Sun Java System Web Server 7.0 Developer's Guide to Java Web Applications

Invoking Servlets

You can invoke a servlet by directly addressing it from a Web page with a URL or by calling it programmatically from an already running servlet.

Calling a Servlet With a URL

You can call servlets by using URLs embedded as links in HTML or JSP pages. The format of these URLs is as follows:

http://server:port/context_roott/servlet/servlet_name?name=value

The following table describes each URL section.

Table 4–1 URL Fields for Servlets Within a Web Application


URL Element	Description
server:port	The IP address or host name and optional port number. To access the default web application for a virtual server, specify only this URL section. You do not need to specify the context_root or servlet_name unless you also wish to specify name-value parameters.
context_root	The context path without the leading “/” at which the web application is installed.
`servlet`	Only needed if no `servlet-mapping` is defined in the `web.xml` file.
servlet_name	The `servlet-name` (or `servlet-mapping` if defined) as configured in the `web.xml` file.
?name=value...	Optional servlet name-value parameters.

In this example, example is the host name, MortPages is the context root, and calcMortgage is the servlet name:

http://www.example.com/MortPages/servlet/calcMortgage?rate=8.0&per=360&bal=180000

Calling a Servlet Programmatically

First, identify which servlet to call by specifying a URI. This URI is normally a path relative to the current application. For example, if your servlet is part of an application with a context root named OfficeFrontEnd, the URL to a servlet called ShowSupplies from a browser is as follows:

http://server:port/OfficeFrontEnd/servlet/ShowSupplies?name=value

You can call this servlet programmatically from another servlet in one of two ways.

To include another servlet's output, use the include() method from the RequestDispatcher interface. This method calls a servlet by its URI and waits for it to return before continuing to process the interaction. The include() method can be called multiple times within a given servlet.

For example:

   RequestDispatcher dispatcher =
       getServletContext().getRequestDispatcher("/servlet/ShowSupplies");
    dispatcher.include(request, response);

To handle interaction control to another servlet, use the RequestDispatcher interfaces forward() method with the servlet's URI as a parameter.

This example shows a servlet using forward():

   RequestDispatcher dispatcher =
       getServletContext().getRequestDispatcher("/servlet/ShowSupplies");
    dispatcher.forward(request, response);