com.sun.tools.xjc.Plugin: Provider not a subtype

Question

I have a CXF JAX-RS app being built with Maven. I\'m working on converting it to Gradle, but using the Ant XJC task.

The current build uses a couple of extensions,

Answer 1

I have tried

java -cp jaxb-api-2.2.7.jar;jaxb-core-2.2.7.jar;jaxb-xjc-2.2.7.jar;commons-logging-1.1.1.jar;commons-lang-2.2.jar;jaxb2-basics-tools-0.6.5.jar;jaxb-xew-plugin-1.3.jar com.sun.tools.xjc.XJCFacade -verbose -extension -d src xsd

and indeed that fails with Exception in thread "main" java.util.ServiceConfigurationError: com.sun.tools.xjc.Plugin: Provider com.sun.tools.xjc.addon.xew.XmlElementWrapperPlugin not a subtype, so the problem is clearly reproducible. I have debugged java.util.ServiceLoader and it turned out that plugins should be passed as argument to XJC (not to classpath of Java). Actually, all maven plugins (like jaxb2-maven-plugin or maven-jaxb2-plugin …) know about this feature and form XJC argments correctly. So the correct command line is:

java -cp jaxb-api-2.2.7.jar;jaxb-core-2.2.7.jar;jaxb-xjc-2.2.7.jar;commons-lang-2.2.jar;commons-logging-1.1.1.jar com.sun.tools.xjc.XJCFacade -classpath jaxb-xew-plugin-1.3.jar;jaxb2-basics-tools-0.6.5.jar -verbose -extension -Xxew -d src xsd

Note that -classpath is argument for XJC. commons-xxx libs can go to system classpath as the packages they export are not screened, but jaxb2-basics-tools should be in XJC classpath. If you are interested in details:

This happens because XJC does classpath loader screening to be able to load higher versions of JAXB API in JRE that has lower build-in version of API. See XJCFacade.java line 69. That means that com.sun.tools.xjc.Plugin is loaded once by custom XJCFacade classloader while the same class is loaded by another (actually, parent) classloader again when Class.forName("com.sun.tools.xjc.addon.xew.XmlElementWrapperPlugin") is called, but now classes are not equal.

Actually you can workaround like this (solution found after source code inspection):

java -Dcom.sun.tools.xjc.XJCFacade.nohack=true -cp jaxb-core-2.2.7.jar;jaxb-xjc-2.2.7.jar;commons-lang-2.2.jar;commons-logging-1.1.1.jar;jaxb2-basics-tools-0.6.5.jar;jaxb-xew-plugin-1.3.jar com.sun.tools.xjc.XJCFacade -verbose -extension -Xxew -d src xsd

Note that I have removed jaxb-api-2.2.7.jar from Java classpath but you'd better put JAXB API into lib/endorsed as it may not work on different Java versions: works fine for Java 7, because it's JAXB API is close to 2.2.7, but may not work on Java 6 + JAXB API 2.2.11.