# MethodInvoker.java

    /*
    ** Module   : MethodInvoker.java
    ** Abstract : simple delegated method invocation mechanism
    **
    ** Copyright (c) 2006-2019, Golden Code Development Corporation.
    **
    ** -#- -I- --Date-- --JPRM-- ----------------------------Description------------------------------
    ** 001 GES 20060723 @28169   Provides a simple delegated method invocation mechanism.
    ** 002 CA  20190324          Changed invoke to performs the call using either ReflectASM or
    **                           Java reflection.
    */
    /*
    ** This program is free software: you can redistribute it and/or modify
    ** it under the terms of the GNU Affero General Public License as
    ** published by the Free Software Foundation, either version 3 of the
    ** License, or (at your option) any later version.
    **
    ** This program is distributed in the hope that it will be useful,
    ** but WITHOUT ANY WARRANTY; without even the implied warranty of
    ** MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    ** GNU Affero General Public License for more details.
    **
    ** You may find a copy of the GNU Affero GPL version 3 at the following
    ** location: https://www.gnu.org/licenses/agpl-3.0.en.html
    **
    ** Additional terms under GNU Affero GPL version 3 section 7:
    **
    **   Under Section 7 of the GNU Affero GPL version 3, the following additional
    **   terms apply to the works covered under the License.  These additional terms
    **   are non-permissive additional terms allowed under Section 7 of the GNU
    **   Affero GPL version 3 and may not be removed by you.
    **
    **   0. Attribution Requirement.
    **
    **     You must preserve all legal notices or author attributions in the covered
    **     work or Appropriate Legal Notices displayed by works containing the covered
    **     work.  You may not remove from the covered work any author or developer
    **     credit already included within the covered work.
    **
    **   1. No License To Use Trademarks.
    **
    **     This license does not grant any license or rights to use the trademarks
    **     Golden Code, FWD, any Golden Code or FWD logo, or any other trademarks
    **     of Golden Code Development Corporation. You are not authorized to use the
    **     name Golden Code, FWD, or the names of any author or contributor, for
    **     publicity purposes without written authorization.
    **
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    **
    **     You may not represent yourself as Golden Code Development Corporation or FWD.
    **
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    **     Golden Code Development Corporation, FWD, or any author or contributor to
    **     the covered work, without written authorization.
    **
    **   3. No Misrepresentation of Source or Origin.
    **
    **     You may not represent the covered work as solely your work.  All modified
    **     versions of the covered work must be marked in a reasonable way to make it
    **     clear that the modified work is not originating from Golden Code Development
    **     Corporation or FWD.  All modified versions must contain the notices of
    **     attribution required in this license.
    */

    package com.goldencode.p2j.util;

    import java.lang.reflect.*;
    import java.util.*;

    import com.esotericsoftware.reflectasm.*;

    /**
     * Helper class to delegate execution of <code>Method.invoke</code>.
     */
    public class MethodInvoker
    implements Invocable
    {
       /** Flag indicating if ReflectASM is available. */
       private static boolean useReflectAsm = true;

       static
       {
          try
          {
             Class.forName("com.esotericsoftware.reflectasm.MethodAccess");
          }
          catch (ClassNotFoundException cnf)
          {
             useReflectAsm = false;
          }
       }

       /** Reference to instance of class which will handle calls. */
       private Object instance = null;

       /** The method to be executed. */
       private Method method = null;

       /** The ReflectASM access point to this method. */
       private MethodAccess access = null;

       /** The method index in the MethodAccess instance. */
       private int index = -1;

       /**
        * Construct an instance that can make an invocation of a specific
        * local method.
        *
        * @param    instance
        *           The object on which the method is invoked or <code>null</code>
        *           if this method is <code>static</code>.
        * @param    method
        *           The method to be executed.
        */
       public MethodInvoker(Object instance, Method method)
       {
          this.instance = instance;
          this.method   = method;

          if (useReflectAsm && !Modifier.isPrivate(method.getModifiers()))
          {
             access = MethodAccess.get(method.getDeclaringClass());
             index = access.getIndex(method.getName(), method.getParameterTypes());
          }
       }

       /**
        * Return a text description of the method being invoked.
        *
        * @return   The description.
        */
       public String describe()
       {
          return method.toString();
       }

       /**
        * Execute or "run" the object's functionality.
        *
        * @param    args
        *           The method arguments or <code>null</code> for no arguments.
        *
        * @return   The called method's return value or <code>null</code> if
        *           there is no return value.  Note that this design does not
        *           allow the caller to determine the difference between a
        *           <code>void</code> return and a return of a genuine
        *           <code>null</code>.
        *
        * @throws   Throwable
        *           If the called method generates any exception or error.
        */
       public Object invoke(Object[] args)
       throws Throwable
       {
          return access == null ? method.invoke(instance, args)
                                : access.invoke(instance, index, args);
       }
    }