Hi;
Class loading in a stand alone java program usually makes classloading
transparent (in most cases).
When operating in a J2EE environment (this includes web apps), there should
be awareness of the classloading scheme of the web container. Without such
knowledge, many problems can arrise. The most common problem of not
underestanding the class loading hirarchy of a container is the class not
found exception.
There are many article about this. You can also take a look at the blue
prints.
Thanks.
-----Original Message-----
From: Gustavo Cebrian [mailto:gustavo.cebrian_at_greenhatconsulting.com]
Sent: Monday, June 23, 2003 4:47 PM
To: JAXB-INTEREST_at_JAVA.SUN.COM
Subject: Re: JAXB, ClassLoaders and Web apps
I do not understand this. I would have thought that loading a class is just
transparent for the programmer.
Apparently it is not.
Have you found out anything else?
Gustavo.
-----Original Message-----
From: Robert Lowe [mailto:rmlowe_at_rmlowe.com]
Sent: 22 June 2003 10:46
To: Gustavo Cebrian
Subject: JAXB, ClassLoaders and Web apps
What is the "right" way to create a JAXBContext instance in a Web
application, assuming the JAXB classes are deployed as part of the Web app
(i.e. not in the system classpath).
Basically, I can use the thread's context loader as follows:
JAXBContext ctx = JAXBContext.getInstance(MY_CONTEXT_PATH);
or I can explicitly use the current class loader:
JAXBContext ctx = JAXBContext.getInstance(MY_CONTEXT_PATH,
ThisClass.class.getClassLoader());
Up until now, I have been doing the latter, on the (possibly flawed)
assumption that it was more likely to pick up the correct classes and
resources from the Web app.
However, when using JUnit 3.8.1 to run a test case that involves JAXB, I get
a java.lang.LinkageError (stack trace below). This error goes away if I
switch to the first method.
Is one method "better" in this situation?
java.lang.LinkageError: Class org/relaxng/datatype/Datatype violates loader
constraints
at java.lang.ClassLoader.defineClass0(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:486)
at java.lang.ClassLoader.defineClass(ClassLoader.java:426)
at junit.runner.TestCaseClassLoader.loadClass(TestCaseClassLoader.java:104)
at java.lang.ClassLoader.loadClass(ClassLoader.java:253)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:313)
at
org.imsglobal.xsd.imsmd_rootv1p2p1.impl.CatalogentryTypeImpl$Unmarshaller.te
xt(CatalogentryTypeImpl.java:197)
at
com.sun.xml.bind.unmarshaller.ContentHandlerEx.revertToParentFromText(Conten
tHandlerEx.java:308)
at
org.imsglobal.xsd.imsmd_rootv1p2p1.impl.EntryImpl$Unmarshaller.text(EntryImp
l.java:149)
at
com.sun.xml.bind.unmarshaller.SAXUnmarshallerHandlerImpl.consumeText(SAXUnma
rshallerHandlerImpl.java:211)
at
com.sun.xml.bind.unmarshaller.SAXUnmarshallerHandlerImpl.processText(SAXUnma
rshallerHandlerImpl.java:215)
at
com.sun.xml.bind.unmarshaller.SAXUnmarshallerHandlerImpl.endElement(SAXUnmar
shallerHandlerImpl.java:125)
at
org.apache.xerces.parsers.AbstractSAXParser.endElement(AbstractSAXParser.jav
a:552)
at
org.apache.xerces.impl.XMLNSDocumentScannerImpl.scanEndElement(XMLNSDocument
ScannerImpl.java:544)
at
org.apache.xerces.impl.XMLDocumentFragmentScannerImpl$FragmentContentDispatc
her.dispatch(XMLDocumentFragmentScannerImpl.java:1533)
at
org.apache.xerces.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocume
ntFragmentScannerImpl.java:346)
at
org.apache.xerces.parsers.DTDConfiguration.parse(DTDConfiguration.java:529)
at
org.apache.xerces.parsers.DTDConfiguration.parse(DTDConfiguration.java:585)
at org.apache.xerces.parsers.XMLParser.parse(XMLParser.java:152)
at
org.apache.xerces.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:114
2)
at
com.sun.xml.bind.unmarshaller.UnmarshallerImpl.unmarshal(UnmarshallerImpl.ja
va:130)
at
javax.xml.bind.helpers.AbstractUnmarshallerImpl.unmarshal(AbstractUnmarshall
erImpl.java:139)
at
javax.xml.bind.helpers.AbstractUnmarshallerImpl.unmarshal(AbstractUnmarshall
erImpl.java:186)
at
com.netdimen.cpackage.MetaDataImporter.getSummary(MetaDataImporter.java:236)
at
com.netdimen.cpackage.MetaDataImporter.getSummary(MetaDataImporter.java:264)
at com.netdimen.scorm.packaging.Metadata.getSummary(Metadata.java:247)
at
com.netdimen.scorm.packaging.Organization.getMetaDataSummary(Organization.ja
va:260)
at com.netdimen.scorm.packaging.Organization.create(Organization.java:282)
at com.netdimen.scorm.packaging.Manifest.create(Manifest.java:167)
at
com.netdimen.scorm.packaging.JaxpContentPackageImporter.readManifest(JaxpCon
tentPackageImporter.java:48)
at
com.netdimen.scorm.packaging.ContentPackageImporter.importContentPackage(Con
tentPackageImporter.java:79)
at
com.netdimen.unittest.scorm.ImportPackageTestCase.testInputScormPackage(Impo
rtPackageTestCase.java:59)
Robert Lowe
http://RMLowe.com/
+852 9520 4722
rmlowe_at_rmlowe.com