Java Servlet Programming

Server-Side Includes

All the servlets you’ve seen so far generate full HTML pages. If this were all that servlets could do, it would still be plenty. Servlets, however, can also be embedded inside HTML pages with something called server-side include (SSI) functionality.

In many servers that support servlets, a page can be preprocessed by the server to include output from servlets at certain points inside the page. The tags used for a server-side include look similar to those used for applets:^[6]

<SERVLET CODE=ServletName CODEBASE=http://server:port/dir
            initParam1=initValue1 
            initParam2=initValue2>
<PARAM NAME=param1 VALUE=value1>
<PARAM NAME=param2 VALUE=value2>
    If you see this text, it means that the web server
    providing this page does not support the SERVLET tag.
</SERVLET>

The CODE attribute specifies the class name or registered name of the servlet to invoke. The CODEBASE attribute is optional. It can refer to a remote location from which the servlet should be loaded. Without a CODEBASE attribute, the servlet is assumed to be local.

Any number of parameters may be passed to the servlet using the PARAM tag. The servlet can retrieve the parameter values using the getParameter() method of ServletRequest. Any number of initialization (init) parameters may also be passed to the servlet appended to the end of the SERVLET tag. We’ll cover init parameters in Chapter 3.

A server that supports SSI detects the SERVLET tag in the process of returning the page and substitutes in ...