User Defined tags:

·         All predefined tags are sufficient to remove java code from jsp. So java people released Tag class which is used to created user defined tags

·         Custom tags are collection of user defined tags

·         Procedure to develop User defined tags

o   Identify all tags

§  Add

§  Sub

§  Mul

§  Div

§  Mod

o   Identify tag library name

§  Arithmetic

o   Develop tag handler class

§  This is a class which can use the Tag interface or TagSupport implementation class.

§  We need to implement the doEndTag() to provide the functionality of a tag

§  It will return the integer value (EVIL_PAGE,SKIP_BODY)

§  EVIL_PAGE ----> JSP will execute the remaining part as well

§  SKIP_BODY-----> JSP will skip the remaining body of page

public class AddTH extends TagSupport {       int one;       int two;       public void setOne(int one) {             this.one = one;             System.out.println(one);       }             public void setTwo(int two) {             this.two = two;             System.out.println(two);       }       public int doEndTag() throws JspException {             try {                   JspWriter out = pageContext.getOut();                   out.print((one+two));             }catch(IOException e) {                   System.out.println(e.getMessage());             }             return EVAL_PAGE;       } }

o   Develop tld file

§  This is a configuration file to specify the tag name as well as java class

§  We need to place in WEB-INF folder

<taglib>       <tlib-version>1.0</tlib-version>       <jsp-version>1.2</jsp-version>       <short-name>arth</short-name>       <uri>http://www.arth.com/tags/</uri>       <tag>             <name>add</name>             <tag-class>com.ibm.taghandlers.AddTH</tag-class>             <attribute>                   <name>one</name>                   <required>true</required>             </attribute>             <attribute>                   <name>two</name>                   <required>true</required>             </attribute>       </tag> </taglib>

o   Configure tld in web.xml

<jsp-config>     <taglib>       <taglib-uri>http://www.arth.com/tags/</taglib-uri>       <taglib-location>/WEB-INF/Arth.tld</taglib-location>     </taglib>   </jsp-config>

o   Jsp to use those tags

<%@ taglib uri="http://www.arth.com/tags/" prefix="arth"%> <arth:add two="10" one="20"></tag:add>

·         Internal process for above class

o   When we use arth:add jsp compiler check the prefix of a tag(arth)

o   JSPC checks the tag lib is configured with this prefix

o   If not configured JSPC will treat it as a template text and display on browser

o   If configured JSPC check for the uri(http://www.arth.com/tags/) and looks into the web.xml file for this with <taglib-uri>

o   Then JSPC checks the tld file for specific uri and opens it check for the tag name(add)

o   JSPC execute the class and return the output to browser. Based on return value JSPC execute the remaining page