我是靠谱客的博主 害怕嚓茶,最近开发中收集的这篇文章主要介绍CopyOnWriteArrayList集合排序异常问题,觉得挺不错的,现在分享给大家,希望可以做个参考。

概述

1、集合自定义排序实现

对List集合的自定义排序想必大家都知道要使用如下的方式,通过实现Comparator接口并实现compare方法来实现。

/**
*
* @方法名 changeChain
* @描述
改变请求链
* @参数
* @返回类型 void
* @作者 cymiao
*/
public static void changeChain(Class<? extends Chain> type){
List<? extends Chain> list = DynamicLoader.getInstance().getChainList(type);
Collections.sort(list, new Comparator<Chain>(){
@Override
public int compare(Chain chain1, Chain chain2) {
int orderO = ((OrderAnnotation)chain1.getClass().getAnnotation(OrderAnnotation.class)).value();
int orderT = ((OrderAnnotation)chain2.getClass().getAnnotation(OrderAnnotation.class)).value();
if(orderO > orderT){
return 1;
}else if(orderO < orderT){
return -1;
}
return 0;
}
});
List<Chain> aList = new CopyOnWriteArrayList<Chain>();
aList.addAll(list);
DynamicLoader.getInstance().setChainList(aList, type);
}

2、CopyOnWriteArrayList集合排序异常问题

在不同版本的JDK时,CopyOnWriteArrayList集合使用如上方法排序的时候会抛出UnsupportedOperationException异常,这是为什么呢?下来让我们通过研究CopyOnWriteArrayList类的源码来说明这个问题:

(1)、我们先来分析下JDK1.6中Collections.sort的实现逻辑

 如下JDK1.6的源码所示,在自定义排序时,先使用Arrays.sort对集合的Object数组进行排序,然后通过调用集合的listIterator()方法获取ListIterator对象,并调用对象的set(E e)方法赋值,我们再看CopyOnWriteArrayList集合的源码,发现listIterator()方法返回的是new COWIterator<E>(getArray(), 0);对象,而这个对象的set方法没有具体实现而是直接抛UnsupportedOperationException异常,所以问题很显而易见了,在JDK1.6版本下是不能对CopyOnWriteArrayList集合使用Comparator来进行自定义排序的。

public static <T> void sort(List<T> paramList, Comparator<? super T> paramComparator)
{
Object[] arrayOfObject = paramList.toArray();
Arrays.sort(arrayOfObject, paramComparator);
ListIterator localListIterator = paramList.listIterator();
for (int i = 0; i < arrayOfObject.length; i++) {
localListIterator.next();
localListIterator.set(arrayOfObject[i]);
}
}

 

/**
* {@inheritDoc}
*
* <p>The returned iterator provides a snapshot of the state of the list
* when the iterator was constructed. No synchronization is needed while
* traversing the iterator. The iterator does <em>NOT</em> support the
* {@code remove}, {@code set} or {@code add} methods.
*/
public ListIterator<E> listIterator() {
return new COWIterator<E>(getArray(), 0);
}
static final class COWIterator<E> implements ListIterator<E> {
/** Snapshot of the array */
private final Object[] snapshot;
/** Index of element to be returned by subsequent call to next.
*/
private int cursor;
private COWIterator(Object[] elements, int initialCursor) {
cursor = initialCursor;
snapshot = elements;
}
public boolean hasNext() {
return cursor < snapshot.length;
}
public boolean hasPrevious() {
return cursor > 0;
}
@SuppressWarnings("unchecked")
public E next() {
if (! hasNext())
throw new NoSuchElementException();
return (E) snapshot[cursor++];
}
@SuppressWarnings("unchecked")
public E previous() {
if (! hasPrevious())
throw new NoSuchElementException();
return (E) snapshot[--cursor];
}
public int nextIndex() {
return cursor;
}
public int previousIndex() {
return cursor-1;
}
/**
* Not supported. Always throws UnsupportedOperationException.
* @throws UnsupportedOperationException always; {@code remove}
*
is not supported by this iterator.
*/
public void remove() {
throw new UnsupportedOperationException();
}
/**
* Not supported. Always throws UnsupportedOperationException.
* @throws UnsupportedOperationException always; {@code set}
*
is not supported by this iterator.
*/
public void set(E e) {
throw new UnsupportedOperationException();
}
/**
* Not supported. Always throws UnsupportedOperationException.
* @throws UnsupportedOperationException always; {@code add}
*
is not supported by this iterator.
*/
public void add(E e) {
throw new UnsupportedOperationException();
}
}

(2)、接下来我们分析下JDK1.8中Collections.sort的实现逻辑

如下Collections类的源码所示,1.8版本中修改了集合排序的逻辑,不是直接在Collections类中排序,而是调用集合对象自己的sort方法实现排序了,在JDK1.6中CopyOnWriteArrayList是没有sort方法实现的,在1.8中添加了sort的实现,源码如下,集合的Object数组排序完成以后,直接把排序后的数据赋值给了集合中的Object数据,所以在JDK1.8中能对CopyOnWriteArrayList集合使用Comparator来进行自定义排序的。

/**
* Sorts the specified list according to the order induced by the
* specified comparator.
All elements in the list must be <i>mutually
* comparable</i> using the specified comparator (that is,
* {@code c.compare(e1, e2)} must not throw a {@code ClassCastException}
* for any elements {@code e1} and {@code e2} in the list).
*
* <p>This sort is guaranteed to be <i>stable</i>:
equal elements will
* not be reordered as a result of the sort.
*
* <p>The specified list must be modifiable, but need not be resizable.
*
* @implNote
* This implementation defers to the {@link List#sort(Comparator)}
* method using the specified list and comparator.
*
* @param
<T> the class of the objects in the list
* @param
list the list to be sorted.
* @param
c the comparator to determine the order of the list.
A
*
{@code null} value indicates that the elements' <i>natural
*
ordering</i> should be used.
* @throws ClassCastException if the list contains elements that are not
*
<i>mutually comparable</i> using the specified comparator.
* @throws UnsupportedOperationException if the specified list's
*
list-iterator does not support the {@code set} operation.
* @throws IllegalArgumentException (optional) if the comparator is
*
found to violate the {@link Comparator} contract
* @see List#sort(Comparator)
*/
@SuppressWarnings({"unchecked", "rawtypes"})
public static <T> void sort(List<T> list, Comparator<? super T> c) {
list.sort(c);
}
public void sort(Comparator<? super E> c) {
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] elements = getArray();
Object[] newElements = Arrays.copyOf(elements, elements.length);
@SuppressWarnings("unchecked") E[] es = (E[])newElements;
Arrays.sort(es, c);
setArray(newElements);
} finally {
lock.unlock();
}
}
/**
* Sets the array.
*/
final void setArray(Object[] a) {
array = a;
}

 

转载于:https://www.cnblogs.com/cymiao/p/8400421.html

最后

以上就是害怕嚓茶为你收集整理的CopyOnWriteArrayList集合排序异常问题的全部内容,希望文章能够帮你解决CopyOnWriteArrayList集合排序异常问题所遇到的程序开发问题。

如果觉得靠谱客网站的内容还不错,欢迎将靠谱客网站推荐给程序员好友。

本图文内容来源于网友提供,作为学习参考使用,或来自网络收集整理,版权属于原作者所有。
点赞(68)

评论列表共有 0 条评论

立即
投稿
返回
顶部