overriding init() to make a database connection:nullpointer Exception

[saima kanwal]

I am extending ActionServlet to override init() i order to make a the database connection with oracle. Previously I was making teh connection in each request, in the overridden action class and my application was working fine. But I think , the databse connection should be made once at the servlet initialization, and not at each request.

My overridden Action Servlet is :

package com.jamesholmes.abc;
   
import java.util.ArrayList;
   

import javax.servlet.http.*;
import javax.servlet.*;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.action.ActionServlet;

import java.sql.*;
   
public final class CustomActionServlet extends ActionServlet { 
	public void init() { 
		ServletContext ctx = getServletContext();
		String connections = getInitParameter("connections");
		String driverClass = getInitParameter("driverclass");
		try { Class.forName(driverClass);
		Connection conn = DriverManager.getConnection(connections);
		ctx.setAttribute("conn",conn);
		} catch (Exception e) { }

		

		}
	}
		

my action class is :

package com.jamesholmes.abc;
   
import java.util.ArrayList;
   
import javax.servlet.http.*;
import javax.servlet.*;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;

import java.sql.*;
   
public final class SearchAction extends Action
{
  public ActionForward execute(ActionMapping mapping,
     ActionForm form,
    HttpServletRequest request,
    HttpServletResponse response)
     throws Exception
  {
    ProjectSearchService service = new ProjectSearchService();
    
    	
    Connection conn =(Connection)getServlet().getServletContext().getAttribute("conn");         
       
 

    ResultSet results;
   
    SearchForm searchForm = (SearchForm) form;
   
    // Perform project search based on the criteria entered.
    String title = searchForm.getTitle();
       if (title != null && title.trim().length() > 0) {
      results = service.searchByTitle(title,conn);
    } else {
      results = service.searchByManager(searchForm.getManager().trim(),conn);
    }
   
    // Place search results in SearchForm for access by JSP.
    searchForm.setResults(results);
   
       // Forward control to this Action's input page.
    return mapping.getInputForward();
  }
}

web.xml is :

<?xml version="1.0"?>
   
<!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>
   
  <!-- Action Servlet Configuration -->
  <servlet>
    <servlet-name>action</servlet-name>
    <servlet-class>com.jamesholmes.abc.CustomActionServlet</servlet-class>
    <init-param>
      <param-name>config</param-name>
      <param-value>/WEB-INF/struts-config.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>
   
  <!-- Action Servlet Mapping -->
  <servlet-mapping>
    <servlet-name>action</servlet-name>
    <url-pattern>*.do</url-pattern>
  </servlet-mapping>
   
  <!-- The Welcome File List -->
  <welcome-file-list>
    <welcome-file>/index.jsp</welcome-file>
  </welcome-file-list>

<context-param>
	<param-name>connections</param-name>
	<param-value>jdbc:oracle:thin:saima/second12@localhost:1521:XE</param-value>
</context-param>

<context-param>
	<param-name>driverclass</param-name>
	<param-value>oracle.jdbc.driver.OracleDriver</param-value>
</context-param>

</web-app>

struts-config.xml is :

<?xml version="1.0"?>
   
<!DOCTYPE struts-config PUBLIC
  "-//Apache Software Foundation//DTD Struts Configuration 1.3//EN"
  "http://struts.apache.org/dtds/struts-config_1_3.dtd">
   
<struts-config>
   
  <!-- Form Beans Configuration -->
  <form-beans>
      <form-bean name="searchForm"
                   type="com.jamesholmes.abc.SearchForm"/>
  </form-beans>
   
  <!-- Global Forwards Configuration -->
  <global-forwards>
    <forward name="search" path="/search.jsp"/>
  </global-forwards>
   
  <!-- Action Mappings Configuration -->
  <action-mappings>
    <action path="/search"
            type="com.jamesholmes.abc.SearchAction"
            name="searchForm"
            scope="request"
            validate="true"
            input="/search.jsp">
    </action>
  </action-mappings>
   
  <!-- Message Resources Configuration -->
  <message-resources
        parameter="com.jamesholmes.abc.MessageResources"/>
   
</struts-config>

and the exception that i am getting is :

org.apache.jasper.JasperException: java.lang.NullPointerException: Module 'null' not found.
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:491)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:419)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

root cause

java.lang.NullPointerException: Module 'null' not found.
org.apache.struts.taglib.TagUtils.getModuleConfig(TagUtils.java:755)
org.apache.struts.taglib.TagUtils.computeURLWithCharEncoding(TagUtils.java:364)
org.apache.struts.taglib.TagUtils.computeURLWithCharEncoding(TagUtils.java:285)
org.apache.struts.taglib.html.LinkTag.calculateURL(LinkTag.java:445)
org.apache.struts.taglib.html.LinkTag.doEndTag(LinkTag.java:353)
org.apache.jsp.index_jsp._jspx_meth_html_005flink_005f0(index_jsp.java:114)
org.apache.jsp.index_jsp._jspService(index_jsp.java:70)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:377)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

note The full stack trace of the root cause is available in the Apache Tomcat/6.0.24 logs.

please help me out.

[Alpesh Padra]

It seems that your struts custom tag has some problem with attributes of <html:link/>. It might be you are missing some attributes.

Try to read specification for <html:link/> or send here your JSP code. so that we can identify the root cause.

[David Newton]

Looks like you're accessing a JSP directly, instead of through an action.

So... there's a single connection, in the application context?! That will almost never work--what happens if you have more than a single user? Or a single user with multiple windows/tabs open? Consider connection pooling, otherwise you were better off the way you had it originally.

Even if you weren't, you should essentially never have to override the action servlet; for one-time application-startup tasks use a context listener.

[saima kanwal]

@ David Newton: thanks for your suggestion of using a context listener. I will try with that. I am not accessing any JSPs directly. My app was working fine before overriding this init().And everything is just the same except that i extend ActionServlet to override the init() and entering its name in web.xml.

So... there's a single connection, in the application context?! That will almost never work--what happens if you have more than a single user? Or a single user with multiple windows/tabs open? Consider connection pooling, otherwise you were better off the way you had it originally.

I do not understand what you mean by single connection? can you please explain and tell me how to implement a pool of connections??

[David Newton]

Are you overriding it without calling the superclass's unit?!

Search the web for connection pooling first-if you have specific questions you can start up a new thread.

[saima kanwal]

Oh yes , i was overrding it without calling the superclass's init. I think that's the mistake. Thanks .

[David Newton]

The original point about having a single application-wide connection is still valid, though--really horrible, bad idea.

[saima kanwal]

ok i got the idea . thanks for correcting.