Refactor definePackage as well.

Yes it is deprecated but seems the right thing to do

src/main/javassist/ClassPool.java

@@ -21,19 +21,16 @@ import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
-import java.lang.reflect.Method;
 import java.net.URL;
-import java.security.AccessController;
-import java.security.PrivilegedActionException;
-import java.security.PrivilegedExceptionAction;
 import java.security.ProtectionDomain;
-import java.util.Hashtable;
-import java.util.Iterator;
 import java.util.ArrayList;
 import java.util.Enumeration;
+import java.util.Hashtable;
+import java.util.Iterator;
 
 import javassist.bytecode.ClassFile;
 import javassist.bytecode.Descriptor;
+import javassist.util.proxy.DefinePackageHelper;
 
 /**
  * A container of <code>CtClass</code> objects.
@@ -69,28 +66,8 @@ import javassist.bytecode.Descriptor;
  * @see javassist.CtClass
  * @see javassist.ClassPath
  */
+@SuppressWarnings({"unchecked", "rawtypes"})
 public class ClassPool {
-    private static java.lang.reflect.Method definePackage = null;
-
-    static {
-        if (ClassFile.MAJOR_VERSION < ClassFile.JAVA_9)
-            try {
-                AccessController.doPrivileged(new PrivilegedExceptionAction(){
-                    public Object run() throws Exception{
-                        Class cl = Class.forName("java.lang.ClassLoader");
-                        definePackage = cl.getDeclaredMethod("definePackage",
-                                new Class[] { String.class, String.class, String.class,
-                                        String.class, String.class, String.class,
-                                        String.class, java.net.URL.class });
-                        return null;
-                    }
-                });
-            }
-            catch (PrivilegedActionException pae) {
-                throw new RuntimeException("cannot initialize ClassPool",
-                                           pae.getException());
-            }
-    }
 
     /**
      * Determines the search order.
@@ -1175,43 +1152,7 @@ public class ClassPool {
     public void makePackage(ClassLoader loader, String name)
         throws CannotCompileException
     {
-        if (definePackage == null)
-            throw new CannotCompileException("give the JVM --add-opens");
-
-        Object[] args = new Object[] {
-                name, null, null, null, null, null, null, null };
-        Throwable t;
-        try {
-            makePackage2(definePackage, loader, args);
-            return;
-        }
-        catch (java.lang.reflect.InvocationTargetException e) {
-            t = e.getTargetException();
-            if (t == null)
-                t = e;
-            else if (t instanceof IllegalArgumentException) {
-                // if the package is already defined, an IllegalArgumentException
-                // is thrown.
-                return;
-            }
-        }
-        catch (Exception e) {
-            t = e;
-        }
-
-        throw new CannotCompileException(t);
+        DefinePackageHelper.definePackage(name, loader);
     }
 
-    private static synchronized Object makePackage2(Method method,
-            ClassLoader loader, Object[] args)
-        throws Exception
-    {
-        method.setAccessible(true);
-        try {
-            return method.invoke(loader, args);
-        }
-        finally {
-            method.setAccessible(false);
-        }
-    }
 }

src/main/javassist/util/proxy/DefinePackageHelper.java

@@ -0,0 +1,179 @@
+/*
+ * Javassist, a Java-bytecode translator toolkit.
+ * Copyright (C) 1999- Shigeru Chiba. All Rights Reserved.
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License.  Alternatively, the contents of this file may be used under
+ * the terms of the GNU Lesser General Public License Version 2.1 or later,
+ * or the Apache License Version 2.0.
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ */
+
+package javassist.util.proxy;
+
+import java.lang.invoke.MethodHandle;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.net.URL;
+
+import javassist.CannotCompileException;
+import javassist.CtClass;
+import javassist.bytecode.ClassFile;
+
+/**
+ * Helper class for invoking {@link ClassLoader#defineClass(String,byte[],int,int)}.
+ *
+ * @since 3.22
+ */
+public class DefinePackageHelper
+{
+            
+    private static enum SecuredPrivileged
+    {
+        JAVA_9 {
+            // definePackage has been discontinued for JAVA 9
+            @Override
+            protected Package definePackage(ClassLoader loader, String name, String specTitle,
+                    String specVersion, String specVendor, String implTitle, String implVersion,
+                    String implVendor, URL sealBase) throws IllegalArgumentException
+            {
+                throw new RuntimeException("define package has been disabled for jigsaw");
+            }
+        },
+        JAVA_7 {
+            private final SecurityActions stack = SecurityActions.stack;
+            private final MethodHandle definePackage = getDefinePackageMethodHandle();
+            private MethodHandle getDefinePackageMethodHandle()
+            {
+                if (stack.getCallerClass() != this.getClass())
+                    throw new IllegalAccessError("Access denied for caller.");
+                try {
+                    return SecurityActions.getMethodHandle(ClassLoader.class, 
+                            "definePackage", new Class[] {
+                                String.class, String.class, String.class, String.class,
+                                String.class, String.class, String.class, URL.class 
+                            });
+                } catch (NoSuchMethodException e) {
+                    throw new RuntimeException("cannot initialize", e);
+                }
+            }
+            
+            @Override
+            protected Package definePackage(ClassLoader loader, String name, String specTitle,
+                    String specVersion, String specVendor, String implTitle, String implVersion,
+                    String implVendor, URL sealBase) throws IllegalArgumentException {
+                if (stack.getCallerClass() != DefinePackageHelper.class)
+                    throw new IllegalAccessError("Access denied for caller.");
+                try {
+                    return (Package) definePackage.invokeWithArguments(loader, name, specTitle,
+                        specVersion, specVendor, implTitle, implVersion, implVendor, sealBase);
+                } catch (Throwable e) {
+                    if (e instanceof IllegalArgumentException) throw (IllegalArgumentException) e;
+                    if (e instanceof RuntimeException) throw (RuntimeException) e;
+                }
+                return null;
+            }
+        },
+        JAVA_OTHER {
+            private final SecurityActions stack = SecurityActions.stack;
+            private final Method definePackage = getDefinePackageMethod();
+            private Method getDefinePackageMethod()
+            {
+                if (stack.getCallerClass() != this.getClass())
+                    throw new IllegalAccessError("Access denied for caller.");
+                try {
+                    return SecurityActions.getDeclaredMethod(ClassLoader.class, 
+                            "definePackage", new Class[] {
+                                String.class, String.class, String.class, String.class,
+                                String.class, String.class, String.class, URL.class 
+                            });
+                } catch (NoSuchMethodException e) {
+                    throw new RuntimeException("cannot initialize", e);
+                }
+            }
+            
+            @Override
+            protected Package definePackage(ClassLoader loader, String name, String specTitle,
+                    String specVersion, String specVendor, String implTitle, String implVersion,
+                    String implVendor, URL sealBase) throws IllegalArgumentException
+            {
+                if (stack.getCallerClass() != DefinePackageHelper.class)
+                    throw new IllegalAccessError("Access denied for caller.");
+                try {
+                    definePackage.setAccessible(true);
+                    return (Package) definePackage.invoke(loader, new Object[] {
+                        name, specTitle, specVersion, specVendor, implTitle,
+                        implVersion, implVendor, sealBase                                
+                    });
+                } catch (Throwable e) {
+                    if (e instanceof InvocationTargetException) {
+                        Throwable t = ((InvocationTargetException) e).getTargetException();
+                        if (t instanceof IllegalArgumentException)
+                            throw (IllegalArgumentException) t;
+                    }
+                    if (e instanceof RuntimeException) throw (RuntimeException) e;
+                }
+                finally {
+                    definePackage.setAccessible(false);
+                }
+                return null;
+            }
+        };
+
+        protected abstract Package definePackage(ClassLoader loader, String name, String specTitle,
+                String specVersion, String specVendor, String implTitle, String implVersion,
+                String implVendor, URL sealBase) throws IllegalArgumentException;
+    }
+
+    private static final SecuredPrivileged privileged = ClassFile.MAJOR_VERSION >= ClassFile.JAVA_9
+            ? SecuredPrivileged.JAVA_9
+            : ClassFile.MAJOR_VERSION >= ClassFile.JAVA_7
+                ? SecuredPrivileged.JAVA_7
+                : SecuredPrivileged.JAVA_OTHER;
+
+
+    /**
+     * Defines a new package.  If the package is already defined, this method
+     * performs nothing.
+     *
+     * <p>You do not necessarily need to
+     * call this method.  If this method is called, then  
+     * <code>getPackage()</code> on the <code>Class</code> object returned 
+     * by <code>toClass()</code> will return a non-null object.</p>
+     *
+     * <p>The jigsaw module introduced by Java 9 has broken this method.
+     * In Java 9 or later, the VM argument
+     * <code>--add-opens java.base/java.lang=ALL-UNNAMED</code>
+     * has to be given to the JVM so that this method can run.
+     * </p>
+     *
+     * @param loader        the class loader passed to <code>toClass()</code> or
+     *                      the default one obtained by <code>getClassLoader()</code>.
+     * @param name          the package name.
+     * @see #getClassLoader()
+     * @see #toClass(CtClass)
+     * @see CtClass#toClass() */
+    public static void definePackage(String className, ClassLoader loader)
+        throws CannotCompileException
+    {
+        try {
+            privileged.definePackage(loader, className, 
+                    null, null, null, null, null, null, null);
+        }
+        catch (IllegalArgumentException e) {
+            // if the package is already defined, an IllegalArgumentException
+            // is thrown.
+            return;
+        }
+        catch (Exception e) {
+            throw new CannotCompileException(e);
+        }
+    }
+    
+    private DefinePackageHelper() {}
+}