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From "Shapira, Yoav" <Yoav.Shap...@mpi.com>
Subject RE: servlets
Date Tue, 28 Jan 2003 21:23:39 GMT
Howdy,
Tomcat won't touch your singleton at all.  All your servlets will call getInstance() on the
singleton.  The constructor for the singleton is private, and the getInstance() method looks
like:

private static MySingleton theInstance;

public static synchronized MySingleton getInstance() {
  if(theInstance == null) {
     theInstance = new MySingleton();
  }

  return theInstance;
}

That way no matter how many servlet instances the container spawns, and no matter how many
of them call getInstance() at the same time, you will only have one instance of your singleton.

Yoav Shapira
Millennium ChemInformatics


>-----Original Message-----
>From: Felipe Schnack [mailto:felipes@ritterdosreis.br]
>Sent: Tuesday, January 28, 2003 4:19 PM
>To: Tomcat Users List
>Subject: RE: servlets
>
>  yes, I know how to do it (private constructor, etc), but how tomcat
>will call an getInstance() method instead of create a new instance of
>it?
>
>On Tue, 2003-01-28 at 19:13, Shapira, Yoav wrote:
>> Howdy,
>>
>> >  If I write an servlet and DO NOT implement the SingleThreadModel, I
>> >have a guarantee that I'll have only one instance of it?
>>
>> No.
>>
>> >If not, here is
>> >a way to do this?
>>
>> No.
>>
>> If you need only one instance of something, put in in a singleton.  Have
>> your servlets use the singleton.  A google search for "the singleton
>> design pattern java" will yield many explanations and examples.
>>
>> Yoav Shapira
>> Millennium ChemInformatics
>>
>> --
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>--
>
>Felipe Schnack
>Analista de Sistemas
>felipes@ritterdosreis.br
>Cel.: (51)91287530
>Linux Counter #281893
>
>Centro Universitário Ritter dos Reis
>http://www.ritterdosreis.br
>ritter@ritterdosreis.br
>Fone/Fax.: (51)32303341
>
>
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