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Posted to users@tomcat.apache.org by pa...@nhs.net on 2008/05/09 12:16:23 UTC
RE: Possible to assign different class loader for each web app with
tomcat
Ok, that's strange because yesterday I had a small problem, and I assumed
that it was due to the same class being loaded on startup by 2 web apps.
I had a url endpoint loaded into a config class on startup from the web.xml,
for some reason no messages were reaching the correct end point. This config
class is also loaded by a test version of the app running under the same
tomcat as pre prod. When the second web app was loaded and its config class
was loaded and the parameter read in from the web.xml it changed the value
for both web apps.
I have not being using java or tomcat for all that long, but I would have
thought if a class loader was assigned for each web app then they would each
have their own copy of the config class? Meaning that web app1 should not
have been pointing at the end point for web app 2? If not then could you
tell me why?
Thanks
-----Original Message-----
From: Mark Thomas [mailto:markt@apache.org]
Sent: 09 May 2008 11:10
To: Tomcat Users List
Subject: Re: Possible to assign different class loader for each web app with
tomcat
paul.ockleford@nhs.net wrote:
> Hi,
>
> Is it possible to configure a separate class loader for each web app
> running under tomcat? A colleague has informed that he can do this
> with web sphere and I am wondering if it is possible with tomcat.
This is the case by default. No configuration is required.
Mark
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RE: Possible to assign different class loader for each web app with
tomcat
Posted by pa...@nhs.net.
Thanks for the replies, I think I understand what is happening now, I think
for safety's sake I will use a separate config file for each web app instead
of trying to share one between them all and load separate copies.
Thank you.
-----Original Message-----
From: Mark Thomas [mailto:markt@apache.org]
Sent: 09 May 2008 13:41
To: Tomcat Users List
Subject: Re: Possible to assign different class loader for each web app with
tomcat
paul.ockleford@nhs.net wrote:
> Ok thanks, it's starting to become clearer now. > The class file is in
> a jar file that lives in tomcat\shared\lib. I am guessing that these
> classes are loaded by a class loader further up the hierarchy
> described in the tomcat docs. I suppose in this instance there would
> only be one class loaded?
Correct. The class would be loaded once but that doesn't prevent multiple
instances of the class being created. However, I suspect the class in
question uses the singleton pattern so there is also only once instance.
This instance will be shared between all webapps.
> I guess if this is the case the only thing confusing me is why this
> class is actually loaded by tomcat when it doesn't have to be? Does
> the <load-on-startup>1</load-on-startup> tag not load a class
> specifically for this web app regardless of where the class file might be?
No. load-on-startup requires Tomcat to load the servlet when the context
starts and the number dictates the order (as per the spec). The class
loaders will be searched in the order described in the docs and the first
instance found of the class will be used.
If (as it appears from your description) you have webapp specific
information being held in a singleton class then you *must* place that class
in WEB-INF/classes or the jar containing it in WEB-INF/lib
shared/lib is for classes that can be safely shared between multiple
webapps. Personally I never used it. It generally caused more problems than
it solved - one of the reasons it is removed by default in 6.0.x onwards.
> Thanks for the help by the way.
No problem.
Mark
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Re: Possible to assign different class loader for each web app with
tomcat
Posted by Mark Thomas <ma...@apache.org>.
paul.ockleford@nhs.net wrote:
> Ok thanks, it's starting to become clearer now. >
> The class file is in a jar file that lives in tomcat\shared\lib. I am
> guessing that these classes are loaded by a class loader further up the
> hierarchy described in the tomcat docs. I suppose in this instance there
> would only be one class loaded?
Correct. The class would be loaded once but that doesn't prevent multiple
instances of the class being created. However, I suspect the class in
question uses the singleton pattern so there is also only once instance.
This instance will be shared between all webapps.
> I guess if this is the case the only thing confusing me is why this class is
> actually loaded by tomcat when it doesn't have to be? Does the
> <load-on-startup>1</load-on-startup> tag not load a class specifically for
> this web app regardless of where the class file might be?
No. load-on-startup requires Tomcat to load the servlet when the context
starts and the number dictates the order (as per the spec). The class
loaders will be searched in the order described in the docs and the first
instance found of the class will be used.
If (as it appears from your description) you have webapp specific
information being held in a singleton class then you *must* place that
class in WEB-INF/classes or the jar containing it in WEB-INF/lib
shared/lib is for classes that can be safely shared between multiple
webapps. Personally I never used it. It generally caused more problems than
it solved - one of the reasons it is removed by default in 6.0.x onwards.
> Thanks for the help by the way.
No problem.
Mark
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RE: Possible to assign different class loader for each web app with
tomcat
Posted by pa...@nhs.net.
Ok thanks, it's starting to become clearer now.
The class file is in a jar file that lives in tomcat\shared\lib. I am
guessing that these classes are loaded by a class loader further up the
hierarchy described in the tomcat docs. I suppose in this instance there
would only be one class loaded?
I guess if this is the case the only thing confusing me is why this class is
actually loaded by tomcat when it doesn't have to be? Does the
<load-on-startup>1</load-on-startup> tag not load a class specifically for
this web app regardless of where the class file might be?
Thanks for the help by the way.
-----Original Message-----
From: Mark Thomas [mailto:markt@apache.org]
Sent: 09 May 2008 12:25
To: Tomcat Users List
Subject: Re: Possible to assign different class loader for each web app with
tomcat
paul.ockleford@nhs.net wrote:
> Thanks for the reply.
>
> To be honest I am not sure, both web apps are separated, have their
> own web.xml files and also are accessed via different ports, however
> as they are effectively the same application at different stages of
> development they each need to load parameters in on start up to a
> class that holds constant values. (I don't know if this is the best or
> a good way to do it, its how it was done before I started).
>
> Here are some excerpts from the web.xml, the only difference in each
> of the
> 2 web apps web.xml is that they load a different value for the url
> endpoint, as they point to different message handling development areas:
>
> <servlet-name>ConfigurationManager</servlet-name>
>
> <servlet-class>application.util.startup.ConfigurationManager</servlet-
> class>
> <load-on-startup>1</load-on-startup>
> <init-param>
> <param-name>MESSAGE.ENDPOINT</param-name>
>
> <param-value>http://192.168.28.193/router/SOAPEndpoint</param-value>
>
> </init-param>
> </servlet>
>
> To be honest I am sure it's a lack of understanding on my part, but
> that's something I want to correct!
It all depends on where you put the .class file or the .jar that contains
the .class file. With this information we should be able to help you fix
this.
Cheers,
Mark
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or take any action in reliance on its contents: to do so is strictly
prohibited and may be unlawful. Please inform us that this message has
gone astray before deleting it. Thank you for your co-operation.
NHSmail is used daily by over 100,000 staff in the NHS. Over a million
messages are sent every day by the system. To find out why more and
more NHS personnel are switching to this NHS Connecting for Health
system please visit www.connectingforhealth.nhs.uk/nhsmail
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Re: Possible to assign different class loader for each web app with
tomcat
Posted by Mark Thomas <ma...@apache.org>.
paul.ockleford@nhs.net wrote:
> Thanks for the reply.
>
> To be honest I am not sure, both web apps are separated, have their own
> web.xml files and also are accessed via different ports, however as they are
> effectively the same application at different stages of development they
> each need to load parameters in on start up to a class that holds constant
> values. (I don’t know if this is the best or a good way to do it, its how it
> was done before I started).
>
> Here are some excerpts from the web.xml, the only difference in each of the
> 2 web apps web.xml is that they load a different value for the url endpoint,
> as they point to different message handling development areas:
>
> <servlet-name>ConfigurationManager</servlet-name>
>
> <servlet-class>application.util.startup.ConfigurationManager</servlet-class>
> <load-on-startup>1</load-on-startup>
> <init-param>
> <param-name>MESSAGE.ENDPOINT</param-name>
> <param-value>http://192.168.28.193/router/SOAPEndpoint</param-value>
>
> </init-param>
> </servlet>
>
> To be honest I am sure it’s a lack of understanding on my part, but that’s
> something I want to correct!
It all depends on where you put the .class file or the .jar that contains
the .class file. With this information we should be able to help you fix this.
Cheers,
Mark
---------------------------------------------------------------------
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RE: Possible to assign different class loader for each web app with
tomcat
Posted by pa...@nhs.net.
Thanks for the reply.
To be honest I am not sure, both web apps are separated, have their own
web.xml files and also are accessed via different ports, however as they are
effectively the same application at different stages of development they
each need to load parameters in on start up to a class that holds constant
values. (I dont know if this is the best or a good way to do it, its how it
was done before I started).
Here are some excerpts from the web.xml, the only difference in each of the
2 web apps web.xml is that they load a different value for the url endpoint,
as they point to different message handling development areas:
<servlet-name>ConfigurationManager</servlet-name>
<servlet-class>application.util.startup.ConfigurationManager</servlet-class>
<load-on-startup>1</load-on-startup>
<init-param>
<param-name>MESSAGE.ENDPOINT</param-name>
<param-value>http://192.168.28.193/router/SOAPEndpoint</param-value>
</init-param>
</servlet>
To be honest I am sure its a lack of understanding on my part, but thats
something I want to correct!
Thanks
-----Original Message-----
From: David Delbecq [mailto:delbd+jakarta@oma.be]
Sent: 09 May 2008 11:35
To: Tomcat Users List
Subject: Re: Possible to assign different class loader for each web app with
tomcat
This all depends on your webapp structure. If your config class is on the
common or system class loader, it's shared by all webapps. Otherwise, (that
mean if class is in WEB-INF/lib or WEB-INF/classes), it shouldn't be shared.
Unless, of course, you specified a specific classloader to use by tomcat in
your context.xml.
Le Friday 09 May 2008 12:16:23 paul.ockleford@nhs.net, vous avez écrit :
> Ok, that's strange because yesterday I had a small problem, and I assumed
> that it was due to the same class being loaded on startup by 2 web apps.
>
> I had a url endpoint loaded into a config class on startup from the
> web.xml, for some reason no messages were reaching the correct end point.
> This config class is also loaded by a test version of the app running
under
> the same tomcat as pre prod. When the second web app was loaded and its
> config class was loaded and the parameter read in from the web.xml it
> changed the value for both web apps.
>
> I have not being using java or tomcat for all that long, but I would have
> thought if a class loader was assigned for each web app then they would
> each have their own copy of the config class? Meaning that web app1 should
> not have been pointing at the end point for web app 2? If not then could
> you tell me why?
>
> Thanks
>
> -----Original Message-----
> From: Mark Thomas [mailto:markt@apache.org]
> Sent: 09 May 2008 11:10
> To: Tomcat Users List
> Subject: Re: Possible to assign different class loader for each web app
> with tomcat
>
> paul.ockleford@nhs.net wrote:
> > Hi,
> >
> > Is it possible to configure a separate class loader for each web app
> > running under tomcat? A colleague has informed that he can do this
> > with web sphere and I am wondering if it is possible with tomcat.
>
> This is the case by default. No configuration is required.
>
> Mark
>
>
> ---------------------------------------------------------------------
> To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe,
> e-mail: users-unsubscribe@tomcat.apache.org
> For additional commands, e-mail: users-help@tomcat.apache.org
>
>
>
> **********************************************************************
> This message may contain confidential and privileged information.
> If you are not the intended recipient please accept our apologies.
> Please do not disclose, copy or distribute information in this e-mail
> or take any action in reliance on its contents: to do so is strictly
> prohibited and may be unlawful. Please inform us that this message has
> gone astray before deleting it. Thank you for your co-operation.
>
> NHSmail is used daily by over 100,000 staff in the NHS. Over a million
> messages are sent every day by the system. To find out why more and
> more NHS personnel are switching to this NHS Connecting for Health
> system please visit www.connectingforhealth.nhs.uk/nhsmail
> **********************************************************************
>
>
> ---------------------------------------------------------------------
> To start a new topic, e-mail: users@tomcat.apache.org
> To unsubscribe, e-mail: users-unsubscribe@tomcat.apache.org
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This message may contain confidential and privileged information.
If you are not the intended recipient please accept our apologies.
Please do not disclose, copy or distribute information in this e-mail
or take any action in reliance on its contents: to do so is strictly
prohibited and may be unlawful. Please inform us that this message has
gone astray before deleting it. Thank you for your co-operation.
NHSmail is used daily by over 100,000 staff in the NHS. Over a million
messages are sent every day by the system. To find out why more and
more NHS personnel are switching to this NHS Connecting for Health
system please visit www.connectingforhealth.nhs.uk/nhsmail
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Re: Possible to assign different class loader for each web app with tomcat
Posted by David Delbecq <de...@oma.be>.
This all depends on your webapp structure. If your config class is on the
common or system class loader, it's shared by all webapps. Otherwise, (that
mean if class is in WEB-INF/lib or WEB-INF/classes), it shouldn't be shared.
Unless, of course, you specified a specific classloader to use by tomcat in
your context.xml.
Le Friday 09 May 2008 12:16:23 paul.ockleford@nhs.net, vous avez écrit :
> Ok, that's strange because yesterday I had a small problem, and I assumed
> that it was due to the same class being loaded on startup by 2 web apps.
>
> I had a url endpoint loaded into a config class on startup from the
> web.xml, for some reason no messages were reaching the correct end point.
> This config class is also loaded by a test version of the app running under
> the same tomcat as pre prod. When the second web app was loaded and its
> config class was loaded and the parameter read in from the web.xml it
> changed the value for both web apps.
>
> I have not being using java or tomcat for all that long, but I would have
> thought if a class loader was assigned for each web app then they would
> each have their own copy of the config class? Meaning that web app1 should
> not have been pointing at the end point for web app 2? If not then could
> you tell me why?
>
> Thanks
>
> -----Original Message-----
> From: Mark Thomas [mailto:markt@apache.org]
> Sent: 09 May 2008 11:10
> To: Tomcat Users List
> Subject: Re: Possible to assign different class loader for each web app
> with tomcat
>
> paul.ockleford@nhs.net wrote:
> > Hi,
> >
> > Is it possible to configure a separate class loader for each web app
> > running under tomcat? A colleague has informed that he can do this
> > with web sphere and I am wondering if it is possible with tomcat.
>
> This is the case by default. No configuration is required.
>
> Mark
>
>
> ---------------------------------------------------------------------
> To start a new topic, e-mail: users@tomcat.apache.org To unsubscribe,
> e-mail: users-unsubscribe@tomcat.apache.org
> For additional commands, e-mail: users-help@tomcat.apache.org
>
>
>
> **********************************************************************
> This message may contain confidential and privileged information.
> If you are not the intended recipient please accept our apologies.
> Please do not disclose, copy or distribute information in this e-mail
> or take any action in reliance on its contents: to do so is strictly
> prohibited and may be unlawful. Please inform us that this message has
> gone astray before deleting it. Thank you for your co-operation.
>
> NHSmail is used daily by over 100,000 staff in the NHS. Over a million
> messages are sent every day by the system. To find out why more and
> more NHS personnel are switching to this NHS Connecting for Health
> system please visit www.connectingforhealth.nhs.uk/nhsmail
> **********************************************************************
>
>
> ---------------------------------------------------------------------
> To start a new topic, e-mail: users@tomcat.apache.org
> To unsubscribe, e-mail: users-unsubscribe@tomcat.apache.org
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