Question

I am newbie to JPA and I tried to do a simple example from the book.
But no matter what I do I receive following error:

Exception in thread "main" javax.persistence.PersistenceException: No Persistence provider for EntityManager named EmployeeService
        at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:89)
        at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:60)
        at com.mycompany.simpleentity.EmployeeTest.main(EmployeeTest.java:18)

I googled a lot and I did all that I read about JPA.
Here is a directory tree of my project:

    .
|-- pom.xml
`-- src
    |-- main
    |   |-- java
    |   |   `-- com
    |   |       `-- mycompany
    |   |           `-- simpleentity
    |   |               |-- Employee.java
    |   |               |-- EmployeeService.java
    |   |               `-- EmployeeTest.java
    |   `-- resources
    |       `-- META-INF
    |           `-- persistence.xml
    `-- test

Here is my pom.xml:

<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.mycompany</groupId>
  <artifactId>SimpleEntity</artifactId>
  <packaging>jar</packaging>
  <version>1.0-SNAPSHOT</version>
  <name>SimpleEntity</name>
  <url>http://maven.apache.org</url>
  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>javax.persistence</groupId>
      <artifactId>persistence-api</artifactId>
      <version>1.0</version>      
    </dependency>
    <dependency>
        <groupId>postgresql</groupId>
        <artifactId>postgresql</artifactId>
        <version>9.0-801.jdbc4</version>
    </dependency>
  </dependencies>

  <build>

      <plugins>
        <plugin>
          <groupId>org.apache.maven.plugins</groupId>
          <artifactId>maven-compiler-plugin</artifactId>
          <configuration>
             <source>1.5</source>
             <target>1.5</target>
          </configuration>
        </plugin>

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-jar-plugin</artifactId>

            <configuration>
                <archive>
                    <manifest>
                        <addClasspath>true</addClasspath>
                        <mainClass>com.mycompany.simpleentity.EmployeeTest</mainClass>
                        <!-- <classpathLayoutType>repository</classpathLayoutType> -->
                        <classpathMavenRepositoryLayout>true</classpathMavenRepositoryLayout>
                        <classpathPrefix>${env.HOME}/.m2/repository</classpathPrefix>

                    </manifest>
                </archive>
            </configuration>
        </plugin>
      </plugins>

  </build> 
</project>

Here is my source code:
EmployeeTest.java:

package com.mycompany.simpleentity;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

public class EmployeeTest {
    public static void main(String[] args) {
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("EmployeeService");
        EntityManager em = emf.createEntityManager();

    }
}

And here is my persistance.xml

<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="EmployeeService" transaction-type="RESOURCE_LOCAL">
        <class>com.mycompany.simpleentity.Employee</class>
        <properties>
            <property name="toplink.jdbc.driver"
                      value="org.postgresql.Driver"/>
            <property name="toplink.jdbc.url"
                      value="jdbc:postgresql://localhost:5432/testdb;create=true"/>
            <property name="toplink.jdbc.user" value="postgres"/>
            <property name="toplink.jdbc.password" value="111"/>

        </properties>
    </persistence-unit>
</persistence>

What do I do wrong?
Thank you in advance.

Answer 1

JPA is a specification implemented by multiple JPA providers (Hibernate, EclipseLink, OpenJPA, Toplink).

You need to choose a provider to use and add the appropriate dependency to your pom.xml. Also you need to specify your provider in persistence.xml.

For example, if you use OpenJPA (I choosed it for this example since its latest version is available in Maven Central Repo, so there is no need to configure vendor-specific repositories):

 <dependencies> 
    <dependency> 
      <groupId>junit</groupId> 
      <artifactId>junit</artifactId> 
      <version>3.8.1</version> 
      <scope>test</scope> 
    </dependency> 
    <!-- Note that you don't need persistence-api dependency - it's transitive -->
    <dependency>
      <groupId>org.apache.openjpa</groupId>
      <artifactId>openjpa-all</artifactId>
      <version>2.0.1</version>
    </dependency>
    <dependency> 
        <groupId>postgresql</groupId> 
        <artifactId>postgresql</artifactId> 
        <version>9.0-801.jdbc4</version> 
    </dependency> 
  </dependencies> 

.

<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="EmployeeService" transaction-type="RESOURCE_LOCAL">   
        <!-- Provider specification -->
        <provider>org.apache.openjpa.persistence.PersistenceProviderImpl</provider>

        <class>com.mycompany.simpleentity.Employee</class>       
        <properties>       
            <property name="javax.persistence.jdbc.driver"       
                      value="org.postgresql.Driver"/>       
            <property name="javax.persistence.jdbc.url"       
                      value="jdbc:postgresql://localhost:5432/testdb;create=true"/>       
            <property name="javax.persistence.jdbc.user" value="postgres"/>       
            <property name="javax.persistence.jdbc.password" value="111"/>       

        </properties>       
    </persistence-unit>       
</persistence>