EJB Transaction

Bean Type	Container-Managed	Bean-Managed
		JTA	JDBC
Entity	Y	N	N
Session	Y	Y	Y
Message-driven	Y	Y	Y

Callback

In computer programming, a callback is a reference to executable code, or a piece of executable code, that is passed as an argument to other code. 

JMS in Spring

If you used JMS before, you knew the drill. Before we could send/receive a message, we need create get a connection factory, then create a connection, start a connection, create a session, create a queue or topic, create a producer/consumer....and after that, we need clean up the connection and session.

Now enter Spring

All we need is inject a JmsTemplate and Destination to producer/consumer bean.

Here is how to send a message in producer bean.

jmsTemplate.send(destination,
    new MessageCreator()
    {
     public Message createMessage(Session session) throws JMSException
     {
      TextMessage message = session.createTextMessage("Hello, World!");
      return message;
     }
    });

Here is how to receive a message in consumer bean.

Message message = (Message) jmsTemplate.receive(destination);

Here is the configuration for JmsTemplate and Destination

<bean id="connectionFactory" class="org.apache.activemq.ActiveMQConnectionFactory">
     <property name="brokerURL" value="tcp://localhost:61616"/>
</bean>

<bean id="queue_destination" class="org.apache.activemq.command.ActiveMQQueue">
     <constructor-arg index="0" value="BolunQueue"/>
</bean>

You are welcome!

Regular Expression Example

^[0-9]+:

This will look for at the start of each line something like 1:

It's very useful to reformat some java codes which were posted with line number.

What's wrong with ActiveMQ version apache-activemq-5.5.0-bin.zip

I am trying to play with the most updated ActiveMQ: apache-activemq-5.5.0-bin.zip.

I thought it should be fairly easy. Download the zip file, unzip it, put lib\ and activemq-all-5.5.0.jar in classpath, and make sure java in PATH, I got everything covered.

But when I try to start activemq, I got an error:

Exception in thread "main" java.lang.UnsupportedClassVersionError: Bad version number in .class file

Dear God, this drives me crazy, I could not figure it out anything that I did wrong to cause this, tried all the options that I could think of, finally I gave up, I told myself, what about try some other version, let's say, apache-activemq-5.4.2-bin.zip. 

Guess what, it is working!

Find + Grep

find . -name "*Extent.java" -exec echo "{}," \; -exec grep " CLASSNAME" '{}' > output.xml \;

This is search all the files ends with "Extent.java", print the name, then grep the line which contains "ClASSNAME", then put everything into output.xml

snippet of output.xml

/advising/src/com/dovetailsys/advising/Q5CNPBankRestrictionExtent.java,
    public static final String CLASSNAME = "CNPBankRestriction";

JEE Transaction

2 types of transactions:
a. Container-managed transactions
b. Bean-managed transactions

Table 14-1 Transaction Attributes and Scope 

Transaction Attribute	Client's Transaction	Business Method's Transaction
Required	None	T2
	T1	T1
RequiresNew	None	T2
	T1	T2
Mandatory	None	error
	T1	T1
NotSupported	None	None
	T1	None
Supports	None	None
	T1	T1
Never	None	None
	T1	Error

Mandatory vs Never
NotSupported vs Supports

@TransactionAttribute(NOT_SUPPORTED)
@Stateful
public class TransactionBean implements Transaction {
...
    @TransactionAttribute(REQUIRES_NEW)
    public void firstMethod() {...}
 
    @TransactionAttribute(REQUIRED)
    public void secondMethod() {...}
 
    public void thirdMethod() {...}
 
    public void fourthMethod() {...}
}