But why wasn't the class found in myapp/WEB-INF/lib ? Sorry, but I don't understand that !?
> AXA eSolutions GmbH > AXA Konzern AG Germany > Oliver Lauer > Web Architect > W�rthstra�e 34 > D-50668 K�ln > Germany > Tel.: +49 221 148 31277 > Fax: +49 221 148 43963 > Mobil: +49 179 59 064 59 > e-Mail: [EMAIL PROTECTED] > _____________________________ > -----Urspr�ngliche Nachricht----- Von: Craig R. McClanahan [mailto:[EMAIL PROTECTED]] Gesendet: Montag, 17. Dezember 2001 18:50 An: Tomcat Users List Betreff: Re: Classloader question On Mon, 17 Dec 2001, Heikki Doeleman wrote: > Date: Mon, 17 Dec 2001 13:06:21 +0100 > From: Heikki Doeleman <[EMAIL PROTECTED]> > Reply-To: Tomcat Users List <[EMAIL PROTECTED]> > To: "'[EMAIL PROTECTED]'" <[EMAIL PROTECTED]> > Subject: Classloader question > > Hi everyone, > > trying to make a web application work using Tomcat 4.0.1 I found the > following behaviour, which I don't quite understand: > > my application uses a library called xhive.jar > > - putting xhive.jar in [catalina]/common/lib > This works fine, as expected > > > - putting it in [myapp]/WEB-INF/lib > Causes a ClassDefNotFoundError. I don't know why this is so, it does not > seem to conform to the description in class-loader-howto.html. However I did > see someone saying that in that directory, only .class files are added to > the classpath, not .jars > (http://www.geocrawler.com/archives/3/193/2000/12/0/4841079/). > > > - putting it in both those places > Causes a ClassCastException ?? Something seems to go terribly wrong when the > jar is placed in both those directories. > > Can anyone explain more about this? I'd like to know exactly how this works, > especially I'd like to know why classes from a jar in my application's > WEB-INF/lib apparently are not loaded. > This has been discussed numerous times in the archives, but the short answer is this: it is fundamental to the way Java class loaders work. The key issues: * A class named "a.b.c.Foo" loaded from two different class loaders is ***not*** the same class, even if the bytecodes are identical. Trying to assign from one to the other will give you ClassCastException errors. * The "new" operator in Java tries to load the specified class from the same classloader that loaded the class containing this code. If the class of that name has already been loaded by the "other" classloader, you again get ClassNotFoundException errors. * Class loader hierarchies can delegate "up" but not "down". Thus, it's also easy to have the "new" operator cause ClassNotFoundException errors, even though you "know" that the class is there. Moral of the story -- you are *always* best off having one and only one copy of a class visible to a web application. There's ways to deal with some of these issues, but they get pretty intricate. > Thanks > Heikki Doeleman > Craig McClanahan -- To unsubscribe: <mailto:[EMAIL PROTECTED]> For additional commands: <mailto:[EMAIL PROTECTED]> Troubles with the list: <mailto:[EMAIL PROTECTED]> ------------------------------------------------------------------------------ Aus Rechts- und Sicherheitsgruenden ist die in dieser E-Mail gegebene Information nicht rechtsverbindlich. Eine rechtsverbindliche Bestaetigung reichen wir Ihnen gerne auf Anforderung in schriftlicher Form nach. Beachten Sie bitte, dass jede Form der unautorisierten Nutzung, Veroeffentlichung, Vervielfaeltigung oder Weitergabe des Inhalts dieser E-Mail nicht gestattet ist.Diese Nachricht ist ausschliesslich fuer den bezeichneten Adressaten oder dessen Vertreter bestimmt. Sollten Sie nicht der vorgesehene Adressat dieser E-Mail oder dessen Vertreter sein, so bitten wir Sie, sich mit dem Absender der E-Mail in Verbindung zu setzen. ---------------------------- For legal and security reasons the information provided in this e-mail is not legally binding. Upon request we would be pleased to provide you with a legally binding confirmation in written form. Any form of unauthorised use, publication, reproduction, copying or disclosure of the content of this e-mail is not permitted. This message is exclusively for the person addressed or their representative. If you are not the intended recipient of this message and its contents, please notify the sender immediately. ============================================================================== -- To unsubscribe: <mailto:[EMAIL PROTECTED]> For additional commands: <mailto:[EMAIL PROTECTED]> Troubles with the list: <mailto:[EMAIL PROTECTED]>
