Struts 1.1 database connection exception

[Trevar Pearce]

Hi, I'm using Struts 1.1 and Oracle 10g and attempting to establish a connection between the two. I have successfully done so by hard-coding the datasource info in my action class but am running into a problem when placing that info in the struts-config.xml. Here's the data-source entry:

<data-sources>
<data-source key="TESTDB">
<set-property property="autoCommit" value="false"/>
<set-property property="description" value="Data Source Configuration"/>
<set-property property="driverClass" value="oracle.jdbc.driver.OracleDriver"/>
<set-property property="url" value="jdbc :-o	 racle:thin:@xps.localhost:1521:CoopDev1"/>
<set-property property="user" value="SYSTEM"/>
<set-property property="password" value="CoopWord"/>
</data-source>
</data-sources>

I call it with this:

 import java.sql.* ;
 
import javax.servlet.http.HttpServletRequest;
 
import javax.sql.DataSource;
 
import org.apache.struts.action.Action;
 
public class HelloDatabase extends Action{
 
public String dbAccess(HttpServletRequest request) throws Exception {
 
Connection c = null ;
String result;
 

 
DataSource dataSource = (DataSource) servlet.getServletContext().getAttribute("TESTDB");
 c = dataSource.getConnection();
 
        CallableStatement cstmt = c.prepareCall("{? = call hello()}");
 
        cstmt.registerOutParameter(1, Types.VARCHAR);
 
        cstmt.execute();
 
        result = cstmt.getString(1);
 
        return result;  

I have determined that it is stumbling on the DataSource line, giving me a java.lang.NullPointerException. If you can see what's going wrong with the code, please let me know.

Thanks

[Naseem Khan]

Getting datasource object from struts-config.xml

There is a method called getDataSource(HttpServletRequest, String) defined in Action
that gets inherited when you extend your class to Action.

call this method and you will get DataSource object...

DataSource dataSource=getDataSource(request, "TESTDB");


Naseem
[ July 13, 2006: Message edited by: Naseem Khan ]

[Trevar Pearce]

Hi, thanks for the reply. I've implemented the code but unfortunately it's still giving me the java.lang.NullPointerException

When I remove the try/catch block from the database access action class, it produces this:

type Exception report
 
message
 
description The server encountered an internal error () that prevented it from fulfilling this request.
 
exception
 
javax.servlet.ServletException
org.apache.struts.action.RequestProcessor.processException(RequestProcessor.java:545)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:486)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
 
root cause
 
java.lang.NullPointerException
org.apache.struts.action.Action.getDataSource(Action.java:532)
HelloDatabase.dbAccess(HelloDatabase.java:18)
fooAction.execute(fooAction.java:40)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:484)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

It's thus still the DataSource line that's breaking. Any ideas?

[Trevar Pearce]

Hi again, so I've narrowed it down a bit. Looks like the getDataSource is calling Action.class and it's stumbling on the following line:

ServletContext context = getServlet().getServletContext()

I've commented all my db access code out and just entered that (and imported javax.servlet.ServletContext) and I get the same NullPointerException. Anybody know what's going on here?

Thanks, Trevar

[Trevar Pearce]

So, I've in fact more or less solved the problem. The solution confuses me however, so if anyone can help me understand, I would very much appreciate it.

My jsp forwards to an action class which calls a class that does the database access. The database access class returns the result to the action class. The action class populates a bean with the results and sets a request attribute with the bean. Finally it forwards back to the jsp, which displays the results from the bean. As you can tell, it's a tiny web-app at this point, but I believe it is structured properly (if you have different information about where the db access should happen, please let me know, I really want this app to be structured to the standards).

The thing that I got hung up on was accessing the application scope attributes (from the ServletContext) in the database access method. I'll post it here:

import java.sql.* ;
 
import javax.servlet.ServletContext;
 
import javax.sql.DataSource;
 
public class HelloDatabase{
 
public String dbAccess(ServletContext context) throws Exception {
 
Connection c = null ;
String result;
 
DataSource dataSource = (DataSource) context.getAttribute("db1");
 
try{
        c = dataSource.getConnection();
 
        CallableStatement cstmt = c.prepareCall("{? = call hello()}");
 
        cstmt.registerOutParameter(1, Types.VARCHAR);
 
        cstmt.execute();
 
        result = cstmt.getString(1);
 
        c.close();
 
        return result;
 
} catch (Exception ex){
        String exception = ex.toString();
        return exception;
}
}
}

As I said, I'm calling this class and its one method rather than forwarding to it. As such, I think it's not being passed the ServletContext unless I do it explicitly(as I do). This is what confuses me. I assumed that because the ServletContext was application scope that it would automatically be available in any class I called in my web-app. I guess that was a poor assumption. Can anyone explain what I'm missing here? There's some bit of theory that hasn't gotten through to me and I'd really appreciate it if someone could explain briefly.

Thanks, Trevar

[Merrill Higginson]

Trevar,

I realize you've already spent a good deal of time on this, but my recommendation is to go a completely different route. I suggest you abandon the use of the Stuts datasource entirely.

My reasons for recommending this are:

1-It's deprecated in the latest release of Struts
2-It was included in Struts only as a "last resort" if your Application server doesn't have it's own connection pooling mechanism
3-For a long time, the authors of Struts have recommended you use your Application Server's connection pooling mechanism instead of the one in Struts

I'd suggest you look in your application server documentation for information on how to set up an Oracle Connection pool. You can then access the DataSource in any of your classes by doing a JNDI lookup.

Example:

      Context ctx = new InitialContext();
      if(ctx == null ) 
          throw new Exception("Boom - No Context");
 
      DataSource ds = 
            (DataSource)ctx.lookup(
               "java:comp/env/jdbc/TestDB");
 
      if (ds != null) {
        Connection conn = ds.getConnection();
        // the rest of your DB logic goes here
       }