Servlet Interview Questions and Answers for 10 years experience

1. What is a Servlet?

   • Answer: A Servlet is a Java program that runs on a server and extends the capabilities of servers that host applications accessed by clients over a request-response programming model. It's a component-based technology used to create dynamic web content. Servlets handle client requests, process them, and generate dynamic responses.

2. Explain the lifecycle of a Servlet.

   • Answer: The Servlet lifecycle involves three main phases:
     1. Loading and Instantiation: The servlet container loads the servlet class, creates an instance of it, and initializes it using the `init()` method. This happens only once.
     2. Request Processing: For each incoming request matching the servlet's mapping, the container calls the `service()` method. This method handles the request and generates the response. The `service()` method internally calls methods like `doGet()`, `doPost()`, etc., depending on the HTTP method used.
     3. Destruction: When the servlet container shuts down or the servlet is removed from service, the `destroy()` method is called, allowing the servlet to release resources.

3. What is the difference between doGet() and doPost()?

   • Answer: `doGet()` handles HTTP GET requests, typically used for retrieving data. `doPost()` handles HTTP POST requests, commonly used for submitting data to the server (e.g., form submissions). `doGet()` parameters are visible in the URL, while `doPost()` parameters are sent in the request body.

4. Explain ServletContext.

   • Answer: `ServletContext` provides a way for servlets to communicate with each other and the container. It's an interface that allows access to server-wide information, such as initialization parameters, context attributes, and resource paths. It acts as a central repository for application-level data.

5. What is ServletConfig?

   • Answer: `ServletConfig` provides information about the servlet's configuration, such as initialization parameters defined in the deployment descriptor (web.xml) or annotations. It’s passed to the servlet's `init()` method.

6. How do you handle exceptions in Servlets?

   • Answer: Use try-catch blocks to handle exceptions within the servlet's methods. For more structured exception handling, you can use a `try-catch` block within the `service()` method or use a filter to handle exceptions globally for all requests. You can also use exception mapping in web.xml to map exceptions to specific error pages.

7. What are Servlet filters?

   • Answer: Servlet filters intercept requests before they reach the servlet and responses before they are sent back to the client. They can be used for various purposes, such as logging, security checks (authentication/authorization), compression, or character encoding. Filters are invoked in a chain.

8. What are Servlet listeners?

   • Answer: Servlet listeners are used to respond to events within the servlet context's lifecycle, such as context initialization, context destruction, session creation, session destruction, and attribute changes. They provide a mechanism to perform actions in response to these events.

9. Explain session management in Servlets.

   • Answer: Session management is crucial for tracking a user's interaction with a web application across multiple requests. Servlets use the `HttpSession` object to manage user sessions. Attributes can be stored in the session to maintain state between requests. Session tracking mechanisms include cookies and URL rewriting.

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