JSP in Actioncontinuation

JSP’s Tag Extension Mechanism• You can define your own actions to replace lengthy scriptlets• By “hiding” functions behind custom tags, • you can increase modularity and maintainability of your pages.

1. Define Java classes that provide the functionality of the new actions, including the definition of their attributes (e.g., myAttributeName). These classes are called tag handlers.

2. Provide a formalized description of your action elements, so that Tomcat knows how to handle them. For example, you need to specify which actions can have a body and which attributes can be omitted. Such a description is called a tag library descriptor (TLD).

3. In the JSP pages, tell Tomcat that the pages need your tag library and specify the prefix that you want to identify those custom tags with.

• Bodyless Custom Action• <wow:weekday date=“date”/>

Step 1: Define the Tag Handler• A tag handler for a bodyless custom tag is a class that implements the

interfaces java.io.Serializable and javax.servlet.jsp.tagext.Tag. • Remember that to satisfy an interface, you have to implement all the

methods it defines. • To satisfy Serializable, you only need to define a unique identifier, like

this:

static final long serialVersionUID = 1L;

Step 2: Define the TLD

Step 3: Use the Custom Action

Bodied Custom Actions

Step 1: Define the Tag Handler• Bodied actions need to implement an interface,

javax.servlet.jsp.tagex.BodyTag instead of Tag.• Implement doEndTag method,and doAfterBody

<wow:weekdayBody></wow:weekdayBody>

Step 2: Define the TLD

Step 3: Use the Custom Action

Tag Files• Tag files are special JSP files that replace tag handlers written in Java. • There are three directives: tag, attribute, and variable.

Bodyless Tag

• The tag directive of a tag file replaces the page directive of a JSP page, and the attribute directive lets you define an input parameter. • Another simplification is in sending the result to the output, because

in the tag file the implicit variable out makes it unnecessary to invoke pageContext.getOut().

Bodied Tag

• If you omit the attribute var, doBody sends the body’s result to the output;• If you replace var with varReader, the result is stored as a java.io.Reader

object instead of a java.lang.String; • If you add the attribute scope, you can specify var/varReader to be defined

as a request, session, or application attribute, instead of in the page scope.• Know that jsp:invoke is very similar to jsp:doBody but operates on a JSP

fragment instead of the action body. • For example, by writing the following two lines in a tag file

<%@attribute name="fragName" fragment="true"%><jsp:invoke fragment="fragName"/>

The tag Directive

The attribute Directive

The variable Directive

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