Aspectj是否可以访问Scala中方法的隐式参数？

Question

I'm using aspectJ to do some user authentication. It would be really nice to have the userId as an implicit parameter to a method. But I don't know if an aspectJ joinPoint can see an implicit parameter.

Anyone else try this?

Answer 1

Given a service

class User(val name: String) {
  override def toString = s"$name"
}

class Service {
  def run()(implicit user: User) {
    println(user.name)
  }

the implicit parameter just turns up as a "normal" argument in the class file (output from javap ):

public class app.scala.Service extends java.lang.Object{
    public void run(app.scala.User);
    public app.scala.Service();
}

so using a "normal" AspectJ pointcut like:

before(Service s, User user) : 
    call(void Service.run(User)) && target(s) && args(user) {

    System.out.println("Hello from AspectJ (before service run)");
    System.out.println("  "  + user);
}

works (applied to the .class files generated by scalac ).

From aspectj's point of view, an implicit parameter is nothing special. The Scala compiler merges arguments from multiple argument lists into a single one, and this is stored in the .class file.