Java Examples In A Nutshell (3rd Edition) [Electronic resources] نسخه متنی

20.13 Packaging a Web Application

Now that we've considered each of the pieces that
constitute our ListManager web
application, we'll look at how those pieces are put
together into a web application WAR file. For completeness,
we'll include all the servlets and JSP pages from
this chapter, not just the ones that implement the mailing list
manager. In order to do this, we must:

1. Write a web.xml file that configures all the
   servlets

2. Arrange that configuration filealong with the servlet
   implementation classes, JSP pages, and related filesin their
   correct places in a directory hierarchy

3. Zip them all up (with the jar tool) to create a
   WAR file

Recall from the start of this chapter that we used these commands to
compile the servlet classes and create the WAR file:

javac -d WEB-INF/classes/ *.java
jar cMf je3.war indexl *.jsp *.jspx ListManager/*.jsp WEB-INF/web.
xml WEB-INF/tags/*.tag WEB-INF/classes

We'll consider the directory hierarchy of the web
application first, and then look at the web.xml
file.

20.13.1 Web Application Directory Structure

Our je3 web application is structured as
follows:

/

This is the root directory for the application. The servlet container
will map a file x in this directory to a
URL like this:

http://localhost:8080/je3/x

/indexl

The default file served for the URL
"je3/". This is just a plain HTML
file that contains links to the various examples contained in the web
application.

/*.jsp

The hello.jsp, hello2.jsp and
hello3.jspx examples go here.

/ListManager/

A directory for the ListManager application, which serves to keep it
separate from this chapter's other servlet and JSP
examples.

/ListManager/login.jsp

The ListManager login page.

/ListManager/edit.jsp

The ListManager edit preferences page.

/WEB-INF/

Most web applications have a WEB-INF/
subdirectory for configuration information, servlet class files, and
other auxiliary files. The servlet container does not expose these
files to the client (although a servlet may do so if it chooses), so
it is reasonably safe to store sensitive configuration information
(such as passwords) beneath this directory.

/WEB-INF/web.xml

The all-important configuration file that maps servlet names to Java
class names and URLs to servlet names. It also defines servlet
initialization parameters and maps tag library URIs to the actual
location of the TLD file.

/WEB-INF/classes/je3/servlet/*.class

Java class files for the Controller servlet, its
User and UserFactory model
classes, and also the HelloNet,
ErrorHandlerServlet, and
Counter servlets.

/WEB-INF/tags/*.tag

.tag files defining the custom JSP 2.0 tags used
in the web application.

20.13.2 The web.xml Configuration File

The WEB-INF/web.xml file is the main
configuration file for a web application. In a well-designed web
application, this is the only file that may need customization when
deploying the application to a new server or in a new network
environment. The web.xml file for the servlet
and JSP examples in this chapter, including the ListManager web
application, is shown in Example 20-14.

The bulk of the web.xml file consists of
<servlet> tags, which map servlet implementation
classes to servlet names and define initialization parameters for
servlets that need them. Note that it is perfectly legal to define
multiple names for the same servlet implementation class. Creating
multiple named instances of the same servlet implementation in this
way allows you to specify different initialization parameters for
each instance. You might set up multiple copies of the ListManager
Controller servlet to manage multiple mailing
lists, for example.

The other important tags in the configuration file are the
<servlet-mapping> tags, which map servlet
names to the URLs by which they may be invoked. Note that there can
be more than one <servlet-mapping> tag for
each servlet and that a <servlet-mapping>
can include wildcard characters. <servlet>
and <servlet-mapping> are the most important
tags for a web.xml file,
but they are by no means the only ones. The example illustrates a few
others; see the Servlet specification for full details on the syntax
of this file.

Example 20-14. web.xml

<?xml version="1.0" encoding="ISO-8859-1"?>
<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 web-app_2_4.xsd"
version="2.4">
<!-- This is descriptive information about the webapp as a whole -->
<display-name>Java Examples in a Nutshell</display-name>
<description>
Servlet and JSP examples from Java Examples in a Nutshell, 3rd
edition, including a simple web application to allow users to
subscribe and unsubscribe from a mailing list, and to set their mail
delivery preferences.
</description>
<!-- Next come servlet tags that map class
 files to servlet names and -->
<!-- also define servlet initialization parameters -->
<servlet>
<servlet-name>Hello</servlet-name>
<servlet-class>je3.servlet.HelloNet</servlet-class>
</servlet>
<servlet>
<servlet-name>ErrorHandler</servlet-name>
<servlet-class>je3.servlet.ErrorHandlerServlet</servlet-class>
</servlet>
<!-- The Counter servlet uses initialization parameters -->
<servlet>
<servlet-name>Counter</servlet-name>  
<servlet-class>je3.servlet.Counter</servlet-class>
<init-param>
<param-name>countfile</param-name>         
<!-- where to save state -->
<param-value>/tmp/counts.ser</param-value>
 <!-- adjust for your system-->
</init-param>
<init-param>
<param-name>saveInterval</param-name>      <!-- how often to save -->
<param-value>30000</param-value>           <!-- every 30 seconds -->
</init-param>
</servlet>
<!-- The Controller servlet for the ListManager application needs -->
<!-- initialization parameters to specify the database to be used. -->
<!-- You'll need to set these before you can use the application. -->
<servlet>
<servlet-name>Controller</servlet-name>
<servlet-class>je3.servlet.Controller</servlet-class>
<init-param> <!-- the JDBC driver class to use -->
<param-name>jdbcDriver</param-name>
<param-value>com.mysql.jdbc.Driver</param-value>
</init-param>
<init-param> <!-- The database to connect to -->
<param-name>jdbcURL</param-name>
<param-value>jdbc:mysql:///test</param-value>
</init-param>
<init-param> <!-- The username to connect as -->
<param-name>jdbcUser</param-name>
<param-value></param-value>
</init-param>
<init-param> <!-- The password to use -->
<param-name>jdbcPassword</param-name>
<param-value></param-value>
</init-param>
<init-param> <!-- the database table to use -->
<param-name>tablename</param-name>
<param-value>testlist</param-value>
</init-param>
<init-param> <!-- the name of the mailing list -->
<param-name>listname</param-name>
<param-value>Test Email List</param-value>
</init-param>
</servlet>
<!-- Next we map URLs and URL patterns to servlet names -->
<servlet-mapping>
<servlet-name>Hello</servlet-name>
<url-pattern>/Hello</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>ErrorHandler</servlet-name>
<url-pattern>/ErrorHandler</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>Counter</servlet-name>
<url-pattern>/Counter</url-pattern>
</servlet-mapping>
<!-- Note the wildcard below: 
any URL ending in .count invokes Counter -->
<servlet-mapping> 
<servlet-name>Counter</servlet-name>
<url-pattern>*.count</url-pattern>
</servlet-mapping>
<!-- These are the different URLs that invoke the
 ListManager Controller -->
<!-- Note that we could also use wildcards here. -->
<servlet-mapping>
<servlet-name>Controller</servlet-name>
<url-pattern>/ListManager/</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>Controller</servlet-name>
<url-pattern>/ListManager/login.action</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>Controller</servlet-name>
<url-pattern>/ListManager/logout.action</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>Controller</servlet-name>
<url-pattern>/ListManager/edit.action</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>Controller</servlet-name>
<url-pattern>/ListManager/unsubscribe.action</url-pattern>
</servlet-mapping>
<!-- ListManager sessions timeout after 15 minutes of inactivity -->
<session-config>
<session-timeout>15</session-timeout>
</session-config>
</web-app>