Hibernate Error

[yuchuang]

org.hibernate.MappingException: Unknown entity: java.util.ArrayList

I got the above error when i click an image button, the image button is supposed to delete the record from the DB. I would like to know what is this error. I can't seem to solve it.

Thanks.

[pegitha]

Can you put the application into debug, step thru it and then zone in on the exact code that is causing the error and post more information here? Apparently you do not have something mapped correctly in your hbm.xml file.

[yuchuang]

I encounter another error. Following is the error.
java.lang.NullPointerException
org.apache.struts.config.FormBeanConfig.createActi onForm(FormBeanConfig.java:286)
org.apache.struts.config.FormBeanConfig.createActi onForm(FormBeanConfig.java:350)
org.apache.struts.chain.commands.CreateActionForm. execute(CreateActionForm.java:89)
org.apache.struts.chain.commands.ActionCommandBase .execute(ActionCommandBase.java:48)
org.apache.commons.chain.impl.ChainBase.execute(Ch ainBase.java:190)
org.apache.commons.chain.generic.LookupCommand.exe cute(LookupCommand.java:304)
org.apache.commons.chain.impl.ChainBase.execute(Ch ainBase.java:190)
org.apache.struts.chain.ComposableRequestProcessor .process(ComposableRequestProcessor.java:280)
org.apache.struts.action.ActionServlet.process(Act ionServlet.java:1858)
org.apache.struts.action.ActionServlet.doGet(Actio nServlet.java:446)
javax.servlet.http.HttpServlet.service(HttpServlet .java:689)
javax.servlet.http.HttpServlet.service(HttpServlet .java:802)
org.netbeans.modules.web.monitor.server.MonitorFil ter.doFilter(MonitorFilter.java:368)

I'm using Struts and Hibernate. I want to retrieve data from the DB and display it out but i got this error above. I don't understand where the null came from.