org.springframework.expression.spel.support.ReflectiveConstructorResolver Maven / Gradle / Ivy

/*
 * Copyright 2002-2010 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.expression.spel.support;

import java.lang.reflect.Constructor;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;

import org.springframework.core.MethodParameter;
import org.springframework.core.convert.TypeDescriptor;
import org.springframework.expression.AccessException;
import org.springframework.expression.ConstructorExecutor;
import org.springframework.expression.ConstructorResolver;
import org.springframework.expression.EvaluationContext;
import org.springframework.expression.EvaluationException;
import org.springframework.expression.TypeConverter;

/**
 * A constructor resolver that uses reflection to locate the constructor that should be invoked
 * 
 * @author Andy Clement
 * @author Juergen Hoeller
 * @since 3.0
 */
public class ReflectiveConstructorResolver implements ConstructorResolver {

	/**
	 * Locate a constructor on the type. There are three kinds of match that might occur:
	 * 
	 * An exact match where the types of the arguments match the types of the constructor
	 * 
An in-exact match where the types we are looking for are subtypes of those defined on the constructor
	 * 
A match where we are able to convert the arguments into those expected by the constructor, according to the
	 * registered type converter.
	 * 
	 */
	public ConstructorExecutor resolve(EvaluationContext context, String typename, List argumentTypes)
			throws AccessException {

		try {
			TypeConverter typeConverter = context.getTypeConverter();
			Class type = context.getTypeLocator().findType(typename);
			Constructor[] ctors = type.getConstructors();

			Arrays.sort(ctors, new Comparator() {
				public int compare(Constructor c1, Constructor c2) {
					int c1pl = c1.getParameterTypes().length;
					int c2pl = c2.getParameterTypes().length;
					return (new Integer(c1pl)).compareTo(c2pl);
				}
			});

			Constructor closeMatch = null;
			int[] argsToConvert = null;
			Constructor matchRequiringConversion = null;

			for (Constructor ctor : ctors) {
				Class[] paramTypes = ctor.getParameterTypes();
				List paramDescriptors = new ArrayList(paramTypes.length);
				for (int i = 0; i < paramTypes.length; i++) {
					paramDescriptors.add(new TypeDescriptor(new MethodParameter(ctor, i)));
				}
				ReflectionHelper.ArgumentsMatchInfo matchInfo = null;
				if (ctor.isVarArgs() && argumentTypes.size() >= (paramTypes.length - 1)) {
					// *sigh* complicated
					// Basically.. we have to have all parameters match up until the varargs one, then the rest of what is
					// being provided should be
					// the same type whilst the final argument to the method must be an array of that (oh, how easy...not) -
					// or the final parameter
					// we are supplied does match exactly (it is an array already).
					matchInfo = ReflectionHelper.compareArgumentsVarargs(paramDescriptors, argumentTypes, typeConverter);
				}
				else if (paramTypes.length == argumentTypes.size()) {
					// worth a closer look
					matchInfo = ReflectionHelper.compareArguments(paramDescriptors, argumentTypes, typeConverter);
				}
				if (matchInfo != null) {
					if (matchInfo.kind == ReflectionHelper.ArgsMatchKind.EXACT) {
						return new ReflectiveConstructorExecutor(ctor, null);
					}
					else if (matchInfo.kind == ReflectionHelper.ArgsMatchKind.CLOSE) {
						closeMatch = ctor;
					}
					else if (matchInfo.kind == ReflectionHelper.ArgsMatchKind.REQUIRES_CONVERSION) {
						argsToConvert = matchInfo.argsRequiringConversion;
						matchRequiringConversion = ctor;
					}
				}
			}
			if (closeMatch != null) {
				return new ReflectiveConstructorExecutor(closeMatch, null);
			}
			else if (matchRequiringConversion != null) {
				return new ReflectiveConstructorExecutor(matchRequiringConversion, argsToConvert);
			}
			else {
				return null;
			}
		}
		catch (EvaluationException ex) {
			throw new AccessException("Failed to resolve constructor", ex);
		}
	}

}