AVAJAVA Web Tutorials

One great thing about JavaSW web application technology is that it's so flexible. In fact, in your web.xmlW file, it's possible to map file extensions (like .html) to a servletW. This tutorial will describe this technique and how you can use it to pass values to a servlet. The tomcat-demo project has a web.xml file and one servlet called TestServlet.

In web.xml, the url-pattern '/normal' maps to TestServlet, so if you hit "http://localhost:8080/tomcat-demo/normal", you get directed to TestServlet. The web.xml file also contains a url-pattern '*.html' mapping to TestServlet, which means that any requests to your application where the URL ends in '.html' will get directed to TestServlet. Examples of this are "http://localhost:8080/tomcat-demo/abc.html" and "http://localhost:8080/tomcat-demo/ok/123.html".

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app id="tomcat-demo" version="2.4"
	xmlns="http://java.sun.com/xml/ns/j2ee"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
	<servlet>
		<servlet-name>TestServlet</servlet-name>
		<servlet-class>test.TestServlet</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>TestServlet</servlet-name>
		<url-pattern>/normal</url-pattern>
	</servlet-mapping>
	<servlet-mapping>
		<servlet-name>TestServlet</servlet-name>
		<url-pattern>*.html</url-pattern>
	</servlet-mapping>
</web-app>

TestServlet displays the request URL. It tries reading in the 'my-param' parameter if it's being passed to the servlet using the standard GET method. If 'my-param' is present, it displays the parameter value. If the parameter isn't present, it looks to see if it can pull out a value from the request URL between the last underscore and a '.html' on the URL. If it can do this, it displays this value. It also contains three hyperlinks that all get directed to TestServlet.

TestServlet.java

package test;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class TestServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
		response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		out.println("This is the Test Servlet<br/>");
		String requestUrl = request.getRequestURL().toString();
		out.println("<br/>Request URL: " + requestUrl);

		String val = request.getParameter("my-param");
		if (val == null) {
			if ((requestUrl.lastIndexOf("_") != -1) && (requestUrl.lastIndexOf(".html") != -1)) {
				val = requestUrl.substring(requestUrl.lastIndexOf("_") + 1, requestUrl.indexOf(".html"));
				out.println("<br/>Value: " + val);
			}
		} else {
			out.println("<br/>Parameter Value: " + val);
		}

		out.println("<br/><br/><a href=\"normal?my-param=blah1\">This hits TestServlet</a>");
		out.println("<br/><a href=\"dynamic_blah2.html\">This looks static but it hits TestServlet</a>");
		out.println("<br/><a href=\"dynamic_blah3.html\">This also looks static but it hits TestServlet</a>");
	}
}

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