• Client JSP using the taglib
• Tag class definition (HelloTag.java)
• Tag configuration (hello.tld)

Using a taglib

Using a taglib in a JSP file has two steps. First, the JSP needs to define the prefix and the tld (tag library descriptor) for the tag.

Normally, JSP copies bytes from the .jsp to the browser without interpreting it. The taglib directive tells the JSP engine to treat elements starting with the prefix as JSP extension tags.

<%@ taglib prefix="ct" uri="WEB-INF/hello.tld" %>
Message: <ct:hello/>

Message: hello, world

Defining the tag

Many simple tags can just extend TagSupport. The hello tag implements doStartTag. When the hello tag starts, the JSP will execute doStartTag. In this case, it'll print "hello, world".

Since the content of the hello tag doesn't matter, HelloTag returns SKIP_BODY. Empty tags will generally return SKIP_BODY.

package test;

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

public class HelloTag extends TagSupport  {
  public int doStartTag() throws JspException
  {
    try {
      pageContext.getOut().println("hello, world");
    } catch (IOException e) {
    }
    
    return SKIP_BODY;
  }
}

Configuring the tag

Finally, you need to configure the tag in a .tld (tag library descriptor) file. The .tld matches the tag name hello with the tag class test.HelloTag.

<taglib>
  <tag>
    <name>hello</name>
    <tagclass>test.HelloTag</tagclass>
  </tag>
</taglib>

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