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Posted to user@geronimo.apache.org by Krishnakumar B <ww...@gmail.com> on 2005/09/13 05:38:32 UTC

Static Variables and ClassLoaders

Hi,

I have a doubt related to usage of Static Variables.

"Static Variables are scoped in the class they r defined. So if a
class is loaded by more than one classloader in same JVM then there
will be multiple copies within same JVM"

How do i used Config Id/Parent Id to ensure that 2 plans use the same
ClassLoader so that i get a single instance of static variable.

Regards
Krishnakumar B

Re: Static Variables and ClassLoaders

Posted by David Jencks <da...@yahoo.com>.

I think you have found the cause of the problems in your other post :-)

I'm assuming you are using M5/Head.

First, make sure that each jar appears in only one plan as a dependency 
or as a module in an .ear.

Then, locate the plans that contain all the jars you need directly as 
dependencies or as parents.

Pick one, and use it's configId as the parentId attribute of your plan.

Include the others using include elements, which have the same xml form 
as dependency elements:
<include>
     <uri>configuIdURI</uri>
</include>

There's an alternate format that may be convenient if you have your 
configurations in a maven-like repository, see the schema.

For your example in the other post, if the jar containing the hello 
class is in the j2ee application, setting the parentId of your plan to 
the configId of the application and leaving out the dependency element 
should be sufficient.

thanks
david jencks

On Sep 12, 2005, at 8:38 PM, Krishnakumar B wrote:

> Hi,
>
> I have a doubt related to usage of Static Variables.
>
> "Static Variables are scoped in the class they r defined. So if a
> class is loaded by more than one classloader in same JVM then there
> will be multiple copies within same JVM"
>
> How do i used Config Id/Parent Id to ensure that 2 plans use the same
> ClassLoader so that i get a single instance of static variable.
>
> Regards
> Krishnakumar B
>

Re: Static Variables and ClassLoaders

Posted by David Jencks <da...@yahoo.com>.

Hi,
That looks to me as if it should work.  Do you see the log statements 
from starting the gbean?  If you put log statements in your servlet 
when it accesses the static instance which occurs first?  You might try 
logging the classloaders involved and their parentIds.

thanks
david jencks

On Sep 12, 2005, at 11:43 PM, Krishnakumar B wrote:

> Hi,
>
> Thanks for the response. I am not sure if i understood ur answer
> right. I tried the following
>
> GBean Plan Config ID = test/Hello
>
> <?xml version="1.0" encoding="UTF-8"?>
> <configuration
>     xmlns="http://geronimo.apache.org/xml/ns/deployment"
>     configId="test/Hello"
>     parentId="org/apache/geronimo/Server" >
>      <dependency>
>             <uri>test/jars/hellogbean.jar</uri>
>         </dependency>
>     <gbean name="HelloGBean" 
> class="com.ibm.dw.reallybigpet.HelloGBean">
>     </gbean>
> </configuration>
>
> Web Application Plan
>
> <?xml version="1.0" encoding="UTF-8"?>
> <web-app
>     xmlns="http://geronimo.apache.org/xml/ns/web"
>     configId="test/Pet"
>     parentId="test/Hello"
>>
>     <context-root>/</context-root>
>     <context-priority-classloader>false</context-priority-classloader>
> </web-app>
>
> I set the Parent ID of WAR plan  to GBean plan Config ID. I have
> removed the dependency jar in Web Plan.
>
> Still i get a null for static reference created in GBean.
>
> Regards
> Krishnakumar B
>
>
>
> On 9/13/05, Krishnakumar B <ww...@gmail.com> wrote:
>> Hi,
>>
>> I have a doubt related to usage of Static Variables.
>>
>> "Static Variables are scoped in the class they r defined. So if a
>> class is loaded by more than one classloader in same JVM then there
>> will be multiple copies within same JVM"
>>
>> How do i used Config Id/Parent Id to ensure that 2 plans use the same
>> ClassLoader so that i get a single instance of static variable.
>>
>> Regards
>> Krishnakumar B
>>
>

Re: Static Variables and ClassLoaders

Posted by Krishnakumar B <ww...@gmail.com>.

Hi,

Thanks for the response. I am not sure if i understood ur answer
right. I tried the following

GBean Plan Config ID = test/Hello

<?xml version="1.0" encoding="UTF-8"?>
<configuration
    xmlns="http://geronimo.apache.org/xml/ns/deployment"
    configId="test/Hello"
    parentId="org/apache/geronimo/Server" >
     <dependency>
            <uri>test/jars/hellogbean.jar</uri>
        </dependency>
    <gbean name="HelloGBean" class="com.ibm.dw.reallybigpet.HelloGBean">
    </gbean>
</configuration>

Web Application Plan

<?xml version="1.0" encoding="UTF-8"?>
<web-app
    xmlns="http://geronimo.apache.org/xml/ns/web"
    configId="test/Pet"
    parentId="test/Hello"
    >
    <context-root>/</context-root>
    <context-priority-classloader>false</context-priority-classloader>
</web-app>

I set the Parent ID of WAR plan  to GBean plan Config ID. I have
removed the dependency jar in Web Plan.

Still i get a null for static reference created in GBean.

Regards
Krishnakumar B



On 9/13/05, Krishnakumar B <ww...@gmail.com> wrote:
> Hi,
> 
> I have a doubt related to usage of Static Variables.
> 
> "Static Variables are scoped in the class they r defined. So if a
> class is loaded by more than one classloader in same JVM then there
> will be multiple copies within same JVM"
> 
> How do i used Config Id/Parent Id to ensure that 2 plans use the same
> ClassLoader so that i get a single instance of static variable.
> 
> Regards
> Krishnakumar B
>