Web development interview questions
1. 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.
2. How can a servlet refresh automatically if some new data has entered the
database? - You can use a client-side Refresh or Server Push.
3. 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.
4. How many messaging models do JMS provide for and what are they? - JMS
provide for two messaging models, publish-and-subscribe and point-to-point
queuing.
5. What information is needed to create a TCP Socket? - The Local System?s IP
Address and Port Number. And the Remote System’s IPAddress and Port
Number.
6. What Class.forName will do while loading drivers? - It is used to create an
instance of a driver and register it with the DriverManager. When you have
loaded a driver, it is available for making a connection with a DBMS.
7. How to Retrieve Warnings? - SQLWarning objects are a subclass of
SQLException that deal with database access warnings. Warnings do not stop the
execution of an application, as exceptions do; they simply alert the user that
something did not happen as planned. A warning can be reported on a Connection
object, a Statement object (including PreparedStatement and CallableStatement
objects), or a ResultSet object. Each of these classes has a getWarnings method,
which you must invoke in order to see the first warning reported on the calling
object
8. SQLWarning warning = stmt.getWarnings();
9. if (warning != null)
10. {
11. while (warning != null)
12. {
13. System.out.println(“Message: ” + warning.getMessage());
14. System.out.println(“SQLState: ” + warning.getSQLState());
15. System.out.print(“Vendor error code: “);
16. System.out.println(warning.getErrorCode());
17. warning = warning.getNextWarning();
18. }
19. }
20. How many JSP scripting elements are there and what are they? - There are
three scripting language elements: declarations, scriptlets, expressions.
21. In the Servlet 2.4 specification SingleThreadModel has been deprecates,
why? - Because it is not practical to have such model. Whether you set
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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.
22. What are stored procedures? How is it useful? - A stored procedure is a set of
statements/commands which reside in the database. The stored procedure is
precompiled and saves the database the effort of parsing and compiling sql
statements everytime a query is run. Each Database has it’s own stored procedure
language, usually a variant of C with a SQL preproceesor. Newer versions of db’s
support writing stored procedures in Java and Perl too. Before the advent of 3-
tier/n-tier architecture it was pretty common for stored procs to implement the
business logic( A lot of systems still do it). The biggest advantage is of course
speed. Also certain kind of data manipulations are not achieved in SQL. Stored
procs provide a mechanism to do these manipulations. Stored procs are also
useful when you want to do Batch updates/exports/houseKeeping kind of stuff on
the db. The overhead of a JDBC Connection may be significant in these cases.
23. 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. The following example shows
the syntax: 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.
24. 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.
25. 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.
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Posted by sujisridhar2 