Re: AspectJ modify property field content or add and/or change method body in a runtime instance

From:

=?ISO-8859-1?Q?Arne_Vajh=F8j?= <arne@vajhoej.dk>

Newsgroups:

comp.lang.java.programmer

Date:

Sat, 08 Aug 2009 21:31:00 -0400

Message-ID:

<4a7e26d6$0$304$14726298@news.sunsite.dk>

Jimmy wrote:

I have all source codes, however, there's no setter method for the
private data members. In the extreme case, if I need to change both
private data member and private method in a private sub class of a
package private class, can this be done still with AspectJ?

The method intercept should be doable using the around
technique in the previous example.

Accessing the private field requires reflection but it
can be facilitated by AspectJ.

Demo:

public class Dummy {
     public int v;
     public Dummy() {
         v = 123;
     }
     public String toString() {
         return "#" + v + "#";
     }
}

public interface Hack {
     public void setV(int v);
}

import java.lang.reflect.*;

public aspect HackImpl {
     declare parents: Dummy implements Hack;
     public void Hack.setV(int v) {
         try {
             Field field = getClass().getDeclaredField("v");
             field.setAccessible(true);
             field.setInt(this, v);
             } catch (NoSuchFieldException nsfe) {
                 nsfe.printStackTrace();
             } catch (IllegalAccessException iae) {
                 iae.printStackTrace();
             }
     }
}

public class Main {
     public static void main(String[] args) {
         Dummy o = new Dummy();
         System.out.println(o);
         ((Hack)o).setV(456);
         System.out.println(o);
     }
}

C:\>ajc Main.java Dummy.java Hack.java HackImpl.aj

C:\>java Main
#123#
#456#

Arne