There are certain limitations and restrictions when modifying the
system classes. Here is what works:
Your aspect:
public privileged aspect StringUtils {
public String String.ltrim() {
return "test ltrim";
}
}
Apply that to the JVM classes:
ajc -inpath rt.jar StringUtils.java -outjar newrt.jar
(rt.jar being the windows jar containing String)
Your main class:
public class Main {
public static void main(String []argv) {
String string = "ABCDEFG";
string = string.ltrim();
System.out.println(string);
}
}
Compiling it:
javac -Xbootclasspath/p:newrt.jar Main.java
(need the newrt ahead of the regular rt, hence the -X)
Running it:
java -Xbootclasspath/p:newrt.jar Main
test ltrim
Basically load time weaving isn't going to work for you as these
classes get loaded early on and by a loader that doesn't get a weaver
attached to it - so we go with compile time weaving. Because we are
compile time weaving we have to ensure our woven classes are used
instead of those the JVM would ordinarily use (-Xbootclasspath/p where
p is for prefix).
I can't comment on the legality of it, but I perhaps wouldn't advise
shipping a product that included a modified set of classes like this.
But it can be done.
cheers,
Andy
On 7 June 2012 10:17, MattOng <on...@yahoo.com> wrote:
>
> From what I can see in sample code:
>
> public class Point{}
>
> public aspect Point
> {
> // a new method is introduced into the Point Class.
> public String Point.toLongString(){
> return "### FROM ASPECT ###";
> }
> }
>
> public class Main{
> public static void main(String[] args){
> Point p1 = new Point();
>
> // This line below works without any error.
> System.out.println("p1.toLongString =" +p1.toLongString());
> System.out.println("p1 =" + p1);
> }
> }
>
> ---------------------------------------------------------------
> However, when I tried this, it does not work
>
> // Extends the String class and provide other useful
> public privileged aspect StringUtils {
>
> public String java.lang.String.ltrim(){
> return "TEST LTRIM";
> }
>
> public String java.lang.String.rtrim(){
> return "TEST RTRIM";
> }
>
> }
>
> public class Main {
> public static void main(String[] args) {
> String string="ABCDEFG";
> // Complians with the error shown below
> string=string.ltrim();
> System.out.println(string);
> }
> }
>
> ---------------------------------------------------------
> Exception in thread "main" java.lang.NoSuchMethodError:
> java.lang.String.ltrim()Ljava/lang/String;
> at
> stringext.StringUtils.ajc$interMethodDispatch1$stringext_StringUtils$java_lang_String$ltrim(StringUtils.aj)
> at stringext.Main.main(Main.java:11)
> ----------------------------------------------------------
>
> Please help to show how this can be done properly. Many thanks in advance.
>
>
> --
> View this message in context:
> http://aspectj.2085585.n4.nabble.com/How-to-add-methods-to-java-lang-String-tp4650376.html
> Sent from the AspectJ - users mailing list archive at Nabble.com.
> _______________________________________________
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> aspectj-users@eclipse.org
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