internally the threads are implemented in servlets

During servicing any request the container will create a
thread or will get a thread from a thread pool.

using Threads

For every request servlet container will create a new 
thread and service method is called

depends on the servlets reload properties.

We have to Make a WEB-INF folder and under it classes 
folder. In WEB-INF we have to write web.xml .

Our compled servelet class file should be stored in classes 
folder.

Make a war file using jar & deploy in Web.

The structure of the web app. is
demo[root]
 - all jsps will go her
 - WEB-INF
   - web.xml
   - tld files
   - classes
     - all java class files will go here

Compile all the files and create a war file
copy the war file into Tomcat_root\webapps folder
if you use weblogic or webspehere the deployment will be 
different.

yes

1. doGet() method is used to get information ,while    
doPost() method is used for posting information.
2.doGet() requests can't send large amount of information 
and is limited to 24-255 characters.How ever doPost() 
requests passes all of it's data ,of unlimited length.
3. A doGet() request is appended to the request URL in a 
query string and this allows the exchange is visible to the 
client,where as a doPost() request passes directly over the 
socket connection as part of its HTTP Request body and the 
exchange are invisible to the client.

Actually wonderful answer thank you

do get() is used for passess the information limited amount 
of data.

do post() is used for passess the information.and it send 
unlimited data..it is providing more secure compare 2 do get
() method..

The diff is that inGeneracicServlet we had to implement the 
service()method the GenericServlets service() method is 
declared as abstract.But the Generic Servlet is not 
implementing keeping the HttpSErvers in mind. Methods we 
have in this class are
init()
log()
service()
While implementing the HTTP Servlet the service() method is 
already implemented .service()method of HTTP sevlet is 
declared as protected.the HTTPServlet is  implementing 
keeping the HttpSErvers in mind. Methods we have in this 
class are
doGet(),doDelete(),doPost()

yes we can a mail through mailAPI

NO

we cant use servlets in javascript but we can call a 
servlet by retrieving the form and setting the action as 
the url.
ex:if our html has a from named 'XXX'

 var formName = document.getElementById('XXX');
 var url = contextPath + '/desiredServlet';
 formName.action = url;
 formName.submit();

Yes you can,
  In 
     PrintWriter out=response.getWriter();
     out.println("<script langauage='javaScript'>");
     out.println("your code here");
     out.println("</script>");

JTree is one of component which is used to display the 
items in tree view.

Jtree is a tree wich is used to disply the items in tree 
view.

JTable is a Swing Componenet which is used to show the datas
in table format. It contains many custom models

We can make it like spreadsheet and we can modify the
cells for JTextField, JCheckBox , JComboBox etc., by using
TableCellEditor.

To design an input dialog for Student database
we can make it by simple table by using JTable and
TableModel no need to design dialog with JButton and 
JLabels with Layout

With the JTable class you can display tables of data, 
optionally allowing the user to edit the data. JTable does 
not contain or cache data; it is simply a view of your data.

Components are basically of two types AWT(abstract window 
tool) components and swing components. The swing components 
provide better look and feel and they are light weight 
components compared to awt components. Swing components are 
derived from the javax.swing.* package and they are 
prefixed with 'J'(like JFrame,JButton,JApplet)....applet is 
derived from the package java.applet.*

Border Layout

BorderLayout is the default lay out of contentpane.

Border layout

borderlayout