Question

I am generating xlsx file using Apache POI. On making the war and deploying to the Jboss server, I am getting this error :

java.lang.LinkageError: loader constraint violation: loader (instance of org/jboss  /classloader/spi/base/BaseClassLoader) previously initiated loading for a different type with name "javax/xml/namespace/QName"
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:616)
    at org.jboss.classloader.spi.base.BaseClassLoader.access$200(BaseClassLoader.java:67)
    at org.jboss.classloader.spi.base.BaseClassLoader$2.run(BaseClassLoader.java:633)  
        .....

Answer 1

The class javax.xml.namespace.QName is present in many jars

http://www.jarfinder.com/index.php/java/info/javax.xml.namespace.QName

and is likely loaded multiple times.

You may have to tune the Jboss class loader for webapps if you cannot resolve the conflict.