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Q.4 Explain different types of JSP tags.

definition

What is JSP?

JSP (JavaServer Pages) is a server-side technology used to create dynamic, platform-independent web applications using Java. It allows embedding Java code directly into HTML pages using special JSP tags.

• JSP files have the .jsp extension.
• They are compiled into Servlets by the web container (like Apache Tomcat).
• It simplifies the development of dynamic web content by separating presentation (HTML) from business logic (Java).

Where is JSP Used?

JSP is mainly used in the presentation layer of web applications. Its typical uses include:

1. Dynamic Web Pages:
   Generate content like user profiles, search results, or dashboards based on user input or database content.
2. Form Handling:
   Collect form data and interact with JavaBeans or databases to process it.
3. Session Management:
   Track user sessions and manage login/logout functionality.
4. Data Display:
   Fetch and display data from a backend (like MySQL) using Java code and custom tags.

1. Directive Tags

• These provide global information about the JSP page to the container.

• Syntax: <%@ directive attribute="value" %>

• Types:

  • Page Directive: Defines page-level settings (e.g., language, errorPage).

    <%@ page language="java" contentType="text/html" %>

  • Include Directive: Includes a file during the translation phase.

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

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2. Declaration Tags

• Used to declare variables and methods that can be used later in the JSP page.
• Syntax: <%! declaration %>
• Example:

<%! int count = 0; %>

<%! public int getCount() { return count++; } %>`

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3. Scriptlet Tags

• Used to write Java code that is executed each time the page is requested.

• Syntax: <% Java code %>

• Example:

  jsp

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  <% int sum = 5 + 10; out.println("Sum: " + sum); %>

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4. Expression Tags

• Used to output the result of Java expressions directly to the client.

• Syntax: <%= expression %>

• Example:

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  <%= new java.util.Date() %>

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5. Action Tags

• Used to control the behavior of the JSP engine.

• Syntax: <jsp:action_name attributes />

• Common action tags:

  • jsp:include – Includes another resource at request time.

    jsp

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

  • jsp:forward – Forwards the request to another resource.

    jsp

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

  • jsp:useBean, jsp:setProperty, jsp:getProperty – For JavaBeans interaction.

    jsp

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    <jsp:useBean id="user" class="com.example.User" scope="session" /> <jsp:setProperty name="user" property="name" value="Alice" /> <jsp:getProperty name="user" property="name" />

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6. Custom Tags

• User-defined tags created using tag libraries.

• Helps in reusing functionality and separating business logic from presentation.

• Requires a tag handler class and a TLD (Tag Library Descriptor) file.

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Summary Table:

Tag Type	Syntax Example	Purpose
Directive	<%@ page language="java" %>	Page-level info
Declaration	<%! int x = 0; %>	Declare variables/methods
Scriptlet	<% int a = 5; %>	Java logic
Expression	<%= a + 10 %>	Output result of expression
Action	<jsp:include page="footer.jsp" />	Built-in actions
Custom	<prefix:tagName />	Reusable user-defined tags