Build failure on Java 16

[fmbenhassine]

The following tests fail on JDK 16:

• XStreamMarshallingTests
• XStreamUnmarshallingTests

Here is the failure:

java.lang.ExceptionInInitializerError
	at com.thoughtworks.xstream.XStream.setupConverters(XStream.java:990)
	at com.thoughtworks.xstream.XStream.<init>(XStream.java:593)
	at org.springframework.oxm.xstream.XStreamMarshaller$1.<init>(XStreamMarshaller.java:432)
	at org.springframework.oxm.xstream.XStreamMarshaller.constructXStream(XStreamMarshaller.java:431)
	at org.springframework.oxm.xstream.XStreamMarshaller.buildXStream(XStreamMarshaller.java:419)
	at org.springframework.util.function.SingletonSupplier.get(SingletonSupplier.java:97)
	at org.springframework.util.function.SingletonSupplier.obtain(SingletonSupplier.java:115)
	at org.springframework.oxm.xstream.XStreamMarshaller.getXStream(XStreamMarshaller.java:624)
	at org.springframework.oxm.xstream.XStreamMarshaller.doMarshal(XStreamMarshaller.java:728)
	at org.springframework.oxm.xstream.XStreamMarshaller.marshalSaxHandlers(XStreamMarshaller.java:687)
	at org.springframework.oxm.xstream.XStreamMarshaller.marshalXmlEventWriter(XStreamMarshaller.java:668)
	at org.springframework.oxm.support.AbstractMarshaller.marshalStaxResult(AbstractMarshaller.java:284)
	at org.springframework.oxm.support.AbstractMarshaller.marshal(AbstractMarshaller.java:236)
	at org.springframework.batch.item.xml.StaxEventItemWriter.write(StaxEventItemWriter.java:806)
	at org.springframework.batch.item.xml.AbstractStaxEventWriterItemWriterTests$2.doInTransaction(AbstractStaxEventWriterItemWriterTests.java:90)
	at org.springframework.batch.item.xml.AbstractStaxEventWriterItemWriterTests$2.doInTransaction(AbstractStaxEventWriterItemWriterTests.java:86)
	at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:140)
	at org.springframework.batch.item.xml.AbstractStaxEventWriterItemWriterTests.testWrite(AbstractStaxEventWriterItemWriterTests.java:86)
	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.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
	at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
	at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at org.junit.runners.ParentRunner.run(ParentRunner.java:413)
	at org.junit.runner.JUnitCore.run(JUnitCore.java:137)
	at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:69)
	at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
	at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:220)
	at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:53)
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 @77f03bb1
	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:40)
	at com.thoughtworks.xstream.converters.collections.TreeMapConverter.<clinit>(TreeMapConverter.java:50)
	... 45 more

The full build log can be found here. The issue com.thoughtworks.xstream.XStream.setupConverters(XStream.java:990) is related to XStream (see x-stream/xstream#218) which was fixed in v1.4.13. Spring Batch currently uses v1.4.12.