How to Resolve InaccessibleObjectException in Java 9

What steps can be taken to resolve the InaccessibleObjectException in Java 9?

The InaccessibleObjectException in Java 9 occurs due to the introduction of the Java Platform Module System (JPMS), which enforces strong encapsulation for modules. This exception typically arises when trying to access properties or methods of a class that aren’t exported to the module in which the code is being executed, particularly when using reflection in libraries such as Spring, Hibernate, or Javassist.

// Example of adding --add-opens option in Gradle build
tasks.withType(JavaExec) {
    jvmArgs '--add-opens', 'java.base/java.lang=ALL-UNNAMED'
}

Causes

• Accessing internal classes or methods without the required module declarations.
• Using reflection to access classes/methods not made accessible by the module system.
• Third-party libraries that have not updated to comply with Java's module system.

Solutions

• Add the `--add-opens` JVM argument to specify modules and packages that should be opened for reflection. For example: ```sh java --add-opens java.base/java.lang=ALL-UNNAMED -jar your-application.jar ```
• Update libraries to their latest versions as they may contain fixes related to module access in Java 9.
• Where applicable, consider using Java's native accessors instead of reflection.
• Consider refactoring your code to avoid reliance on private/protected members whenever possible.

Mistake: Forgetting to include the `--add-opens` option when starting the JVM, which leads to persistent InaccessibleObjectException.

Solution: Always include the necessary --add-opens options specific to the modules in your application startup arguments.

Mistake: Using outdated versions of libraries that might not comply with Java 9's module system.

Solution: Regularly update all dependencies to the latest versions that are compatible with Java 9.