java.lang.LinkageError --- json-lib -- issue? - jboss

Question

java.lang.LinkageError: Failed to link net/sf/json/JSONException
(Module "MYAPP:lib" from local module loader #4c3e4790 (finder: local
module finder #38cccef (roots:
C:\MYAPPS\EAP-6.4.0\jboss-eap-6.4\modules,C:\MYAPPS\EAP-6.4.0\jboss-eap-6.4\modules\system\layers\base,C:\MYAPPS\EAP-6.4.0\jboss-eap-6.4,C:\MYAPP\Utils\JBossUtils\VLSEnv\VLS1,C:\MYAPP,C:\,C:\MYAPP\Utils\JBossUtils\VLSEnv\VLS1\VLS\bin)))
2017-02-01 02:59:08:450 package1.fusion [272396945]
java.lang.LinkageError: Failed to link net/sf/json/JSONException
(Module "MYAPP:lib" from local module loader #4c3e4790 (finder: local
module finder #38cccef (roots:
C:\MYAPPS\EAP-6.4.0\jboss-eap-6.4\modules,C:\MYAPPS\EAP-6.4.0\jboss-eap-6.4\modules\system\layers\base,C:\MYAPPS\EAP-6.4.0\jboss-eap-6.4,C:\MYAPP\Utils\JBossUtils\VLSEnv\VLS1,C:\MYAPP,C:\,C:\MYAPP\Utils\JBossUtils\VLSEnv\VLS1\VLS\bin)))
we are using an older version of json-lib, is the above problem due to that ?

Answer 1

LinkageError is what you'll get in a classic case where you have a class C loaded by more than one classloader and those classes are being used together in the same code (compared, cast, etc). It doesn't matter if it is the same Class name or even if it's loaded from the identical jar - a Class from one classloader is always treated as a different Class if loaded from another classloader.
This can be happened when you included a library twice. See the link:
https://docs.jboss.org/jbossas/docs/Server_Configuration_Guide/beta422/html/Class_Loading_and_Types_in_Java-LinkageErrors___Making_Sure_You_Are_Who_You_Say_You_Are.html