Persistence 问题

[llcmb]

UserManager.java
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import shoppingcart.model.Cart;
import shoppingcart.model.User;

public class UserManager {
public static final String persistenceUnit="shoppingCart";
private EntityManager em;

public UserManager(String persistenceUnit){
EntityManagerFactory emf=Persistence.createEntityManagerFactory(persistenceUnit);
this.em=emf.createEntityManager();
}



Exception:
java.lang.NoSuchMethodError: org.apache.log4j.Logger.isTraceEnabled()Z
at org.slf4j.impl.Log4jLoggerAdapter.trace(Log4jLoggerAdapter.java:104)
at org.hibernate.ejb.Ejb3Configuration.configure(Ejb3Configuration.java:221)
at org.hibernate.ejb.HibernatePersistence.createEntityManagerFactory(HibernatePersistence.java:125)
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:52)
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:34)
at shoppingcart.service.UserManager. <init>(UserManager.java:15)
at shoppingcart.servlet.LoginServlet. <init>(LoginServlet.java:37)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at java.lang.Class.newInstance0(Unknown Source)
at java.lang.Class.newInstance(Unknown Source)
at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1115)
at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:808)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:129)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Unknown Source)

[llcmb]

没人会还是我没说清楚？

[llcmb]

EntityManagerFactory emf=Persistence.createEntityManagerFactory(persistenceUnit);
这行出错，大家看看是什么原因