Java Doc for ServletContext.java in  » EJB-Server-resin-3.1.5 » jsdk » javax » servlet » Java Source Code / Java DocumentationJava Source Code and Java Documentation

Each application is entirely distinct. Each has its own:

• Class loader -- each application gets its own beans and servlets.
• ServletContext attributes
• Servlets and servlet mappings (e.g. *.jsp could map to different servlets in different applications.)
• File root
• Mime mapping
• Real-path mapping (aliases)

URIs are relative to the application root (e.g. /myapp) for most ServletContext methods. So you can define user workspaces with identical JSP files and servlets in different applications.

Including and forwarding

Forwarding and including files, the Servlet equivalent of SSI are handled by the RequestDispatcher methods.

Global initialization

There is no direct equivalent of a global.jsa. To initialize and cleanup shared classes on start and stop, use a load-on-startup servlet. The init() method will be called when the application starts and the destroy() method will be called when the application finishes.

 <servlet servlet-name='global'
 servlet-class='test.InitServlet'
 load-on-startup/>
 

Basic configuration

 <web-app id='/myapp' app-dir='/www/myweb'/>
 

Servlet and Bean locations (class loaders)

Load balancing

So the application object is best used as a cache rather than as a way for servlets to communicate.

 <web-app id='/myapp' app-dir='/www/myapp'>
 <context-param name1='value1'/>
 <context-param name2='value2'/>
 </web-app>
 

See ServletRequest to return the real path relative to the request uri.
Parameters:
  uri - path relative to the application root to be translated. native file path for the uri.

The following example includes the result of executing inc.jsp into the output stream. If the context path is /myapp, the equivalent uri is /myapp/inc.jsp

 RequestDispatcher disp;
 disp = getRequestDispatcher("/inc.jsp?a=b");
 disp.include(request, response);
 

See ServletRequest to return a request dispatcher relative to the request uri.
Parameters:
  uri - path relative to the app root (including query string)for the included file. RequestDispatcher for later inclusion or forwarding.

A typical initialization of an application attribute will look like:

 ServletContext app = getServletContext();
 Object value;
 synchronized (app) {
 value = app.getAttribute("cache");
 if (value == null) {
 value = new Cache();
 app.setAttribute("cache", value);
 }
 }