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Servlet Interview Questions and Answers


What is Servlet?
A servlet is a Java technology-based Web component, managed by a container called servlet container or servlet engine, that generates dynamic content and interacts with web clients via a request\/response paradigm.

Why is Servlet so popular?
Because servlets are platform-independent Java classes that are compiled to platform-neutral byte code that can be loaded dynamically into and run by a Java technology-enabled Web server.

What is servlet container?
The servlet container is a part of a Web server or application server that provides the network services over which requests and responses are sent, decodes MIME-based requests, and formats MIME-based responses. A servlet container also contains and manages servlets through their lifecycle.

When a client request is sent to the servlet container, how does the container choose which servlet to invoke?
The servlet container determines which servlet to invoke based on the configuration of its servlets, and calls it with objects representing the request and response.

If a servlet is not properly initialized, what exception may be thrown?
During initialization or service of a request, the servlet instance can throw an UnavailableException or a ServletException.

Given the request path below, which are context path, servlet path and path info?
/bookstore/education/index.html

context path: /bookstore
servlet path: /education
path info: /index.html

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.

When using servlets to build the HTML, you build a DOCTYPE line, why do you do that?

[_private/tble_firefox.htm]

I know all major browsers ignore it even though the HTML 3.2 and 4.0 specifications require it. But building a DOCTYPE line tells HTML validators which version of HTML you are using so they know which specification to check your document against. These validators are valuable debugging services, helping you catch HTML syntax errors.

What is new in ServletRequest interface ? (Servlet 2.4)
The following methods have been added to ServletRequest 2.4 version:
public int getRemotePort()
public java.lang.String getLocalName()
public java.lang.String getLocalAddr()
public int getLocalPort()

Request parameter How to find whether a parameter exists in the request object?
1.boolean hasFoo = !(request.getParameter("foo") == null || request.getParameter("foo").equals(""));
2. boolean hasParameter = request.getParameterMap().contains(theParameter);
(which works in Servlet 2.3+)

How can I send user authentication information while making URL Connection?
You'll want to use HttpURLConnection.setRequestProperty and set all the appropriate headers to HTTP authorization.

Can we use the constructor, instead of init(), to initialize servlet?
Yes , of course you can use the constructor instead of init(). There's nothing to stop you. But you shouldn't. The original reason for init() was that ancient versions of Java couldn't dynamically invoke constructors with arguments, so there was no way to give the constructur a ServletConfig. That no longer applies, but servlet containers still will only call your no-arg constructor. So you won't have access to a ServletConfig or ServletContext.

How can a servlet refresh automatically if some new data has entered the database?
You can use a client-side Refresh or Server Push

The code in a finally clause will never fail to execute, right?
Using System.exit(1); in try block will not allow finally code to execute.

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