Java Enterprise Best Practices

Consider Using Filters to Simplify URLs

One drawback with the simple templating solution implemented by a layout page is that all links to the JSP pages must include the layout page name plus a query string—e.g., layout.jsp?page=page1. Example 9-6 shows parts of the navigation menu page with this type of link.

Example 9-6. Navigation page with links to layout page

<%@ taglib prefix="c" uri="http://java.sun.com/jstl/core" %>
   
<table bgcolor="lightblue">
  <tr>
    <td>
      <c:choose>
        <c:when test="${param.page =  = 'page1'}">
          <b>Page 1</b>
        </c:when>
        <c:otherwise>
          <a href="<c:url value="layout.jsp?page=page1" />">Page 1</a>
        </c:otherwise>
      </c:choose>
    </td>
  </tr>
   . . . 
</table>

If you want to be able to use more traditional URLs instead, you can use a filter. The filter component type was introduced in the Servlet 2.3 specification. A filter is invoked before a request is delivered to the target servlet or JSP page and is a powerful tool for applying request and response processing to a group of web application resources. The filter shown in Example 9-7 converts URLs of the form pageName.jsp to URLs of the form layout.jsp?page=pageName, which are behind the scenes at runtime.

Example 9-7. Filter that allows the layout page to be invoked with regular URLs

package com.ora.j2eebp.jsp; import java.io.*; import java.net.*; import javax.servlet.*; import javax.servlet.http.*; public class URLConversionFilter implements Filter { private static final String LAYOUT_PAGE = "/layout.jsp"; private static final ...