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Custom Tag Libraries

- making abbreviations for commonly used JSP fragments

Example JSP page with custom tag: 
<%@ taglib uri="/WEB-INF/tlds/mytags.tld" prefix="my" %>
<my:wrapper style="k00l">
  <b>hello!</b>
</my:wrapper>

Tag Handler code (compile and put in WEB-INF/classes/mytaglib/WrapperTag.class): 
package mytaglib;

import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;
import java.io.*;

public class WrapperTag extends TagSupport {
    private String style;

    public void setStyle(String style) {
        this.style = style;
    }

    public int doStartTag() {
        try {
            JspWriter out = pageContext.getOut();
            if (style.equals("k00l")) {
              out.print("<html><head><title>MyCoolService</title></head><body bgcolor=\"red\">");
            } else {
              // ...
            }
        } catch (IOException e) { System.out.println("Error in WrapperTag: "+e); }
        return EVAL_BODY_INCLUDE;
    }

    public int doEndTag() {
        try {
            JspWriter out = pageContext.getOut();
            out.print("</body></html>");
        } catch (IOException e) { System.out.println("Error in WrapperTag: "+e); }
        return EVAL_PAGE;
    }
}

(See the API.)

Tag Library Descriptor file (put in WEB-INF/tlds/mytags.tld): 
<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE taglib
          PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN"
          "http://java.sun.com/j2ee/dtd/web-jsptaglibrary_1_2.dtd">
<taglib>
  <tlib-version>1.0</tlib-version>
  <jsp-version>1.2</jsp-version>
  <short-name>MyTags</short-name>

  <tag>
    <name>wrapper</name>
    <tag-class>mytaglib.WrapperTag</tag-class>
    <body-content>JSP</body-content>
    <attribute>
      <name>style</name>
      <required>true</required>
    </attribute>
  </tag>

</taglib>

There are lots of free tag libraries!

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