MVC Architecture of OpenJPA

In the development process the standard way is to use Model View Controller architecture, where the separation of each component comes into play. 

1.      Model – Model represents the data & rules that govern access & update of data. That means basically it will contain database objects to be accessed.

2.      View – View is the web pages that we can display. The HTML, JSP pages are under the View category.

3.      Controller – This is the controlling mechanism between model & view. This will communicate with Model & View & translate & transport data objects.

Figure MVC Architecture of JPA

1.      DAO – DAO means Data Access Objects & it provides an abstract interface to the databases. Basically in DAO layer we write queries to access the database. We can write DAO’s & include methods as much as we wanted. When writing DAO we can use OpenJPA NamedQueries directly.

2.      Domain – Domain means the entity classes for the tables in the database. For each table in the database, we can create a mapping entity class & define the table entities as objects. It is much more efficient way than traditional relational database mapping. Domain also called as POJO (Plain Old Java Objects).

 In order to create the connection between database & domains, need to create an xml file including such details. That xml file is named as “persistance.xml” by default. It is similar to the normal database connection establishment, but it is defined in xml format. A typical persistance.xml file would contain following details.

This holds the connection details & there are two ways to retrieve the data objects. One method is using Entity manager & other way is using Session factory. I used entity manager factory in the DAO layers.

Hope this post would help you to understand the MVC architecture of the OpenJPA. Stay in touch :)

What is Spring MVC Architecture

As I mentioned earlier, Spring has a MVC architecture which make the Spring a high performance framework comparing to others. in the MVC architecture of Spring, there are important parts to be noted as dispatcher Servlet, handler mapping, view resolver & views. The abstract communication between these components is as follows. the communication steps are as follows.

 1. The user request is received by the dispatcher servlet. This dispatcher servlet is the key for mapping the resources to the correct requests. It contains xml mapping codes defining each resource with the path to the resource. 

2. Then the dispatcher servlet will invoke the controller for the request. 

3. The Controller process the request by calling the appropriate service methods and returns a ModeAndView object to the DispatcherServlet. The ModeAndView object contains the model data and the view name.

 4. The DispatcherServlet sends the view name to a ViewResolver to find the actual View to invoke. 

5. Now the DispatcherServlet will pass the model object to the View to render the result & the View with the help of the model data will render the result back to the user.

What is Dispatcher-Servlet in Spring

When you work with Spring framework, you will find an xml file called dispatcher-servlet is created when we create a new project. If we use Maven to build the project we can define the name for this servlet instead of the default name "dispatcher-servlet.xml". Normally we give the project name as the prefix & keep the servlet part as it is. For example, if the project name is Navigator, then dispatcher servlet can be "navigater-servlet.xml". 

the purpose of the dispatcher is to receive the requests & map those requests to the correct resources such as models & views. that means when a request is received it should be handled to meet with the correct resources & output the results. therefore we define all the request mapping codes within the dispatcher servlet. It is an xml file which contains java beans. 

when we define the beans tag, we must include all relevant bean URLs within it in order to map the resources. A sample beans tag definition is as follows.

After defining the beans, we can define the resource mapping tags. For example, we can define view resolvers, annotation URLs or any other DAO resource URLs within the xml.

In order to map the requests the request mapping code must be included within the java controller pages. such mapping code can be shown as follows.

@RequestMapping("/enterdetails")

This @RequestMapping denotes that the current page is mapped with the dispatcher servlet. so if the mapping is correct, the request will be directed to this controller & controller will do the rest if the things.

Now you may have a clear idea on the dispatcher servlet. Stay tuned for the next post.

How to Use Spring Framework With Maven

In earlier post I was describing about Spring framework & its components. Now let me describe you how we can use this to our development process. I am using Ubuntu for the development form the beginning, so this is also going under Ubuntu.
First you need to download the latest version of the Spring framework from HERE.

Then you need to untar the tar file & move the folder to your preferred place. In the installation process, you n=only need to do that.The folder will contain sub folders such as dist, projects & src which contains all the Spring dependencies required for the development.
In order to use Spring in your java projects with maven, you need to add the Spring to the POM file of the Maven. I think now all of you are aware of Maven & the POM as I've described them in my earlier posts.
so to add Spring to Maven you need to add it as a Dependency to the POM. This is how you need to do it.

1. Create a Maven based project using following code.
mvn archetype:create -DgroupId=com.maven.test -DartifactId=TestProject -DarchetypeArtifactId=maven-archetype-webapp

now this will create an empty POM in your project folder.

2. Open the pom & you will see something similar to this.

<?xml version="1.0" encoding="UTF-8"?>

<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

<modelVersion>4.0.0</modelVersion>

<groupId>org.springsource.maven</groupId>

<artifactId>example1</artifactId>

<version>1.0-SNAPSHOT</version>

<name>Our Simple Project</name>

</project>

3. Now insert the following code within the < dependencies > </dependencies > tags.

<dependency>

<groupId>org.springframework</groupId>

<artifactId>spring-context</artifactId>

<version>3.0.5.RELEASE</version>

</dependency>

4. This tag will tell java that Spring framework is installed & ready to use for the project.

Now you can use all the Spring dependencies under this as required for the project. Following are the most used dependencies. The version can be varied so that it can be given like a variable & define it in the top of the POM under properties.


-<dependency> <groupId>org.springframework</groupId> <artifactId>spring-expression</artifactId> <version>${org.springframework.version}</version> </dependency>

<!-- Bean Factory and JavaBeans utilities (depends on spring-core) Define this if you use Spring Bean APIs (org.springframework.beans.*) -->
 -<dependency> <groupId>org.springframework</groupId> <artifactId>spring-beans</artifactId> <version>${org.springframework.version}</version> </dependency>

<!-- Aspect Oriented Programming (AOP) Framework (depends on spring-core, spring-beans) Define this if you use Spring AOP APIs (org.springframework.aop.*) -->
 -<dependency> <groupId>org.springframework</groupId> <artifactId>spring-aop</artifactId> <version>${org.springframework.version}</version> </dependency>

<!-- Application Context (depends on spring-core, spring-expression, spring-aop, spring-beans) This is the central artifact for Spring's Dependency Injection Container and is generally always defined -->
 -<dependency> <groupId>org.springframework</groupId> <artifactId>spring-context</artifactId> <version>${org.springframework.version}</version> </dependency>

<!-- Various Application Context utilities, including EhCache, JavaMail, Quartz, and Freemarker integration Define this if you need any of these integrations -->
 -<dependency> <groupId>org.springframework</groupId> <artifactId>spring-context-support</artifactId> <version>${org.springframework.version}</version> </dependency>
<!-- Transaction Management Abstraction (depends on spring-core, spring-beans, spring-aop, spring-context) Define this if you use Spring Transactions or DAO Exception Hierarchy (org.springframework.transaction.*/org.springframework.dao.*) -->
 -<dependency> <groupId>org.springframework</groupId> <artifactId>spring-tx</artifactId> <version>${org.springframework.version}</version> </dependency>

<!-- JDBC Data Access Library (depends on spring-core, spring-beans, spring-context, spring-tx) Define this if you use Spring's JdbcTemplate API (org.springframework.jdbc.*) -->
 -<dependency> <groupId>org.springframework</groupId> <artifactId>spring-jdbc</artifactId> <version>${org.springframework.version}</version> </dependency>

<!-- Object-to-Relation-Mapping (ORM) integration with Hibernate, JPA, and iBatis. (depends on spring-core, spring-beans, spring-context, spring-tx) Define this if you need ORM (org.springframework.orm.*) -->
 -<dependency> <groupId>org.springframework</groupId> <artifactId>spring-orm</artifactId> <version>${org.springframework.version}</version> </dependency>

<!-- Object-to-XML Mapping (OXM) abstraction and integration with JAXB, JiBX, Castor, XStream, and XML Beans. (depends on spring-core, spring-beans, spring-context) Define this if you need OXM (org.springframework.oxm.*) -->
 -<dependency> <groupId>org.springframework</groupId> <artifactId>spring-oxm</artifactId> <version>${org.springframework.version}</version> </dependency>

<!-- Web application development utilities applicable to both Servlet and Portlet Environments (depends on spring-core, spring-beans, spring-context) Define this if you use Spring MVC, or wish to use Struts, JSF, or another web framework with Spring (org.springframework.web.*) -->
 -<dependency> <groupId>org.springframework</groupId> <artifactId>spring-web</artifactId> <version>${org.springframework.version}</version> </dependency>

<!-- Spring MVC for Servlet Environments (depends on spring-core, spring-beans, spring-context, spring-web) Define this if you use Spring MVC with a Servlet Container such as Apache Tomcat (org.springframework.web.servlet.*) -->
 -<dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc</artifactId> <version>${org.springframework.version}</version> </dependency>

<!-- Spring MVC for Portlet Environments (depends on spring-core, spring-beans, spring-context, spring-web) Define this if you use Spring MVC with a Portlet Container (org.springframework.web.portlet.*) -->
 -<dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc-portlet</artifactId> <version>${org.springframework.version}</version> </dependency>

<!-- Support for testing Spring applications with tools such as JUnit and TestNG This artifact is generally always defined with a 'test' scope for the integration testing framework and unit testing stubs -->
 -<dependency> <groupId>org.springframework</groupId> <artifactId>spring-test</artifactId> <version>${org.springframework.version}</version> <scope>test</scope> </dependency>

So this is how you integrate Spring into Maven using the POM dependencies. So enjoy development with Spring until the next post.