Jdk9: an Illegal Reflective Access Operation Has Occurred. Org.Python.Core.Pysystemstate

What is an illegal reflective access?

Apart from an understanding of the accesses amongst modules and their respective packages. I believe the crux of it lies in the Module System#Relaxed-strong-encapsulation and I would just cherry-pick the relevant parts of it to try and answer the question.

What defines an illegal reflective access and what circumstances
trigger the warning?

To aid in the migration to Java-9, the strong encapsulation of the modules could be relaxed.

• An implementation may provide static access, i.e. by compiled bytecode.

• May provide a means to invoke its run-time system with one or more packages of one or more of its modules open to code in all unnamed modules, i.e. to code on the classpath. If the run-time system is invoked in this way, and if by doing so some invocations of the reflection APIs succeed where otherwise they would have failed.

In such cases, you've actually ended up making a reflective access which is "illegal" since in a pure modular world you were not meant to do such accesses.

How it all hangs together and what triggers the warning in what
scenario?

This relaxation of the encapsulation is controlled at runtime by a new launcher option --illegal-access which by default in Java9 equals permit. The permit mode ensures

The first reflective-access operation to any such package causes a
warning to be issued, but no warnings are issued after that point.
This single warning describes how to enable further warnings. This
warning cannot be suppressed.

The modes are configurable with values debug(message as well as stacktrace for every such access), warn(message for each such access), and deny(disables such operations).

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Few things to debug and fix on applications would be:-

• Run it with --illegal-access=deny to get to know about and avoid opening packages from one module to another without a module declaration including such a directive(opens) or explicit use of --add-opens VM arg.
• Static references from compiled code to JDK-internal APIs could be identified using the jdeps tool with the --jdk-internals option

The warning message issued when an illegal reflective-access operation
is detected has the following form:

WARNING: Illegal reflective access by $PERPETRATOR to $VICTIM

where:

$PERPETRATOR is the fully-qualified name of the type containing the
code that invoked the reflective operation in question plus the code
source (i.e., JAR-file path), if available, and

$VICTIM is a string that describes the member being accessed,
including the fully-qualified name of the enclosing type

Questions for such a sample warning: = JDK9: An illegal reflective access operation has occurred. org.python.core.PySystemState

Last and an important note, while trying to ensure that you do not face such warnings and are future safe, all you need to do is ensure your modules are not making those illegal reflective accesses. :)

How can I throw an exception for an illegal reflective access warning?

1. Open the Eclipse development environment.
2. Choose Run menu –> Run Configurations... –> Java Application –> (your configuration) –> Arguments.
3. In the VM arguments text box, type "--illegal-access=deny" [0].
4. Click the Apply button.
5. Click the Run button.
6. Illegal access will throw the java.lang.reflect.InaccessibleObjectException [1].

[0] http://mail.openjdk.java.net/pipermail/jigsaw-dev/2017-May/012673.html

[1] http://docs.oracle.com/javase/9/docs/api/java/lang/reflect/InaccessibleObjectException.html

How to hide warning Illegal reflective access in java 9 without JVM argument?

There are ways to disable illegal access warning, though I do not recommend doing this.

1. Simple approach

Since the warning is printed to the default error stream, you can simply close this stream and redirect stderr to stdout.

public static void disableWarning() {
    System.err.close();
    System.setErr(System.out);
}

Notes:

• This approach merges error and output streams. That may not be desirable in some cases.
• You cannot redirect warning message just by calling System.setErr, since the reference to error stream is saved in IllegalAccessLogger.warningStream field early at JVM bootstrap.

2. Complicated approach without changing stderr

A good news is that sun.misc.Unsafe can be still accessed in JDK 9 without warnings. The solution is to reset internal IllegalAccessLogger with the help of Unsafe API.

public static void disableWarning() {
    try {
        Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
        theUnsafe.setAccessible(true);
        Unsafe u = (Unsafe) theUnsafe.get(null);

        Class cls = Class.forName("jdk.internal.module.IllegalAccessLogger");
        Field logger = cls.getDeclaredField("logger");
        u.putObjectVolatile(cls, u.staticFieldOffset(logger), null);
    } catch (Exception e) {
        // ignore
    }
}

Illegal reflective access by org.springframework.cglib.core.ReflectUtils$1

In JDK 9+, add the following option to the JVM to disable the warning from Spring's use of CGLIB:

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

for example:

java --add-opens java.base/java.lang=ALL-UNNAMED -jar target/*.jar

No need to report it; it's a known Spring bug.

This happens because the new JDK 9 module system detected an illegal access that will be disallowed sometime in the (near) future. You can read more about the JDK 9 Module system here.

Update:

A fix for this issue is available JDK 9+ with Spring 5.1+.

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