I’ll show you how to:
- Write a Java class for the tag
- Configure a TLD file (Tag Library Descriptor)
- Use your custom tag inside a JSP page
- Pass a parameter (attribute) to the tag
🎯 Goal:
We will create a custom tag <my:greet name="Stanley" />
that outputs:
Hello, Stanley!
🔵 Step 1: Write the Java Class for the Tag
Create a Java class that extends SimpleTagSupport.
File: GreetTag.java
package mytags;
import javax.servlet.jsp.tagext.SimpleTagSupport;
import javax.servlet.jsp.JspWriter;
import java.io.IOException;
public class GreetTag extends SimpleTagSupport {
private String name;
// Setter (for the attribute 'name')
public void setName(String name) {
this.name = name;
}
@Override
public void doTag() throws IOException {
JspWriter out = getJspContext().getOut();
if (name != null) {
out.write("Hello, " + name + "!");
} else {
out.write("Hello, Guest!");
}
}
}
✅ Important:
- The method
setName(String name)is automatically called when you usename="..."in the tag! doTag()defines what the tag will output.
🔵 Step 2: Create a TLD File
Create a TLD (Tag Library Descriptor) file that describes your tag.
File: /WEB-INF/mytags.tld
<?xml version="1.0" encoding="UTF-8" ?>
<taglib xmlns="http://java.sun.com/xml/ns/javaee"
version="2.1">
<tlib-version>1.0</tlib-version>
<short-name>MyTags</short-name>
<uri>http://example.com/mytags</uri>
<tag>
<name>greet</name>
<tag-class>mytags.GreetTag</tag-class>
<body-content>empty</body-content>
<attribute>
<name>name</name>
<required>false</required>
</attribute>
</tag>
</taglib>
✅ Key things:
name: how you will call the tag (greet)tag-class: full class name (including package)attribute name="name": defines the tag’s parameter
🔵 Step 3: Use the Custom Tag in a JSP Page
Now, use your custom tag in a JSP page!
File: greet.jsp
<%@ taglib uri="http://example.com/mytags" prefix="my" %>
<html>
<head><title>Custom Tag Example</title></head>
<body>
<!-- Use our custom tag -->
<my:greet name="Stanley" />
<br>
<!-- Without providing name -->
<my:greet />
</body>
</html>
✅ Output:
Hello, Stanley!
Hello, Guest!
📜 Summary of What We Did:
| Step | What We Created |
|---|---|
| Java Tag Handler | GreetTag.java (the logic) |
| Tag Library Descriptor | mytags.tld (the description) |
| JSP Page | greet.jsp (the usage) |
✅ Now you have your own custom JSP tag working!
📢 Notes:
- You can add multiple attributes by writing more setters in Java (
setXxx()). - You can create tags with a body (using
<jsp:doBody/>) if you need more advanced behavior. - In modern apps, tag files (
.tag) are sometimes used instead of Java classes for simple cases.