GAE JPA Can't get Vogella example to work

[Laurence Turpin]

Hello,

I'm using Windows 7, Eclipse Indigo and GAE 1.6.6
I'm trying to learn how to use Java Persistence API on Google App Engine.
At this moment I'm trying to do the example from the following site vogella

I have the following package structure:

When I run the program it fails with an http error 500 and says javax persistence is a restricted class



Here is the code for the PersistsServlet.java file

package de.vogella.gae.persistence.jpa;
 
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
 
import javax.persistence.EntityManager;
import javax.persistence.Query;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
import de.vogella.gae.persistence.jpa.model.EMFService;
import de.vogella.gae.persistence.jpa.model.Todo;
 
@SuppressWarnings("serial")
public class PersistsServlet extends HttpServlet {
    public void doGet(HttpServletRequest req, HttpServletResponse resp)
            throws IOException {
        Todo todo = new Todo();
 
        todo.setSummary("This is my todo");
 
        EntityManager em = EMFService.get().createEntityManager();
        List<Todo> todos = null;
        try {
            em.persist(todo);
            Query q = em.createQuery("select t from Todo t");
            todos = new ArrayList(q.getResultList());
        } finally {
            em.close();
        }
 
        resp.setContentType("text/plain");
        if (todos != null) {
            resp.getWriter().println(
                    "Hello, JPA. We have " + todos.size()
                            + " number of entries.");
        } else {
            resp.getWriter().println("Should not happen");
        }
    }
}

Here is the code for EMFService.java

package de.vogella.gae.persistence.jpa.model;
 
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
 
public class EMFService {
    private static final EntityManagerFactory emfInstance = Persistence.createEntityManagerFactory("transactions-optional");
 
    private EMFService() {
    }
 
    public static EntityManagerFactory get() {
        return emfInstance;
    }
}

Here is the Todo.java file:

package de.vogella.gae.persistence.jpa.model;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
 
@Entity
public class Todo {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long todoId;
    private String summary;
 
    public String getSummary() {
        return summary;
    }
 
    public void setSummary(String summary) {
        this.summary = summary;
    }
}

Here is the web.xml file:
<?xml version="1.0" encoding="utf-8"?> <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" version="2.5"> <servlet> <servlet-name>persists</servlet-name> <servlet-class>de.vogella.gae.persistence.jpa.PersistsServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>persists</servlet-name> <url-pattern>/persists</url-pattern> </servlet-mapping> <welcome-file-list> <welcome-file>index.html</welcome-file> </welcome-file-list> </web-app>

This is the persistence.xml
<?xml version="1.0" encoding="UTF-8" ?> <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="transactions-optional"> <provider> org.datanucleus.store.appengine.jpa.DatastorePersistenceProvider </provider> <properties> <property name="datanucleus.NontransactionalRead" value="true" /> <property name="datanucleus.NontransactionalWrite" value="true" /> <property name="datanucleus.ConnectionURL" value="appengine" /> </properties> </persistence-unit> </persistence>

and finally the error trace
HTTP ERROR 500 Problem accessing /persists. Reason: javax.persistence.Persistence is a restricted class. Please see the Google App Engine developer's guide for more details. Caused by: java.lang.NoClassDefFoundError: javax.persistence.Persistence is a restricted class. Please see the Google App Engine developer's guide for more details. at com.google.appengine.tools.development.agent.runtime.Runtime.reject(Runtime.java:51) at de.vogella.gae.persistence.jpa.model.EMFService.<clinit>(EMFService.java:7) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:169) at com.google.appengine.tools.development.agent.runtime.RuntimeHelper.checkRestricted(RuntimeHelper.java:69) at com.google.appengine.tools.development.agent.runtime.Runtime.checkRestricted(Runtime.java:64) at de.vogella.gae.persistence.jpa.PersistsServlet.doGet(PersistsServlet.java:24) at javax.servlet.http.HttpServlet.service(HttpServlet.java:617) at javax.servlet.http.HttpServlet.service(HttpServlet.java:717) at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511) at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166) at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:35) at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157) at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:60) at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157) at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43) at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157) at com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:122) at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157) at com.google.appengine.tools.development.BackendServersFilter.doFilter(BackendServersFilter.java:97) at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157) at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388) at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216) at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182) at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765) at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418) at com.google.appengine.tools.development.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:78) at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152) at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:369) at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152) at org.mortbay.jetty.Server.handle(Server.java:326) at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542) at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:923) at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:547) at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:212) at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404) at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409) at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)

[Laurence Turpin]

At last I have managed to get this to work.
I reinstalled a new version of eclipse Juno release.
and the latest version of the gae plugin 4.2
The latest plugin includes a persistence.xml
The difference between the persistence.xml that I was using and this one
is in the <provider> section.

In the new persistence.xml it is:

<provider>
org.datanucleus.api.jpa.PersistenceProviderImpl
</provider>

Anyway all is working now.