Saturday, June 19, 2010

Getting started with Scala, Spring, Hibernate & Wicket

Introduction


Below is a tutorial to document what I did to create a fully working Scala project utilizing the best or the most popular frameworks or tools in enterprise Java such as Spring, Hibernate/JPA, Wicket, Maven and Intellij IDEA. The purpose is to help other Java programmers get started quickly with a fully working enterprise Scala project.

Setting up the IDE


First, download the Intellij IDEA 9.0.x (community edition) as it is the best scala IDE right now. Then choose File | Settings | Plugins, choose the Available tab to install the Scala plugin.

Creating the Maven project


In IDEA, choose File | New Project and choose the Maven module to create a Maven project. Then modify pom.xml as shown below. This will add all the dependencies you need and set up the compilation of Scala classes in the build processes:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.foo</groupId>
<artifactId>myapp</artifactId>
<packaging>war</packaging>
<version>1.0-SNAPSHOT</version>
<name>myapp Java EE 6 Webapp</name>
<url>http://maven.apache.org</url>
<properties>
<spring.version>3.0.3.RELEASE</spring.version>
</properties>
<repositories>
<repository>
<id>java.net2</id>
<name>Repository hosting the jee6 artifacts</name>
<url>http://download.java.net/maven/2</url>
</repository>
<repository>
<id>scala-tools.org</id>
<name>Scala-tools Maven2 Repository</name>
<url>http://scala-tools.org/repo-releases</url>
</repository>
<repository>
<id>wpt-release</id>
<url>http://wicketpagetest.sourceforge.net/m2-repo/releases</url>
</repository>
<repository>
<id>wpt-snapshot</id>
<url>http://wicketpagetest.sourceforge.net/m2-repo/snapshots</url>
</repository>
</repositories>
<pluginRepositories>
<pluginRepository>
<id>scala-tools.org</id>
<name>Scala-tools Maven2 Repository</name>
<url>http://scala-tools.org/repo-releases</url>
</pluginRepository>
</pluginRepositories>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-context</artifactId>
<version>${spring.version}</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
<version>${spring.version}</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-web</artifactId>
<version>${spring.version}</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-orm</artifactId>
<version>${spring.version}</version>
</dependency>
</dependencies>
</dependencyManagement>
<dependencies>
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
<version>1.2.120</version>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-entitymanager</artifactId>
<version>3.4.0.GA</version>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-orm</artifactId>
</dependency>
<dependency>
<groupId>com.ttdev</groupId>
<artifactId>wpt-core</artifactId>
<version>1.5.2-SNAPSHOT</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>com.ttdev</groupId>
<artifactId>wpt-runtime-spring</artifactId>
<version>1.5.2-SNAPSHOT</version>
</dependency>
<dependency>
<groupId>javax</groupId>
<artifactId>javaee-web-api</artifactId>
<version>6.0</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>3.8.2</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.scala-lang</groupId>
<artifactId>scala-library</artifactId>
<version>2.8.0.RC3</version>
</dependency>
<dependency>
<groupId>org.apache.wicket</groupId>
<artifactId>wicket</artifactId>
<version>1.4.9</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.4.2</version>
</dependency>
</dependencies>
<build>
<pluginManagement>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>2.0.2</version>
</plugin>
<plugin>
<groupId>org.scala-tools</groupId>
<artifactId>maven-scala-plugin</artifactId>
<version>2.9.1</version>
</plugin>
</plugins>
</pluginManagement>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<executions>
<execution>
<phase>compile</phase>
<goals>
<goal>compile</goal>
</goals>
</execution>
</executions>
<configuration>
<source>1.6</source>
<target>1.6</target>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-war-plugin</artifactId>
<version>2.1-beta-1</version>
<configuration>
<failOnMissingWebXml>false</failOnMissingWebXml>
</configuration>
</plugin>
<plugin>
<groupId>org.scala-tools</groupId>
<artifactId>maven-scala-plugin</artifactId>
<executions>
<execution>
<id>scala-compile-first</id>
<phase>process-resources</phase>
<goals>
<goal>add-source</goal>
<goal>compile</goal>
</goals>
</execution>
<execution>
<id>scala-test-compile</id>
<phase>process-test-resources</phase>
<goals>
<goal>testCompile</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
<finalName>myapp</finalName>
</build>
</project>

Wait for a while and IDEA will prompt you on whether to import the changes into the project. Say yes.

Setting up web.xml


Next, modify main/webapp/WEB-INF/web.xml as below. This sets up the Wicket filter, the Spring filter to open the JPA entity manager and the Spring listener to initialize Spring itself.

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
<filter>
<filter-name>f2</filter-name>
<filter-class>org.springframework.orm.jpa.support.OpenEntityManagerInViewFilter</filter-class>
</filter>
<filter>
<filter-name>f1</filter-name>
<filter-class>org.apache.wicket.protocol.http.WicketFilter</filter-class>
<init-param>
<param-name>applicationClassName</param-name>
<param-value>com.foo.myapp.MyApp</param-value>
</init-param>
</filter>
<filter-mapping>
<filter-name>f1</filter-name>
<url-pattern>/app/*</url-pattern>
</filter-mapping>
<filter-mapping>
<filter-name>f2</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:/beans.xml</param-value>
</context-param>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
</web-app>

Setting up the Spring beans for database access and transaction


To define those Spring beans, create main/resources/beans.xml with the content below. This defines the entity manager factory, the transaction manager and etc.

<?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:tx="http://www.springframework.org/schema/tx"
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
http://www.springframework.org/schema/tx
http://www.springframework.org/schema/tx/spring-tx-3.0.xsd">
<context:component-scan base-package="com.foo.myapp"/>
<bean id="emf" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
<property name="persistenceXmlLocation" value="classpath:/META-INF/my-persistence.xml"/>
</bean>
<bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
<property name="entityManagerFactory" ref="emf"/>
</bean>
<tx:annotation-driven />
</beans>

The entity manager factory will read the database configuration from the my-persistence.xml file. So, create it in main/resources/META-INF with the content below. Here, you'll access an H2 database named myapp in your home directory.

<persistence xmlns="http://java.sun.com/xml/ns/persistence"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"
version="2.0">
<persistence-unit name="myapp" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<properties>
<property name="hibernate.connection.driver_class" value="org.h2.Driver"/>
<property name="hibernate.connection.url" value="jdbc:h2:tcp://localhost/~/myapp"/>
<property name="hibernate.connection.username" value="sa"/>
<property name="hibernate.connection.password" value=""/>
<property name="hibernate.dialect" value="org.hibernate.dialect.H2Dialect"/>
<property name="hibernate.hbm2ddl.auto" value="create"/>
</properties>
</persistence-unit>
</persistence>

Creating the Wicket page


Here, you'll create a Wicket page to display some products loaded from the database. So, create the main/scala folder, right click it and choose New | Scala Class. Name the class as MyPage and put it into the com.foo.myapp package. The class is shown below:


package com.foo.myapp

import org.apache.wicket.markup.html._
import basic.Label
import list.{ListItem, ListView}
import org.apache.wicket.spring.injection.annot.SpringBean
import org.apache.wicket.model.CompoundPropertyModel

class MyPage extends WebPage {
@SpringBean
var ps: ProductService = _
val productListView = new ListView[Product]("productListView", ps.getAll) {
def populateItem(item: ListItem[Product]) = {
item.setModel(new CompoundPropertyModel[Product](item.getDefaultModelObject))
item.add(new Label("name"))
item.add(new Label("price"))
}
}
add(productListView)
}

Note that it is using a ProductService object to load the products. You'll create it later. In addition, note that the field is assigned to an underscore (_), which tells the Scala compile to NOT initialize, but leave it at the default state (null in this case). This is required for the injection to work. If you assign it to null explicitly, you
will overwrite the Spring bean as the injection will occur before the constructor of MyPage is executed.
Now, create the MyPage.html file in src/main/resources/com/foo/myapp:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<table border="1">
<tr wicket:id="productListView">
<td wicket:id="name"></td>
<td wicket:id="price"></td>
</tr>
</table>
</html>

Creating the ProductService


Right click the com.foo.myapp package in the src/main/scala folder and choose New | Scala Class, then choose to create a trait named ProductService:

package com.foo.myapp

import java.util.List

trait ProductService {
def getAll: List[Product]
}


This is the interface. To create the implementation, create a DefaultProductService Scala class in the same package:

package com.foo.myapp

import javax.persistence.{PersistenceContext, EntityManager}
import org.springframework.stereotype.{Service}
import org.springframework.transaction.annotation.Transactional
import org.springframework.beans.factory.annotation.Autowired

@Service
@Transactional
class DefaultProductService extends ProductService {
@Autowired
var products: Products = _

def getAll = products.getAll
}

Note that it is using a DAO named of type Products to do the work.

Creating the Products DAO


To create the DAO, create a trait named Products in the same package:

package com.foo.myapp

import java.util.List

trait Products {
def getAll: List[Product]
}

Then create the implementation Scala class DefaultProducts in the same package:

package com.foo.myapp

import javax.persistence.{PersistenceContext, EntityManager}
import org.springframework.stereotype.Repository
import java.util.List

@Repository
class DefaultProducts extends Products {
@PersistenceContext
var em: EntityManager = _

def getAll = {
em.createQuery("select p from Product p").getResultList.asInstanceOf[List[Product]]
}
}

Creating the entity class


Create the Product class and map it to the database:

package com.foo.myapp

import javax.persistence.{GeneratedValue, Id, Entity}

@Entity
class Product {
@Id
@GeneratedValue
var id: Long = _
var name: String = _
var price: Double = _
}

Creating the Wicket application class


Finally, create MyApp Scala class in the same package:


package com.foo.myapp

import org.apache.wicket.protocol.http.WebApplication
import com.ttdev.wicketpagetest.MockableSpringBeanInjector

class MyApp extends WebApplication {
def getHomePage = classOf[MyPage]

override def init = {
MockableSpringBeanInjector.installInjector(this)
}
}

Here you specify MyPage as the home page and install an injector that can inject Spring beans (as well as mock objects, even though you won't use this capability here).

Running the application


As the Intellij IDEA community edition doesn't include the integration with app servers, you'll embed Jetty to run your application. This is easy. Just create a Scala class ManualTest in the com.foo.myapp package in the test/scala folder (NOT the main/scala folder). The content is below:

package com.foo.myapp

import com.ttdev.wicketpagetest.{WebAppJettyConfiguration, WicketAppJettyLauncher}

object ManualTest {
def main(args: Array[String]) {
val l = new WicketAppJettyLauncher
l.startAppInJetty(new WebAppJettyConfiguration)
}
}

To run the application, you need to have the H2 database server running first. So, go to http://www.h2database.com to download and unpack it. Then change into h2/bin and run h2.bat (or h2.sh on Linux).
While the ManualTest class is the active editor in IDEA, choose Run | Run in IDEA. It will run ManualTest which will launch Jetty to run your application.
To test it, try accessing http://localhost:8888/app in a browser. It should display nothing as there is no product in the database. However, it will create the table required.
To add some products, go to http://localhost:8082 to access the H2 web client. Enter jdbc:h2:tcp://localhost/~/myapp as the JDBC URL. Click Connect. Then issue the SQL statement:

SELECT * FROM PRODUCT


to select the product. Nothing should be there. That's fine. In the result display, click the plus sign to create a product record. Feel free to add more.
Finally, reload http://localhost:8888/app and you should see the products displayed in the Wicket page.
Updated: You can download the project folder.