Calling an EJB from within a Servlet - problem with lookup()

[James Adams]

Just for grins I am trying to call an EJB's business method from within a Tomcat web application. I have tried to call a simple EJB, the AdviceBean from the AdviceApp (first tutorial of "Head First EJB"), using the same code from the AdviceApp client, from within the servlet's doPost() method. I am getting a NameNotFoundException, complaining that the "Name Advisor is not bound in this Context". The J2EE RI server is running, the EJB is deployed, and the client jar file with all of the EJB classes and interfaces (created by RI container at deploy time) is included in the WEB-INF/lib directory of the webapp.
The servlet code is below, maybe someone can see what it is I'm doing wrong or leaving out. Basically the servlet's job is to fill a JavaBean with the advice string from the EJB's getAdvice() method, then add the bean to the session, to be displayed on a following JSP using a <jsp:getProperty> tag. Also included after the servlet code is the Tomcat web application's web.xml, which has an <ejb-ref> for the bean, but this doesn't seem to be enough to get my EJB bound into the context (I guessed at what the correct <ejb-ref> element values should be).
Any comments or suggestions will be quite appreciated.

package ejbwebapp.servlet;
// Java imports
import java.io.*;
import java.net.*;
import java.util.*;
// J2EE imports for web component
import javax.servlet.*;
import javax.servlet.http.*;
// J2EE imports for business component
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.rmi.PortableRemoteObject;
import javax.ejb.*;
import java.rmi.*;
// external imports
import org.apache.log4j.Category;
// internal imports
import ejbwebapp.bean.EjbAdviceBean;
import headfirst.*;

/**
 * This servlet loads an advice bean with advice from an advisor EJB.
 *
 *
 *@author James Adams
 */
public class EjbAdviceServlet
    extends HttpServlet
{
    // log4j logger
    private Category m_logger;
    // the advice page
    private String m_advicePagePath;
    /**
     * This method handles HTTP GET requests.  It immediately redirects to doPost().
     *
     *@param request the HTTP request to service
     *@param response the HTTP response to return to the browser
     *@throws IOException if an input or output exception occurred
     *@throws ServletException
     */
    public void doGet (HttpServletRequest request,
                       HttpServletResponse response)
        throws ServletException, IOException
    {
        doPost(request, response);
    }
    /**
     * This method handles HTTP POST requests.  It will get a reference to an advisor
     * EJB's component interface and call the business method for getting advice.
     * The advice returned is placed in a bean which is set into the user's session.
     * The user is then redirected to a page which can display the bean's contents.
     *
     *@param request the HTTP request to service
     *@param response the HTTP response to return to the browser
     *@throws IOException if an input or output exception occurred
     *@throws ServletException
     */
    public void doPost (HttpServletRequest request,
                        HttpServletResponse response)
        throws ServletException, IOException
    {
        // get the session object
        HttpSession session = request.getSession(true);
        // if it's a new session then something is wrong (shouldn't be here)
        if (session.isNew())
        {
            // log the error
            m_logger.error("Made it into doPost() without an HttpSession");
            // send the error
            response.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR,
                               "Made it into doPost() without an HttpSession");
        }
        // check to see if the user is logged in
        EjbAdviceBean ejbAdviceBean = (EjbAdviceBean) session.getAttribute("ejbAdviceBean");
        // make sure that we have an advice bean
        if (ejbAdviceBean == null)
        {
            ejbAdviceBean = new EjbAdviceBean();
        }
        // now get a reference to the advice EJB's component interface,
        // call the advice EJB's business method, and put the result into
        // the advice bean
        try
        {
            // get an entry point into the JNDI naming service
            Context initContext = new InitialContext();
            // lookup the AdviceBean EJB using its JNDI name
            Object adviceBeanObject = initContext.lookup("Advisor");
            // ensure that the AdviceBean object can be cast as an AdviceHome, then cast it
            AdviceHome adviceHome = (AdviceHome) PortableRemoteObject.narrow(adviceBeanObject, AdviceHome.class);
            // get an EJB component interface for the AdviceBean EJB
            Advice advisor = adviceHome.create();
            // here's where we actually use the advice EJB's business method
            // get some advice from the EJB
            String adviceString = advisor.getBetterAdvice();
            // add he advice to the advice bean
            ejbAdviceBean.setAdvice(adviceString);
        }
        catch (Exception e)
        {
            // log the error
            m_logger.error("Exception caught while getting advice from the EJB: " + e);
            // write error to console
            System.out.println("\n\nEjbAdviceServlet: Caught Exception: " + e);
            e.printStackTrace();
        }
        // add the advice ban to the session
        session.setAttribute("ejbAdviceBean", ejbAdviceBean);
        // encode the advice page URL that we'll redirect to
        String advicePageURL = response.encodeRedirectURL(m_advicePagePath);;
        // redirect to the advice page
        response.sendRedirect(advicePageURL);
        //finished
        return;
    }
    /**
     * This method will be called once for the servlet during its lifetime.
     * It initializes the error logger used in the getPost() method.
     *
     *@throws ServletException
     */
    public void init ()
        throws ServletException
    {
        // get a log4j category instance
        m_logger = Category.getInstance("EjbAdviceServlet.class");
        // get the path of the advice page
        m_advicePagePath = getServletContext().getInitParameter("advicePagePath");
        // make sure we got a path
        if (m_advicePagePath == null)
        {
            // log the error
            m_logger.error("Missing context init-param: advicePagePath");
            // throw an exception to the container
            throw new ServletException("Missing advice page path initialization parameter");
        }
        // finished
        return;
    }
}

And the XML:

<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE web-app
    PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
    "http://java.sun.com/dtd/web-app_2_3.dtd">

<web-app>
    <display-name>Advice EJB Web Application</display-name>

    <!-- CONTEXT CONFIGURATION -->
    <!-- the login page of the application -->
    <context-param>
        <param-name>loginPagePath</param-name>
        <param-value>EjbWebAppLogin.jsp</param-value>
    </context-param>
    <!-- the login success page of the application -->
    <context-param>
        <param-name>loginSuccessPath</param-name>
        <param-value>EjbAdviceForm.jsp</param-value>
    </context-param>

    <!-- LISTENERS -->
    <!-- declare an application listener which initializes log4j upon context
         (application) initialization-->
    <listener>
        <listener-class>ejbwebapp.listener.Log4jStartupListener</listener-class>
    </listener>
    <!-- declare the session listener which initializes a session when it's created
         and cleans up after it when it's destroyed -->
    <listener>
        <listener-class>ejbwebapp.listener.SessionListener</listener-class>
    </listener>

    <!-- SERVLETS -->
    <!-- declare the servlet which handles user logins -->
    <servlet>
        <servlet-name>LoginServlet</servlet-name>
        <display-name>LoginServlet</display-name>
        <description>A servlet which authenticates users</description>
        <servlet-class>ejbwebapp.servlet.LoginServlet</servlet-class>
        <!-- the file which contains username/password pairs -->
        <init-param>
            <param-name>authFile</param-name>
            <param-value>ejbwebapp-users.properties</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <!-- declare the servlet which handles user logins -->
    <servlet>
        <servlet-name>LogoutServlet</servlet-name>
        <display-name>LogoutServlet</display-name>
        <description>A servlet logs out user and send's them back to the
                     login page
        </description>
        <servlet-class>ejbwebapp.servlet.LogoutServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <!-- declare the servlet which checks the user session at the top of each JSP -->
    <servlet>
        <servlet-name>SessionCheckServlet</servlet-name>
        <display-name>SessionCheckServlet</display-name>
        <description>A servlet which validates the user's session and redirects the
                     request if the session isn't valid (== not logged in)
        </description>
        <servlet-class>ejbwebapp.servlet.SessionCheckServlet</servlet-class>
    </servlet>
    <!-- declare the servlet which fills the advice bean with advice -->
    <servlet>
        <servlet-name>EjbAdviceServlet</servlet-name>
        <display-name>EjbAdviceServlet</display-name>
        <description>A servlet which places advice into an advice bean</description>
        <servlet-class>ejbwebapp.servlet.EjbAdviceServlet</servlet-class>
        <init-param>
            <param-name>advicePagePath</param-name>
            <param-value>EjbAdvice.jsp</param-value>
        </init-param>
    </servlet>

    <!-- SERVLET MAPPINGS -->
    <!-- map <Servlet> to $WEBAPP_DIR/WEB-INF/classes/<Servlet>.class -->
    <servlet-mapping>
        <servlet-name>LoginServlet</servlet-name>
        <url-pattern>/LoginServlet</url-pattern>
    </servlet-mapping>
    <!-- map <Servlet> to $WEBAPP_DIR/WEB-INF/classes/<Servlet>.class -->
    <servlet-mapping>
        <servlet-name>SessionCheckServlet</servlet-name>
        <url-pattern>/SessionCheckServlet</url-pattern>
    </servlet-mapping>
    <!-- map <Servlet> to $WEBAPP_DIR/WEB-INF/classes/<Servlet>.class -->
    <servlet-mapping>
        <servlet-name>EjbAdviceServlet</servlet-name>
        <url-pattern>/EjbAdviceServlet</url-pattern>
    </servlet-mapping>

    <!-- SESSION CONFIG -->
    <!-- configure the application to time out sessions after 30 minutes of inactivity -->
    <session-config>
        <session-timeout>30</session-timeout>
    </session-config>

    <!-- TAG LIBRARIES -->
    <!-- declare the error messages tag library -->
    <taglib>
        <taglib-uri>errorMessages</taglib-uri>
        <taglib-location>/WEB-INF/tlds/errorMessages-taglib.tld</taglib-location>
    </taglib>
    <!-- declare the error messages tag library -->
    <taglib>
        <taglib-uri>adviceMessages</taglib-uri>
        <taglib-location>/WEB-INF/tlds/adviceMessages-taglib.tld</taglib-location>
    </taglib>
    <!-- LOGIN CONFIGURATION -->
    <login-config>
        <auth-method>FORM</auth-method>
        <realm-name></realm-name>
        <form-login-config>
          <form-login-page>/EjbWebAppLogin.jsp</form-login-page>
          <form-error-page>/EjbWebAppLogin.jsp</form-error-page>
        </form-login-config>
    </login-config>
    <!-- EJB reference -->
    <ejb-ref>
        <ejb-ref-name>Advisor</ejb-ref-name>
        <ejb-ref-type>Session</ejb-ref-type>
        <home>headfirst.AdviceHome</home>
        <remote>headfirst.Advice</remote>
        <ejb-link>AdviceBean</ejb-link>
    </ejb-ref>

</web-app>

[ December 07, 2003: Message edited by: Michael Ernest ]

[James Adams]

Sorry that the above code is so ugly - I guess this forum system doesn't preserve indentation. Just for future reference, is there a way to have code indentation preserved in postings ?
Thanks.

-James

[Sunil Patil]

Hi James,
As far as i know Tomcat is Servlet Container and it does not have a EJB Container.So i guess your deploying your EJB in Reference implementation or some other EJB server and trying to access it from application deployed in Tomcat.
In that case Tomcat will have its own Context which will be different from EJB Containers Context and when you do Context initContext = new InitialContext(); in Tomcat you will get Tomcat's context which will be different from EJB Containers Context where name Advice is registered for AdviceBean.
I had tried deploying both Servlet and EJB in Reference implementation and it works fine.
Sunil

[Michael Ernest]

James - you can use the UBB CODE tag to preserve indentation, as I did above.

[James Adams]

Thanks for the reply to my posting and for the tip on getting code formatting preserved on this forum.
Yes it makes sense that Tomcat and the RI both have their own JNDI contexts. I am confused however by the fact that the client code (which is run at the command line) should also have its own context separate from the context of the RI, but it runs fine without doing anything special (it just gets a context with "new InitialContext();") and it is then able to do the lookup with no problem. I assumed that my servlet running in Tomcat would be able to do the same thing but this is obviously wrong by virtue of the Tomcat server having its own context, and the vanilla call to construct an InitialContext returns Tomcat's context instead of the RI context which is what I need. Does the client code just get the RI's context by default since it's not running in some sort of container with a context ?
Perhaps this is getting into JNDI details which are tangential to my objective of learning EJBs. However it's interesting to find out how all of this works, so if there's a simple explanation or solution I'd appreciate the chance to learn more about this (i.e. please comment!). Also it never occured to me that the RI is a J2EE server so I can deploy and run web applications there as well, no need to use Tomcat and the RI in tandem. I guess I should learn how to do that now (hopefully it's as easy as deploying on Tomcat).
Thanks in advance for any further feedback/insight.

-James

[Roger Chung-Wee]

If you look into the j2ee.jar file, you'll see the same files you get when you download Tomcat, eg in the org.apache.catalina package. I suspect that RI is basically an EJB container which seamlessly runs Tomcat to provide servlet container services.