CODEWITHSUNDEEP
javagenericsreflectiongroovytype-erasure
Dónal
Dónal

Reputation: 187529

get property types at runtime

I have a Groovy class such as

class User {
    List<Foo> someFoos = new ArrayList<Foo>()
    List<Bar> someBars = new ArrayList<Bar>()    
}

I can iterate over these properties at runtime using

def user = new User()
List<MetaProperty> setProperties = user.metaClass.properties.findAll {MetaProperty property ->
    property.name.startsWith('some')
}

If I inspect the type of each of these properties Set is returned

setProperties.each {MetaProperty setProperty -> 
    assert setProperty.type == Set    
}

Is there any way at runtime I can get the generic type parameter (Foo and Bar) for each of these properties?

I strongly suspect I cannot due to type erasure, but If someone could confirm my suspicions, I'd appreciate it.

Upvotes: 7

Views: 5121

Answers (1)

Bozho
Bozho

Reputation: 597076

Yes, you can. These are field definitions and they retain their type definitions at runtime. I'll give you the java code, you can also use it in groovy (I don't know a groovy-specific solution)

Field[] fields = User.class.getDeclaredFields();
for (Field field : fields) {
    ParameterizedType pt = (ParameterizedType) field.getGenericType();
    Type concreteType = pt.getActualTypeArguments()[0];
}

Upvotes: 14

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