servlet in seam application

[jason_rency]

All,
my question may looks strange,

I tried to get a common java servlet work within a seam application by adding the following line in web.xml: (calculator is the servlet name)

<servlet>
 <servlet-name>Calculator</servlet-name>
 <servlet-class>server.Calculator</servlet-class>
 </servlet>

 <servlet-mapping>
 <servlet-name>Calculator</servlet-name>
 <url-pattern>/Calculator</url-pattern>
 </servlet-mapping>

the servlet worked fine (I called it from a mobile phone, that's why I need a servlet) after I deployed the seam app with this servlet. but when I tried to use the seam app itself by browser (the hotel booking example), it just didn't work. seems there are conflicts between the new lines I added and the old lines in web.xml .

then I changed the servlet by adding ejb3 annotation (it's strange, huh? a ejb3 staless session bean servlet) and re-deploy the app again (with the new lines in the web.xml). then the servlet (also a session bean) worked well and the hotel booking example worked fine as normal.

then added persistency statement to this servlet (the session bean) but I got a NPE, which seems the Entity manager is null and I can't get the entity manager properly in a servlet which is also a ejb3 session bean?

the code is like this:

package server;

import javax.ejb.Stateless;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.text.*;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;


@Stateless
public class Calculator extends HttpServlet implements cacu
{
 @PersistenceContext
 private EntityManager em;
 private Reguser user;

 public void doPost(HttpServletRequest request,HttpServletResponse response)
 throws IOException, ServletException
 {
 response.setContentType("text/plain");
 PrintWriter out = response.getWriter();
 String uid = request.getParameter("uid");
 String passwd =request.getParameter("passwd");
 user = em.find(Reguser.class, "rency"); (exception here, em is null)
 String email = user.getEmail();
 System.out.print(email);
 out.println("just a test: "+ uid);
 }

}

exception was:

10:16:49,501 ERROR [[Calculator]] Servlet.service() for servlet Calculator threw exception
java.lang.NullPointerException
 at server.Calculator.doPost(Calculator.java:26) (the entity manager) at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
 at javax.servlet.http.HttpServlet.service(HttpServlet.java:810)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
 at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
 at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
 at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
 at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
 at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
 at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:175)
 at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:74)
 at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
 at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
 at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
 at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
 at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:869)
 at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:664)
 at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
 at org.apache.tomcat.util.net.MasterSlaveWorkerThread.run(MasterSlaveWorkerThread.java:112)
 at java.lang.Thread.run(Thread.java:595)

also I added a ejb3 web service in the app, the web service work well: code like this:

interface:

package server;

import javax.jws.WebService;
import javax.jws.WebMethod;


@WebService
public interface findEmail {

 @WebMethod public String findemail(String username);

}

the implementation:

package server;

import javax.ejb.Stateless;
import javax.jws.WebService;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;


@Stateless
@WebService(endpointInterface="server.findEmail")

public class findemailimpl implements findemail {

 @PersistenceContext
 private EntityManager em;
 private Reguser user;

 public String finduser(String username)
 {
 em.find(Reguser.class, username);
 String email = user.getEmail();
 return email;
 }
}

[basel]

Injecting an EntityManager into a servlet is not recommended since the former is not thread safe. Here is what I do in my current web application:

@PersistenceUnit(name = "myPU")
private EntityManagerFactory factory;

protected void doGet(HttpServletRequest request,
 HttpServletResponse response) throws ServletException,
 IOException{
 try{
 if(factory == null){
 String name = "java:/myEntityManagerFactory";
 factory = (EntityManagerFactory)
 Naming.getInitialContext().lookup(name);
 }
 if(em == null){
 em = factory.createEntityManager();
 }
 }
 }catch(NamingException e){
 err.println("NamingException when trying to get an " +
 "EntityManager: "+e.getMessage());
 e.printStackTrace();
 }
}

[jason_rency]

thanks basel,

I tried to add the your code in my servlet,
em is not null but I got the following exceptions:

2:06:51,995 ERROR [[Calculator]] Servlet.service() for servlet Calculator threw exception
java.lang.IllegalStateException: No transaction.
 at org.jboss.tm.TxManager.setRollbackOnly(TxManager.java:397)
 at org.hibernate.ejb.AbstractEntityManagerImpl.markAsRollback(AbstractEntityManagerImpl.java:392)
 at org.hibernate.ejb.AbstractEntityManagerImpl.throwPersistenceException(AbstractEntityManagerImpl.java:545)
 at org.hibernate.ejb.AbstractEntityManagerImpl.throwPersistenceException(AbstractEntityManagerImpl.java:567)
 at org.hibernate.ejb.AbstractEntityManagerImpl.find(AbstractEntityManagerImpl.java:168)
 at src.reg.server.Calculator.doPost(Calculator.java:46)

another question, I should place the servlet class in the war file if it a pure servlet?

thanks a lot
Jason

[basel]

With EJB3 the application server makes sure that your methods are executed within a transaction. This is not the case with Servlets so you have to start and commit the transaction yourself. Here is the code:

UserTransaction utx = Transactions.getUserTransaction();
if(utx.getStatus() != Status.STATUS_ACTIVE)
 utx.begin();
em.joinTransaction();
utx.commit();

The if statement is not required however I needed that in my web application due to an exception that I don't recall right now.

[basel]

em.joinTransaction();
em.createQuery(query)
 .setParameter("param1", param1)
 .getSingleResult();
utx.commit();