Elements and Directives, Action Elements, Creating Custom tags, and Using beans

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1. Elements and Directives in JSP

JSP Directives

Directives are instructions to the JSP container that provide global information about the page or how the page should be processed. They are placed at the top of the JSP page and affect the entire page. There are three main types of directives:

  • Page Directive (<%@ page %>): Used to define properties related to the page (like the content type, language, etc.).

    jsp
    <%@ page language="java" contentType="text/html;charset=UTF-8" %>

    Example attributes:

    • language: The programming language used (typically java).
    • contentType: Defines the MIME type (e.g., text/html).

  • Include Directive (<%@ include %>): Used to include other files (like header, footer, etc.) in the JSP page at compile time.

    jsp
    <%@ include file="header.jsp" %>

  • Taglib Directive (<%@ taglib %>): Used to declare a tag library in the JSP page. Tag libraries provide custom tags for reusability.

    jsp
    <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>

JSP Elements

  • Scripting Elements: These elements allow you to embed Java code within the HTML structure.

    • Scriptlet (<% %>): Contains Java code that is executed when the page is requested.

      jsp
      <% 
    int x = 10;
    out.println("The value of x is " + x);
%>

    • Expression (<%= %>): Used to evaluate an expression and print the result.

      jsp
      <%= "Hello, World!" %>

    • Declaration (<%! %>): Used to declare variables or methods that are part of the JSP class.

      jsp
      <%! 
    private int count = 0;
    public int getCount() {
        return count;
    }
%>

2. Action Elements in JSP

Action elements are used to invoke server-side processing. They help interact with JavaBeans, perform file inclusions, and direct flow to other resources.

  • <jsp:include>: Used to include another resource at request time (runtime).

    jsp
    <jsp:include page="header.jsp" />

  • <jsp:forward>: Used to forward the request to another resource, such as a servlet or JSP page.

    jsp
    <jsp:forward page="anotherPage.jsp" />

  • <jsp:useBean>: Used to declare a JavaBean and make it available to the page.

    jsp
    <jsp:useBean id="user" class="com.example.UserBean" scope="session" />

  • <jsp:setProperty>: Used to set a property of a bean.

    jsp
    <jsp:setProperty name="user" property="username" value="john_doe" />

  • <jsp:getProperty>: Used to get the value of a bean’s property.

    jsp
    <jsp:getProperty name="user" property="username" />

3. Creating Custom Tags in JSP

Custom tags allow you to create reusable components with specialized behavior. JSP provides a tag extension mechanism, called tag libraries, to define custom tags.

Steps to Create Custom Tags: https://beginnersbook.com/2014/01/jsp-custom-tags-with-example-jsp-tutorial/

4. Using Beans in JSP

Beans are Java objects that follow the JavaBeans conventions (e.g., having getter and setter methods). In JSP, beans are often used to encapsulate data and business logic.

Using Beans in JSP:

  • Declare a Bean: Using the <jsp:useBean> tag, you can declare a bean and make it available to the page.

    jsp
    <jsp:useBean id="user" class="com.example.UserBean" scope="session" />

  • Set Property: Use <jsp:setProperty> to set a property of the bean.

    jsp
    <jsp:setProperty name="user" property="username" value="john_doe" />

  • Get Property: Use <jsp:getProperty> to get the value of a property from the bean.

    jsp
    <jsp:getProperty name="user" property="username" />

Example:

java
// UserBean.java (JavaBean)
public class UserBean {
    private String username;
    
    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }
}

jsp
<%@ page contentType="text/html;charset=UTF-8" %>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<jsp:useBean id="user" class="com.example.UserBean" scope="session" />
<jsp:setProperty name="user" property="username" value="john_doe" />

<h1>Welcome, <jsp:getProperty name="user" property="username" />!</h1>

Conclusion:

  • JSP Directives like page, include, and taglib control the overall configuration and behavior of a JSP page.
  • Action Elements such as jsp:useBean, jsp:setProperty, and jsp:getProperty interact with JavaBeans and other resources in JSP.
  • Custom Tags allow you to extend the capabilities of JSP with reusable components by creating tag handlers and defining them in a Tag Library Descriptor (TLD).
  • Using Beans in JSP provides a way to manage and encapsulate data in Java objects that can be accessed, modified, and displayed within the JSP page.

By combining these elements, you can create powerful, dynamic web applications with reusable code and efficient data management.

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