What is filter? Can filter be used as request or response?

Servlet Interview Questions and Answers

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7. What is filter? Can filter be used as request or response?

A filter is a reusable piece of code that can transform the content of HTTP requests,responses, and header information. Filters do not generally create a response or respond to a request as servlets do, rather they modify or adapt the requests for a resource, and modify or adapt responses from a resource.

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Other Interview Questions

• What is Servlet?
• Why is Servlet so popular?
• What is servlet container?
• When a client request is sent to the servlet container, how does the container choose which servlet to invoke?
• If a servlet is not properly initialized, what exception may be thrown?
• Given the request path below, which are context path, servlet path and path info?
• What is filter? Can filter be used as request or response?
• When using servlets to build the HTML, you build a DOCTYPE line, why do you do that?
• What is new in ServletRequest interface?(Servlet 2.4)
• Request parameter How to find whether a parameter exists in the request object?
• How can I send user authentication information while makingURLConnection?
• Can we use the constructor, instead of init(), to initialize servlet?
• How can a servlet refresh automatically if some new data has entered the database?
• The code in a finally clause will never fail to execute, right?
• What mechanisms are used by a Servlet Container to maintain session information?
• Difference between GET and POST
• What is session?
• What is servlet mapping?
• What is servlet context ?
• Which interface must be implemented by all servlets?
• Explain the life cycle of Servlet.
• When is the servlet instance created in the life cycle of servlet? What is the importance of configuring a servlet?
• Why don't we write a constructor in a servlet?
• When we don't write any constructor for the servlet, how does container create an instance of servlet?
• Once the destroy() method is called by the container, will the servlet be immediately destroyed? What happens to the tasks(threads) that the servlet might be executing at that time?
• What is the difference between callling a RequestDispatcher using ServletRequest and ServletContext?
• Why is it that we can't give relative URL's when using ServletContext.getRequestDispatcher() when we can use the same while calling ServletRequest.getRequestDispatcher()?