j2ee: Creating Tags [8/27]

A custom tag consists of a tag handler and a tag library descriptor

• Tag handler is a Java class
• Tag Library Descriptor is an XML configuration file

Types:

• Classic tags - Java classes that implement either Tag, BodyTag or IterationTag interfaces.
• Simple Tags -- Java classes that implement SimpleTag or tag extensions created using only JSP syntax instead of Java

To use the tag:

• Import into a page using the taglib directive
• Use the custom tag in a JSP

A custom tag must implement the javax.servlet.jsp.tagext.Tag or javax.servlet.jsp.tagext.SimpleTag interface (which now extends javax.servlet.jsp.tagext.JspTag for organizational purposes

This is usually done by extending a base utility class

• javax.servlet.jsp.tagext.SimpleTag implements JspTag
• javax.servlet.jsp.tagext.TagSupport implements IterationTag, Tag
• javax.servlet.jsp.tagext.BodyTagSupport implements BodyTag, IterationTag, Tag
• IterationTag extends Tag
• BodyTag extends IterationTag

The Tag interface supplies doStartTag() and doEndTag()

BodyTag supplies doInitBody(), setBodyContent()

IterationTag supplies doAfterBody()

TryCatchFinally supplies doCatch(), doFinally() and helps tags manage resources better