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The servlet life cycle

Servlets have a prescribed life cycle. Servers load and run servlets. Servers accept requests from clients, and may use their servlets to return data to the clients.

Servers can also remove servlets. So, the stages of a servlet's life cycle are:

  • The servlet is loaded and initialized.
  • The servlet is used to satisfy client requests.
  • The servlet is removed or unloaded.

A server runs the servlet's init method when it loads the servlet. Most servlets are run in multi-threaded servers. However, there are no concurrency issues during servlet initialization. The server calls the init method when it loads the servlet, and does not call it again unless it is reloading the servlet.

The server cannot reload a servlet until after it has removed the servlet by calling the destroy method. Initialization is allowed to complete before client requests are handled or the servlet is destroyed.

A practical problem

This can be a problem when you are developing a servlet and repeatedly testing it with a server. Once the servlet is initially loaded from the class file, for some servers simply providing a new class file does not cause the server to remove the old version of the servlet and load the new version. (This appears to be the case with the Apache Tomcat server that we will be using for some of these modules.)

With the Apache Tomcat server , you must stop and restart the server to cause it to load the new version of a servlet. (It may be possible to use some feature of the administration tool to force the server to remove an old version and load a new version of a servlet without stopping and restarting the server but I have never investigated thatpossibility.)

The second stage

The second stage in the life of the servlet begins after the servlet has been loaded and initialized. At that point, the server may call upon the servlet to respond to client requests. In so doing, the servlet handles client requests by processing them in its service method, which is called by the server. Normally, the service request from each client is run in a separate thread by the servlet.

Generic versus HTTP servlets

If you are writing a generic servlet, you will probably override the service method. However, if you are writing servlets to be used with HTTP servers, you probably won't need to override service . The service method of the HttpServlet class handles the setup and dispatches the request to methods such as doGet and doPost . When writing HTTP servlets, you will normally extend the HttpServlet class and override the doXXX methods instead of overriding the service method.

Multithreaded operation

Servlets can process requests from multiple clients concurrently in a multithreaded manner. This means that the service methods should be written to be thread safe. One description that I have seen for how to write a thread-safe method is to:

Use the fewest possible number of instance variables, and synchronize access to them if you use them.

Single-threaded operation

In some cases and for some reason known only to you, you may decide to prevent your servlet from processing concurrent client requests. In this case, you should cause your servlet to implement the SingleThreadModel interface. This interface guarantees that no two threads will execute the servlet's service methods concurrently. Implementing the interface does not require writing any extra methods. Merely declaring that the servlet implements the interface is sufficient to prevent the server from making concurrent calls to the service method.

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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