To be honest, I got exactly the same impression when I read this document half a year ago. However, when I tried to clarify all the "grey" areas in this document with Sun, here is the response from their Java engineer:
*** The standard "delegation model" used by Java does say that a child classloader should look first to its parent classloader when searching for classes. As you know, this model works against us in your situtation, since the application classloader for a web app is a child of the system class loader (where the 1.4 parsers are loaded). However, the servlet specification requires that a web app obtain its class definition from the WAR file. Therefore, most vendors have implemented a way for the application classloader to look in the WAR file first before going to a parent, thereby overriding the standard delegation model. *** So, it seems to me that the servlet spec. should supersede the "endorsed mechanism" in the web application environment. William. -----Original Message----- From: Cox, Charlie [mailto:[EMAIL PROTECTED] Sent: Friday, October 10, 2003 1:17 PM To: 'Tomcat Developers List' Subject: RE: Webapp classloader question. ok, I just found this link from the archives. Sun defined that you have to use the 'endorsed' directory or take the Sun-supplied versions of the packages listed. http://java.sun.com/j2se/1.4.2/docs/guide/standards/index.html tomcat's classloading is enforcing this requirement explicitly since it does not delegate to the parent classloader first. so you can only replace the version in /endorsed Charlie > -----Original Message----- > From: Lee, William [mailto:[EMAIL PROTECTED] > Sent: Friday, October 10, 2003 12:05 PM > To: 'Tomcat Developers List' > Subject: RE: Webapp classloader question. > > > It seems to me that we are going for "bandaid" solution here. > By moving > around the files, it will work for one particular webapp, but at the > expensive of the compatibility of other webapp under the same > tomcat. As > soon as we move the parser out of one webapp, we are forcing all other > webapp using the same parser, which I believed is not the > right way to go. > > Rather, why forcing the delegate model for these two > particular packages > (xerces & xalan)? Isn't it true that the endorse mechanism > only required > that the endorsed directory should be traverse before the system? > > I still didn't see the reason how this "endorsed mechanism" > has anything to > do with the servlet spec., and that it would force servlet > container to skip > the one in webapps? > > Thanks again. > William. > > > -----Original Message----- > From: Cox, Charlie [mailto:[EMAIL PROTECTED] > Sent: Friday, October 10, 2003 8:46 AM > To: 'Tomcat Developers List' > Subject: RE: Webapp classloader question. > > > you want to put the one from endorsed into server/lib, then > put yours in > WEB-INF. This way only one is visible to any tree of the > classloader. But > I'm not sure if you will still end up with the JDK version > since the one in > WEB-INF is not "endorsed" to override it. > > The other thing I would try is to put your version in > /common/endorsed with > the tomcat version in /server/lib. > > btw, have you just tried replacing the version in /endorsed > with your newer > one? > > Charlie > > > -----Original Message----- > > From: Lee, William [mailto:[EMAIL PROTECTED] > > Sent: Thursday, October 09, 2003 4:54 PM > > To: 'Tomcat Developers List' > > Subject: RE: Webapp classloader question. > > > > > > This won't work since, all jar files in commons/lib, > > commons/endorsed, and commons/classes are all visible to the > > tomcat's "commons" classloader. So, > > there is no difference whether we put the xerces jar files > in "lib" or > > "endorsed", the one from webapps will be skipped. > > > > I think the question boiled down to, if we have Xerces on both > > "endorsed" and "webapps", which one should be used? For tomcat, I > > would thought that > > the order for class searching will be "webapps", "shared", "commons" > > (including "endorsed"), then "system". > > > > I believed tomcat put "endorsed" before "system" is to follows the > > "endorsed classloading spec.". But I also believed forcing delegate > > model for xerces > > and xalan maybe overkill? > > > > Indeed, the tomcat's "class-loader-howto" document also indicated > > that the one from webapps should be used instead. > > > > Frankly speaking, I'm no expert on these topics, so please feel free > > to correct me if I mis-understanding anything here. > > > > Thanks. > > William. > > > > -----Original Message----- > > From: Shapira, Yoav [mailto:[EMAIL PROTECTED] > > Sent: Thursday, October 09, 2003 12:44 PM > > To: Tomcat Developers List > > Subject: RE: Webapp classloader question. > > > > > > > > Howdy, > > Tomcat 4.1.x implements the endorsed classloader spec. It's > > compliant with the Servlet Specification v2.3. What you can do if > > you want your webapp to > > use the latest xerces/JAXP, is: > > - Move $CATALINA_HOME/common/endorsed/* to $CATALINA_HOME/common/lib > > - Put your later xerces etc. in WEB-INF/lib as you've been doing. > > > > Yoav Shapira > > Millennium ChemInformatics > > > > > > >-----Original Message----- > > >From: Lee, William [mailto:[EMAIL PROTECTED] > > >Sent: Thursday, October 09, 2003 12:38 PM > > >To: [EMAIL PROTECTED] > > >Subject: Webapp classloader question. > > > > > > > > >Hi all, > > > > > >I'm not sure if this message reaches you guys yet, so here > > it go again. > > >Sorry for any inconvenience if you receiving this message twice. > > > > > >Thanks. > > >William. > > > > > >-----Original Message----- > > >From: Lee, William [mailto:[EMAIL PROTECTED] > > >Sent: Tuesday, October 07, 2003 3:55 PM > > >To: '[EMAIL PROTECTED]' > > >Subject: Webapp classloader question. > > > > > > > > >Hi all, > > > > > >When moving from tomcat 4.0.x to 4.1.x, we discovered that the > > >WebappClassLoader.java had been changed such that all classes from > > >"org.apache.xerces" and "org.apache.xalan" are forced to be loaded > > using > > >the > > >delegate model first, before looking into the webapp > directory. This > > seems > > >to related to the JDK 1.4 support of the xml and xslt parser. > > > > > >However, after a long conversation with the Sun's Java engineer, he > > point > > >out that, even JDK 1.4 shipped with the default xml and > xslt parser, > > >application server and servlet container should continue to > > use the one > > >provided from the webapp directory as described in the > servlet spec. > > 2.3. > > > > > >Could someone please hint some lights on why tomcat 4.1.x > decided to > > >enforce the delegate model for these two packages? > > > > > >(The reason I'm asking is that, we try to use the latest > > Xerces in our > > >webapps, and since it always look and found the one from > > common/endorsed > > >directory, our latest version will always be skipped.) > > > > > >Thanks in advance for your help. > > >William. > > > > > >Join us at Cognos' biggest event of the year Enterprise 2003, The > > Cognos > > >Business Forum. Taking place in over 25 cities around the > > world, it's > > an > > >opportunity for Business and IT leaders to learn about > > strategies for > > >driving performance. Visit > http://www.cognos.com/enterprise03 for more > >details. > > > >This message may contain privileged and/or confidential information. > If > >you > >have received this e-mail in error or are not the intended recipient, > you > >may not use, copy, disseminate or distribute it; do not open any > >attachments, delete it immediately from your system and notify the > sender > >promptly by e-mail that you have done so. Thank you. > > > > This e-mail, including any attachments, is a confidential business > communication, and may contain information that is confidential, > proprietary and/or privileged. This e-mail is intended only for the > individual(s) to > whom it is addressed, and may not be saved, copied, printed, > disclosed or > used by anyone else. 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