Experienced / Expert level questions
Experienced / Expert level questions & answers
Ques 1. Why are JSP pages the preferred API for creating a web-based client program?
Because no plug-ins or security policy files are needed on the client systems(applet does). Also, JSP pages enable cleaner and more module application design because they provide a way to separate applications programming from web page design. This means personnel involved in web page design do not need to understand Java programming language syntax to do their jobs.
Ques 2. 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.
Ques 3. How can a servlet refresh automatically if some new data has entered the database?
You can use a client-side Refresh or Server Push.
Ques 4. Is JSP technology extensible?
YES. JSP technology is extensible through the development of custom actions, or tags, which are encapsulated in tag libraries.
Ques 5. What is the ResourceBundle class in JSP?
The ResourceBundle class is used to store locale-specific resources that can be loaded by a program to tailor the program's appearance to the particular locale in which it is being run.
Ques 6. How can a servlet refresh automatically if some new data has entered the database?
You can use a client-side Refresh or Server Push.
Ques 7. 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.
Ques 8. In the Servlet 2.4 specification SingleThreadModel has been deprecated, why?
Because it is not practical to have such model. Whether you set isThreadSafe to true or false, you should take care of concurrent client requests to the JSP page by synchronizing access to any shared objects defined at the page level.
Ques 9. How do I include static files within a JSP page?
Static resources should always be included using the JSP include directive. This way, the inclusion is performed just once during the translation phase. Do note that you should always supply a relative URL for the file attribute. Although you can also include static resources using the action, this is not advisable as the inclusion is then performed for each and every request.
Ques 10. Why does JComponent have add() and remove() methods but Component does not? because JComponent is a subclass of Container, and can contain other components and jcomponents. How can I implement a thread-safe JSP page?
You can make your JSPs thread-safe by having them implement the SingleThreadModel interface. This is done by adding the directive
<%@ page isThreadSafe="false" % > within your JSP page.
Ques 11. How can I enable session tracking for JSP pages if the browser has disabled cookies?
We know that session tracking uses cookies by default to associate a session identifier with a unique user. If the browser does not support cookies, or if cookies are disabled, you can still enable session tracking using URL rewriting. URL rewriting essentially includes the session ID within the link itself as a name/value pair.
However, for this to be effective, you need to append the session ID for each and every link that is part of your servlet response. Adding the session ID to a link is greatly simplified by means of of a couple of methods: response.encodeURL() associates a session ID with a given URL, and if you are using redirection, response.encodeRedirectURL() can be used by giving the redirected URL as input.
Both encodeURL() and encodeRedirectedURL() first determine whether cookies are supported by the browser; if so, the input URL is returned unchanged since the session ID will be persisted as a cookie. Consider the following example, in which two JSP files, say hello1.jsp and hello2.jsp, interact with each other.
Ques 12. How do I prevent the output of my JSP or Servlet pages from being cached by the browser?
You will need to set the appropriate HTTP header attributes to prevent the dynamic content output by the JSP page from being cached by the browser. Just execute the following scriptlet at the beginning of your JSP pages to prevent them from being cached at the browser. You need both the statements to take care of some of the older browser versions.
Ques 13. How do you restrict page errors display in the JSP page?
You first set "Errorpage" attribute of PAGE directory to the name of the error page (ie Errorpage="error.jsp")in your jsp page .Then in the error jsp page set "isErrorpage=TRUE". When an error occur in your jsp page it will automatically call the error page.
Ques 14. What is JSP Compiler and where are compiled JSP Java files?
JSP are automatically compiled at runtime.
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