genericcollectiontyperesolver.java

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/*
 * Copyright 2002-2008 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.core;

import java.lang.reflect.Array;
import java.lang.reflect.Field;
import java.lang.reflect.GenericArrayType;
import java.lang.reflect.Method;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.lang.reflect.TypeVariable;
import java.lang.reflect.WildcardType;
import java.util.Collection;
import java.util.Map;

/**
 * Helper class for determining element types of collections and maps.
 *
 * <p>Mainly intended for usage within the framework, determining the
 * target type of values to be added to a collection or map
 * (to be able to attempt type conversion if appropriate).
 *
 * <p>Only usable on Java 5. Use an appropriate JdkVersion check before
 * calling this class, if a fallback for JDK 1.4 is desirable.
 *
 * @author Juergen Hoeller
 * @since 2.0
 * @see org.springframework.beans.BeanWrapperImpl
 * @see JdkVersion
 */
public abstract class GenericCollectionTypeResolver {

	/**
	 * Determine the generic element type of the given Collection class
	 * (if it declares one through a generic superclass or generic interface).
	 * @param collectionClass the collection class to introspect
	 * @return the generic type, or <code>null</code> if none
	 */
	public static Class getCollectionType(Class collectionClass) {
		return extractTypeFromClass(collectionClass, Collection.class, 0);
	}

	/**
	 * Determine the generic key type of the given Map class
	 * (if it declares one through a generic superclass or generic interface).
	 * @param mapClass the map class to introspect
	 * @return the generic type, or <code>null</code> if none
	 */
	public static Class getMapKeyType(Class mapClass) {
		return extractTypeFromClass(mapClass, Map.class, 0);
	}

	/**
	 * Determine the generic value type of the given Map class
	 * (if it declares one through a generic superclass or generic interface).
	 * @param mapClass the map class to introspect
	 * @return the generic type, or <code>null</code> if none
	 */
	public static Class getMapValueType(Class mapClass) {
		return extractTypeFromClass(mapClass, Map.class, 1);
	}

	/**
	 * Determine the generic element type of the given Collection field.
	 * @param collectionField the collection field to introspect
	 * @return the generic type, or <code>null</code> if none
	 */
	public static Class getCollectionFieldType(Field collectionField) {
		return getGenericFieldType(collectionField, Collection.class, 0, 1);
	}

	/**
	 * Determine the generic element type of the given Collection field.
	 * @param collectionField the collection field to introspect
	 * @param nestingLevel the nesting level of the target type
	 * (typically 1; e.g. in case of a List of Lists, 1 would indicate the
	 * nested List, whereas 2 would indicate the element of the nested List)
	 * @return the generic type, or <code>null</code> if none
	 */
	public static Class getCollectionFieldType(Field collectionField, int nestingLevel) {
		return getGenericFieldType(collectionField, Collection.class, 0, nestingLevel);
	}

	/**
	 * Determine the generic key type of the given Map field.
	 * @param mapField the map field to introspect
	 * @return the generic type, or <code>null</code> if none
	 */
	public static Class getMapKeyFieldType(Field mapField) {
		return getGenericFieldType(mapField, Map.class, 0, 1);
	}

	/**
	 * Determine the generic key type of the given Map field.
	 * @param mapField the map field to introspect
	 * @param nestingLevel the nesting level of the target type
	 * (typically 1; e.g. in case of a List of Lists, 1 would indicate the
	 * nested List, whereas 2 would indicate the element of the nested List)
	 * @return the generic type, or <code>null</code> if none
	 */
	public static Class getMapKeyFieldType(Field mapField, int nestingLevel) {
		return getGenericFieldType(mapField, Map.class, 0, nestingLevel);
	}

	/**
	 * Determine the generic value type of the given Map field.
	 * @param mapField the map field to introspect
	 * @return the generic type, or <code>null</code> if none
	 */
	public static Class getMapValueFieldType(Field mapField) {
		return getGenericFieldType(mapField, Map.class, 1, 1);
	}

	/**
	 * Determine the generic value type of the given Map field.
	 * @param mapField the map field to introspect
	 * @param nestingLevel the nesting level of the target type
	 * (typically 1; e.g. in case of a List of Lists, 1 would indicate the
	 * nested List, whereas 2 would indicate the element of the nested List)
	 * @return the generic type, or <code>null</code> if none
	 */
	public static Class getMapValueFieldType(Field mapField, int nestingLevel) {
		return getGenericFieldType(mapField, Map.class, 1, nestingLevel);
	}

	/**
	 * Determine the generic element type of the given Collection parameter.
	 * @param methodParam the method parameter specification
	 * @return the generic type, or <code>null</code> if none
	 */
	public static Class getCollectionParameterType(MethodParameter methodParam) {
		return getGenericParameterType(methodParam, Collection.class, 0);
	}

	/**
	 * Determine the generic key type of the given Map parameter.
	 * @param methodParam the method parameter specification
	 * @return the generic type, or <code>null</code> if none
	 */
	public static Class getMapKeyParameterType(MethodParameter methodParam) {
		return getGenericParameterType(methodParam, Map.class, 0);
	}

	/**
	 * Determine the generic value type of the given Map parameter.
	 * @param methodParam the method parameter specification
	 * @return the generic type, or <code>null</code> if none
	 */
	public static Class getMapValueParameterType(MethodParameter methodParam) {
		return getGenericParameterType(methodParam, Map.class, 1);
	}

	/**
	 * Determine the generic element type of the given Collection return type.
	 * @param method the method to check the return type for
	 * @return the generic type, or <code>null</code> if none
	 */
	public static Class getCollectionReturnType(Method method) {
		return getGenericReturnType(method, Collection.class, 0, 1);
	}

	/**
	 * Determine the generic element type of the given Collection return type.
	 * <p>If the specified nesting level is higher than 1, the element type of
	 * a nested Collection/Map will be analyzed.
	 * @param method the method to check the return type for
	 * @param nestingLevel the nesting level of the target type
	 * (typically 1; e.g. in case of a List of Lists, 1 would indicate the
	 * nested List, whereas 2 would indicate the element of the nested List)
	 * @return the generic type, or <code>null</code> if none
	 */
	public static Class getCollectionReturnType(Method method, int nestingLevel) {
		return getGenericReturnType(method, Collection.class, 0, nestingLevel);
	}

	/**
	 * Determine the generic key type of the given Map return type.
	 * @param method the method to check the return type for
	 * @return the generic type, or <code>null</code> if none
	 */
	public static Class getMapKeyReturnType(Method method) {
		return getGenericReturnType(method, Map.class, 0, 1);
	}

	/**
	 * Determine the generic key type of the given Map return type.
	 * @param method the method to check the return type for
	 * @param nestingLevel the nesting level of the target type
	 * (typically 1; e.g. in case of a List of Lists, 1 would indicate the
	 * nested List, whereas 2 would indicate the element of the nested List)
	 * @return the generic type, or <code>null</code> if none
	 */
	public static Class getMapKeyReturnType(Method method, int nestingLevel) {
		return getGenericReturnType(method, Map.class, 0, nestingLevel);
	}

	/**
	 * Determine the generic value type of the given Map return type.
	 * @param method the method to check the return type for