The `web.xml` File

This is the config file for a java web app.

What’s a `web.xml` file?

The web.xml file is where your web app is configured.
For this class, we’ll just be configuring our servlets and JSP pages.

Here’s the basic structure of the web.xml file we started out with.

<?xml version="1.0" encoding="ISO-8859-1"?>

<web-app xmlns="http://java.sun.com/xml/ns/javaee"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
   version="3.0">

  <display-name>Welcome to Tomcat</display-name>
  <description>
     Welcome to My Java112 Site
  </description>

<!-- Context Parameters ************************************************** -->

<!-- Servlet and JSP Configurations ************************************** -->

<!-- Servlet Mappings **************************************************** -->

<!-- Home Page *********************************************************** -->

  <welcome-file-list>
    <welcome-file>/WEB-INF/index.jsp</welcome-file>
  </welcome-file-list>

</web-app>

We configure our servlets like this:

@WebServlet(
    name = "trivialServlet", 
    urlPatterns = { "/trivial", "/simple" }
)

The Old Way

Here’s what the older version of the file looks like. You will probably have to know this form, too.

<web-app xmlns="http://java.sun.com/xml/ns/javaee"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
   version="2.5">

<?xml version="1.0" encoding="ISO-8859-1"?>

  <display-name>Welcome to My Shiny App</display-name>
  <description>
     Welcome to My Shiny App.
  </description>

<!-- Servlet and JSP Declarations -->

  <!-- A JSP page -->
  <servlet>
    <servlet-name>Declarations</servlet-name>
    <jsp-file>/declarations.jsp</jsp-file>
  </servlet>

  <!-- A Servlet -->
  <servlet>
    <servlet-name>TrivialServlet</servlet-name>
    <servlet-class>java112.project2.TrivialServlet</servlet-class>
  </servlet>

<!-- Servlet and JSP Mappings -->

  <!-- A Mapping for a JSP page -->
  <servlet-mapping>
    <servlet-name>Declarations</servlet-name>
    <url-pattern>/declarations</url-pattern>
  </servlet-mapping>

  <!-- A Mapping for a Servlet -->
  <servlet-mapping>
    <servlet-name>TrivialServlet</servlet-name>
    <url-pattern>/trivial</url-pattern>
  </servlet-mapping>

</web-app>

When you add a JSP page or a Servlet to your web app, you need to both declare them and map them.
IMPORTANT NOTE! All the declarations have to be together and all the mappings have to be together. You can’t intermingle them!

Adding a new JSP Page

To add a new JSP page to your web app you need to do these steps.
1. Create your .jsp file and place it in your public_html/ directory.
2. Open the web.xml file from your config directory.
3. In the Servlet and JSP Declarations section of the web.xml file, add an element like this.
  
  Declarations /declarations.jsp
The <servlet-name> can be anything you want without spaces. It will have to be unique from all the other declarations.
The <jsf-file> is the name of the jsp file. You will have to all the “/” to the front of the name. If you have your jsp files in another directory inside of public_html, then you need to add that: /jsp/declarations.jsp.
Next, add a mapping element to the Servlet and JSP Mappings section of the web.xml file.
The <servlet-name> must match the declaration element that you are mapping to.
The <url-pattern> element can be anything you want without spaces. You can even map to a different extension, like .html or .asp.
I recommend not using an extension and making a nice simple, pretty URL.
You should not use an extension of .jsp!

Adding a new Servlet

To add a new servlet to your web app you need to follow these steps.

Create your packaged servlet class and place it in the correct directory for that package.

In the Servlet and JSP Declarations section of the web.xml file, add an element like this.

<servlet>
  <servlet-name>TrivialServlet</servlet-name>
  <servlet-class>java112.project2.TrivialServlet</servlet-class>
</servlet>

The <servlet-name> can be anything you want without spaces. It will have to be unique from all the other declarations.
The <servlet-class> element will be the full package name of your class.

Next, add a mapping element to the Servlet and JSP Mappings section of the web.xml file.

<servlet-mapping>
  <servlet-name>TrivialServlet</servlet-name>
  <url-pattern>/trivial</url-pattern>
</servlet-mapping>

The <servlet-name> element must match the declaration that you are mapping to.
The <url-pattern> element can be anything you want without spaces. You can even map to a different extension, like .html or .asp.
I recommend not using an extension and making a nice simple, pretty URL.
You should also not use the word “servlet” in this URL.

Accessing Mapped Pages and Servlets

In your web app, you will always use the mapped URL when accessing your pages and servlets.

Here’s an example:

<li><a href="/java112/declarations">JSP Declarations</a></li>

You need to have the name of your web app in front of the mapped URL. In this case that’s “/java112/”.

The web.xml File

What’s a web.xml file?