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Dynamically load classes with servlets

Posted on 2003-12-11
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Last Modified: 2013-11-24
Hi all,
A variable is based to my servlet and a lookup is preformed in the database. Depending on what this variable is a class is loaded. I've written an abstract to handle all this. When I was testing I didn't use a servlet initially but instead wrote a main and tested on the command line to make sure the lookup and creation was working. This test file began with:
public class TestUser extends DecisionCreator
      {
      public static void main(String args[])
            {
etc...

Where DecisonCreator is:
public abstract class DecisionCreator
{
                protected static Decision createDecision(String name) throws DecisionNotCreatedException
      {
      Decision myDecision;
      try
            {
            Class DecisionClass = Class.forName(name);
            myDecision = (Decision) DecisionClass.newInstance();
            }
                //omitted catches
      return myDecision;
      }
Decision is a simple interface:
public interface Decision
      {            
      String[] launch(String user);
      }
When I went to put use my code in the servlet I came up against this problem. My servlet is called Link:
public class Link extends HttpServlet
I cannot extend DecisionCreator as I did in my test file. Is there a solution to this or do I have to re-design everything?
If anything is not clear please let me know

Thanks,
Shane
0
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Question by:fast74
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6 Comments
 
LVL 35

Expert Comment

by:girionis
ID: 9919499
 Call the TestUser class from your Servlet and let it (the TestUser) do the loading of the classes.
0
 
LVL 35

Accepted Solution

by:
girionis earned 250 total points
ID: 9919510
 For instance:

MyServlet extends HttpServlet
{
  public void doPost(...)
  {
      if (value read from db == something)
      {
           TestUser tu = new TestUser();
           tu.loadClass(something);
           ...
      }
  }
}
0
 
LVL 35

Expert Comment

by:TimYates
ID: 9919512
yeah incorporate an instance, don't try to extend :-)
0
 
LVL 30

Expert Comment

by:Mayank S
ID: 9919978
If you want to do it without TestUser, then do you necessarily need to make the DecisionCreater class as abstract? If not, then you can use its instance....
0
 
LVL 30

Expert Comment

by:Mayank S
ID: 11665346
Accept girinois' comment as answer.
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