Java Web development interview questions

* 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.

* 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.

* 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.

* 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.

* 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
SQLWarning warning = stmt.getWarnings();
if (warning != null)
{
while (warning != null)
{
System.out.println("Message: " + warning.getMessage());
System.out.println("SQLState: " + warning.getSQLState());
System.out.print("Vendor error code: ");
System.out.println(warning.getErrorCode());
warning = warning.getNextWarning();
}
}

* How many JSP scripting elements are there and what are they? - There are three scripting language elements: declarations, scriptlets, expressions.

* 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.

* 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 pre-compiled and saves the database the effort of parsing and compiling sql statements everytime a query is run. Each database has its 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.

* 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.

* 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.

Java Web development interview questions

Database, Networking, Java interview questions

* 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.

* 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.

* 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.

* 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.

* 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
SQLWarning warning = stmt.getWarnings();
if (warning != null)
{
while (warning != null)
{
System.out.println("Message: " + warning.getMessage());
System.out.println("SQLState: " + warning.getSQLState());
System.out.print("Vendor error code: ");
System.out.println(warning.getErrorCode());
warning = warning.getNextWarning();
}
}

* How many JSP scripting elements are there and what are they? - There are three scripting language elements: declarations, scriptlets, expressions.

* 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.

* 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 pre-compiled and saves the database the effort of parsing and compiling sql statements everytime a query is run. Each database has its 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.

* 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.

* 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.

Job Questions for Java Servlet

1. What is the servlet?

2. What are the JSP atrributes?

3. What is the need of super.init(config) in servlets?

4. How to know whether we have to use jsp or servlet in our project?

5. Can we call destroy() method on servlets from service method?

6. What is the Servlet Interface?

7. What is the difference between GenericServlet and HttpServlet?

8. How we can check in particular page the session will be alive or not?

9. What is the importance of deployment descriptor in servlet?

10. When we increase the buffer size in our project using page directive attribute ‘buffer’ what changes we observe?

11. What is the difference between ServetConfig and ServletContext..?

12. When a servlet accepts a call from a client, it receives two objects. What are they?

13. What are the differences between GET and POST service methods?

14. In which conditions we have to use the ServletContext?

15. What methods will be called in which order?((i.e)service(),doget(),dopost())

16. Servlet is Java class. Then why there is no constructor in Servlet? Can we write the constructor in Servlet

17. What is the use of ServletConfig and ServletContext..?

18. What information that the ServletRequest interface allows the servlet access to?

19. What is the difference between ServletContext and ServletConfig?

20. When do you have action=get?

21. What is a Singleton class. How do you write it?

22. What is difference between sendRedirect() and forward()..? Which one is faster then other and which works on server?

23. What information that the ServletResponse interface gives the servlet methods for replying to the client?

24. Can I invoke a JSP error page from a servlet?

25. Can a init(ServletConfig config) method be overrided in servlets?

26. How many ServletConfig and servlet context objects are present in one application?

27. Do we have a constructor in servlet? can we explictly provide a constructor in servlet programme as in java program?

28. What are the uses of Servlets?

29. Can I just abort processing a JSP?

30. Is servlet is used to create a dynamic webpage or Static webpage or both?

31. If you want a servlet to take the same action for both GET and POST request, what should you do?

32. What is the difference between JSP and SERVLETS?

33. What are the advantages using servlets than using CGI?

34. What is a better approach for enabling thread-safe servlets and JSPs? SingleThreadModel Interface or synchronization?

35. We have two applications in that we have two servlets each.How they(servlets) communicate with each other?

36. How the server will know (i.e) when it can invoke init, service,destroy methods of servlet life cycle?

37. How to communicate between two servlets?

38. What is the difference between servlets and applets?

39. How will u pass the argument from one servlet to another servlet?

40. What method used to add a jsp to the servlet?

41. How HTTP Servlet handles client requests?

42. How to get one Servlet’s Context Information in another Servlet?

43. Difference between single thread and multi thread model servlet

44. What is the super class of All servlets?

45. How are Servlet Applet communication achieved?

46. What is servlet context and what it takes actually as parameters?

47. What is the servlet life cycle?

48. Types of Servlets?

49. Why is that we deploy servlets in a webserver.What exactly is a webserver?

50. Which code line must be set before any of the lines that use the PrintWriter?