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With JDK 17, it's not possible anymore to make a field accessible using reflection, at least not for java.lang-classes. Following snippet:

final Process process = new ProcessBuilder().directory(new File("d:/temp")).command("cmd.exe").start();
final Field handleField = process.getClass().getDeclaredField("handle");
handleField.setAccessible(true);

fails with:

Exception in thread "main" java.lang.reflect.InaccessibleObjectException: Unable to make field private final long java.lang.ProcessImpl.handle accessible: module java.base does not "opens java.lang" to unnamed module @254989ff
    at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:354)
    at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:297)
    at java.base/java.lang.reflect.Field.checkCanSetAccessible(Field.java:178)
    at java.base/java.lang.reflect.Field.setAccessible(Field.java:172)

Is there a way to work around this problem?

mstrap
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    maybe this helps: https://stackoverflow.com/questions/41265266/how-to-solve-inaccessibleobjectexception-unable-to-make-member-accessible-m – Jens Jul 14 '22 at 15:23
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    "How to solve [...]": by rewriting your code so that this is no longer required. – Thomas Kläger Jul 14 '22 at 15:49
  • @ThomasKläger What exactly do you suggest to get the launched process' handle (to being able to kill the whole process tree)? – Thomas S. Jul 15 '22 at 07:37
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    @ThomasS. by using the methods that Java supports since Java 9 (see the last code fragment at https://stackoverflow.com/a/10124625, using `ProcessHandle`) – Thomas Kläger Jul 15 '22 at 09:00

2 Answers2

5

As this answer points out, one solution is to add following VM option:

java --add-opens java.base/java.lang=ALL-UNNAMED
mstrap
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1

Alternative Java 17 solution:

Field field = MyClass.class.getDeclaredField("myField");
MethodHandle getter = MethodHandles.lookup().unreflectGetter(field);
Object value = getter.invokeExact(new MyClass()); ```
greencodes
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