未找到类[org.apache.derby.jdbc.ClientDriver]。 尝试连接到db时

Question

I have set up a project in Netbeans, created a script, made a new database with javadb. I can connect to it by gui - display the tables contents etc, but when i run an application with:

 EntityManager em = Persistence.createEntityManagerFactory("lab5PU").createEntityManager();

i get this quite long exception:

[EL Info]: 2013-04-05 21:40:45.554--ServerSession(1198260109)--EclipseLink, version: Eclipse Persistence Services - 2.3.0.v20110604-r9504
[EL Severe]: 2013-04-05 21:40:45.574--ServerSession(1198260109)--Local Exception Stack: 
Exception [EclipseLink-4003] (Eclipse Persistence Services - 2.3.0.v20110604-r9504): org.eclipse.persistence.exceptions.DatabaseException
Exception in thread "AWT-EventQueue-0" javax.persistence.PersistenceException: Exception [EclipseLink-4003] (Eclipse Persistence Services - 2.3.0.v20110604-r9504): org.eclipse.persistence.exceptions.DatabaseException
Exception Description: Configuration error.  Class [org.apache.derby.jdbc.ClientDriver] not found.
Exception Description: Configuration error.  Class [org.apache.derby.jdbc.ClientDriver] not found.
    at org.eclipse.persistence.exceptions.DatabaseException.configurationErrorClassNotFound(DatabaseException.java:82)

I can see the javadb drivers in the driver section in services, so i have no idea what the error might be.

EDIT: persistance.xml as requested:

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" 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">
  <persistence-unit name="lab5PU" transaction-type="RESOURCE_LOCAL">
    <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
    <class>lab5.Colleagues</class>
    <properties>
      <property name="javax.persistence.jdbc.url" value="jdbc:derby://localhost:1527/lab5"/>
      <property name="javax.persistence.jdbc.password" value="mypass"/>
      <property name="javax.persistence.jdbc.driver" value="org.apache.derby.jdbc.ClientDriver"/>
      <property name="javax.persistence.jdbc.user" value="admin"/>
      <property name="eclipselink.ddl-generation" value="create-tables"/>
    </properties>
  </persistence-unit>
</persistence>

Answer 1

I think the problem you have is that you don't have the Derby driver in the classpath of the project.

You can easily achieve that adding the JavaDB library to your project:

• Right-click on the project
• Properties -> Libraries
• Add Library -> JavaDB driver

This includes derby.jar , derbyclient.jar and derbynet.jar in your project's classpath.

The derbyclient.jar contains the class org.apache.derby.jdbc.ClientDriver your code is complaining about.