How to Solve Java 9's InaccessibleObjectException: Reflection and Module System Conflicts?

Addressing InaccessibleObjectException in Java 9: Unable to Make Members Accessible

The InaccessibleObjectException arises in Java 9 due to the Java Platform Module System's strict encapsulation, granting access only under certain conditions like public visibility and package exportability.

Causes and Scenarios

This exception typically occurs when:

• A library or framework uses reflection to accessJDK module elements (case 1), such as java.lang.ClassLoader.defineClass().
• Reflection-basedlibraries/frameworks (e.g., Spring) access application code's beans or entities (case 2).

Resolving Case 1: Reflective Call Into JDK

As JDK modules are immutable, the solution lies in command-line flags that open packages for reflection. For example, to resolve the exception:

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

Resolving Case 2: Reflection Over Application Code

If the reflecting code is in an editable module, consider enhancing its module descriptor:

• exports: Publish the package, making it available to all code at compile and runtime.
• exports ... to: Publish the package to the accessing module specifically.
• opens: Allow runtime access (with or without reflection) to the package for all code.
• opens ... to: Allow runtime access (with or without reflection) to the package for a specific module.
• open module: Open the entire module for runtime access (with or without reflection) to all code.

Other Remedies

In Java 9 only, you can disable encapsulation protection with:

java --permit-illegal-access

Note: This flag should be used sparingly due to security implications. Consult the linked resources for further details on module configurations and best practices.

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