Using SPEL to call a method in the same class passing a variable taken from the actual method

Question

I want to be able to call another method of my class by passing the value of a parameter of the calling method, so suppose:

public class MyClass{

   @MySpelAnnotation("#this.otherMethod()") //how to I pass "arg" as parameter?
   public void mainMethod(String arg){
        ...
   }

   public void otherMethod(String arg){

   }

How can I be able to take arg from the first method and pass it to the second one?

Answer 1

You need to evaluate the expression against an evaluation context that contains the argument bound as a variable under the #arg name:

@MySpelAnnotation("#this.otherMethod(#arg)")

You can use Spring's MethodBasedEvaluationContext for this:

@Aspect
static class MyAspect {
    @After("@annotation(annotation)")
    void after(JoinPoint joinPoint, MySpelAnnotation annotation) {
        MethodSignature signature = (MethodSignature) joinPoint.getSignature();

        // expression should be cached for better performance
        Expression expression = new SpelExpressionParser()
                .parseExpression(annotation.value());

        MethodBasedEvaluationContext context =
                new MethodBasedEvaluationContext(
                        joinPoint.getTarget(),
                        signature.getMethod(),
                        joinPoint.getArgs(),
                        new DefaultParameterNameDiscoverer());

        expression.getValue(context);
    }
}

Note that parsing the expression is a non-trivial operation that should ideally be cached.