Logging: more classloader problems.

Richard Sitze Thu, 06 Jun 2002 12:11:45 -0700

I'm new this part of the game (classloaders), but I'm becoming more and more aware of the issues. So, I'd like to add to your question some bigger issues surrounding the placement of commons-logging & other apache utility/libraries in web application servers: 1. How do we find & overload factories (I think this is the issue you set forth below)? 2. How do we find & overload resources in general (NLS messaging/properties files)? 3. How do we configure (NOT System properties as we do today - that has global implications)? The fundamental problem I have is how do we sync classloader mechanisms with other algorithms in common use (including the logger): try resource named "resource", then try resouce named "package.resource". This last one conflicts with classloader in application servers because what we get is: 1. Classloader(s) look for "resource" in application context 2. Classloader(s) look for "resource" in system context 3. Classloader(s) look for "package.resource" in application context 4. Classloader(s) look for "package.resource" in system context but what we want is: 1. Classloader(s) look for "resource" in application context 2. Classloader(s) look for "package.resource" in application context 3. Classloader(s) look for "resource" in system context 4. Classloader(s) look for "package.resource" in system context I think we may need to design a solution, and - of course - provide an implementation as part of the commons project. If there are answers out there, I'd like to see them in a developers guide (common-doc - general guidelines?) <ras> ******************************************* Richard A. Sitze [EMAIL PROTECTED] CORBA Interoperability & WebServices IBM WebSphere Development [EMAIL PROTECTED]
To: Jakarta Commons Developers List <[EMAIL PROTECTED]> 06/06/2002 01:08
cc: List Tomcat-Dev <[EMAIL PROTECTED]> PM
Subject: Logging: more classloader problems. Please respond to "Jakarta Commons Developers List" The problem: it won't work if commons-logging.jar is installed in the parent class loader, and log4j.jar ( or another logger ) is installed in a child loader ( like WEB-INF/lib ). What happens: - the factory uses the thread class loader to check if the log4j ( or any other impl. ) exists ( and it does ). - it creates an instance of the Logger adapter. This will be created using parent loader ( the one that loads commons-logging ). - the Logger instance makes references to Category or other classes that are used in it's implementation. End of story, since the class loader can't find the reference. This works fine for JAXP because the adapter for a parser is part of the parser jar. It doesn't work for c-l because the adapter is in the root loader ( with the API), not with the logging impl. That doesn't affect people who just use a single logger or can put the logger impl. in the same place with common-logging. It only affect containers like tomcat, when you want to let each webapp use it's own logger impl. of choice. I tried all kind of introspection games, it won't work. The only solution I see is to make sure the adapters are in the same place with the logger. Solution: Split commons-logging.jar in commons-logging-api.jar ( only the API and the LogFactoryImpl, no adapteer ) and commons-logging-impl.jar. Alternatively, leave commons-logging.jar as it is and create a second commons-logging-api.jar. The -api will be included in the common loader. Each webapp will have to include commons-logging.jar ( or -impl ), and it's own logger. Or course, the best would be to have the adapter included in the logger impl. What do you think ? Craig, Remy can we make another c-l dot release with this change ? ( I'll do some more testing to see how it works ) Costin -- To unsubscribe, e-mail: <mailto:[EMAIL PROTECTED]. org> For additional commands, e-mail: <mailto:[EMAIL PROTECTED]. org> --1__=09BBE143DFF5E87F8f9e8a93df938690918c09BBE143DFF5E87F Content-type: text/html; charset=US-ASCII Content-Disposition: inline <html><body>I'm new this part of the game (classloaders), but I'm becoming more and more aware of the issues. So, I'd like to add to your question some bigger issues surrounding the placement of commons-logging & other apache utility/libraries in web application servers: 1. How do we find & overload factories (I think this is the issue you set forth below)? 2. How do we find & overload resources in general (NLS messaging/properties files)? 3. How do we configure (NOT System properties as we do today - that has global implications)? The fundamental problem I have is how do we sync classloader mechanisms with other algorithms in common use (including the logger): try resource named "resource", then try resouce named "package.resource". This last one conflicts with classloader in application servers because what we get is: 1. Classloader(s) look for "resource" in application context 2. Classloader(s) look for "resource" in system context 3. Classloader(s) look for "package.resource" in application context 4. Classloader(s) look for "package.resource" in system context but what we want is: 1. Classloader(s) look for "resource" in application context 2. Classloader(s) look for "package.resource" in application context 3. Classloader(s) look for "resource" in system context 4. Classloader(s) look for "package.resource" in system context I think we may need to design a solution, and - of course - provide an implementation as part of the commons project. If there are answers out there, I'd like to see them in a developers guide (common-doc - general guidelines?) <ras> ******************************************* Richard A. Sitze [EMAIL PROTECTED] CORBA Interoperability & WebServices IBM WebSphere Development <img src=""cid:[EMAIL PROTECTED]" width="16" height="16" alt="">[EMAIL PROTECTED] <table V5DOTBL=true width="100%" border="0" cellspacing="0" cellpadding="0"> <tr valign="top"><td width="1%"><img src=""cid:[EMAIL PROTECTED]" border="0" height="1" width="72" alt=""> </td><td style="background-image:url(cid:[EMAIL PROTECTED]); background-repeat: no-repeat; " width="1%"><img src=""cid:[EMAIL PROTECTED]" border="0" height="1" width="220" alt=""> <ul> <ul> <ul> <ul>[EMAIL PROTECTED] 06/06/2002 01:08 PM Please respond to "Jakarta Commons Developers List"</ul> </ul> </ul> </ul> </td><td width="100%"><img src=""cid:[EMAIL PROTECTED]" border="0" height="1" width="1" alt=""> To: Jakarta Commons Developers List <[EMAIL PROTECTED]> cc: List Tomcat-Dev <[EMAIL PROTECTED]> Subject: Logging: more classloader problems. </td></tr> </table> <tt> The problem: it won't work if commons-logging.jar is installed in the parent class loader, and log4j.jar ( or another logger ) is installed in a child loader ( like WEB-INF/lib ). What happens: - the factory uses the thread class loader to check if the log4j ( or any other impl. ) exists ( and it does ). - it creates an instance of the Logger adapter. This will be created using parent loader ( the one that loads commons-logging ). - the Logger instance makes references to Category or other classes that are used in it's implementation. End of story, since the class loader can't find the reference. This works fine for JAXP because the adapter for a parser is part of the parser jar. It doesn't work for c-l because the adapter is in the root loader ( with the API), not with the logging impl. That doesn't affect people who just use a single logger or can put the logger impl. in the same place with common-logging. It only affect containers like tomcat, when you want to let each webapp use it's own logger impl. of choice. I tried all kind of introspection games, it won't work. The only solution I see is to make sure the adapters are in the same place with the logger. Solution: Split commons-logging.jar in commons-logging-api.jar ( only the API and the LogFactoryImpl, no adapteer ) and commons-logging-impl.jar. Alternatively, leave commons-logging.jar as it is and create a second commons-logging-api.jar. The -api will be included in the common loader. Each webapp will have to include commons-logging.jar ( or -impl ), and it's own logger. Or course, the best would be to have the adapter included in the logger impl. What do you think ? Craig, Remy can we make another c-l dot release with this change ? ( I'll do some more testing to see how it works ) Costin -- To unsubscribe, e-mail:   <</tt><tt><a href=""mailto:[EMAIL PROTECTED]">mailto:[EMAIL PROTECTED]</a></tt><tt>> For additional commands, e-mail: <</tt><tt><a href=""mailto:[EMAIL PROTECTED]">mailto:[EMAIL PROTECTED]</a></tt><tt>> </tt></body></html> --1__=09BBE143DFF5E87F8f9e8a93df938690918c09BBE143DFF5E87F-- --0__=09BBE143DFF5E87F8f9e8a93df938690918c09BBE143DFF5E87F Content-type: image/gif; name="graycol.gif" Content-Disposition: inline; filename="graycol.gif" Content-ID: <[EMAIL PROTECTED]> Content-transfer-encoding: base64 R0lGODlhEAAQAKECAMzMzAAAAP///wAAACH5BAEAAAIALAAAAAAQABAAAAIXlI+py+0PopwxUbpu ZRfKZ2zgSJbmSRYAIf4fT3B0aW1pemVkIGJ5IFVsZWFkIFNtYXJ0U2F2ZXIhAAA7 --0__=09BBE143DFF5E87F8f9e8a93df938690918c09BBE143DFF5E87F Content-type: image/gif; name="ecblank.gif" Content-Disposition: inline; filename="ecblank.gif" Content-ID: <[EMAIL PROTECTED]> Content-transfer-encoding: base64 R0lGODlhEAABAIAAAAAAAP///yH5BAEAAAEALAAAAAAQAAEAAAIEjI8ZBQA7 --0__=09BBE143DFF5E87F8f9e8a93df938690918c09BBE143DFF5E87F--

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