Error Page Recipe

Serving Tapestry Pages as Servlet Error Pages

Do you want to dress up your site and use a snazzy Tapestry page instead of the default 404 error page? Using modern servlet containers, this is a snap!

Simply upgrade your application web.xml to the 2.4 version, and make a couple of changes:

web.xml
<?xml version="1.0" encoding="UTF-8"?>

<web-app 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"
  version="2.4">

  <display-name>Cookbook</display-name>
  <context-param>
    <param-name>tapestry.app-package</param-name>
    <param-value>com.example.newapp</param-value>
  </context-param>

  <filter>
    <filter-name>app</filter-name>
    <filter-class>org.apache.tapestry5.TapestryFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>app</filter-name>
    <url-pattern>/*</url-pattern>
    <dispatcher>REQUEST</dispatcher>
    <dispatcher>ERROR</dispatcher>
  </filter-mapping>

  <error-page>
    <error-code>404</error-code>
    <location>/error404</location>
  </error-page>

</web-app>

Tapestry's filter must be marked as a handler for both standard requests and errors. That's accomplished with the <dispatcher> elements inside the <filter-mapping> section.

You must then map error codes to Tapestry URLs. In this case, the 404 error is send to the /error404 resource, which is really the "Error404" Tapestry page.

We'll create a simple Error404 page, one that displays a message and (in development mode) displays the details about the incoming request.

Error404.tml
<html xmlns:t="http://tapestry.apache.org/schema/tapestry_5_4.xsd">
 <head>

        <title>Resource not found.</title>
    </head>
    <body>

        <div class="container">

            <h1>Page or resource not found.</h1>

            <t:if test="! productionMode">
                <t:renderobject object="request"/>
            </t:if>
        </div>

    </body>
</html>

The page simply makes the request and productionMode properties available:

Error404.java
package com.example.newapp.pages;

import org.apache.tapestry5.SymbolConstants;
import org.apache.tapestry5.annotations.Property;
import org.apache.tapestry5.ioc.annotations.Inject;
import org.apache.tapestry5.ioc.annotations.Symbol;
import org.apache.tapestry5.services.Request;

public class Error404
{
    @Property
    @Inject
    private Request request;

    @Property
    @Inject
    @Symbol(SymbolConstants.PRODUCTION_MODE)
    private boolean productionMode;
}


The end-result, in when not in production mode, looks like this:

An issue with an application that has a root Index page is that any invalid path, which would normally generate a 404 error, is instead routed to the Index page (because the invalid path looks like page's activation context). See Issue TAP5-2070.