----- Original Message -----
From: "Peters, Jim" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Tuesday, November 13, 2001 2:33 PM
Subject: Utility class and multi-threaded servlets
> I searched the archives for an answer to my question, but did not see one
> posed exactly like mine.
>
> I am developing a multi-threaded servlet app, and have developed a utility
> class (all static methods) that all the servlets use.
> For example:
>
> public class Utility
> {
> public static String convertDouble(double val)
> {
> NumberFormat nf = NumberFormat.getInstance();
> nf.setMaximumFractionDigits(2);
> nf.setMinimumFractionDigits(2);
> return nf.format(val);
> }
> }
>
> The above is used in my servlets by invoking the method in this manner:
>
> String str = Utility.convertDouble(setUp);
>
> My question is this ... Do I have to synchronize the static methods in my
> Utility class ? Will one thread stomp on another one in the event that
> multiple are executing the code at the same time ?
>
> I suspect the answer is yes but I am also worried about all the threads
> waiting for synchronized methods.
>
> Thanks in advance and I apologize if this is too basic for this forum ...
> maybe I'm brain dead today.
>
> Jim Peters
> EDS/Michigan Solution Centre
> 901 Tower Drive, Mail Stop 1084
> Troy, MI 48098
> * 248.265.4637
> * [EMAIL PROTECTED]
>[...]
I also think you don't need to use "synchronized" here(I did a simple test)
when you use "Utility.convertDouble(setUp)" in YourServlet(a multi-thread
enviroment), but one of the reasons I can do it without "synchronized" is
because the implementation of java.text.NumberFormat::getInstance() :
private static NumberFormat getInstance(Locale desiredLocale,
int choice)
{
...
return new DecimalFormat(numberPatterns[choice],
new DecimalFormatSymbols(desiredLocale));
}
i.e., it returns a new object every time when I invoke getInstance(),
this implementation guarantee the "stateless" property.
another reason is you set nf with the same property/parameter(2):
nf.setMaximumFractionDigits(2);
nf.setMinimumFractionDigits(2);
i.e., you didn't adjust the property of nf according to the
input-parameter "val"
so if you keep other condition(still static...), but(in a worse case):
- you replace NumberFormat with another class
- and the method "getInstance()" of this class is a SingleTon
pattern, or a "recycling/reusing/pool" pattern
- and you set diferent property according the input-parameter, for ex.,
if(val<1.0){
nf.setMaximumFractionDigits(5);
nf.setMinimumFractionDigits(5);
}else{
nf.setMaximumFractionDigits(2);
nf.setMinimumFractionDigits(2);
}
then perhaps:
- sometimes you will get the same object for more than one thread
- and if now those threads have a intermixing action which destroy
the atom-property of the following 3 lines:
1-1 nf.setMaximumFractionDigits(2);
1 -2 nf.setMinimumFractionDigits(2);
2 return nf.format(val);
then the result will be not always right.
Bo
Nov.13, 2001
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