Question

Can I implement Groovy’s getProperty in Java Objects

I have a mixed Java/Groovy project, and I’m trying to add some “sugar” to my Java objects to make the Groovy side cleaner.

Is it possible to implement Object getProperty(String) in a Java class and have Groovy see it when accessing properties on that instance?

I have a failing test case as follows:

// HasProperty.java
public class HasProperty {
    public Object getProperty(String name) {
        return "pie";
    }
}

// TestHasProperty.groovy
class HasPropertyTest {
    @org.junit.Test 
    public void testCanGetProperty() {
        def h = new HasProperty()
        assert h.name == "pie"
    }
}

The test fails without fanfare:

groovy.lang.MissingPropertyException: No such property: name for class: HasProperty
    at org.codehaus.groovy.runtime.ScriptBytecodeAdapter.unwrap(ScriptBytecodeAdapter.java:50)
    at org.codehaus.groovy.runtime.callsite.GetEffectivePojoPropertySite.getProperty(GetEffectivePojoPropertySite.java:63)
    at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callGetProperty(AbstractCallSite.java:227)
    at [...]

This is Groovy 1.8.6 and Java 6.

Answer 1

To make this work without implementing GroovyObject as per @tim_yates’s answer, you can wrap the object with a very simple groovy object. For example:

class GroovyWrapper extends groovy.util.Proxy {
    def wrapped
    GroovyWrapper(obj) {
        wrapped = obj
        adaptee = obj
    }
    def getProperty(String name) {
        wrapped.getProperty()
    }
}

def h = new GroovyWrapper(new HasProperty())
assert h.name == "pie"