<< Chapter < Page Chapter >> Page >

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

What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
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.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Berger describes sociologists as concerned with
Mueller Reply
Got questions? Join the online conversation and get instant answers!
Jobilize.com Reply

Get the best Algebra and trigonometry course in your pocket!

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
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Object-oriented programming (oop) with java' conversation and receive update notifications?