ValueFieldExtractor.java

package moulder.values;

import moulder.Value;

import java.beans.BeanInfo;
import java.beans.IntrospectionException;
import java.beans.Introspector;
import java.beans.PropertyDescriptor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class ValueFieldExtractor<T, S> extends ValueTransformer<S, T> {

    private Method m;

    public ValueFieldExtractor(Value<S> delegate, String field,
                               Class<S> delegateResultClass) {
        super(delegate);

        try {
            BeanInfo bi = Introspector.getBeanInfo(delegateResultClass);
            PropertyDescriptor[] pds = bi.getPropertyDescriptors();
            for (PropertyDescriptor propertyDescriptor : pds) {
                if (field.equals(propertyDescriptor.getName())) {
                    m = propertyDescriptor.getReadMethod();
                    break;
                }
            }
            if (m == null) {
                throw new IllegalArgumentException("No property '" + field
                        + "' in " + delegateResultClass);
            }

        } catch (IntrospectionException e) {
            throw new RuntimeException(e);
        }
    }

    @SuppressWarnings("unchecked")
    @Override
    protected T transform(S s) {
        try {
            return (T) m.invoke(s);
        } catch (IllegalArgumentException e) {
            throw new RuntimeException(e);
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        } catch (InvocationTargetException e) {
            throw new RuntimeException(e);
        }
    }

}