org.springframework.util.AutoPopulatingList Maven / Gradle / Ivy
/*
* Copyright 2002-2016 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
*
* https://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.util;
import java.io.Serializable;
import java.lang.reflect.Modifier;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
/**
* Simple {@link List} wrapper class that allows for elements to be
* automatically populated as they are requested. This is particularly
* useful for data binding to {@link List Lists}, allowing for elements
* to be created and added to the {@link List} in a "just in time" fashion.
*
* Note: This class is not thread-safe. To create a thread-safe version,
* use the {@link java.util.Collections#synchronizedList} utility methods.
*
*
Inspired by {@code LazyList} from Commons Collections.
*
* @author Rob Harrop
* @author Juergen Hoeller
* @since 2.0
*/
@SuppressWarnings("serial")
public class AutoPopulatingList implements List, Serializable {
/**
* The {@link List} that all operations are eventually delegated to.
*/
private final List backingList;
/**
* The {@link ElementFactory} to use to create new {@link List} elements
* on demand.
*/
private final ElementFactory elementFactory;
/**
* Creates a new {@code AutoPopulatingList} that is backed by a standard
* {@link ArrayList} and adds new instances of the supplied {@link Class element Class}
* to the backing {@link List} on demand.
*/
public AutoPopulatingList(Class elementClass) {
this(new ArrayList(), elementClass);
}
/**
* Creates a new {@code AutoPopulatingList} that is backed by the supplied {@link List}
* and adds new instances of the supplied {@link Class element Class} to the backing
* {@link List} on demand.
*/
public AutoPopulatingList(List backingList, Class elementClass) {
this(backingList, new ReflectiveElementFactory(elementClass));
}
/**
* Creates a new {@code AutoPopulatingList} that is backed by a standard
* {@link ArrayList} and creates new elements on demand using the supplied {@link ElementFactory}.
*/
public AutoPopulatingList(ElementFactory elementFactory) {
this(new ArrayList(), elementFactory);
}
/**
* Creates a new {@code AutoPopulatingList} that is backed by the supplied {@link List}
* and creates new elements on demand using the supplied {@link ElementFactory}.
*/
public AutoPopulatingList(List backingList, ElementFactory elementFactory) {
Assert.notNull(backingList, "Backing List must not be null");
Assert.notNull(elementFactory, "Element factory must not be null");
this.backingList = backingList;
this.elementFactory = elementFactory;
}
@Override
public void add(int index, E element) {
this.backingList.add(index, element);
}
@Override
public boolean add(E o) {
return this.backingList.add(o);
}
@Override
public boolean addAll(Collection c) {
return this.backingList.addAll(c);
}
@Override
public boolean addAll(int index, Collection c) {
return this.backingList.addAll(index, c);
}
@Override
public void clear() {
this.backingList.clear();
}
@Override
public boolean contains(Object o) {
return this.backingList.contains(o);
}
@Override
public boolean containsAll(Collection c) {
return this.backingList.containsAll(c);
}
/**
* Get the element at the supplied index, creating it if there is
* no element at that index.
*/
@Override
public E get(int index) {
int backingListSize = this.backingList.size();
E element = null;
if (index < backingListSize) {
element = this.backingList.get(index);
if (element == null) {
element = this.elementFactory.createElement(index);
this.backingList.set(index, element);
}
}
else {
for (int x = backingListSize; x < index; x++) {
this.backingList.add(null);
}
element = this.elementFactory.createElement(index);
this.backingList.add(element);
}
return element;
}
@Override
public int indexOf(Object o) {
return this.backingList.indexOf(o);
}
@Override
public boolean isEmpty() {
return this.backingList.isEmpty();
}
@Override
public Iterator iterator() {
return this.backingList.iterator();
}
@Override
public int lastIndexOf(Object o) {
return this.backingList.lastIndexOf(o);
}
@Override
public ListIterator listIterator() {
return this.backingList.listIterator();
}
@Override
public ListIterator listIterator(int index) {
return this.backingList.listIterator(index);
}
@Override
public E remove(int index) {
return this.backingList.remove(index);
}
@Override
public boolean remove(Object o) {
return this.backingList.remove(o);
}
@Override
public boolean removeAll(Collection c) {
return this.backingList.removeAll(c);
}
@Override
public boolean retainAll(Collection c) {
return this.backingList.retainAll(c);
}
@Override
public E set(int index, E element) {
return this.backingList.set(index, element);
}
@Override
public int size() {
return this.backingList.size();
}
@Override
public List subList(int fromIndex, int toIndex) {
return this.backingList.subList(fromIndex, toIndex);
}
@Override
public Object[] toArray() {
return this.backingList.toArray();
}
@Override
public T[] toArray(T[] a) {
return this.backingList.toArray(a);
}
@Override
public boolean equals(Object other) {
return this.backingList.equals(other);
}
@Override
public int hashCode() {
return this.backingList.hashCode();
}
/**
* Factory interface for creating elements for an index-based access
* data structure such as a {@link java.util.List}.
*/
public interface ElementFactory {
/**
* Create the element for the supplied index.
* @return the element object
* @throws ElementInstantiationException if the instantiation process failed
* (any exception thrown by a target constructor should be propagated as-is)
*/
E createElement(int index) throws ElementInstantiationException;
}
/**
* Exception to be thrown from ElementFactory.
*/
public static class ElementInstantiationException extends RuntimeException {
public ElementInstantiationException(String msg) {
super(msg);
}
public ElementInstantiationException(String message, Throwable cause) {
super(message, cause);
}
}
/**
* Reflective implementation of the ElementFactory interface,
* using {@code Class.newInstance()} on a given element class.
*/
private static class ReflectiveElementFactory implements ElementFactory, Serializable {
private final Class elementClass;
public ReflectiveElementFactory(Class elementClass) {
Assert.notNull(elementClass, "Element class must not be null");
Assert.isTrue(!elementClass.isInterface(), "Element class must not be an interface type");
Assert.isTrue(!Modifier.isAbstract(elementClass.getModifiers()), "Element class cannot be an abstract class");
this.elementClass = elementClass;
}
@Override
public E createElement(int index) {
try {
return this.elementClass.newInstance();
}
catch (InstantiationException ex) {
throw new ElementInstantiationException(
"Unable to instantiate element class: " + this.elementClass.getName(), ex);
}
catch (IllegalAccessException ex) {
throw new ElementInstantiationException(
"Could not access element constructor: " + this.elementClass.getName(), ex);
}
}
}
}