customcollectioneditor.java

一个关于Spring框架的示例应用程序,简单使用,可以参考.

/*
 * Copyright 2002-2004 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.beans.propertyeditors;

import java.beans.PropertyEditorSupport;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Collection;
import java.util.List;
import java.util.SortedSet;
import java.util.TreeSet;

import org.springframework.core.CollectionFactory;

/**
 * Property editor for Collections, converting any source Collection
 * to a given target Collection type.
 *
 * <p>By default registered for Set, SortedSet and List,
 * to automatically convert any given Collection to one of those
 * target types if the type does not match the target property.
 *
 * @author Juergen Hoeller
 * @since 1.1.3
 * @see java.util.Collection
 * @see java.util.Set
 * @see java.util.SortedSet
 * @see java.util.List
 */
public class CustomCollectionEditor extends PropertyEditorSupport {

	private final Class collectionType;

	/**
	 * Create a new CustomCollectionEditor for the given target type.
	 * <p>If the incoming value is of the given type, it will be used as-is.
	 * If it is a different Collection type or an array, it will be converted
	 * to a default implementation of the given Collection type.
	 * If the value is anything else, a target Collection with that single
	 * value will be created.
	 * <p>The default Collection implementations are: ArrayList for List,
	 * TreeSet for SortedSet, and LinkedHashSet or HashSet for Set.
	 * @param collectionType the target type, which needs to be a
	 * sub-interface of Collection
	 * @see java.util.Collection
	 * @see java.util.ArrayList
	 * @see java.util.TreeSet
	 * @see org.springframework.core.CollectionFactory#createLinkedSetIfPossible
	 */
	public CustomCollectionEditor(Class collectionType) {
		if (collectionType == null) {
			throw new IllegalArgumentException("Collection type is required");
		}
		if (!collectionType.isInterface()) {
			throw new IllegalArgumentException("Collection type has to be an interface");
		}
		if (!Collection.class.isAssignableFrom(collectionType)) {
			throw new IllegalArgumentException(
					"Collection type [" + collectionType.getName() + "] does not implement [java.util.Collection]");
		}
		this.collectionType = collectionType;
	}

	/**
	 * Convert the given text value to a Collection with a single element.
	 */
	public void setAsText(String text) throws IllegalArgumentException {
		setValue(text);
	}

	/**
	 * Convert the given value to a Collection of the target type.
	 */
	public void setValue(Object value) {
		if (this.collectionType.isInstance(value)) {
			// Use the source value as-is, as it matches the target type.
			super.setValue(value);
		}
		else if (value instanceof Collection) {
			// Convert Collection elements to array elements.
			Collection source = (Collection) value;
			Collection target = createCollection(this.collectionType, source.size());
			target.addAll(source);
			super.setValue(target);
		}
		else if (value != null && value.getClass().isArray()) {
			// Convert array elements to Collection elements.
			int length = Array.getLength(value);
			Collection target = createCollection(this.collectionType, length);
			for (int i = 0; i < length; i++) {
				target.add(Array.get(value, i));
			}
			super.setValue(target);
		}
		else {
			// A plain value: convert it to a Collection with a single element.
			Collection target = createCollection(this.collectionType, 1);
			target.add(value);
			super.setValue(target);
		}
	}

	/**
	 * Create a Collection of the given type, with the given
	 * initial capacity (if supported by the Collection type).
	 * @param collectionType a sub-interface of Collection
	 * @param initialCapacity the initial capacity
	 * @return the new Collection instance
	 */
	protected Collection createCollection(Class collectionType, int initialCapacity) {
		if (List.class.equals(collectionType)) {
			return new ArrayList(initialCapacity);
		}
		else if (SortedSet.class.equals(collectionType)) {
			return new TreeSet();
		}
		else {
			return CollectionFactory.createLinkedSetIfPossible(initialCapacity);
		}
	}

}