[appengine-java] Why I encountered this error : "The class "java.lang.String" is not persistable."

[Jolam]

I have defined a class :

import javax.jdo.annotations.IdentityType;
import javax.jdo.annotations.PersistenceCapable;
import javax.jdo.annotations.Persistent;
import javax.jdo.annotations.PrimaryKey;

@SuppressWarnings("serial")

@PersistenceCapable(identityType = IdentityType.APPLICATION,
detachable="true")
public class UrlInformation implements Serializable{

        @PrimaryKey
        private String key;

        @Persistent
        private String url = new String();

        @Persistent
        private String code = new String();

        @Persistent
        private boolean isBlocked = false;

//get and set methods....

}

when i try to make it persistent, i encounter this :

HTTP ERROR: 500

The class "The class "java.lang.String" is not persistable. This means
that it either hasnt been enhanced, or that the enhanced version of
the file is not in the CLASSPATH (or is hidden by an unenhanced
version), or the Meta-Data/annotations for the class are not found."
is not persistable. This means that it either hasnt been enhanced, or
that the enhanced version of the file is not in the CLASSPATH (or is
hidden by an unenhanced version), or the Meta-Data for the class is
not found.

RequestURI=/initserver
Caused by:

org.datanucleus.jdo.exceptions.ClassNotPersistenceCapableException:
The class "The class "java.lang.String" is not persistable. This means
that it either hasnt been enhanced, or that the enhanced version of
the file is not in the CLASSPATH (or is hidden by an unenhanced
version), or the Meta-Data/annotations for the class are not found."
is not persistable. This means that it either hasnt been enhanced, or
that the enhanced version of the file is not in the CLASSPATH (or is
hidden by an unenhanced version), or the Meta-Data for the class is
not found.
        at
org.datanucleus.jdo.NucleusJDOHelper.getJDOExceptionForNucleusException(NucleusJDOHelper.java:
241)
        at
org.datanucleus.jdo.JDOPersistenceManager.jdoMakePersistent(JDOPersistenceManager.java:
674)
        at
org.datanucleus.jdo.JDOPersistenceManager.makePersistent(JDOPersistenceManager.java:
694)
        at tk.jo32.s.util.UrlConverter.shorten(UrlConverter.java:26)
        at tk.jo32.s.operation.InitServlet.doGet(InitServlet.java:22)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:693)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:806)
        at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:
487)
        at org.mortbay.jetty.servlet.ServletHandler
$CachedChain.doFilter(ServletHandler.java:1093)
        at
com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:
43)
        at org.mortbay.jetty.servlet.ServletHandler
$CachedChain.doFilter(ServletHandler.java:1084)
        at
com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:
121)
        at org.mortbay.jetty.servlet.ServletHandler
$CachedChain.doFilter(ServletHandler.java:1084)
        at
org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:
360)
        at
org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:
216)
        at
org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:
181)
        at
org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:
712)
        at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:
405)
        at
com.google.apphosting.utils.jetty.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:
70)
        at
org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:
139)
        at com.google.appengine.tools.development.JettyContainerService
$ApiProxyHandler.handle(JettyContainerService.java:352)
        at
org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:
139)
        at org.mortbay.jetty.Server.handle(Server.java:313)
        at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:
506)
        at org.mortbay.jetty.HttpConnection
$RequestHandler.headerComplete(HttpConnection.java:830)
        at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:514)
        at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:211)
        at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:381)
        at
org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:
396)
        at org.mortbay.thread.BoundedThreadPool
$PoolThread.run(BoundedThreadPool.java:442)

-- 
You received this message because you are subscribed to the Google Groups 
"Google App Engine for Java" group.
To post to this group, send email to google-appengine-j...@googlegroups.com.
To unsubscribe from this group, send email to 
google-appengine-java+unsubscr...@googlegroups.com.
For more options, visit this group at 
http://groups.google.com/group/google-appengine-java?hl=en.