具有参数的Scala 2.11反射和注释（Java）

Question

I have a simple class-level annotation written in Java:

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface Collection {
    String name();
}

used like:

@Collection(name="mytable")
case class Foo(...)

I need to introspect classes in Scala 2.11 to obtain the value of the name parameter. How can I get this info? I'm up to here:

val sym = currentMirror.classSymbol(Class.forName(fullName))
val anno = sym.annotations.head
val annoType = anno.tree.tpe  // I can get this...works
println(anno.tree.children.tail)  // prints List(name = "mytable")

I'm close! I can see my name parameter and its value but this doesn't seem to be accessible like a Map or anything friendly. How can I get the value of my annotation's parameter?

Answer 1

树形api实现了将元素取出的产品，因此这是一个很烂的演示，但是您可以取出元素：

  println(anno.tree.children.last.productElement(1))  // prints "mytable"

Answer 2

If you can handle using Jackson, then I'd re-use its annotation processing functionality instead of using scala reflection.

object Test {
  @Collection(name="mytable")
  case class Foo(bar: String)

  def main(args: Array[String]): Unit = {
    val introspector = new JacksonAnnotationIntrospector
    val ac = AnnotatedClass.construct(classOf[Foo], introspector, null)
    val annotation = ac.getAnnotations.get(classOf[Collection])

    println(annotation.name())
  }
}

If the class does not have the annotation then annotation is null.