Top questions with answers asked in MNC on Advance Java Servlet

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Advanced Java Servlet interview questions along with their answers:

  1. What is a Servlet, and how does it differ from other Java classes?
    • Answer: A Servlet is a Java class that extends the javax.servlet.HttpServlet class and handles HTTP requests and responses on a web server. Servlets are specifically designed for server-side programming and are used to create dynamic web applications. Unlike regular Java classes, Servlets are deployed on a web server (e.g., Apache Tomcat) and are invoked by the server to process client requests.
  2. What are the main life-cycle methods of a Servlet, and what is their purpose?
    • Answer: The main life-cycle methods of a Servlet are:
      • init(): Called by the server when the Servlet is initialized, typically during application startup. It is used to perform one-time initialization tasks, such as loading configuration settings or establishing database connections.
      • service(): Called by the server to handle client requests. It is responsible for processing HTTP requests, generating responses, and dispatching to appropriate methods (e.g., doGet(), doPost()).
      • destroy(): Called by the server when the Servlet is being unloaded, typically during application shutdown. It is used to perform cleanup tasks, such as releasing resources or closing database connections.
  3. What is the difference between doGet() and doPost() methods in Servlets?
    • Answer:
      • doGet(): Handles HTTP GET requests sent by clients. It is typically used for requests that retrieve data from the server without modifying it. Data is appended to the URL as query parameters.
      • doPost(): Handles HTTP POST requests sent by clients. It is typically used for requests that submit data to the server for processing, such as form submissions or API calls. Data is sent in the request body, which can be of any size.
  4. How can you pass data between Servlets in a web application?
    • Answer: There are several ways to pass data between Servlets:
      • Request Attributes: Set data as request attributes using request.setAttribute() method and retrieve it in another Servlet using request.getAttribute().
      • Session Attributes: Store data in the HTTP session using session.setAttribute() method and retrieve it in another Servlet using session.getAttribute().
      • URL Rewriting: Append data as query parameters to URLs and extract them in another Servlet using request.getParameter().
      • Cookies: Store data in cookies using response.addCookie() method and retrieve it in another Servlet using request.getCookies().
  5. What is Servlet mapping, and how is it configured in a web application?
    • Answer: Servlet mapping is the process of associating a Servlet with a URL pattern, so that when a client sends a request to that URL, the Servlet is invoked to handle the request. Servlet mapping can be configured using:
      • Web Deployment Descriptor (web.xml): Define <servlet> and <servlet-mapping> elements in the web.xml file to map Servlet classes to URL patterns.
      • Annotation-Based Mapping: Use @WebServlet annotation to specify the URL pattern directly in the Servlet class file, without the need for web.xml configuration. For example:

      java

      @WebServlet("/example")
      public class ExampleServlet extends HttpServlet {
      // Servlet code here
      }