Category Archives: Annotations

Configuring @Configuration ApplicationContext for Spring Test Framework @ContextConfiguration

Here is a @Configuration class, RabbitTestConfiguration, truncated for the sake of a simple example. Bootstrapping this for testing using Spring’s Test Framework is simple. First make sure you have @ImportResource mapping via classpath to your xml which here has 2 simple declarations:


<?xml version="1.0" encoding="UTF-8"?>
<beans:beans xmlns:beans="http://www.springframework.org/schema/beans"
xmlns="http://www.springframework.org/schema/context"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd">

<component-scan base-package=”org.hyperic.hq.plugin.rabbitmq”/>

<property-placeholder location=”/etc/test.properties”/>

</beans:beans>

Next, make sure you remove the @Configuration annotation declared at the class level. We will be bootstrapping this a different way.

@ImportResource("classpath:/org/hyperic/hq/plugin/rabbitmq/*-context.xml")
public class RabbitTestConfiguration {

    private @Value("${hostname}") String hostname;

    private @Value("${username}") String username;

    private @Value("${password}") String password;

    @Bean
    public SingleConnectionFactory singleConnectionFactory() {
        SingleConnectionFactory connectionFactory = new SingleConnectionFactory(hostname);
        connectionFactory.setUsername(username);
        connectionFactory.setPassword(password);
        return connectionFactory;
    }
// ... shortened for brevity
}

Now let’s build an abstract Spring base test

/**
 * AbstractSpringTest
 * @author Helena Edelson
 */
@ContextConfiguration(loader = TestContextLoader.class)
@RunWith(SpringJUnit4ClassRunner.class)
public abstract class AbstractSpringTest {
    /** Inheritable logger */
    protected final Log logger = LogFactory.getLog(this.getClass().getName());

    /** Now we can autowire our beans that all child tests will need. Note that they are protected. */
    @Autowired
    protected org.springframework.amqp.rabbit.connection.SingleConnectionFactory singleConnectionFactory;

   @Before
    public void before() {
        assertNotNull("singleConnectionFactory should not be null", singleConnectionFactory);
        //... more assertion checks for other beans, removed for brevity.
    }

And finally, build a test context loader, override customizeContext() and bootstrap your annotational config class. Since the config class bootstraps the minimal context xml config, now we’re all set.

/**
 * TestContextLoader
 * @author Helena Edelson
 */
public class TestContextLoader extends GenericXmlContextLoader {

    @Override
    protected void customizeContext(GenericApplicationContext context) {
        AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
        ctx.register(RabbitTestConfiguration.class);
        ctx.refresh();
        /** This is really the key */
        context.setParent(ctx);
        assertTrue(ctx.isRunning());
    }
}

Now all of my Spring test classes can simply extend the base class and freely call the inherited shared beans or declare any @Autowired dependency

public class RabbitGatewayTest extends AbstractSpringTest {
     @Autowired protected Queue marketDataQueue;

    @Test
    public void getConnections() throws Exception {
        com.rabbitmq.client.Connection conn = singleConnectionFactory.createConnection();
        // ... etc
    }
}

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Spring DAO Exception Translation with @Repository

In Spring, when you mark a DAO/Repository classes with the Spring stereotype annotation, @Repository:

@Repository
public class MyDaoImpl implements MyDao { .. }

spring creates an instance of it in the IoC container as with any other stereotype annotation (@Component, @Service) but it can also add exception translation if you explicitly add this bean declaration to your config:
<bean class=”org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor”/>

This enables translation of native runtime resource exceptions that would otherwise be vendor-specific (database (oracle, etc), orm (hibernate, jpa, etc) to Spring’s runtime exception hierarchy regardless of what vendors you use over time. As it is simply enabling a feature in the Spring Framework vs something you would use, it does not require a bean id.

Also as the stereotype annotations are meta annotations you can do this to enrich behavior easily

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Repository
@Primary
@Lazy
public @interface MyRepository {
}
@MyRepository
public class OtherFooDao implements FooDao { .. }

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Simple Asynchronous Processing with Spring’s TaskExecutor

This post is merely meant as a starting guide to tinkering for a light-weight solution to handing off execution of a task for async processing without the overhead of Spring Batch or Spring JMS and Message Brokers, among other middleware solutions.

1. I have a simplistic junit test that merely kicks off the service method to view the path of execution:

/**
 * TaskTests
 *
 * @author Helena Edelson
 * @since v 1.0
 */
@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration({"classpath:infrastructure-context.xml"})
public class TaskTests extends BaseTest {
    protected static final Logger logger = Logger.getLogger(TaskTests.class);
    @Autowired private OrderService orderService;

    @Test
    public void testExecution(){
        logger.debug("Starting execution thread...");
        orderService.dispatch(new Order());
    }
}

2. A simple context config:

<?xml version=”1.0″ encoding=”UTF-8″?>
<beans xmlns=”http://www.springframework.org/schema/beans”
xmlns:xsi=”http://www.w3.org/2001/XMLSchema-instance”
xmlns:context=”http://www.springframework.org/schema/context”
xmlns:task=”http://www.springframework.org/schema/task”
xmlns:aop=”http://www.springframework.org/schema/aop”
xmlns:p=”http://www.springframework.org/schema/p”
xsi:schemaLocation=”
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.0.xsd
http://www.springframework.org/schema/task http://www.springframework.org/schema/task/spring-task-3.0.xsd”>

<bean id=”taskExecutor” class=”org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor” p:corePoolSize=”5″ p:maxPoolSize=”25″/>

<!– OR alternately: Creates a org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor –>
<task:executor id=”taskExecutor” pool-size=”5-25″ queue-capacity=”100″ rejection-policy=”CALLER_RUNS”/>

</beans>

3. OrderService that delegates to the ThreadPoolTaskExecutor:

/**
 * OrderServiceImpl is used for both orders and returns
 *
 * @author Helena Edelson
 * @MessageEndpoint which is a @Component
 * @since Dec 29, 2009
 */
@Service("orderService")
public class OrderServiceImpl implements OrderService {
    private OrderDao orderDao;
    private MerchantService merchantService;
    private ReceivingService receivingService;
    @Autowired private TaskExecutor taskExecutor;

    @Autowired
    public OrderServiceImpl(OrderDao orderDao, ReceivingService receivingService, MerchantService merchantService) {
        this.orderDao = orderDao;
        this.receivingService = receivingService;
        this.merchantService = merchantService;
    }

    public final void dispatch(final Order order) {
        logger.debug("Starting dispatch execution...");

        if (this.taskExecutor != null) {
            this.taskExecutor.execute(new Runnable() {
                public void run() {
                    executorAsync(order);
                }
            });
        }

        logger.debug("Completed dispatch execution...");
    }

    private final void executorAsync(final Order order) {
        logger.debug("Starting Async execution...");

        daoDatasourceOne.createOrder(order);
        daoDatasourceTwo.createOrder(order);

        logger.debug("Completed Async execution...");
    }

/* Where the output will be: Note the dispatch method returns control to its caller before the async method begins:
2010-01-27 13:23:27,546 [main] DEBUG org.springsource.oms.infrastructure.TaskTests  - Starting execution thread...
2010-01-27 13:23:27,546 [main] DEBUG org.springsource.oms.domain.services.OrderServiceImpl  - Starting dispatch execution...
2010-01-27 13:23:27,546 [main] DEBUG org.springsource.oms.domain.services.OrderServiceImpl  - Completed dispatch execution...
2010-01-27 13:23:27,546 [taskExecutor-1] DEBUG org.springsource.oms.domain.services.OrderServiceImpl  - Starting Async execution...
persisting org.springsource.oms.domain.entities.Order@1f10a67
*/

/**
* Alternately for a different scenario you can play around with this:
*/
public void withExecutor(final Order order) {
        try {
            CompletionService completionService = new ExecutorCompletionService(taskExecutor);

            Object result1 = completionService.submit(new Callable() {
                public Object call() {
                    return daoDatasourceOne.createOrder(order);
                }
            });
            Object result2 = completionService.submit(new Callable() {
                public Object call() {
                    return daoDatasourceTwo.createOrder(order);
                }
            });

            completionService.take().get();
            completionService.take().get();

        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }

    }
}

I recommend looking into the @Async annotation, which I will post on shortly. In the meantime here is the ref page for Spring Task and Scheduling: http://static.springsource.org/spring/docs/3.0.x/reference/html/scheduling.html

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Decoupling Asynchronous Messaging With Spring JMS and Spring Integration

The importance of decoupling in applications is vital but it is not easy to do it well, I am constantly working to improve my strategies. Even more important is the role of Messaging in an enterprise context and in the design. I think Message-driven architecture is perhaps the most important to integrate into applications in terms of its scope of applicability and how it lends to scalability. In this vein, Spring Integration becomes a highly intriguing element worthy of study, testing, and integration. I barely touch on Spring Integration here, particulary in its standard usage but simply use a few classes programmatically to decouple JMS implementation from its clients.

Messaging and Decoupling

Messaging is everywhere and so subtle we are not aware of it, it just happens all around us, all the time. Consider this: in Genetics on a cellular level, which is nongranular in the scope of genetics itself, the major elements in a cell communicate, but how? They are not connected by any physical construct save the mutual environment they are in so how do they do it? They message each other with signals, receptors and a means to translate those messages, which contain instructions.

In Gene expression, DNA/RNA within eukaryote cells (think systems within systems within systems…elements moving in space and time under specific, ever changing constraints and environmental fluctuations (put that in your Agile timebox!) ) communicate by transmitting messages, intercepting, translating and even performing message amplification. There are specialized elements, mRNA specifically, Messenger RNA, which are translated by signal recognition particles… Cool, right? But this happens all around us, outside, in space, everywhere. And it is all decoupled, and therein lies the beauty of messaging.

So what about our applications? Here is one very simple, isolated application of using Spring Integration ( a low-level usage, not very sophisticated ) to decouple your client and server messaging code:

So I wrote a little java package that integrates Spring JMS, ActiveMQ, Spring Integration and Flex Messaging for the front end which hooks into either BlazeDS or Livecycle Data Services. I had a bunch of constraints to solve for such as all Destinations had to come from the database, there were lifecycle issues as far as timing of element initializations with the IoC bean creation and Flex Messaging elements being created and having what they needed such as the Flex Messaging adaptors which I resolved by flex java bootstrapping. In another post I will go into the JMS package further. For the topic here let’s focus on the JMS-Spring JMS-Spring Integration bridge.

The image to the left shows the layout of my jms package to facilitate the mapping. In this system, messages come in from 2 areas: the client and java services on the server. Complicated systems will have many more but let’s talk about the 2 that most would have.  The client sends messages to the server that are both user messages and operational messages by the system. Java services send messages when certain business rules and criteria are triggered, passing business data and any message-aware object could be sending messages.

Sending on the server

To insure proper usage I created an interface that a service must implement to send to ActiveMQ, called JMSClientSupport. Note all code in this post is simplified. Here, I actually have it returning a validation message if errors occurred so that a business service developer could implement handling per requirements.

A Business Entity
public class Foo implements Serializable {...}

A Service
public class FooServiceImpl implements BusinessService, FooService, SMTPClientSupport, JMSClientSupport {
public void insert(Foo foo) {
..//do some important business stuff
publish(foo);
}
public void publish(Object object) {
if ((someBusinessValidation((Foo) object)) {
jmsService.send(destinationId, object);
}
}
}


public interface JMSClientSupport {
void publish (Object object);
}

Sending from the Client

You could have any client sending messages of any nature to the server. In this case I am using Flex. Messages of type <T> are wrapped on the client as an IMessage {AsyncMessage,CommandMessage etc}. When these messages make their way through Blaze or Livecycle, I have it wired to hit this java adapter which is represented in a Hash per FlexDestination for 1:1 FlexDestination : JMS Destination by Flex.

For this example I am implementing the JMS MessageListener to show tight coupling as well as decoupling:

public class FlexMessagingAdapter extends MessagingAdapter implements MessageListener {
// Invoked by Flex when a message comes in from the client to this adapter's Destination
public Object invoke(Message message) {
// a custom interceptor that extracts partition Destination info like ActiveMQ message group or subtopics like STOCKS.NASDAQ for more specific routing
String partition = new DestinationPartitionInterceptor(message).intercept();
jmsService.send(destination, new IntegrationMessageCreator (message, partition));
}
return null;
}


// Decoupled: Invoked when a Message is received from the Spring Integration channel
public void handleMessage(org.springframework.integration.core.Message<?> message) {....}

// Sets the Spring Integration MessageChannel for sending and receiving messages
public void setMessageChannel(MessageChannel messageChannel) {
this.messageChannel = messageChannel;
}


// Tightly coupled with JMS by the MessageListener.onMessage() method
public void onMessage(javax.jms.Message jmsMessage) {
flex.messaging.messages.Message message = new IntegrationMessageCreator(jmsMessage).createMessage(getDestination().getId(), getSubscribers());
if (getMessageService().getMessageBroker().getChannelIds().contains("streaming-amf")) {
MessageBroker broker = MessageBroker.getMessageBroker(null);
broker.routeMessageToService(message, null);
} else {
getMessageService().pushMessageToClients(message, true);
}
}}

The Transformer: Where Messages Intersect

I have a second post that show an even more decoupled messaging strategy with Spring Integration but this is purely a a basic idea using Flex Messaging, Spring Integration, Spring JMS and ActiveMQ. I will post the more broad strategy next :)

Step 1: Client messages are transformed here by extending the JMS MessageCreator. In this class I pull out the data from any Object type but specifically Flex Message and a JMSMessage types.

public class IntegrationMessageCreator implements MessageCreator {
// a few constructors here to handle multiple message types: JMSMessage, Flex Message, Object message, etc

private MessageBuilder createBuilder() {
MessageBuilder builder = null;
if (this.object != null) {
builder = MessageBuilder.withPayload(object);
} else if (this.flexMessage != null && flexMessage.getBody() != null) {
builder = MessageBuilder.withPayload(flexMessage.getBody()).copyHeaders(flexMessage.getHeaders());
}
// ActiveMQ Message Groups
if (this.partition != null) builder.setHeader(MessageConstants.Headers.JMSXGROUPID, partition);

return builder;
}

// to JMS
public javax.jms.Message createMessage(Session session) throws JMSException {
return new IntegrationMessageConverter().toMessage(createBuilder().build(), session);
}

// To Flex
public flex.messaging.messages.Message createMessage(String destinationId, int subscribers) {
Message integrationMessage = (Message) new IntegrationMessageConverter().fromMessage(this.jmsMessage);

flex.messaging.messages.Message flexMessage = new AsyncMessage();
flexMessage.setBody(integrationMessage.getPayload());
flexMessage.setDestination(destinationId);
flexMessage.setHeaders(integrationMessage.getHeaders());
// …and other good jms to flex data

return flexMessage;
}
}

The Converter


import org.springframework.integration.jms.HeaderMappingMessageConverter;
import org.springframework.integration.core.Message;
import javax.jms.Session;

public class IntegrationMessageConverter extends HeaderMappingMessageConverter {

// Converts from a JMS Message to an Integration Message. You should do a try catch but I cut it out for brevity
public Object fromMessage(javax.jms.Message jmsMessage) throws Exception {
return (Message) super.fromMessage(jmsMessage);
}

// Converts from an Integration Message to a JMS Message. You should do a try catch but I cut it out for brevity
public javax.jms.Message toMessage(Object object, Session session) throws Exception {
return jmsMessage = super.toMessage(object, session);
}
}

JMS Asynchronous Reception

In my jmsConfig.xml I configured one Spring MessageListenerAdapter which I have wired with a message delegate, a POJO and its overloaded handleMessage method name:

<bean id=”messageListenerAdapter”>
<property name=”delegate” ref=”defaultMessageDelegate”/>
<property name=”defaultListenerMethod” value=”handleMessage”/>
<property name=”messageConverter” ref=”simpleMessageConverter”/>
</bean>

As the application loads and all Spring beans are initialized, I initialize all of my JMS Destinations. As I do this, I also initialize a MessageListenerAdapter for each Destination. I have a stateless JMSService, which is called by another service, MessagingGateway, to initialize each Destination and which calls PollingListenerContainerFactory to create child MessageListenerAdaptors for each Destination. The adapters are configured based on an abstract parent configuration:

<bean id=”abstractListenerContainer” abstract=”true” destroy-method=”destroy”>
<property name=”connectionFactory” ref=”pooledConnectionFactory”/>
<property name=”transactionManager” ref=”jmsTransActionManager”/>
<property name=”cacheLevel” value=”3″/>
<property name=”taskExecutor” ref=”taskExecutor”/>
<property name=”autoStartup” value=”true”/>
</bean>

Snippet from PollingListenerContainerFactory:

/**
* Gets the parent from the IoC to reduce runtime config and
* resources to create children.
* <p/>
* DefaultMessageListenerContainer is Responsible for all threading
* of message reception and dispatches into the listener for processing.
* Supports dynamic scaling for a higher during peakloads.
*
* @param destination
* @param messageListener
* @return
*/
public static DefaultMessageListenerContainer createMessageListenerContainer(Destination destination, MessageListener messageListener) {

ChildBeanDefinition childBeanDefinition = new ChildBeanDefinition(“abstractListenerContainer”, configureListenerContainer(destination, messageListener));

String beanID = IdGeneratorUtil.getStringId();
ConfigurableListableBeanFactory beanFactory = ApplicationContextAware.getConfigurableListableBeanFactory();
((DefaultListableBeanFactory) beanFactory).registerBeanDefinition(beanID, childBeanDefinition);

DefaultMessageListenerContainer container = (DefaultMessageListenerContainer) ApplicationContextAware.getBean(beanID);
container.setDestination(destination);
return container;
}

/**
* Configures the child listener, based on the parent in jmsConfig.xml.
* <p>Configures Queue or Topic consumers:
* Queue: stick with 1 consumer for low-volume queues: default is
* Topic: there’s no need for more than one concurrent consumer
* Durable Subscription: Only 1 concurrent consumer supported
* <p/>
* props.addPropertyValue(“messageSelector”, “”); sets a message selector for this listener
*
* @param destination
* @param messageListener
* @return
*/
private static MutablePropertyValues configureListenerContainer(Destination destination, MessageListener messageListener) {
MutablePropertyValues props = new MutablePropertyValues();
props.addPropertyValue(“destination”, destination);
props.addPropertyValue(“messageListener”, messageListener);

// Enable throttling on peak loads
if (destination instanceof Queue) {
props.addPropertyValue(“maxConcurrentConsumers”, 50); // modify to needs
}
// Override default setting Point-to-Point (Queues)
if (destination instanceof Topic) {
props.addPropertyValue(“pubSubDomain”, true);
}

return props;
}

this is overkill to this topic but its cool stuff. So we now have a JMS listener for asynchronous JMS reception as well as flex, but now let’s look at the message delegate we wired into the MessageListenerAdapter:

public interface MessageDelegate {

void handleMessage(String message);

void handleMessage(Map message);

void handleMessage(Serializable message);
}

Pretty simple, right? It’s a POJO with absolutely no JMS code whatsoever for asynchronous message reception. How does it work? Spring abstracts the JMS code and calls it behind the scenes, if you look at the source code for Spring’s SimpleMessageConverter, it does the fromMessage() toMessage() handling for you and throws the resultant “message” into the appropriate overloaded method above. Now this is great for simple message abstraction but the above with JMS-Flex and Spring Integration is an example of more complicated handling. With clients you often need to translate and transfer the data from message type 1 to message type 2. In the adapter code above, you would use the handleMessage() method to get the message from Spring Integration and into the message type of your choice, here, a Flex message.

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JMX MBean Proxying for Export via Remoting to the Client

I wanted to expose mbeans related to application monitoring and services such as a JMS broker, users in session, etc and remote that data to the client which in my case was Flex.  First I checked out using annotations for automated registration and mbean creation but that wouldn’t help me export to a remoting format..without creating my own classes. Something for another post, but what I did was create a package with some classes, which I will explain here. You can certainly deliver this strategy more minimally but I’ve found that to come back and bite me later so I’ve added in some type safety to the proxy creation of the MBeans.

The Basic Components

There are a few important components you need to set this up as a framework

1. An MBeanConnection

2. A type-safe proxy generator

3. An applicable JMX service URL, Port, Hostname

To export mbeans to the client

1. ObjectName that can be connected to if they are services

2. Ports for those services where applicable (i.e. a broker)

3. Interfaces to proxy

I. The Goal: export mbean data by remoting to the client

I created a service which is mirrored as a Flex actionscript class for remoting which encapsulates the calls for various system monitoring data via jmx: This I registered for remoting in the framework of choice, in my case it was Flex. I have a custom annotation that handles this which I don’t include in this snippet.

public class ClientMBeanService implements IClientMBeanService { ..view the code… }

II. The Delegate

With the idea of each component to be exported create a Delegate class that implements the interface dictating the contract that it must implement a method to provide the port, the ObjectName and export the mbean:

public class BrokerDelegate implements IMBeanDelegate { ..view the code… }

All Delegates must implement

public interface IMBeanDelegate { ..view the code… }

III. For Remote and Local MBeanConnections

public class MBeanConnection { ..view the code… }

IV. The Cool Part: Get a Typesafe Proxy Intance of The MBean

public final class MBeanProxyInstance { ..view the code… }

V. Typesafing: I did not originally write this class, only modified it for Java 6, but the crux is:

public class TypeSafeMBeanProxy { ..view the code… }

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Annotational MBean Export with Spring and JMX

If you just want to easily export mbeans to jconsole or an external profiling tool this is pretty sweet:

I. Create a Spring schema config file for JMX

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

<!-- This bean needs to be eagerly pre-instantiated in order for the exporting to occur: -->
<!-- ***************** Autodetects Annotated Beans JMX Exposure *********************** -->
<bean id="annotationalMbeanExporter" class="org.springframework.jmx.export.MBeanExporter" lazy-init="false">
<property name="autodetect" value="true"/>
<property name="namingStrategy" ref="namingStrategy"/>
<property name="assembler" ref="assembler"/>
<!-- one of many optional config options -->
<property name="registrationBehaviorName" value="REGISTRATION_IGNORE_EXISTING"/>
</bean>
<bean id="attributeSource" class="org.springframework.jmx.export.annotation.AnnotationJmxAttributeSource"/>
<bean id="assembler" class="org.springframework.jmx.export.assembler.MetadataMBeanInfoAssembler">
<property name="attributeSource" ref="attributeSource"/>
</bean>
<bean id="namingStrategy" class="org.springframework.jmx.export.naming.MetadataNamingStrategy">
<property name="attributeSource" ref="attributeSource"/>
</bean>
</beans>

II. Annotate a component, bean, etc

@Service
@ManagedResource(objectName = "bean:name=applicationMonitor")
public class ClientMBeanService implements IClientMBeanService {

@ManagedOperation(description = "Monitor the JMS broker")
public BrokerStatistics exposeBroker() {
return new BrokerDelegate().exposeMBean();
}
}

@Component
@ManagedResource(objectName = "spring:name=broker", description = "ActimemMQ Broker")
public class BrokerStatistics {

private String brokerId;
private String brokerName;
private long totalMessages;
private long totalConsumers;
private long totalTopics;
private long totalQueues;
private List<Map> topics;
private List<Map> queues;

@ManagedAttribute
public String getBrokerId() {
return brokerId;
}
...etc
}

The annotational configuration in the mbean exporter allows automatic registration and mbean creation of beans. It’s that simple.

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JPA 2.0 Concurrency and locking and AOP Around Advice for Deadlock Retry

This article by Carol McDonald from Sun on JPA 2.0 Concurrency and locking is interesting. I like the idea of using AOP for handling crosscutting concerns such as Deadlocks, such as this:

1. You define your Deadlock Aspect
2. Write your @Around advice for stateless or idempotent operations that throw HibernateException from classes marked @Repository:

Around any idempotent operation, such as in a stateless business service, when a DataAccessException is thrown, keep track of how many tries, and re-execute:

@Around("idempotentOperation()")
public Object retryDeadlockLosers(ProceedingJoinPoint pjp) throws Throwable {
int attempts = 0;
DeadlockLoserDataAccessException looserEx = null;
while (attempts++ < maxAttempts) {
try {
return pjp.proceed();
} catch(DeadlockLoserDataAccessException ex) {
loserEx = ex;
}
throw loserEx;

}

Which is more a pattern you can use wherever needed and how such as you can apply to go to another rack, hop to another database, what have you.

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SuMQ Messaging Framework

I’ve just started staging my new project, SuMQ, and appreciate patience as this will take me a while to get the code standardized and on google.

SuMQ is a light-weight enterprise messaging framework built in Java, leveraging Spring, JMS, and ActiveMQ. It plugs into Flex Messaging via BlazeDS for the client. This can also be configured for other clients aside from Flex.

The sample will be ready for clustered BlazeDS instances and load balanced Application Servers.

code.google.com/p/sumq

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Creating Custom Annotations

Here is a very simplistic example on creating custom annotations in java.


package com.foo.infrastructure.annotations;
import java.lang.annotation.*;
@Documented
@Retention (RetentionPolicy.SOURCE)
@Inherited
@Target({ElementType.TYPE, ElementType.METHOD, ElementType.FIELD, ElementType.CONSTRUCTOR,ElementType.ANNOTATION_TYPE})
public @interface Unfinished {

public enum Priority { LOW, MEDIUM, HIGH }
String value();
String[] owners() default “”;
Priority priority() default Priority.MEDIUM;
}

}

And here is an equally simplistic example of using it

package com.foo.jms.infrastructure.delegates;

import com.foo.jms.infrastructure.async.JMSConsumerImpl;
import com.foo.infrastructure.annotations.Unfinished;
import org.apache.log4j.Logger;
import org.springframework.jms.core.SessionCallback;
import org.springframework.jms.core.support.JmsGatewaySupport;
import org.springframework.jms.support.JmsUtils;
import javax.jms.*;
/**
*JMSMessageDelegateImpl delegates JMS input to the appropriate handler.
* Delegates asynchronous and synchronous reception
* @author Holly Edelson
*/
@Unfinished(value=”Class scope”, priority=Unfinished.Priority.LOW, owners=”Holly”)
public class JMSMessageDelegateImpl extends JmsGatewaySupport implements JMSMessageDelegate {

private static final Logger logger = Logger.getLogger(JMSMessageDelegateImpl.class);
….
public void handleMessage(Map message) {

Map receivedMessage = (Map) getJmsTemplate().receiveAndConvert(destination);
logger.debug(“nn” + receivedMessage);

}

}

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