DWR converter for Grails ORM classes. Uses the hasMany map to determine the type of collections so we can convert them inbound.

DwrGormConverter.java

package com.noahsloan.grails.dwr;

import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.util.Collection;
import java.util.Map;

import org.directwebremoting.convert.BeanConverter;
import org.directwebremoting.convert.CollectionConverter;
import org.directwebremoting.extend.InboundContext;
import org.directwebremoting.extend.Property;
import org.directwebremoting.extend.TypeHintContext;
import org.directwebremoting.util.Logger;

import com.sun.tools.jdi.LinkedHashMap;

/**
 * Converter for Grails ORM classes. Uses the hasMany map to determine the type
 * of collections so we can convert them inbound.
 * 
 * @author noah
 * 
 */
@SuppressWarnings("unchecked")
public class DwrGormConverter extends BeanConverter {

	private static final Logger LOG = org.directwebremoting.util.Logger
			.getLogger(DwrGormConverter.class);

	protected TypeHintContext createTypeHintContext(InboundContext inctx,
			final Property property) {
		// check collections
		if (Collection.class.isAssignableFrom(property.getPropertyType())) {
			final Class type = getCollectionType(property);
			if (type != null) {
				return createHint(property.getSetter(), type);
			}
		}
		return super.createTypeHintContext(inctx, property);
	}

	/**
	 * Pulled out for readability. Creates a type hint for the
	 * {@link CollectionConverter} with the given type.
	 * 
	 * @param setter TODO is this necessary?
	 * @param type
	 * @return
	 */
	protected TypeHintContext createHint(final Method setter,
			final Class type) {
		return new TypeHintContext(converterManager, setter, 0) {
			public TypeHintContext createChildContext(int newParameterNumber) {
				return new TypeHintContext(converterManager, setter, 0) {
					public Class getExtraTypeInfo() {
						return type;
					}
				};
			}
		};
	}

	protected static Map<Class, Map<String, Class>> _cache = new LinkedHashMap();

	/**
	 * Determines the type of the collection by examining the declaring class'
	 * static hasMany property.
	 * 
	 * @param property
	 * @return the type of the elements of the collection property.
	 */
	protected Class getCollectionType(Property property) {
		// determine the class the collection is attached to by examining
		// the setter (which is the domain class)
		Method setter = property.getSetter();
		if (setter == null) {
			// XXX in theory this should not happen because BeanConverter should
			// always provide PropertyDescriptionPropertys
			LOG.error("setter for "
					+ property.getName() + " is null."
					+ " Property is not a PropertyDescriptionProperty.");
			return null;
		}
		Class gormType = setter.getDeclaringClass();
		if (_cache.containsKey(gormType)) {
			Map<String, Class> map = _cache.get(gormType);
			return map == null ? null : map.get(property.getName());
		}
		try {
			Field field = gormType.getDeclaredField("hasMany");
			Map<String, Class> map = null;
			if (field != null) {				
				if (!field.isAccessible()) {
					field.setAccessible(true);
				}
				map = ((Map<String, Class>) field.get(null));
			}
			_cache.put(gormType, map);
			return map == null ? null : map.get(property.getName());
		} catch (Exception e) {
			LOG.error("Exception getting GORM collection type info.", e);
			return null;
		}
	}

}