redefine static methods with ByteBuddy - byte-buddy

Question

Can homebody help me please to give me a hint how to redefine static methods using byte-buddy 1.6.9 ?
I have tried this :
public class Source {
public static String hello(String name) {return null;}
}
public class Target {
public static String hello(String name) {
return "Hello" + name+ "!";
}
}
String helloWorld = new ByteBuddy()
.redefine(Source.class)
.method(named("hello"))
.intercept(MethodDelegation.to(Target.class))
.make()
.load(getClass().getClassLoader())
.getLoaded()
.newInstance()
.hello("World");
I got following Exception :
Exception in thread "main" java.lang.IllegalStateException: Cannot inject already loaded type: class delegation.Source
Thanks

Answer 1

Classes can only be loaded once by each class loader. In order to replace a method, you would need to use a Java agent to hook into the JVM's HotSwap feature.
Byte Buddy provides a class loading strategy that uses such an agent, use:
.load(Source.class.getClassLoader(),
ClassReloadingStrategy.fromInstalledAgent());
This does however require you to install a Java agent. On a JDK, you can do so programmatically, by ByteBuddyAgent.install() (included in the byte-buddy-agent artifact). On a JVM, you have to specify the agent on the command line.