Thoughts...!!!!!!: JPA basic example with EntityManager

JPA basic example with EntityManager , Spring and Maven

Our pom.xml will be like this..

<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/xsd/maven-4.0.0.xsd">

<groupId>com.hopcroft.examples.spring</groupId>

<artifactId>simpledao</artifactId>

<version>0.0.1-SNAPSHOT</version>

<id>maven-annotation</id>

<url>http://maven-annotation-plugin.googlecode.com/svn/trunk/mavenrepo</url>

</pluginRepository>

</pluginRepositories>

<build>

<groupId>org.apache.maven.plugins</groupId>

<artifactId>maven-compiler-plugin</artifactId>

<processor>org.hibernate.jpamodelgen.JPAMetaModelEntityProcessor</processor>

</compilerArguments>

</configuration>

</plugin>

<groupId>org.bsc.maven</groupId>

<artifactId>maven-processor-plugin</artifactId>

<id>process</id>

<goals>

<goal>process</goal>

</goals>

<phase>generate-sources</phase>

<outputDirectory>src/main/generated-java</outputDirectory>

</configuration>

</execution>

</executions>

</plugin>

<groupId>org.codehaus.mojo</groupId>

<artifactId>build-helper-maven-plugin</artifactId>

<id>add-source</id>

<phase>generate-sources</phase>

<goals>

<goal>add-source</goal>

</goals>

<source>src/main/generated-java</source>

</sources>

</configuration>

</execution>

</executions>

</plugin>

</plugins>

</build>

<groupId>org.hibernate</groupId>

<artifactId>ejb3-persistence</artifactId>

<scope>compile</scope>

</dependency>

<groupId>org.springframework</groupId>

<artifactId>spring-core</artifactId>

<version>3.0.5.RELEASE</version>

<scope>compile</scope>

</dependency>

<groupId>org.springframework</groupId>

<artifactId>spring-orm</artifactId>

<version>3.0.0.RELEASE</version>

<scope>compile</scope>

</dependency>

<groupId>org.springframework</groupId>

<artifactId>spring-beans</artifactId>

<version>3.0.5.RELEASE</version>

<scope>compile</scope>

</dependency>

<groupId>javax.security</groupId>

<scope>compile</scope>

</dependency>

<groupId>mysql</groupId>

<artifactId>mysql-connector-java</artifactId>

<scope>compile</scope>

</dependency>

<groupId>junit</groupId>

<artifactId>junit</artifactId>

<scope>compile</scope>

</dependency>

<groupId>commons-dbcp</groupId>

<artifactId>commons-dbcp</artifactId>

<scope>compile</scope>

</dependency>

<groupId>org.springframework</groupId>

<artifactId>spring-test</artifactId>

<version>3.0.5.RELEASE</version>

<scope>compile</scope>

</dependency>

<scope>compile</scope>

</dependency>

<groupId>javassist</groupId>

<artifactId>javassist</artifactId>

<scope>compile</scope>

</dependency>

<groupId>org.hibernate</groupId>

<artifactId>hibernate-core</artifactId>

<version>3.5.0-Final</version>

<scope>compile</scope>

</dependency>

<groupId>org.hibernate</groupId>

<artifactId>hibernate-annotations</artifactId>

<version>3.5.0-Final</version>

<scope>compile</scope>

</dependency>

<groupId>org.codehaus.openxma</groupId>

<artifactId>dsl-platform</artifactId>

</dependency>

<groupId>org.hibernate</groupId>

<artifactId>hibernate-jpamodelgen</artifactId>

<version>1.0.0.Final</version>

<scope>compile</scope>

</dependency>

</dependencies>

</project>

Our application will have the next structure

We have a domain model layer where there is a Car entity that mirrors the database table.

Our car entity:

package com.hopcroft.examples.domain;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.Id;

import javax.persistence.Table;

@Entity

@Table(name = "Car")

public class Car {

@Id

@Column(name = "id")

private long id;

@Column(name = "company")

private String company;

@Column(name = "model")

private String model;

@Column(name = "price")

private long price;

public void setId(long id) {

this.id = id;

}

public long getId() {

return id;

}

public String getCompany() {

return company;

}

public void setCompany(String company) {

this.company = company;

}

public String getModel() {

return model;

}

public void setModel(String model) {

this.model = model;

}

public long getPrice() {

return price;

}

public void setPrice(long price) {

this.price = price;

}

We have also a data access layer where there is a interface called CarDao that defines the methods that we use to interact with our database. This interface will be implemented by the CarDaoImpl.
In some of the later projects we have use a HibernateTemplate object to get the data from our database. Instead of that we are going to use an EntityManager instance. An EntityManager will be a instance of an EntityManagerFactory within JPA. This type of factory means the configuration used to access to our database.
To use JPA in our project we are going to create a persistence unit in the META-INF/persistence.xml file. Within this file we will have a specified persistence unit. What we should do is choosing the transaction type. We need to use the provider that will implement JPA. In our case, we are going to use Hibernate.

<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_1_0.xsd"

version="1.0">

<persistence-unit name="JpaPersistenceUnit"

transaction-type="RESOURCE_LOCAL">

<provider>org.hibernate.ejb.HibernatePersistence</provider>

</persistence-unit>

</persistence>

We need to configure our application context in the same way we did when we used an Hibernate sessionFactory. That means, we have to add a dataSource within our context file where we define our url , user, password and the database we are going to use. We define an entityManagerFactory to which we pass the newly created dataSource. This entityManagerFactory object will be controlled by a transactionManager. As we are using JPA we need a org.springframework.orm.jpa.JpaTransactionManager.
There is also a component-scan element. We will explain it when we see our Dao.

Our context file is as follows:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:p="http://www.springframework.org/schema/p" xmlns:tx="http://www.springframework.org/schema/tx"

xmlns:context="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/tx

http://www.springframework.org/schema/tx/spring-tx-3.0.xsd

http://www.springframework.org/schema/context

http://www.springframework.org/schema/context/spring-context-3.0.xsd">

<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource"

p:driverClassName="com.mysql.jdbc.Driver" p:url="jdbc:mysql://localhost/test"

p:username="root" p:password="" p:initialSize="5" p:maxActive="10">

</bean>

<bean

class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"

id="entityManagerFactory">

</bean>

<context:component-scan base-package="com.hopcroft.examples.dao">

<context:include-filter type="annotation"

expression="org.springframework.stereotype.Repository" />

</context:component-scan>

<bean class="org.springframework.orm.jpa.JpaTransactionManager"

id="transactionManager">

</bean>

<tx:annotation-driven mode="aspectj"

transaction-manager="transactionManager" />

<context:spring-configured />

<context:annotation-config />

</beans>

After take a look to our configuration files we need to explain our Dao (interface and its implementation).

package com.hopcroft.examples.dao;

import java.util.List;

import org.springframework.dao.DataAccessException;

import com.hopcroft.examples.domain.Car;

public interface CarDao {

public List<Car> getCars() throws DataAccessException;

public Car getCar(Long carId) throws DataAccessException;

}

package com.hopcroft.examples.dao;

import java.util.List;

import javax.persistence.EntityManager;

import javax.persistence.PersistenceContext;

import javax.persistence.Query;

import org.springframework.dao.DataAccessException;

import org.springframework.stereotype.Repository;

import org.springframework.transaction.annotation.Transactional;

import com.hopcroft.examples.domain.Car;

@Repository

public class CarDaoImpl implements CarDao {

protected EntityManager entityManager;

public EntityManager getEntityManager() {

return entityManager;

}

@PersistenceContext

public void setEntityManager(EntityManager entityManager) {

this.entityManager = entityManager;

}

@Transactional

public List<Car> getCars() throws DataAccessException {

Query query = getEntityManager().createQuery("select c from Car c");

List<Car> resultList = query.getResultList();

return resultList;

}

@Transactional

public Car getCar(Long carId) throws DataAccessException {

return getEntityManager().find(Car.class, carId);

}

There is no much to say about the carDao interface. Two methods that we implement within the CarDaoImpl class. We need to explain a couple of things.

First of all we notice that CarDaoImpl is annotated as @Repository. This is an annotation we use to say to the Spring context that our CarDaoImpl is included within its context as a component. Besides the @Repository annotation there are a @Service annotation and a @Controller one. Every annotation extends to the @Component annotation. There is a meaning difference among them, @Repository will indicate our Spring context that we want to add a Dao bean, @Controller a controller and @Service … easy to guess. Do you remenber thecomponent-scan element within our testApplicationContext file?, in this file we tell Spring we are going to incluide as beans every single class with the @Repository annotation, in our case, CarDaoImpl car.

The second annotation we notice is @PersistenceContext. It is in the EntityManager setter method. We get an EntiyManagerFactory object we need for address our database.

We can notice that our methods are annontated as transactional. That means our methods belong to a unique transaction that will be management by the transactionManager we explained in our context file.

Our method logic is quite straightforward. We have a couple of methods, the first one list every car we have stored in our database and the second one use an id to find a specified car. To that we have to use an entityManager. As with HibernateTemplate, our entityManager class will have some basic methods like persist, refresh ó remove. Once our application is created we are going to make a test class.

package com.hopcroft.examples.test;

import java.util.List;

import java.util.logging.Logger;

import org.junit.Assert;

import org.junit.Before;

import org.junit.Test;

import org.junit.runner.RunWith;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.test.context.ContextConfiguration;

import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

import com.hopcroft.examples.dao.CarDao;

import com.hopcroft.examples.domain.Car;

@RunWith(SpringJUnit4ClassRunner.class)

@ContextConfiguration(locations = { "/testApplicationContext.xml" })

public class CarTest {

@Autowired

private CarDao carDao;

private Logger logger = Logger.getLogger("myLog");

private Long id;

@Before

public void init() {

// carNumber = carDao.getCars().size();

id = 1L;

}

@Test

public void listCarsTest() {

List<Car> cars = carDao.getCars();

// logger.info("Cars: " + cars.size());

Assert.assertNotNull(cars);

Assert.assertEquals(15, cars.size());

}

@Test

public void getCarTest() {

Car car = carDao.getCar(id);

Assert.assertEquals(id.longValue(), car.getId());

Assert.assertEquals("Boxster", car.getModel());

}

We annotate our class as always, pointing that we are going to use JUnit4 and the context file we have already created. We are going to get our CarDao from the Spring context. We have some method that we are going to test from a Maven test configuration within STS.

Thoughts...!!!!!!

Tuesday, August 12, 2014

JPA basic example with EntityManager

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