Web.xml

To understand web.xml, first let us uderstand what is xml?

  • xml stands Extensible Markup Language.
  • xml is markup language much like html.
  • Xml defines set of rules for encoding document in a format that readable by both as human and machine.
  • Xml was designed to carry and store data, not to display data. Xml is designed to be self-descriptive.

Web.xml defines mapping between URL paths and servlets that handle requests with those paths. The web.xml file provides configuration and deployment deployment information for the Web components that comprise a Web application. The web.xml descriptor files represents the core of the java application. The web.xml file is located in WEB-INF directory of web application.

Example of web.xml File:

<web-app>
<servlet>
<servlet-name>HelloWorld</servlet-name>
<servlet-class>servletexample.createHelloWorlExample</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>HelloWorld</servlet-name>
<url-pattern>/HelloworldExample/*</url-pattern>
</servlet-mapping>
</web-app>

Elements in Web.xml

Description of elements Used in web.xml file:

  1. <web-aap>: This element represents whole application of web.xml file
  2. <servlet>: This is the sub element of and represents the servlet
  3. <servlet-name>: This is the sub element of servlet and used to represents the name of servlet
  4. <servlet-class>: This is the sub element of servlet and used to represents the class of servlet
  5. <servlet-mapping>: This is the sub element of and used to map the servlet
  6. <url-pattern>: This is the sub element of servlet-mapping and used to client side to invoke the servlet

Web.xml Tags

Tags used in web.xml file are:

  1. Welcome-file-list tag; This tag is used to specify the default page of web application if none is specified.
    Example:

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

    In the above example index.jsp used as web page for web application

  2. Session config tag: This tag is used to specify the session configuration parameter
    Example:

    <session-config>
    <session-timeout>
         15
     </session-timeout>
    </session-config>

    In the above example session-config tag contains another tag session-timeout which specifies the http session timeout. The time specify in minutes.

  3. Error page tag: This tag is used to specify the error occurred in the while weblogic server is responding ti a HTTP request, returns an HTML page that displays either the HTTP error code.
    <error-page>
    <error-code>105</error-code>
    <location>/jsp/error/PageNotFound.jsp</location>
    </error page>

    In the above example error-page tag specify the error code as 105 and location describes the location of the jsp page.

Advantages of web.xml file

  • The first benefit of the xml is we can write it in our won markup language. There is a no restricted to limited sets of tags. By defining our own tag we can create a markup language in terms of specific problem.
  • Searching the data is easy and efficient.
  • Completely compatible with Java™ and 100% portable.

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About Krishna Srinivasan

He is Founder and Chief Editor of JavaBeat. He has more than 8+ years of experience on developing Web applications. He writes about Spring, DOJO, JSF, Hibernate and many other emerging technologies in this blog.

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