Using Groovy MetaClass to overwrite Methods

Question

I have a POJO that uses a service to do something:

public class PlainOldJavaObject {

    private IService service;

    public String publicMethod(String x) {
          


        

Answer 1

If your POJO really is a Java class, and not a Groovy class, then that is your problem. Java classes don't invoke methods via the metaClass. e.g., in Groovy:

pojo.publicMethod('arg')

is equivalent to this Java:

pojo.getMetaClass().invokeMethod('publicMethod','arg');

invokeMethod sends the call through the metaClass. But this method:

public String publicMethod(String x) {
    return doCallService(x);
}

is a Java method. It doesn't use invokeMethod to call doCallService. To get your code to work, PlainOldJavaObject needs to be a Groovy class so that all calls will go through the metaClass. Normal Java code doesn't use metaClasses.

In short: even Groovy can't override Java method calls, it can only override calls from Groovy or that otherwise dispatch through invokeMethod.