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Monday, February 13, 2006

Interview Questions ::

Difference between resultset and rowset
By using ResultSet, We have to open up the connection untill the fetching of data. But it is not with the case of rowset. because by using the concept of chaceRowset we fetch the record into the memory, close the connection and use the memory for further need.
the ResultSet is closed as soon as the Statement itself is closed, or used to retrieve another ResultSet. Therefore, the pointer that once provided a handle to the query results is no longer valid, and this is where CachedRowSet comes in. Unlike a ResultSet, a CachedRowSet stores all rows obtained from a query in local memory, which can be extremely convenient at times.
How to retrive only IntegerObjects from a vector in which all types of objects are stored ::
The example code may help you out::
Vector v = getDataVector();
//getDataVector() may be some method where you will put all your objects into vector.
int size = v.size();
for(int i = 0 ; i
Object obj = v.elementAt(i);
if( obj instanceof Integer){
//dosomething
}else{
//dosomething else
}
}


What is session tracking ? Session tracking is done to maintain the state, as HTTP is an stateless protocol.
Session tracking can be done in following ways -
1. Cookies.
2. Hidden variables.
3. URL rewriting.
When you use GET, then the data appears in the querystring of the web browser and the data goes in the environmental variable i.e you can only send 255 bytes of data. For ex www.somename.com?name=naim&job=IT
When you use POST, the data goes in the request object and it does not appear in the querystring and you can send any no of data.
What is the difference between Generic servlet and HTTPServlet HttpServlet is used to handle only http request & response but whereas Generic servlet can be used to handle any type of requests and responses , such as FTP... The other difference which we can fine between both of them is..
A GenericServlet has a service() method aimed to handle requests. HttpServlet extends GenericServlet and adds support for doGet(), doPost(), doHead() methods (HTTP 1.0) plus doPut(), doOptions(), doDelete(), doTrace() methods (HTTP 1.1).
Both these classes are abstract
In servlets, what is the use of sendredirect(),include( ), forward() ?and in applecation level at what scnario they will be used??
When you invoke a forward request, the request is sent to another resource on the server, without the client being informed that a different resource is going to process the request. This process occurs completly with in the web container. When a sendRedirtect method is invoked, it causes the web container to return to the browser indicating that a new URL should be requested. Because the browser issues a completly new request any object that are stored as request attributes before the redirect occurs will be lost. This extra round trip a redirect is slower than forward.
The include action, on the other hand, executes for each client request of the JSP, which means the file is not parsed but included in place. This provides the capability to dynamically change not only the content that you want to include, but also the output of that content. The syntax for the include action is . Note that the flush attribute must always be included (in JSP 1.1) to force a flush of the buffer in the output stream

Types of Servlets?

Servlets must implement the interface javax.servlet.Servlet. There are two main types of servlets:
  • Generic servlets extend javax.servlet.GenericServlet. Generic servlets are protocol independent, meaning that they contain no inherent support for HTTP or any other transport protocol.
  • HTTP servlets extend javax.servlet.HttpServlet. These servlets have built-in support for the HTTP protocol and are much more useful in an Browser environment
::: The Class GenericServlet is the super class of all known servlets. This class is extended by other classes like HttpServlet. The GenericServlet class is protocol independent.

:::: Servlet is used to create a static and dynamic webpage: it also create a static webpage using serverside include. It is .shtml extension,and so servlet is flexible character.

:::
In servlet init() method itself acts as constructor,here initialisation of servlet takes place. so no constructor !

Diff Between Get() & Post ()::

POST request are not idempotent, which means that they are not safely repeatable; and web browsers treat them specially. For example, a browser cannot bookmark or, in some cases, reload a POST request.
On the other hand, GET requests are idempotent, so they can safely be bookmarked, and a browser is free to issue the request repeatedly without necessarily consulting th user.

::> 1.Get method is used to retrive data from the resources.Post method is used to store the data into the resources.2.In Get method data is send via URL.So,the transaction is very fast.In Post method data is send as packets via sockets.So the process is very slow.3.In Get method the query string is limited.Upto 255 chars only we can send.In Post method there is no such limitations.4.Get method Unsecured. Since,any one can see the data in the address bar.Post method is very secure.

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