Why does using an action name that is the same as a configured SpringBean name result in a ClassCastException?

Question

To reproduce this problem use the following steps.

1. Create a new Grails application.
2. Create a new controller called FooController
3. Add an action "bar" to FooController
4. In src/groovy, create a new class called Bar

5. In resources.groovy configure a SpringBean called bar

   bar(Bar) {bean -> bean.autowire = 'byName' }

6. Start the application and navigate to http:localhost:8080/[appContext]/foo/bar
7. You should get a stacktrace similar to this:

java.lang.ClassCastException: Bar cannot be cast to groovy.lang.Closure at org.grails.plugin.resource.DevModeSanityFilter.doFilter(DevModeSanityFilter.groovy:44) at java.lang.Thread.run(Thread.java:680)'

Why is this occuring? Is it a bug in Grails or expected behaviour?

I would expect that there should not be name clashes between configured SpringBeans and action names.

Answer 1

The problem is that Groovy syntax like

class FooController {
  def bar = {
    // do something
  }
}

gives the FooController class two public methods

public Object getBar() {
  return bar;
}

public void setBar(Object newBar) {
  bar = newBar;
}

The existence of the setBar method makes Spring consider it as a property to be autowired, and it replaces the closure value with your bean. Grails itself only requires the getter method, so if instead you say

class FooController {
  final bar = {
    // do something
  }
}

(i.e. declare bar to be final) then Groovy will synthesize only the getter and not the setter, and Spring will not see bar as a property it can autowire.