Unable to build with Java 16

[erichwang]

When using Java 16 to build the project, we quickly get the following error:

Exception in thread "main" java.lang.reflect.InvocationTargetException
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:567)
	at org.apache.maven.wrapper.BootstrapMainStarter.start(BootstrapMainStarter.java:39)
	at org.apache.maven.wrapper.WrapperExecutor.execute(WrapperExecutor.java:122)
	at org.apache.maven.wrapper.MavenWrapperMain.main(MavenWrapperMain.java:50)
Caused by: java.lang.ExceptionInInitializerError
	at com.thoughtworks.xstream.XStream.setupConverters(XStream.java:807)
	at com.thoughtworks.xstream.XStream.<init>(XStream.java:574)
	at com.thoughtworks.xstream.XStream.<init>(XStream.java:496)
	at com.thoughtworks.xstream.XStream.<init>(XStream.java:465)
	at com.thoughtworks.xstream.XStream.<init>(XStream.java:411)
	at com.thoughtworks.xstream.XStream.<init>(XStream.java:350)
	at ca.vanzyl.provisio.model.io.RuntimeReader.<init>(RuntimeReader.java:61)
	at ca.vanzyl.maven.plugins.provisio.Provisio.parseDescriptor(Provisio.java:97)
	at ca.vanzyl.maven.plugins.provisio.Provisio.findDescriptorsInFileSystem(Provisio.java:68)
	at ca.vanzyl.maven.plugins.provisio.ProvisioningLifecycleParticipant.gleanDependenciesFromExternalResource(ProvisioningLifecycleParticipant.java:115)
	at ca.vanzyl.maven.plugins.provisio.ProvisioningLifecycleParticipant.afterProjectsRead(ProvisioningLifecycleParticipant.java:69)
	at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:264)
	at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:192)
	at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:105)
	at org.apache.maven.cli.MavenCli.execute(MavenCli.java:957)
	at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:289)
	at org.apache.maven.cli.MavenCli.main(MavenCli.java:193)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:567)
	at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:282)
	at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:225)
	at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:406)
	at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:347)
	... 7 more
Caused by: java.lang.reflect.InaccessibleObjectException: Unable to make field private final java.util.Comparator java.util.TreeMap.comparator accessible: module java.base does not "opens java.util" to unnamed module @6b0615ae
	at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:357)
	at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:297)
	at java.base/java.lang.reflect.Field.checkCanSetAccessible(Field.java:177)
	at java.base/java.lang.reflect.Field.setAccessible(Field.java:171)
	at com.thoughtworks.xstream.core.util.Fields.locate(Fields.java:39)
	at com.thoughtworks.xstream.converters.collections.TreeMapConverter.<clinit>(TreeMapConverter.java:50)
	... 32 more

[amitds1997]

The issue is likely because of the dependency of maven plugins on xstream which has not been updated.
xstream fixed this issue in 1.4.13 (source)

However, we are at 1.4.7.

$ ./mvnw dependency:tree
[INFO] Scanning for projects...
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by com.thoughtworks.xstream.core.util.Fields (file:/Users/amitsingh/.m2/repository/com/thoughtworks/xstream/xstream/1.4.7/xstream-1.4.7.jar) to field java.util.TreeMap.comparator
WARNING: Please consider reporting this to the maintainers of com.thoughtworks.xstream.core.util.Fields
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

My guess is we have a maven plugin which is using an older version of xstream.

[hashhar]

It's being pulled in from provisio-model which we use for packaging. It's updated upstream in jvanzyl/provisio@d70e158 but there hasn't been a new release since.

@nineinchnick might know if there's a release coming since he got something merged-in upstream.

[nineinchnick]

It's being pulled in from provisio-model which we use for packaging. It's updated upstream in jvanzyl/provisio@d70e158 but there hasn't been a new release since.

@nineinchnick might know if there's a release coming since he got something merged-in upstream.

There was a new release two days ago.

[electrum]

Updated the CI to use JDK 16 in #7952