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Streamline Your JSP Management with Enhydra
by Benoy Jose
Anybody who has worked with large Web applications understands how difficult it is to manage JSP pages. JSP pages are particularly difficult to modify and maintain because of the hundreds of HTML tags and stylesheets used in them. Once a JSP page is created and all the business logic is embedded into it, it becomes impossible for a UI designer to load the JSP back into any graphic editing tool and modify the HTML. Embedding business logic into a JSP page after changes in HTML have been made can also be a difficult job.
Enhydra proposes an XML- and object-oriented approach to deal with UI screens by introducing presentation objects. Presentation objects replace JSP pages with an XML/DOM tree-based structure that's easy to manipulate and simple to maintain.
The Enhydra Architecture
The Enhydra architecture consists of a number of loosely coupled components that work together to create scalable Web applications. The main components in its application server include the Multiserver, presentation manager, administration manager, session manger, and database manager, which will be discussed later. All requests from a client (such as a browser, PDA, etc.) are routed to a Web server, where an Enhydra plugin helps route those requests to an Enhydra Multiserver. The Multiserver then delegates the request to the presentation manager, which then uses the session manager and the database manager to fulfill the request.
The Multiserver
The Enhydra multiserver manages the life-cycle of all Enhydra application components. This includes all the application objects, servlets, and other Java classes used in the Enhydra application. The multiserver also manages the configuration settings required for the proper setup of the multiserver and all the applications within it. Every servlet or application in the Enhydra multiserver has a custom class loader, which is used to load the classes specific to that application. Separate class loaders help to reduce dependencies between applications and minimize problems related to wrong classpaths and wrong classes in memory. New applications and servlets can be modified and loaded into the multiserver without affecting existing applications.
The Enhydra multiserver connects to Web servers through a variety of protocols. Applications can be connected through the WAI, HTTP, and RMI protocols. This enables multiple Enhydra applications to connect to multiple Web servers simultaneously using different protocols. An Enhydra application can serve requests to a browser client through HTTP protocol and also service a remote client through the RMI protocol.
The Presentation Manager
The presentation manager manages presentation objects. Mappings between presentation objects and the URLs they represent are stored in the presentation manager. When a request is made to a URL through the browser, the presentation manager finds the appropriate presentation object from its database and forwards the request to the appropriate presentation object. Each Enhydra application has its own presentation manager that instantiates the HttpPresentationManager.
Session Manger
The session manager in Enhydra handles sessions for individual users. For each browser client, the session manager opens a new session and assigns a unique session ID. This session ID is used to retrieve the stored session when subsequent requests are made from the same client.
The session timeout can be pre-configured in a configuration file called appName.conf. Each Enhydra application will have its own session manager managing sessions for those applications. All session manager implementations should instantiate the StandardSessionManager class.
The Database Manager
The Database manager controls the database connections to and from the Enhydra application. It allocates and releases connections to the Database, routes the queries to the database, and manages transactions. The database manager is also responsible for maintaining connection pools to the database and manages the different JDBC connections to the database.
The Administration Manager
The administration manager allows you to configure and manage the Enhydra server. It also allows you to deploy and manage applications within the Enhydra server. Information about the Enhydra server and all its applications are stored in configuration files. During startup the Administration manager reads these configuration files and loads the applications accordingly. The administration manager can do management operations like starting and stopping applications, adding and removing applications, and checking the status of applications.
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