does not require any change to the configuration. If you want to change it, see:

• For Artemis, broker/etc/broker.xml in the directory when you ran bash install. Network is configured in the acceptors tag.
• For ActiveMQ Classic, conf/activemq.xml in the root of the unpacked ActiveMQ archive. Network is configured in the transportConnectors tag.

Lab activity task

• There is a message broker running at tcp://lab.d3s.mff.cuni.cz:5000
  • When connecting, use username "labUser" and password "sieb5w9"
  • Our client consumes messages from queue LabQueue
  • When it receives a text message, it hashes the content and sends it as a text message to topic LabTopic
• Your task is:
  • subscribe to the topic LabTopic (see code below)
  • choose a unique nickname (other users may see it)
  • send a TextMessage containing the nickname to LabQueue
  • your consumer will receive a TextMessage from LabTopic containing the hash
  • send the content of the message to the teaching assistant (Vlastimil Dort) by e-mail
  • that counts as lab activity
• Notes:
  • The order of operations is important in order to receive the answer.
  • If you get permission errors involving advisory features, add ?jms.watchTopicAdvisories=false to the connection string

Code

You can use the following code snippets to modify the example:

Connect to the broker (when using ActiveMQ Classic):

ActiveMQConnectionFactory connectionFactory =
  new ActiveMQConnectionFactory("labUser", "sieb5w9", "tcp://lab.d3s.mff.cuni.cz:5000?jms.watchTopicAdvisories=false");

Connect to the broker (when using ActiveMQ Artemis):

ActiveMQConnectionFactory connectionFactory =
  new ActiveMQConnectionFactory("tcp://lab.d3s.mff.cuni.cz:5000", "labUser", "sieb5w9");

Create a message consumer for LabTopic:

Topic topic = session.createTopic("LabTopic");
MessageConsumer consumer = session.createConsumer(topic);
consumer.setMessageListener(...);

Create a message producer for LabQueue:

Queue queue = session.createQueue("LabQueue");
MessageProducer producer = session.createProducer(queue);

Read the homework assignment

• https://d3s.mff.cuni.cz/files/teaching/nswi080/labs/Files/task-3-en.html

• Task: a simple trading system

  • Implement a client of a trading system
  • Clients must communicate with each other and with the bank
  • Clients publish their lists of goods and buy goods from each other on user request
  • The payments go through the bank

Explore assignment source codes

The source code (Input-Classic or Input-Artemis) is a base for your solution. You will need to design the application protocol and implement the missing parts.

Bank

• Java application
• Consumes messages from queue "BankQueue"
• Supports two commands
  • create new account
    • responds with account number
  • send money
    • sends confirmation message to the client that received the money

Goods

• simple data class representing goods (has a name and a price)

Client

• Java application
• Has a randomly generated list of goods to sell
• Creates an account by sending a message to the bank
• Sets up some receivers
• Missing pieces need to be implemented
• Enters a loop to process commands from the standard input
  • p - publish the list of goods to other clients
  • l - print goods lists of other clients
  • b - buy goods
    • asks for seller name and goods name

Running

• Running the incomplete application
  • bash make to compile java code
  • start the broker
  • bash bank to run the bank
  • bash client NAME to run a client