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UNIT - 3 SERVLETS

1. LIFE CYCLE OF SERVLETS (Do it yourself)

2. SERVLETCONTEXT AND SERVLETCONFING INTERFACE

3. EXPLORING SESSION TRACKING MECHANISMS

4.ADVANTAGES AND DISADVANTAGES OF SERVLET

2. ServletContext and ServletConfig Interfaces

ServletConfig:

• Provides configuration information specific to a single servlet.
• Set up in the servlet deployment descriptor (web.xml).

Key Methods:

1. String getServletName(): Returns the name of the servlet.
2. String getInitParameter(String name): Retrieves initialization parameters.
3. ServletContext getServletContext(): Provides access to the ServletContext.

Example:

public void init(ServletConfig config) {
    String paramValue = config.getInitParameter("myParam");
    System.out.println("Initialization parameter value: " + paramValue);
}

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ServletContext:

• Represents the entire web application.
• Used for application-wide settings or resources shared by all servlets.

Key Methods:

1. String getInitParameter(String name): Retrieves context initialization parameters.
2. Object getAttribute(String name): Accesses attributes shared across servlets.
3. void setAttribute(String name, Object value): Sets shared attributes.

Example:

ServletContext context = getServletConfig().getServletContext();
context.setAttribute("sharedData", "This is shared");



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3. Exploring Session Tracking Mechanisms

Session tracking is the process of maintaining a user’s state across multiple requests. Servlet API provides several mechanisms for this:

1. Cookies:

• Stores session information on the client side.
• Sent with each HTTP request.
• Simple to use but can be disabled by the user.

Example:

Cookie cookie = new Cookie("sessionID", "12345");
response.addCookie(cookie);

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2. URL Rewriting:

• Embeds session data as a query string in the URL.
• Useful when cookies are disabled.

Example:

String url = response.encodeURL("welcomePage.jsp");

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3. Hidden Form Fields:

• Passes session data using hidden fields in HTML forms.
• Requires forms for every interaction.

Example:

<input type="hidden" name="sessionID" value="12345">

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4. HTTP Session (Recommended):

• Managed by the servlet container.
• Stores session data on the server side.

Key Methods:

• HttpSession session = request.getSession();
• session.setAttribute("user", "John");
• String user = (String) session.getAttribute("user");

Example:

HttpSession session = request.getSession();
session.setAttribute("username", "JohnDoe");



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4. Advantages and Disadvantages of Servlets

Advantages:

1. Platform Independence:

   • Written in Java, servlets are platform-independent.

2. Efficiency:

   • Servlets are faster than CGI as they don’t create a new process for each request.

3. Rich API:

   • Provides extensive APIs for handling requests, sessions, cookies, and more.

4. Scalability:

   • Handles multiple requests using a single servlet instance with multithreading.

5. Integration:

   • Easily integrates with other Java-based technologies like JSP, EJB, and frameworks.

6. Robustness:

   • Strong exception handling and type safety due to Java.

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Disadvantages:

1. Complexity:

   • Managing presentation and business logic in servlets can become cumbersome.

2. Thread Safety:

   • Must handle multithreading carefully, as multiple threads access the same servlet instance.

3. Limited to Java:

   • Requires knowledge of Java, restricting non-Java developers.

4. Verbose Code:

• Writing HTML in servlets is cumbersome compared to JSP or modern frameworks.

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CH 4 IMP