title: How to solve InaccessibleObjectException ("Unable to make {member} accessible: module {A} does not 'opens {package}' to {B}") on Java 9?
body: <p>This exception occurs in a wide variety of scenarios when running an application on Java 9.
  Certain libraries and frameworks (Spring, Hibernate, JAXB) are particularly prone to it.
  Here's an example from Javassist:</p>
  
  <pre><code>java.lang.reflect.InaccessibleObjectException: Unable to make protected final java.lang.Class java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain) throws java.lang.ClassFormatError accessible: module java.base does not "opens java.lang" to unnamed module @1941a8ff
      at java.base/jdk.internal.reflect.Reflection.throwInaccessibleObjectException(Reflection.java:427)
      at java.base/java.lang.reflect.AccessibleObject.checkCanSetAccessible(AccessibleObject.java:201)
      at java.base/java.lang.reflect.Method.checkCanSetAccessible(Method.java:192)
      at java.base/java.lang.reflect.Method.setAccessible(Method.java:186)
      at javassist.util.proxy.SecurityActions.setAccessible(SecurityActions.java:102)
      at javassist.util.proxy.FactoryHelper.toClass2(FactoryHelper.java:180)
      at javassist.util.proxy.FactoryHelper.toClass(FactoryHelper.java:163)
      at javassist.util.proxy.ProxyFactory.createClass3(ProxyFactory.java:501)
      at javassist.util.proxy.ProxyFactory.createClass2(ProxyFactory.java:486)
      at javassist.util.proxy.ProxyFactory.createClass1(ProxyFactory.java:422)
      at javassist.util.proxy.ProxyFactory.createClass(ProxyFactory.java:394)
  </code></pre>
  
  <p>The message says:</p>
  
  <blockquote>
    <p>Unable to make protected final java.lang.Class java.lang.ClassLoader.defineClass(java.lang.String,byte[],int,int,java.security.ProtectionDomain) throws java.lang.ClassFormatError accessible: module java.base does not "opens java.lang" to unnamed module @1941a8ff</p>
  </blockquote>
  
  <p>What can be done to avoid the exception and have the program run successfully?</p>