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UNIT - 4 JAVA SERVER PAGE 

1. ARCHITECTURE OF JSP

2. JSP LIFECYCLE

3. JSP ELEMENTS

4. COMPARE JSP AND SERVLETS

5. FORM AND INPUT ELEMENTS

1. Architecture of JSP (Java Server Pages)

The architecture of JSP is based on the Model-View-Controller (MVC) design pattern and integrates seamlessly with Java Servlets. A JSP page is essentially a servlet that simplifies content generation by allowing embedded HTML with Java code.

Key Components of JSP Architecture

1. Client (Browser):

   • Sends requests to the server (via HTTP) and receives responses.

2. JSP Container:

   • Part of the web server or application server (e.g., Apache Tomcat).
   • Converts JSP pages into servlets and handles their execution.

3. Translation Phase:

   • The JSP engine translates the JSP file into a Java servlet.

4. Compilation Phase:

   • The generated servlet is compiled into bytecode (a .class file).

5. Servlet Execution:

   • The servlet processes requests and generates dynamic responses.

6. Backend (Database/Services):

• JSP interacts with databases, APIs, or other services to fetch or store data.

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2. JSP Lifecycle

The JSP lifecycle describes how a JSP page is executed by the JSP container.

Phases in the JSP Lifecycle:

1. Translation Phase:

   • The JSP page is translated into a servlet.

2. Compilation Phase:

   • The servlet is compiled into a .class file.

3. Initialization (jspInit()):

   • Called once when the servlet is initialized.

4. Request Handling (_jspService()):

   • Handles each client request.
   • The container invokes this method automatically.

5. Destruction (jspDestroy()):

   • Called once when the JSP page is removed from memory.

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Lifecycle Methods

1. jspInit():

   • One-time setup tasks (e.g., resource initialization).
   • Called only once during the JSP's lifecycle.

2. _jspService(HttpServletRequest, HttpServletResponse):

   • Handles client requests.
   • Called every time the JSP page is accessed.

3. jspDestroy():

• Cleanup tasks before the JSP page is unloaded from memory.

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3. JSP Elements

JSP elements enable the embedding of Java code in HTML pages. These include:

1. Directives:

• Provide global information about the JSP page.
• Syntax: <%@ directive attribute="value" %>
• Types:
  • Page Directive: Defines attributes like imports, error pages, etc.

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

  • Include Directive: Includes a static resource.

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

2. Scriptlets:

• Embed Java code within JSP.
• Syntax: <% Java Code %>
• Example:

  jsp
  <% int x = 10; out.println("Value of x: " + x); %>
  

3. Expressions:

• Output dynamic content to the client.
• Syntax: <%= expression %>
• Example:

  jsp
  <p>Current Time: <%= new java.util.Date() %></p>
  

4. Declarations:

• Define methods or variables that can be used in the JSP page.
• Syntax: <%! Java Code %>
• Example:

  jsp
  <%! int square(int x) { return x * x; } %>
  

5. Standard Actions:

• Perform specific tasks like including resources or forwarding requests.
• Syntax: <jsp:action />
• Example:

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

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4. Comparison of JSP and Servlets

Aspect	JSP	Servlets
Definition	A technology for generating dynamic web pages with embedded Java code.	A Java class that processes requests and generates responses.
Ease of Use	Easier to write; combines HTML and Java code.	More verbose; requires embedding HTML in Java code.
Separation of Concerns	Better separation of presentation and logic.	Logic and presentation are tightly coupled.
Compilation	Automatically compiled into a servlet.	Needs to be manually compiled.
Preferred Use	Suitable for view (presentation layer).	Suitable for controller (business logic).
Performance	Slightly slower due to additional translation and compilation steps.	Faster as it's directly a Java class.

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5. Form and Input Elements

Forms and input elements in JSP are used for user data collection and interaction. JSP can process form data submitted via HTML.

HTML Form Elements:

1. <form>:

   • Defines the form.
   • Attributes:
     • method="POST" or method="GET"
     • action="target.jsp"

   Example:

   html
   <form method="POST" action="processForm.jsp">
       <label for="name">Name:</label>
       <input type="text" id="name" name="username">
       <input type="submit" value="Submit">
   </form>
   

2. <input>:

   • Types:
     • text: Single-line text input.
     • password: Obscured text input.
     • radio: Radio buttons.
     • checkbox: Checkboxes.
     • submit: Submit button.

3. <textarea>:

   • Multi-line text input.

   Example:

   html
   <textarea name="message" rows="4" cols="50"></textarea>
   

4. <select>:

   • Dropdown menu.

   Example:

   html
   <select name="gender">
       <option value="male">Male</option>
       <option value="female">Female</option>
   </select>
   

5. <button>:

• Customizable button.

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