Servlets are a key component of Java web development, often forming the backbone of web applications by handling requests and responses. If you’re preparing for a servlet-related interview, knowing the common questions and their answers is essential. Here’s a comprehensive guide to help you get ready.
1. What is a Servlet?
A Servlet is a Java class that runs on a server and processes client requests. It acts as a middle layer between the client and server, typically used to generate dynamic web content. Servlets are part of the Java EE (Enterprise Edition) framework and extend the capabilities of servers hosting web applications.
2. Explain the Servlet Lifecycle.
The servlet lifecycle consists of three main methods:
init(): Called once when the servlet is initialized.service(): Handles client requests. Called every time a request is made.destroy(): Invoked when the servlet is being taken out of service.
These methods are managed by the servlet container.
3. What is the difference between doGet() and doPost()?
doGet(): Handles HTTP GET requests. Used to request data from the server. The data is appended to the URL, making it visible.doPost(): Handles HTTP POST requests. Used to send data to the server. The data is included in the request body, making it more secure.
4. What is the purpose of the web.xml file?
The web.xml file is the deployment descriptor for a servlet-based web application. It is used to:
- Define servlets and their mappings.
- Configure initialization parameters.
- Specify filters, listeners, and other components.
5. How does the servlet container handle multiple requests?
The servlet container creates a single instance of each servlet and uses multiple threads to handle concurrent requests. Each thread executes the service() method independently.
6. What are Filters in Servlets?
Filters are objects that intercept requests and responses. They can:
- Modify request and response objects.
- Perform logging or authentication tasks.
- Implement compression or encryption.
Filters are defined in the web.xml file or through annotations.
7. What is the difference between a Servlet and JSP?
- Servlet: Java code embedded in HTML. Used for dynamic processing but requires more effort to write and maintain.
- JSP: HTML embedded with Java code. Easier to write and preferred for presentation layers.
8. How can you handle sessions in Servlets?
Servlets support session tracking through:
- Cookies
- URL Rewriting
- HttpSession objects
- Hidden form fields
9. What are the advantages of Servlets over CGI?
- Efficiency: Servlets are multithreaded, whereas CGI creates a new process for each request.
- Portability: Servlets run on any server supporting Java.
- Integration: They easily integrate with other Java technologies like JDBC and JSP.
10. What is a RequestDispatcher in Servlets?
A RequestDispatcher is used to forward a request to another resource (e.g., servlet, JSP) or include the content of another resource in the response.
11. Explain the difference between Forward and Redirect.
- Forward: Happens on the server side; the client is unaware of the change.
- Redirect: Happens on the client side; the client’s browser is instructed to make a new request.
12. What is the difference between Context and Config objects?
- ServletContext: Shared across the whole web application, used for global configuration.
- ServletConfig: Specific to a single servlet, used for servlet-specific initialization.
Conclusion
Mastering servlet concepts is crucial for Java web developers. By understanding these questions and their answers, you’ll be well-prepared to impress your interviewer and demonstrate your expertise in servlet development. Good luck!