Creating your own ATG droplets is not difficult. Servicing a default open parameter (oparam) in an ATG droplet is surprisingly extremely easy.

ATG has these things called “droplets” that you use from within your “dsp” tag library. You can –nay– you SHOULD make your own droplets. You should have as little Java code in your JSP pages as humanly possible.

To do this takes a few steps:

1. Create the .java file

   Create it under /modules/base/src/java/com/yourlibrary/

2. Extend “DynamoServlet”

   The inside of your Java file should look something like this (to begin):
   
package com.yourlibrary;

   import java.io.IOException;
   import javax.servlet.ServletException;
   import atg.nucleus.naming.ParameterName;
   import atg.repository.*;
   import atg.servlet.*;

   public class YourDroplet extends DynamoServlet{
@Override
public void service(DynamoHttpServletRequest request, DynamoHttpServletResponse response)
throws ServletException, IOException
{
}
}

3. Create the .properties file

   Create it under /modules/base/config/yourlibrary/

4. Define your properties

   
$class=com.yourlibrary.YourDroplet
$scope=global
$description=For documentation purposes only


   global scope makes it so there is only 1 instance of the droplet per JVM. You can do session or request scope as well. This is all server admin magic voodoo. I can give you no recommendations here, that’s a topic for it’s own entire post

5. Implement the droplet

   Create a jsp page somehwere (probably something like /modules/base/j2ee-apps/base/web-app.war) if you haven’t already, and then add this code:

   
<%@ taglib uri="/dspTaglib" prefix="dsp"%>
<dsp:importbean bean="/yourlibrary/YourDroplet" />
<dsp:page>
<dsp:droplet name="YourDroplet">
</dsp:droplet>
</dsp:page>


OK, at this point you have the skeleton for your droplet created. Go ahead and burn incense, sacrafice a chicken and compile and run and see if it worked. If not, don’t ask for help here, I’m just a poor Java hating front-end dev trying to document an insane procress. Go to StackOverflow.com instead.

Now, let’s make it serve a purpose. Let’s say you just want, like, the user name or something:

Your .java file


package com.yourlibrary;

request.setParameter("username", username);
request.serviceLocalParameter("ousername", request, response);
}
}

Your .jsp file


<%@ taglib uri="/dspTaglib" prefix="dsp"%>
<dsp:importbean bean="/yourlibrary/YourDroplet" />
<dsp:page>
<dsp:droplet name="YourDroplet">
<dsp:oparam name="ousername">
<dsp:valueof param="username" />
</dsp:oparam>
</dsp:droplet>
</dsp:page>


Now, let’s say that some of your users are admins, and in some places you want to have a special thing that happens when the user is an admin, but in others, just the normal thing happens no matter what. You can use a default for this. Here’s how:

Your .java file


package com.yourlibrary;

if(!handled){
request.serviceLocalParameter("ouser", request, response);
}
}
}

Your .jsp file


<%@ taglib uri="/dspTaglib" prefix="dsp"%>
<dsp:importbean bean="/yourlibrary/YourDroplet" />
<dsp:page>
<!--Special case for admin-->
<dsp:droplet name="YourDroplet">
<dsp:oparam name="oadmin">
Admin <dsp:valueof param="username" />
</dsp:oparam>
<dsp:oparam name="ouser">
<dsp:valueof param="username" />
</dsp:oparam>
</dsp:droplet>

<!--No special case for admin, admin falls back on ouser-->
<dsp:droplet name="YourDroplet">
<dsp:oparam name="ouser">
<dsp:valueof param="username" />
</dsp:oparam>
</dsp:droplet>
</dsp:page>


You can take this to any level you want. Here is a more complex basic example:

Your .java file


package com.yourlibrary;

if(!handled){
request.serviceLocalParameter("default", request, response);
}
}
}

Your .jsp file


<%@ taglib uri="/dspTaglib" prefix="dsp"%>
<dsp:importbean bean="/yourlibrary/YourDroplet" />
<dsp:page>
<!--Each special case is used-->
<dsp:droplet name="YourDroplet">
<dsp:oparam name="oadmin">
Admin <dsp:valueof param="username" />
</dsp:oparam>
<dsp:oparam name="omoderator">
Moderator <dsp:valueof param="username" />
</dsp:oparam>
<dsp:oparam name="ouser">
User <dsp:valueof param="username" />
</dsp:oparam>
</dsp:droplet>

<!--No special case for admin or moderator, they fall back on default-->
<dsp:droplet name="YourDroplet">
<dsp:oparam name="ouser">
User <dsp:valueof param="username" />, you are not permitted here. Begone!
</dsp:oparam>
<dsp:oparam name="default">
Welcome <dsp:valueof param="username" />. Access granted!
</dsp:oparam>
</dsp:droplet>
</dsp:page>