Creating and Using Your Own JSP Tag Library
Java Server Pages (JSP) is a well-established technology for implementing the View layer in web applications using the MVC (Model-View-Controller) pattern. JSP makes it easy to embed HTML and Java logic together, offering a standardized and streamlined approach to building dynamic web interfaces.
JSP also supports custom tag libraries, allowing developers to create reusable components that encapsulate presentation logic. This leads to cleaner, more maintainable code. In this article, we'll explore how to create and use a custom JSP tag library, as well as review the JSP life cycle.
Why Use Custom JSP Tags?
JSP provides standard tags such as <jsp:include> and <jsp:useBean>, but sometimes, application-specific logic needs to be reused across multiple pages. Custom tags help you:
- Encapsulate and reuse complex logic
- Write cleaner JSP pages with less embedded Java code
- Separate business logic from view code more effectively
JSP Life Cycle
Before creating tags, it's important to understand how JSPs work behind the scenes:
- Translation: The JSP file is converted into a servlet source file by the container.
- Compilation: The servlet source is compiled into a class file.
- Initialization: The
jspInit() method is called once for setup.
- Request Processing: For each request,
_jspService() is invoked.
- Destruction: The
jspDestroy() method is called before the servlet is unloaded.
Creating a Custom Tag Library
1. Create a Tag Handler Class
Start by creating a Java class that extends SimpleTagSupport:
package com.example.tags;
import java.io.IOException;
import javax.servlet.jsp.tagext.SimpleTagSupport;
import javax.servlet.jsp.JspWriter;
public class HelloTag extends SimpleTagSupport {
private String name;
public void setName(String name) {
this.name = name;
}
public void doTag() throws IOException {
JspWriter out = getJspContext().getOut();
out.println("Hello, " + name + "!");
}
}
2. Create the TLD File
Create a file called hello.tld in the WEB-INF directory:
<?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>helloTag</short-name>
<uri>http://example.com/hello</uri>
<tag>
<name>greet</name>
<tag-class>com.example.tags.HelloTag</tag-class>
<body-content>empty</body-content>
<attribute>
<name>name</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
</taglib>
3. Use the Tag in a JSP File
<%@ taglib prefix="h" uri="http://example.com/hello" %>
<html>
<body>
<h:greet name="Alice" />
</body>
</html>
Output:
Hello, Alice!
Packaging the Tag Library
To distribute your tag library:
- Compile your Java classes and place them in the correct package structure
- Put the TLD file inside the
META-INF directory of a JAR file
- Place the JAR inside your application's
WEB-INF/lib folder
Benefits of Custom Tags
- Reduce duplication by reusing presentation logic
- Keep JSPs clean and easy to read
- Improve separation between logic and markup
Conclusion
Custom JSP tags allow you to extend the capabilities of JSP pages by hiding complex Java logic behind simple tag interfaces. They're a great way to promote reusability and maintain clean, modular web pages.
Start by creating simple tags, then expand into more advanced tag features as your application grows.
