Web.xml

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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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