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I will explain the program code in fragments. The first fragment in Listing 1 shows the import directives necessary to support servlet programming.

Listing 1 - Import directives.
import java.io.*; import javax.servlet.*;import javax.servlet.http.*;

The Servlet interface

All servlets must implement the Servlet interface. You can implement it directly. However, it is more common to implement it indirectly by extending a class that implements the interface (such as HttpServlet ).

The Servlet interface declares methods for managing the servlet and its communications with clients. You will need to override some or all of those methods when you write your servlet.

Listing 2 shows the beginning of the controlling class for the servlet. Note that the servlet class extends HttpServlet . By extending the HttpServlet class, the servlet implements the Servlet interface indirectly.

Listing 2 - Beginning of the class definition.
public class Servlet01 extends HttpServlet{

Request and response objects

Two object references are passed to a servlet when it called by a client:

  • ServletRequest - encapsulates the communication from the client to the server.
  • ServletResponse - encapsulates the communication from the servlet back to the client

Access to these objects can be accomplished in more than one way. This servlet overrides the doGet method, which receives references to the two objects as incoming parameters.

The overridden doGet method

The beginning of the overridden doGet method is shown in Listing 3 .

Listing 3 - Beginning of the overridden doGet method.
public void doGet(HttpServletRequest req, HttpServletResponse res)throws ServletException, IOException{

Note that the doGet method throws an exception of type ServletException . In this servlet, some of the code inside the doGet method also throws an IOException , which is not handled inside the method. Thus, it is declared in the method signature.

Browser commands and servlet methods

A Java-enabled server provide a method corresponding to each of the commands that an HTTP client can send to its server. When the server receives a command from the client, the corresponding method is called on the servlet.

As the servlet programmer, you override some or all of those methods to provide the desired behavior.

The doGet method and the HTTP GET command

The doGet method corresponds to the HTTP GET command. If you don't override the method, the default implementation reports an HTTP BAD_REQUEST error when the browser sends a GET command.

Overriding the doGet method to support the GET command also automatically supports the HTTP HEAD command.

(The HEAD command is a GET command that returns no body in the response. It just returns the requested header fields.)

The fundamental purpose of the GET command makes it possible for the client to get something from the server. When you override the doGet method, you should

  • Read data from the request
  • Construct the proper headers in the response
  • Gain access to either the writer or the output stream (depending on whether the material to be returned is text or binary data)
  • Write the response data

Questions & Answers

Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Object-oriented programming (oop) with java. OpenStax CNX. Jun 29, 2016 Download for free at https://legacy.cnx.org/content/col11441/1.201
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