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JSP custom tags

JSP (JavaServer Pages) custom tags allow developers to create their own custom tags to encapsulate complex functionality and make JSP code more modular, readable, and maintainable. Custom tags can be used to hide complex business logic, simplify page design, or provide a higher level of abstraction for reusable components.

Here's an example of how to create and use a simple custom tag in JSP:

  • Define the tag in a tag library descriptor (TLD) file, which is an XML file that describes the tag and its attributes:
xml
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<taglib xmlns="http://java.sun.com/xml/ns/j2ee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee web-jsptaglibrary_2_0.xsd"
    version="2.0">
    <tlib-version>1.0</tlib-version>
    <short-name>mytags</short-name>
    <uri>http://example.com/mytags</uri>

    <tag>
        <name>mytag</name>
        <tag-class>com.example.MyTag</tag-class>
        <body-content>JSP</body-content>
        <attribute>
            <name>name</name>
            <required>true</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
    </tag>
</taglib>

In this example, the TLD file defines a custom tag called mytag with a required attribute called name. The tag-class attribute specifies the Java class that implements the tag logic.

  • Implement the tag logic in a Java class:
java
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package com.example;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;

public class MyTag extends TagSupport {
    private String name;

    public void setName(String name) {
        this.name = name;
    }

    public int doStartTag() throws JspException {
        try {
            pageContext.getOut().print("Hello, " + name + "!");
        } catch (Exception e) {
            throw new JspException(e);
        }
        return SKIP_BODY;
    }
}

In this example, the MyTag class extends TagSupport and overrides the doStartTag method to print a greeting message to the JSP output stream using the name attribute.

  • Use the custom tag in a JSP page:
jsp
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<%@ taglib prefix="my" uri="http://example.com/mytags" %>

<my:mytag name="John" />

In this example, the JSP page includes the custom tag library using the taglib directive, and then uses the mytag tag to output a greeting message to the client with the name attribute set to "John".

Custom tags can be used to encapsulate more complex logic, such as generating tables or handling form input, and can include additional custom tag attributes and nested tags. They provide a way to make JSP code more modular, reusable, and easier to maintain, especially for larger applications.



Next: JSP Expression Language

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