线程“ main”中的异常javax.persistence.PersistenceException：没有名为EntityTest的EntityManager的持久性提供程序

Question

I am trying to use oracle database in my java web app, but I keep getting the error when I run my code as a java application:

Exception in thread "main" javax.persistence.PersistenceException: No Persistence provider for EntityManager named databaseTest

here is my code just a simple code to create an entity manager:

 package com.sabir.test;

import javax.persistence.Persistence;

public class DatabaseService {

    public static void main(String[] args) {
        System.out.println("test");
        Persistence.createEntityManagerFactory("databaseTest");
    }

}

and here is my persistence.xml file

<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 persistence_1_0.xsd" version="1.0">
    <persistence-unit name= "databaseTest" transaction-type="RESOURCE_LOCAL">
        <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
        <exclude-unlisted-classes>false</exclude-unlisted-classes>
        <properties>
            <property name="javax.persistence.jdbc.driver" value="oracle.jdbc.OracleDriver"/>
            <property name="javax.persistence.jdbc.url" value="jdbc:oracle:thin:@localhost:1521:orcl"/>
            <property name="javax.persistence.jdbc.user" value="HR"/>
            <property name="javax.persistence.jdbc.password" value="password"/>
        </properties>
    </persistence-unit>
</persistence>

and if required here is my pom.xml file :

<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.sabir.test</groupId>
  <artifactId>databaseTest</artifactId>
  <packaging>war</packaging>
  <version>0.0.1-SNAPSHOT</version>
  <name>databaseTest Maven Webapp</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>com.oracle</groupId>
    <artifactId>ojdbc6</artifactId>
    <version>11.2.0.3</version>
</dependency>
<dependency>
   <groupId>org.eclipse.persistence</groupId>
   <artifactId>eclipselink</artifactId>
   <version>2.5.0-RC1</version>
   <scope>compile</scope>
</dependency>

  </dependencies>

   <repositories>
    <repository>
      <id>codelds</id>
      <url>https://code.lds.org/nexus/content/groups/main-repo</url>
    </repository>
    <repository>
    <id>oss.sonatype.org</id>
    <name>OSS Sonatype Staging</name>
    <url>https://oss.sonatype.org/content/groups/staging</url>
</repository>
<repository>
   <id>EclipseLink</id>
   <url>http://download.eclipse.org/rt/eclipselink/maven.repo</url>
</repository>
  </repositories>

  <build>
    <finalName>databaseTest</finalName>
  </build>
</project>

I don't know why I am getting the error! here is also my files structure :

I am suspecting the file structure but after I checked many websites, I believe this is the correct one. I also imported the eclipslink in maven so I believe that is all I need, I also added the repository or oracle.

my database is also up and running and I can query from the oracle developer tool

Answer 1

First of all check if you have Maven Libraries on the build path. In Eclipse you would go to

Project Properties -> Java Build Path -> Libraries.

If you do, check below:

You don't have provider you are referring to on your classpath.

<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>

I suggest to add the following to your dependencies(and remove eclipselink dependency):

<dependency>
    <groupId>javax</groupId>
    <artifactId>javaee-api</artifactId>
    <version>7.0</version>
    <scope>provided</scope>
</dependency>

or change eclipselink dependency to

<dependency>
    <groupId>org.eclipse.persistence</groupId>
    <artifactId>org.eclipse.persistence.jpa</artifactId>
    <version>2.6.4</version>
</dependency>

How and where do you obtain EntityManager from EntityManagerFactory? I see only that you are creating instance of EntityManagerFactory only. It should be

EntityManagerFactory emf = Persistence.createEntityManagerFactory("databaseTest");
EntityManager em = emf.createEntityManager();

In general this approach is useful only if you want to bootstrap in Java SE environment. Instead you might use dependency injection:

@PersistenceContext
EntityManager em;

or

@PersistenceUnit(unitName="myUnit")
EntityMangerFactory emf;

then in your methods you can get EntityManager again as follows

EntityManager em = emf.createEntityManager();

Or you can use JNDI lookup.