Difference between HTML & XHTML

The most important difference between two markup language is:
HTML(Hypertext markup language)  is an application of SGML(standard generalized  markup language) & allow author to omit certain tags and use attribute minimization.
XHTML(Extensible  HTML )  is an application of XML.It doesn’t  permit permission of any tags or use of attribute minimization.
however ,XHTML provides the shorthand notation for empty [...]

Hypertext Transfer Protocol — HTTP/1.1[ Error Code 4xx & 5xx ]

The 4xx class of status code is a Client side error.Whenever a Client request for any method or resource to server and if there is some error while requesting method or resource,the error will display at Client side.
1. 404 —- NOT FOUND
When server ha s not found anyhthing matching the request [...]

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http://j2eebrain.com/j2ee_tut_main/j2eetutdownloadmain1.htm
http://struts.javabeat.net/tutorials/index.php
http://www.onjava.com/pub/a/onjava/2005/08/03/hibernate.html
http://java.sun.com/j2ee/1.4/docs/devguide/dgsecure.html#wp25790
http://www.roseindia.net/struts/struts-projects.shtml
gud site to learn CSS
http://reference.sitepoint.com/css/css