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Web

Overview

The web module is used to provide HTTP connectivity to a station via the BWebService. The web module provides a layered set of abstractions for serving HTTP requests and building a web interface:

• Servlet: a standard javax.servlet API provides the lowest level of web integration.
• ServletView: is used to provide object views in a web interface.
• Web Workbench: is technology which enables the standard workbench to be run in a browser.
• Hx: is technology used to build web interfaces using only standards: HTML, JavaScript, and CSS.

Servlet

Niagara provides a standard javax.servlet API to service HTTP requests. The WebOp class is used to wrap HttpServletRequest and HttpServletResponse. WebOp implements Context to provide additional Niagara specific information. These APIs form the basis for the rest of the web framework.

The BWebServlet component is used to install a basic servlet which may be installed into a station database. The servletName is used to define how the servlet is registered into the URI namespace. A servletName of "foo" would receive all requests to the host that started with "/foo". Servlets are automatically registered into the URI namespace on their component started() method and unregistered on stopped(). The service() or doGet()/doPost() methods are used to process HTTP requests.

Note: The current javax.servlet implementation is based on version 2.4. The following interfaces and methods are not supported:

• javax.servlet.Filter: Unsupported interface
• javax.servlet.FilterChain: Unsupported interface
• javax.servlet.FilterConfig: Unsupported interface
• javax.servlet.RequestDispatcher: Unsupported interface
• javax.servlet.ServletContext: Unsupported methods
  • getNamedDispatcher(String)
  • getRequestDispatcher(String)
  • getResource(String)
  • getResourceAsStream(String)
  • getResourcePaths(String)
  • getServlet(String)
  • getServlets()
  • getServletContextName(String)
• javax.servlet.ServletRequest: Unsupported method
  • getRequestDispatcher(String)
• javax.servlet.ServletRequestAttributeListener: Unsupported interface
• javax.servlet.ServletRequestListener: Unsupported interface
• javax.servlet.http.HttpSessionActivationListener: Unsupported interface
• javax.servlet.http.HttpSessionAttributeListener: Unsupported interface
• javax.servlet.http.HttpSessionListener: Unsupported interface

ServletView

The web framework follows an object oriented model similar to the workbench. The user navigates to objects within the station using ords. One or more web enabled views are used to view and edit each object.

When navigating objects using ords, Niagara must map ords into the URI namespace. This is done with the URI format of "/ord?ord".

The BServletView class is used to build servlets that plug into the ord space using the "view:" scheme. For example if you wish to display an HTML table for every instance of component type "Foo", you could create a ServletView called "FooTable". Given an instance of "Foo", the URI to access that view might be "/ord?slot:/foo3|view:acme:FooTable". The WebOp passed to BServletView.service() contains the target object being viewed (note WebOp subclasses from OrdTarget).

Niagara Web Launcher

Note: WebLauncher will be removed in the future, as it is older technology that has become increasingly difficult to support and maintain. In the meantime, we strongly recommend users implement new Niagara views using bajaux and migrate all existing views to incorporate bajaux therein.

A nice feature of Niagara's web framework is the ability to run the entire Workbench right in a browser embedded inside a lightweight client application called the Niagara Web Launcher. This application allows almost any view (or plugin) to run transparently in both a desktop and browser environment. The following process illustrates how Niagara Web Launcher works:

1. User launches the application via a link on the login screen.
2. The application must be pre-installed on the client's machine. If not the user is redirected to another web page that contains installation instructions.
3. The application loads modules from the station as needed, and caches them on the local drive.
4. The Workbench opens a fox connection under the covers for Workbench to station communication.
5. The Workbench displays itself inside the application using the respective WbProfile and WbView.

Niagara Web Launcher allows a sophisticated UI to be downloaded to a lightweight application directly from the JACE. It is downloaded the first time and cached - speeding up subsequent access. Development for web versus desktop Workbench is completely transparent. The only difference is that the BWbProfile used for a web interface must subclass from BWbWebProfile. Some functionality is limited only to the desktop like the ability to access the console and Jikes compiler. Also note that Niagara Web Launcher session is limited to a specific station. So it doesn't make sense to navigate to ords outside that station such a "local:|file:".

Note: in order for web workbench to be used, the client browser machine must have access to the station's fox port. This may require the fox port to be opened up in the firewall.

Hx

There are cases where using the workbench is overkill or we don't wish to require the Java Plugin. For these use cases, Niagara provides the hx technology. Hx is a mini-framework used to build real-time web interfaces only with standard HTML, JavaScript, and CSS. See the hx chapter for details.

WebProfileConfig

The web experience of a given user is controlled via the BWebProfileConfig class. WebProfileConfig is a MixIn added to every User component. The web profile determines whether web workbench or hx is used by specifying an WbProfile or HxProfile for the user.

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