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Top Servlet Interview Questions(2023)

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A servlet is a server's extension. It's a Java class loaded to increase the server's capabilities. It enhances the functionality of web servers by allowing for dynamic responses and data durability. These are often used with web servers and can be used instead of CGI scripts. A servlet is safe and portable because it operates inside a Java Virtual Machine (JVM) on the server. Servlets can only work within the domain of the server. Java support in the web browser is not required for these.

Top Servlet  Interview Questions.

Sun Microsystems came up with the initial servlet specification. Sun announced the servlet interface, which added Internet functionality to Java. In June 1997, the first draught was completed. With version 2.3, the Java Community Process was used to design the servlet standard. In comparison to the previous CGI, Servlets have a more efficient design.

Must Read: What is Servlet

There are some Servlet Interview Questions that are important and need to be done before an interview. So let us go through some of the Top Servlet Interview questions. 

Most Asked Servlet Interview Questions

Here are some of the important Servlet Interview Questions.

1. What is a Servlet?

A servlet is a small Java program that runs on a Web server. Servlets take requests from Web clients and respond to them, most typically via HTTP (HyperText Transfer Protocol). Servlets can also take advantage of a library of HTTP-specific calls, as well as all of the features of the mature Java language, such as portability, performance, reusability, and crash protection. Servlets are commonly used in browsers to provide users extensive interaction features (clicking link, form submission, etc.)

2. Explain the life cycle of a servlet.

A servlet goes through four stages of the life cycle: loading, initializing, request handling, and destroying. 

  • Initially, the client will send the request to the server using the browser. 
  • Then, the server will accept the request and send it to the required servlet container. Servlet container has other names like servlet engine or web container. It handles the life cycle of the servlet. 
  • The Servlet container tries to understand the URL of the request and makes a call to the specific container. 
  • After the call, it starts a thread to run the servlet. If the same servlet receives several requests, only one thread will be started for each request. 
  • After communicating with the database or carrying out any other actions, the servlet processes the request object, prepares the response object, and then delivers the response object back to the web server. 
  • Finally, the server will send back the response to the client or the browser, and once it has fulfilled its duty, it calls the destroy() method and it releases all the inferences of the servlet instance.

3. How many objects of a servlet are created?

At the time of the first servlet or web container request, there is just one object.

4. How do you write a servlet that is part of a web application?

Follow these steps to create a servlet for a web application:

Create a Java class that extends javax.servlet.http.HttpServlet
Import all the classes from servlet.jar (or servlet-api.jar). 

5. Name some of the advantages of Servlets?

In comparison to other approaches, servlets provide several advantages. To name a few, there are power, integration, efficiency, safety, portability, endurance, elegance, extensibility, and adaptability. Servlets have the following advantages:

  • A Servlet helps edit normal HTML.
  • The servlet code can be written in the JSP.
  • Java's multithreading functionality is included in servlets.
  • Exception handling can be utilized.
  • In the application, Servlets contain a separate layer of business logic.
  • It's simple for developers to display and process data.
  • Servlets make it easy to make changes to HTML pages.
  • In the application, Servlets contain a separate layer of business logic.
  • Servlets have all of the benefits of Java-style multithreading, exception handling, etc.

6. Explain the Servlet API.

In contrast to a typical Java application, a servlet, like an applet, does not contain a main() function. The server uses some servlet methods to handle requests. Whenever the server sends a request to a servlet, it calls the service() method.

A common servlet's service() method must be overridden to handle requests that are appropriate for the servlet. The request object and the response object are two parameters that the service() function accepts. The request object is used to notify the servlet of the request, and the response object is used to respond to the request.
On the other hand, an HTTP servlet does not usually override the service() method. However, it overrides the doGet() and doPost() functions to handle GET and POST requests, respectively. An HTTP servlet can override either or both of these methods, depending on the requests it must handle.

7. Explain the difference between the Get and Post method.

The main difference is that the GET method requests some data from a particular resource. And the POST method sends the data to the server to create or upgrade a resource. The GET method can only send limited data, while the POST method can send huge amounts of data.

8. Who is in charge of creating the servlet object?

The web container, also known as the servlet container, is responsible for creating the servlet objects.

9. When is the servlet object created?

The servlet object is generated when the first request is made. 

10. What is the difference between PrintWriter and ServletOutputStream?

ServletOutputStream is a byte-stream class, whereas PrintWriter is a character-stream class. Only character-based information may be written with the PrintWriter class, whereas the ServletOutputStream class can write both primitive values and character-based information. 

11. What is the RequestDispatcher Interface's purpose?

The RequestDispacher interface allows you to send a request to another resource, such as HTML, servlet, or JSP. The content of another resource can also be included with this interceptor.

12. What do you mean by Servlet chaining?

When one servlet's output is piped into the input of other servlets, and that servlet's output is piped into the input of yet some other servlet, and so on, this is known as servlet chaining. The incoming request can be changed or extended by each servlet in the pipeline. The response is returned to the browser by the last servlet in the servlet chain. Each servlet's output is supplied as an input to the middle servlet, allowing each servlet in the chain to update or extend the content.

13. In servlets, what do you mean by 'filtering'?

In most cases, a succession of servlets for an incoming request can be initiated in one of two ways. The server bound to the URLs should be treated with the defined chain in the first scenario. The other option is to tell the server to send all of the output from a certain piece of content through a specific servlet before returning it to the client. A series is effectively built on the fly. When a servlet transforms one sort of content into another, this is referred to as filtering.

14. What is Session Tracking?

The term "session" merely refers to a certain period of time.

Session Tracking is a mechanism to keep track of a user's state. The HTTP protocol is a stateless protocol, which means that each time a user sends a request to the server, the server treats it as a new request. As a result, we need to keep track of a user's state in order to recognize that user.

15. What are Cookies?

A cookie is a little bit of data that is stored in the browser between client requests. A cookie is made up of a name, a single value, and optional features like a comment, path and domain qualifiers, a maximum age, and a version number.

16. Explain the difference between Cookies and HttpSession?

While both of them are used to store data across multiple web pages, the main difference between the two is that cookies are used to store data on the client side (the browser), and sessions are stored on the server side. Cookies are bound to expire after the user-specifier timeline, and sessions are dependent on cookies.

17. What do you mean by Servlet Reloading?

Although servlet reloading appears to be a simple function, it's actually quite a trick—and it necessitates quite a hack. ClassLoader objects are designed to load a class just once. Servers utilize custom class loaders to overcome this limitation and load servlets numerous times. These custom class loaders use the default servlets directory to load servlets.
Before sending a request to a servlet, the server checks to see if the servlet's class file has changed on the disc. If the change occurs, the server discards the class that the loader used to load the previous version and instead loads the new version with a new instance of the custom class loader. Older servlet versions can be kept in memory indefinitely, but they are no longer used to handle requests.

18. What methods may a servlet utilize to retrieve information about the server?

Four alternative approaches can be used to learn about a servlet's server. The ServletRequest object is used to call two of these methods. The servlet receives these parameters. The ServletContext object is used to invoke the other two. The servlet is running in these. 

19. How can we take any action during the deployment of the project?

With the help of the ServletContextListener interface, we can take any action during the deployment of the project. 

20. How does Background Processing take place in servlets?

Servlets are capable of more than merely persisting between requests. They can even run in the middle of accesses. Even after the response has been received, a thread initiated by a servlet can continue to execute. This capability is especially beneficial for jobs that take a long time to complete and whose incremental results should be shared with several clients. A background thread that was created in init() continues to work in the background. With doGet(), it also conducts request-handling threads and displays the current status. 

21. What is load-on-startup in servlet?

The load-on-startup servlet element in web.xml is used to load the servlet when the project is deployed or the server is started. As a result, it reduces the time it takes to respond to the first request. 

22. What is a war file?

The web elements are specified in a war (web archive) file. A war file can be created from a servlet or JSP project. Because each servlet project is merged into a single file, moving it from one location to another will be quick.

23. Can you call a jsp from the servlet?

Yes, we can call a jsp from the servlet. We can achieve it with the functionality of standard javax.servlet.RequestDispatcher interface. We can also do it through jsp:include(includes contents of starting and destination web components) and jsp:forward(includes content of destination web component) action tags.

24. Explain the Single-Thread Model in servlets.

For each registered name of the servlet, it is normal to have a separate servlet instance. Instead, a servlet can choose to create a pool of instances for each of its names that all share the duty of handling requests. The javax.servlet.SingleThreadModel interface is implemented by these servlets to signal this activity.

A server loading the SingleThreadModel servlet should ensure that "no two threads will execute concurrently the service method of that servlet," according to the Servlet API documentation. To accomplish this, each thread makes use of a free servlet instance from the pool. As a result, any servlet that uses the SingleThreadModel is thread-safe because it doesn't need to synchronize use to its instance variables. 

25. What do you mean by Servlet Manipulation?

Servlet manipulation occurs when one servlet accesses the loaded servlets on its server. It can also perform a task on one or more of them if desired. The ServletContext object provides information about other servlets to a servlet. To get a specific servlet, we use getServlet():

public Servlet ServletContext.getServlet(String name) throws ServletException

26. What are the reasons for using inter-servlet communication?

The inter-servlet communication is used for three main reasons:

  • Direct servlet manipulation
  • Servlet reuse
  • Servlet collaboration

27. What is servlet collaboration?

A servlet collaboration is mainly an exchange of information between servlets of a specific Java web application. This makes it possible to pass or share information from one servlet to another via method invocations, HttpServletResponse object, or RequestDispatcher interface.

28. Explain the difference between forward() method and sendRedirect() method?

The main difference between the two is that the forward() method gets executed on the server side that is not visible to the client while, sendRedirect() method gets executed on the client side which is visible to the server. Also, the forward() method is faster. While, sendRedirect() is slow due to extra network trips because it is useful when the request gets transferred to some other resource on a different server.

29. What's the difference between an HTTP Servlet and a Generic Servlet?

The fact that both Generic Servlet and HTTP Servlet are Abstract Classes is a common trait. They do, however, have certain differences, which are explained below.

Generic Servlet

HTTP Servlet

Protocol IndependentProtocol Specific
Belongs to javax.servlet packageBelongs to javax.servlet.http package
supports only service() method supports doGet(), doPost(), doHead() methods

30. What is the workflow of a servlet? 

A Servlet is a Java utility for developing Java Web Applications. It is a server-side component that aids in generating dynamic web pages by acting as a conduit between the incoming HTTP request from the browser and the database. Servlet is a server-side programming language that is resilient.


31. Can you create a Deadlock condition on a servlet?

Yes, a deadlock condition can be formed on a servlet by calling the doPost() method inside the doGet() method or by calling the doGet() method inside the doPost() method.

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