Random Thoughts

Recently I have been working on a Maven multi module project with ear, war and ejb artifacts. It has been a pleasant experience till I got to versioning my modules. Consider a multi module project with the following structure:

parent-project
|
|- child-moudle
| |
| |–pom.xml
|
|- pom.xml

The parent project pom.xml holds the version information of the parent project:

com.inflinx
project-parent
1.0.0-SNAPSHOT
pom

Now the child module pom contains a reference to the parent information:

	com.inflinx
	project-parent
	1.0.0-SNAPSHOT


4.0.0
com.inflinx
child-module
jar

Now this is where the problem starts. Since all the child modules need to have an explicit reference to the parent pom version, when it is time to do a release, we have to change the version in parent pom and all the child module poms. This can be a real pain and is very error prone. With a little help from Google, here is what I found:

1. Ceki on his blog suggested using a property in the parent pom to control the version numbering.
2. Several maven users would like “automatic parent versioning” according this improvement
3. Use maven release plugin which would automate the process of changing version numbers across the project

Option three seems to be the correct approach to solve this problem here. But I have heard horrible things about the release plugin and how fragile it is. I will be giving it a try soon. I still think that Maven should support automatic parent versioning as an option for users who don’t (or cannot) get to use the release plugin.

Maven Archetypes are project templates that allow users easily create new projects. Maven Archetypes are great way to share best practices and enforce consistency beyond Maven’s standard directory structure. For example, an organization can provide its developers an archetype bundled with company’s approved CSS and JavaScript libraries.

Recently, I have been creating a lot of Spring MVC based projects and each time I do, I copy a lot of information (configuration files, css files, dependency information etc) from an existing project. Following the DRY principles, I decided to create several Spring MVC based archetypes that can help me bootstrap my projects quickly. In this post I will share my experiences creating and using a new Maven Archetype.

Maven provides several ways to create a new archetype as described here. Since I have an existing Spring MVC project, I will be using the archetype:create-from-project goal.

 

Creating Archetype

Step 1: Identify the Maven Project that would be used as prototype for the archetype. Make sure it has only the resources (configuration, properties and Java files) that you would like to be part of the archetype. It is recommended to remove IDE specific files (.project, .classpath etc) from the project directory. Here is the spring-mvc-prototype project that I will be using:

Step 2: Using command line, navigate to the project folder spring-mvc-prototype and run the following command:

	mvn archetype:create-from-project
	

Upon completion of the command, you should see the message “Archetype created in target/generated-sources/archetype”. The newly created archetype is now under spring-mvc-prototype/target/generated-sources/archetype

Step 3: The next step is to move the newly created archetype into a separate folder so that it can be tweaked and published. I have moved the content inside the spring-mvc-simple-archetype folder.

Step 4: Modify the artifactId in the archetype’s pom.xml located at the root of spring-mvc-simple-archetype folder.

Existing pom.xml:

  com.inflinx.blog
  spring-mvc-prototype-archetype
  1.0.0-SNAPSHOT
  maven-archetype
  spring-mvc-prototype-archetype

Modified pom.xml:

	com.inflinx.blog
	spring-mvc-simple-archetype
	1.0.0-SNAPSHOT
	maven-archetype
	spring-mvc-simple-archetype	

Step 5: Modify the finalName in the resource’s pom.xml file located at spring-mvc-simple-archetypesrcmainresourcesarchetype-resources.

		 
		spring-mvc-prototype

		
		${artifactId}
	

During project creation, maven will replace the ${artifactId} expression with the user supplied artifactId value.

Step 6: When creating a project from an archetype, Maven prompts the user for a package name. Maven will create the package in the source folder (srcmainjava) of the project being created and will move the contents under archetype-resourcessrcmainjava into the package.

While generating the “testproject” above, the user specified the package “com.inflinx.blog.testproject”. So the SomeJavaClass.java file got moved to the root of the package and the HomeController.java got moved under the web.controller subpackage.

Step 7: The next step is to verify that the generated archetype.xml (located under src/main/resources/META-INF/maven) has all the files listed and they are located in the right directories. For example, the HomeController is located under archetype-resources/src/main/java/web/controller/HomeController.java. So there should be an entry under sources in the archetype.xml that looks something like this:

	  
	    src/main/java/com/inflinx/blog/mvcprototype/web/controller/HomeController.java
	  

Step 8: Modify the configuration files to correctly use the ${package} variable. For example, the webContext.xml file is modified so that the controllers located under web.controller sub package are picked up:

Step 9: The final step in creating the archetype is to run the following on command line inside the folder spring-mvc-simple-archetype:

	mvn clean install
	

 

Using the archetype

Once the archetype is installed, there are several ways to create a project from it.

Generate goal: Create an empty folder and run the following command:

 		
 		mvn archetype:generate -DarchetypeCatalog=local
		

This goal would scan the local catalog for archetypes and prompts the user to select an archetype to use.

Once the user enters 1, Maven selects the spring-mvc-simple-archteype for project creation.

m2Eclipse Plugin: If you are an Eclipse user, use the New Project Wizard and search and select the spring-mvc-simple-archetype.

Using m2Eclipse plugin is a real time saver since it creates the associated IDE specific configuration files.

 

Adding Custom Properties

On some projects, additional information such as user name or web application context might be needed to generate the project. Here are the steps to prompt the user for information and use it:

Step 1: Add to the archetype-metadata.xml file located under spring-mvc-simple-archetypesrcmainresourcesMETA-INFmaven a required properties entry:

Step 2: Modify the file where you would like to use the information. Below, I have modified weblogic.xml to have the context root value the user has provided:

 
	
		
	        true
	    
		${contextRoot}	
	

When the user uses the archetype with the above modifications, he will be prompted for the contextRoot.

I recently worked on a Spring application that used Hibernate as JPA provider and JTA for transaction demarcation. In this post I will create a simple Order Processing Message Driven Bean that showcases this integration. I will be using an Oracle database and deploy the application on a WebLogic 10.3 server.

To keep things manageable, the Message Driven Bean is designed to consume messages from a Queue. When a new message gets added to the Queue, the Application Server delivers it to the MDB. The MDB then uses a Spring Managed Service/Repository to persist a new “Order” JPA Entity in the database. The application is configured such that this entire process runs in a container managed transaction. I will be using the Blog Queue I created in a previous post.

Step 1: The first step is to create an Order Entity and the corresponding database table to store the newly created orders.

 
package com.inflinx.blog.orderprocessing.domain;

import java.util.Date;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name="ORDER_TABLE", schema="BLOGDEMO")
public class Order 
{
	@Id
	@Column(name="ORDER_ID")
	private Long id;
	
	@Column(name="NAME")
	private String name;
	
	@Column(name="CREATED_DATE")
	private Date createdDate;

	public Long getId() {
		return id;
	}
	public void setId(Long id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public Date getCreatedDate() {
		return createdDate;
	}
	public void setCreatedDate(Date createdDate) {
		this.createdDate = createdDate;
	}
}

I have created the ORDER_TABLE in an Oracle database under the BLOGDEMO schema:

Step 2: In the WebLogic console, create a XA datasource to the database with the JNDI name jdbc.blgods.

The XA datasource is necessary for Hibernate to participate in a JTA global transaction. WebLogic also provides an option to emulate XA with the Emulate Two-Phase Commit.

Step 3: The next step is to create an OrderRepository that deals with persistence logic such as creating a new Order.

package com.inflinx.blog.orderprocessing.repository;

import com.inflinx.blog.orderprocessing.domain.Order;

public interface OrderRepository 
{
	public void createOrder(Order order);
}

package com.inflinx.blog.orderprocessing.repository;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

import org.springframework.stereotype.Repository;

import com.inflinx.blog.orderprocessing.domain.Order;

@Repository("orderRepository")
public class OrderRepositoryImpl implements OrderRepository 
{
	// Spring injected EntityManager
	@PersistenceContext
    private EntityManager entityManager;
	
	@Override
	public void createOrder(Order order) 
	{
		 entityManager.persist(order);
	}
}

Step 4: Following the principles of layered architecture, the next step is to create an OrderService and its implementation.

package com.inflinx.blog.orderprocessing.service;

import com.inflinx.blog.orderprocessing.domain.Order;

public interface OrderService {
	public void createOrder(Order order);
}

package com.inflinx.blog.orderprocessing.service;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import com.inflinx.blog.orderprocessing.domain.Order;
import com.inflinx.blog.orderprocessing.repository.OrderRepository;

@Service("orderService")
@Transactional
public class OrderServiceImpl implements OrderService {

	@Autowired
	@Qualifier("orderRepository")
	private OrderRepository orderRepository;
	
	@Override
	public void createOrder(Order order) {
		// Simply delegate the call to repository layer
		orderRepository.createOrder(order);
	}
}

As you can see, the implementation is annotated with @Transactional to make the service call transactional.

Step 5: The next step is to create a persistence.xml file without any JPA provider information.

 

	
		
			com.inflinx.blog.orderprocessing.domain.Order
		

		

Step 6: The next step is to create a Spring configuration application-context.xml file to hold bean and transaction definition. In addition, the file also holds the JPA provider information.

       
	     
    
     
    
    
    
	
	
	
	
    
	    
    
    			
    				
    					
    					
    				
    			
    			
    				
    					hibernate.transaction.factory_class=org.hibernate.transaction.JTATransactionFactory
					hibernate.transaction.manager_lookup_class=org.hibernate.transaction.WeblogicTransactionManagerLookup
					hibernate.current_session_context_class=jta
					hibernate.transaction.flush_before_completion=true						
					hibernate.connection.release_mode=auto
    				
    			
    			
    	
             

Step 7: With the above configuration in place, the next step is to create a Message Driven Bean that processes incoming messages. The MDB is annotated to use container managed transactions:

 
package com.inflinx.blog.mdb;

import java.util.Date;

import javax.ejb.ActivationConfigProperty;
import javax.ejb.MessageDriven;
import javax.ejb.TransactionAttribute;
import javax.ejb.TransactionAttributeType;
import javax.ejb.TransactionManagement;
import javax.ejb.TransactionManagementType;
import javax.interceptor.Interceptors;
import javax.jms.Message;
import javax.jms.MessageListener;

import org.apache.commons.lang.RandomStringUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.ejb.interceptor.SpringBeanAutowiringInterceptor;

import com.inflinx.blog.orderprocessing.domain.Order;
import com.inflinx.blog.orderprocessing.service.OrderService;


@MessageDriven(
		mappedName = "jndi.blogQueue",
		name="orderProcessor",
		activationConfig = { @ActivationConfigProperty(
				propertyName = "destinationType", propertyValue = "javax.jms.Queue"
		)}
)
@Interceptors(SpringBeanAutowiringInterceptor.class)
@TransactionManagement(TransactionManagementType.CONTAINER)
public class OrderProcessor implements MessageListener
{
	@Autowired
	@Qualifier("orderService")
	private OrderService orderService;
	
    @Override
    @TransactionAttribute(TransactionAttributeType.REQUIRED)
	public void onMessage(Message message) 
	{
    	// Create a new Order
    	Order order = new Order();
    	order.setId(System.currentTimeMillis());
    	order.setName(RandomStringUtils.randomAlphabetic(5));
    	order.setCreatedDate(new Date());
    	
    	// Save the order
    	orderService.createOrder(order);
	}
	
}

Step 8: The SpringBeanAutowiringInterceptor by default looks for a beanRefContext.xml file to create a spring context. So the final step in the process is to create a beanRefContext.xml with a reference to the application-context.xml.

			 
		
							
				application-context.xml
			
		 		
	
	 

Now when a new message gets added to the Queue, the onMessage method will run inside a transaction and will create a new Order. Here is a new Order record in the database:

I have been wanting to try JRebel for a long time and finally installed the 30 day trial version on Eclipse. The Windows Installer made the installation very easy. The documentation in the Configuration Wizard was great help to complete IDE integration.

I am using JRebel in a Spring 3.x project and the only problem I see so far is this Exception being thrown once in a while:

JRebel: Reloading class ‘com.blog.inflinx……SearchCommand’.
JRebel: An error occured in a JRebel plugin while handling a class reload event:
java.lang.NoClassDefFoundError: org/springframework/beans/factory/CannotLoadBeanClassException
at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanNamesForType(DefaultListableBeanFactory.java:305)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeansOfType(DefaultListableBeanFactory.java:382)

Looks like the package changes made in Spring 3.x is causing this. I will be posting updates on this experimentation.

Update 1: I am using JRebel in a multi module Maven project and it is working great. However, I once noticed that it didn’t update my changes in a Spring bean.

Update 2: I just upgraded to 3.0 and did not run into any issues. I wish there was an upgrade guide with the download.