Servlet Interview questions and Answers

The Servlet is a class used in Java applications for enhancing the capabilities of the server. Servlets respond to a request from the browser and return response content and also run on web application server container and are used to generate HTML content that shows on the web browser.

There are two types of servlets - generic and HTTP

Servlert’s life cycle is the entire process from its creation until its destruction. A Servlet follows this path:

• Initialized by calling init( ) method
• Calls service( ) method to process request
• Terminated by destroy( ) method

Finally, the servlet is nothing but the garbage that gets collected by JVM's garbage collector.

CGI or Common Gateway Interface provides dynamic content to users by executing a program that resides in the server. This program processes data to produce dynamic content. Other programs that reside in the server can be written in the native OS such as C++.

Session tracking is a technique that servlets use to maintain a record of a series of requests originating from the same user or the same browser across a period of time. These sessions are shared between the servlets that are accessed by a client.

There are 4 techniques to track sessions:

• Cookies
• Hidden Fields.
• URL Rewriting.
• Session Tracking API.

A filter is an object that filters tasks that are either request to a resource, or response from a resource, or both. Filtering is performed in doFilter method. Filters get configured in deployment descriptor of your application.

RequestDispatcher interface defines an object that can dispatch the request to resources like HTML, JSP, and Servlet, on the server. This interface provides two methods

forward (ServletRequest request, ServletResponse response) will forward a request from Servlet to another resource such as a Servlet, JSP, or HTML, on the server.

Include (ServletRequest request, ServletResponse response) will include the content of a resource such as Servlet, JSP, or HTML, in the response.

Both WAR and JAR have the same file structure of a single file that is compressed and contains multiple files inside it. WAR files combine servlets, JSPs, Java and XML files, JAR libraries, javascript libraries, static web pages, and other resources that are needed to run the applications.

HTTP outlines a set of request methods that indicate the action to be performed for a resource. Each request method implements a different semantic, but they also share some common features. Here are the 7 HTTP request methods every web developer preparing for Servlet interview questions and answers should know:

• GET
• HEAD
• POST
• PUT
• DELETE
• OPTIONS
• PATCH

In order to create a WAR file, use JDK's JAR tool. Use -c switch of jar for creating the war file. Enter the project directory of your project and write this command: jar -cvf projectname.war * Here, -c is for creating file, -v for generating verbose output and -f for specifying name of the archive file.

The SingleThreadModel interface ensures that only one thread is executed at a given point of time in a given servlet service method. This is a marker interface and contains no methods. This interface also ensures thread-safe servlets.

URL Encoding process transforms user input to a Common Gateway Interface (CGI) form. It is fit to travel across the network through stripping spaces, punctuation and replacement with escape characters.

The url-pattern associates a servlet with a set of URLs. When a request from the user arrives, the container uses basic process to match the URL in the request with a URL pattern in the web.xml file. A URL pattern may sometimes contains subsets of US-ASCII characters.

Here are 2 methods for getting client’s IP address in Servlet:

HttpServletRequest.getRemoteAddr method returns IP of the client that sends request.

HttpServletRequestgetRemoteHost method returns the hostname of the client that is sending the request. However, it may return an empty string if hostname is unknown.

Servlet 3.0 is an update of Servlet 2.5. Servlet 3.0 focuses on extensibility and pluggability. Key features in Servlet 3.0 can be categorized into the following areas:

• Easier development with annotations.
• Web application modularity.
• Asynchronous Servlet.
• Programmatic instantiation of Servlets/Filters.
• Security Enhancements.

There are ways of servlet authentication:

• HTTP basic authentication.
• HTTP digest authentication.
• HTTPS client authentication.
• Form-based authentication.

You can invoke a JSP web page from a servlet via the functionality of the popular javax.servlet.RequestDispatcher interface. Complete the following steps in your code to use this mechanism:

• Get a servlet context instance from the servlet instance:
  ServletContext sc = this.getServletContext();
• Get a request dispatcher from the servlet context instance, specifying the page-relative or application-relative course of the goal JSP page as enter to the getRequestDispatcher() method:
  RequestDispatcher rd = sc.getRequestDispatcher("/jsp/mypage.jsp");
  Prior to or in the course of this step, you can optionally make facts on hand to the JSP page thru attributes of the HTTP request object. See the next section, "Passing Data Between a JSP Page and a Servlet", for information.
• Invoke the include() or forward() approach of the request dispatcher, specifying the HTTP request and response objects as arguments. The performance of these techniques is similar to that of jsp:include and jsp:forward actions. The include() approach solely briefly transfers control; execution returns to the invoking servlet afterward.

Servlet 3.0 has introduced javax.servlet.annotation that provides annotation types, which can annotate servlet classes. Annotation also represents metadata. So, if you are using annotation, you may not require deployment descriptor.

Note: This is very essential java servlet interview questions which is asked in every interviews.

Accepting a request from the browser and processing it using multiple servlets in a chain is called Servlet Chaining. In this process, communication occurs between chains of servlets and servlet programs in order to process the client's request. This process may make the user requests visible to multiple servlets.

Note: This is a very important Servlet Interview Questions.