The Web Graph Database

Viewlet Framework: Creating a JSP-only Viewlet

To add a JSP-only Viewlet to an InfoGrid application, the following steps need to be performed:

  • Decide on a fully-qualified name for the new Viewlet, using the reverse domain name convention as it is common for Java classes. For example, com.example.viewlet.CustomerViewlet.
  • Decide on the exact criteria which types of MeshObject can be rendered by this Viewlet. For example, it may apply to any MeshObject of type com.example.models.CustomerModel/Customer, or only to a MeshObject of type com.example.models.CustomerModel/Customer whose com.example.models.CustomerModel/Customer_Balance is less than $10 while it is also related to at least one MeshObject of type com.example.models.CustomerModel/Order.
  • Determine which other Viewlets this Viewlet may compete with, and decide which of them should be the default.
  • In your application's ViewletFactory, encode your rule, e.g.: 
        if( subject.isBlessedBy( CustomerModelSubjectArea.CUSTOMER )) {
        ret.add( DefaultJspViewlet.choice( "com.example.viewlet.CustomerViewlet", ViewletFactoryChoice.GOOD_MATCH_QUALITY ));
    }
  • Create the JSP file with name /v/com/example/viewlet/CustomerViewlet.jsp that contains the JSP code to run when the Viewlet is run.

Within the JSP file, the following variables are pre-defined:

Variable Description
lid-appcontext The application context, e.g. whether this is the main window or a popup. May be null.
Subject The MeshObject whose URL was accessed. Always provided.
Viewlet Instance of the subtype of Viewlet that backs this JSP file. Here, this is an instance of DefaultJspViewlet. Always provided.
ViewletState The desired JeeViewletState. May be null.
ViewletStateTransition The desired JeeViewletStateTransition. May be null.

See also: