Java開発におけるJPAオプティミスティックロック例外

<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">
    <modelVersion>4.0.0</modelVersion>

    <groupId>naveen.examples</groupId>
    <artifactId>jpa</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>jpa</name>
    <url>http://maven.apache.org</url>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <java.version>1.8</java.version>
        <hibernate.version>4.3.6.Final</hibernate.version>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>

    <dependencies>

        <!-- JPA -->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-entitymanager</artifactId>
            <version>${hibernate.version}</version>
        </dependency>

        <!-- For connection pooling -->
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-c3p0</artifactId>
            <version>${hibernate.version}</version>
        </dependency>

        <!-- Database -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.31</version>
        </dependency>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>

    </dependencies>

</project>

<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
    http://xmlns.jcp.org/xml/ns/persistence/persistence__2__1.xsd"
    version="2.1">

    <persistence-unit name="jpa-example" transaction-type="RESOURCE__LOCAL">
        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
        <properties>
            <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost/employee"/>
            <property name="javax.persistence.jdbc.user" value="root"/>
            <property name="javax.persistence.jdbc.password" value="root"/>
            <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
            <property name="hibernate.show__sql" value="true"/>
            <property name="hibernate.format__sql" value="true"/>
            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQL5InnoDBDialect"/>
            <property name="hibernate.hbm2ddl.auto" value="validate"/>
            <!-- Configuring Connection Pool -->
            <property name="hibernate.c3p0.min__size" value="5"/>
            <property name="hibernate.c3p0.max__size" value="20"/>
            <property name="hibernate.c3p0.timeout" value="500"/>
            <property name="hibernate.c3p0.max__statements" value="50"/>
            <property name="hibernate.c3p0.idle__test__period" value="2000"/>
        </properties>
    </persistence-unit>
</persistence>

public static final String FIND__ALL = "naveen.examples.jpa.entity.EmployeeBE.find__all";

@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private int id;

@Column(name = "NAME")
private String name;

    @Column(name = "version__num")
    @Version
    private int version;
// Getters and setters

EmployeeCrud.java

....//Interface for CRUD operations.
package naveen.examples.jpa.business;

import java.util.List;

import naveen.examples.jpa.entity.EmployeeBE;

public interface EmployeeCrud {

    List<EmployeeBE> findAllEmployeeBECol();

    EmployeeBE saveEmployee(EmployeeBE employeeBE);

    EmployeeBE updateEmployee(EmployeeBE employeeBE);

    EmployeeBE findById(int id);

}

public EmployeeBE saveEmployee(EmployeeBE employeeBE) {
    EntityManager em = EntityManagerUtil.getEntityManager();
    em.getTransaction().begin();
    em.persist(employeeBE);
    em.getTransaction().commit();
    return employeeBE;
}

public EmployeeBE updateEmployee(EmployeeBE employeeBE) {
    EntityManager em = EntityManagerUtil.getEntityManager();
    em.getTransaction().begin();
    em.merge(employeeBE);
    em.getTransaction().commit();
    return employeeBE;
}

@SuppressWarnings("unchecked")
public List<EmployeeBE> findAllEmployeeBECol() {
    EntityManager em = EntityManagerUtil.getEntityManager();
    Query query = em.createNamedQuery(EmployeeBE.FIND__ALL);
    return query.getResultList();
}

public EmployeeBE findById(int id) {
    EntityManager em = EntityManagerUtil.getEntityManager();
    return em.find(EmployeeBE.class, id);
}

EntityManagerUtil.java

....//Entity Manager
public class EntityManagerUtil {

    private static EntityManager  entityManager;

    private EntityManagerUtil() {
    }

    public static EntityManager getEntityManager() {
        if(entityManager==null){
            EntityManagerFactory emFactory = Persistence.createEntityManagerFactory("jpa-example");
            return emFactory.createEntityManager();
        }
        return entityManager;
    }
}

public class Application {

    public static void main(String args[]) {

        EmployeeCrud employeeCrud = new EmployeeCrudImpl();

        List<EmployeeBE> employeeBEs = employeeCrud.findAllEmployeeBECol();
        if(!employeeBEs.isEmpty()){
            EmployeeBE employeeBE = employeeBEs.get(0);
            employeeBE.setName("Updated");
            employeeCrud.updateEmployee(employeeBE);
           //Here Optimistic lock exception
            employeeCrud.updateEmployee(employeeBE);
        }else{
            EmployeeBE employeeBE = new EmployeeBE();
            employeeBE.setName("Naveen");
            employeeBE = employeeCrud.saveEmployee(employeeBE);
        }
    }