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
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**     name Golden Code, FWD, or the names of any author or contributor, for
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*/

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);
   }
}