Java多线程篇之List与Collections集合工具类

Collections是一个Java处理集合的强大工具类，可以进排序，对集合进行简单的多线程封装。本章我们将讲解多线程封装接口

Collections的List<T> synchronizedList(List<T> list)类是一个封装list对象的方法，简单点就是专门对list的内部方法synchronized，以达到多线程操作。

用法如下：

public void collectionsSyncListTest() {List<String> list = new ArrayList<>(); // 原始列表，没有多线程保护List<String> syncList = Collections.synchronizedList(list);  //  通过Collections包装类生产一个新的自动synchronized的listsyncList.add("hello");  // add方法被调用的时候会自动synchornized对象list自身，达到多线程操作保护syncList.add("hello");// for-each循环被调用的时候会自动synchornized对象list自身，达到多线程操作保护for (String text : syncList) {System.out.println(text);}syncList.clear();  // clear方法被调用的时候会自动synchornized对象list自身，达到多线程操作保护
}

接下来我们通过具体源码感受一下吧

public static <T> List<T> synchronizedList(List<T> list) {return (list instanceof RandomAccess ?new SynchronizedRandomAccessList<>(list) :new SynchronizedList<>(list));
}static <T> List<T> synchronizedList(List<T> list, Object mutex) {return (list instanceof RandomAccess ?new SynchronizedRandomAccessList<>(list, mutex) :new SynchronizedList<>(list, mutex));
}/*** @serial include*/
static class SynchronizedList<E>extends SynchronizedCollection<E>implements List<E> {private static final long serialVersionUID = -7754090372962971524L;final List<E> list;SynchronizedList(List<E> list) {super(list);this.list = list;}SynchronizedList(List<E> list, Object mutex) {super(list, mutex);this.list = list;}public boolean equals(Object o) {if (this == o)return true;synchronized (mutex) {return list.equals(o);}}public int hashCode() {synchronized (mutex) {return list.hashCode();}}public E get(int index) {synchronized (mutex) {return list.get(index);}}public E set(int index, E element) {synchronized (mutex) {return list.set(index, element);}}public void add(int index, E element) {synchronized (mutex) {list.add(index, element);}}public E remove(int index) {synchronized (mutex) {return list.remove(index);}}public int indexOf(Object o) {synchronized (mutex) {return list.indexOf(o);}}public int lastIndexOf(Object o) {synchronized (mutex) {return list.lastIndexOf(o);}}public boolean addAll(int index, Collection<? extends E> c) {synchronized (mutex) {return list.addAll(index, c);}}public ListIterator<E> listIterator() {return list.listIterator(); // Must be manually synched by user}public ListIterator<E> listIterator(int index) {return list.listIterator(index); // Must be manually synched by user}public List<E> subList(int fromIndex, int toIndex) {synchronized (mutex) {return new SynchronizedList<>(list.subList(fromIndex, toIndex),mutex);}}@Overridepublic void replaceAll(UnaryOperator<E> operator) {synchronized (mutex) {list.replaceAll(operator);}}@Overridepublic void sort(Comparator<? super E> c) {synchronized (mutex) {list.sort(c);}}/*** SynchronizedRandomAccessList instances are serialized as* SynchronizedList instances to allow them to be deserialized* in pre-1.4 JREs (which do not have SynchronizedRandomAccessList).* This method inverts the transformation.  As a beneficial* side-effect, it also grafts the RandomAccess marker onto* SynchronizedList instances that were serialized in pre-1.4 JREs.** Note: Unfortunately, SynchronizedRandomAccessList instances* serialized in 1.4.1 and deserialized in 1.4 will become* SynchronizedList instances, as this method was missing in 1.4.*/private Object readResolve() {return (list instanceof RandomAccess? new SynchronizedRandomAccessList<>(list): this);}
}/*** @serial include*/
static class SynchronizedCollection<E> implements Collection<E>, Serializable {private static final long serialVersionUID = 3053995032091335093L;final Collection<E> c;  // Backing Collectionfinal Object mutex;     // Object on which to synchronizeSynchronizedCollection(Collection<E> c) {this.c = Objects.requireNonNull(c);mutex = this;}SynchronizedCollection(Collection<E> c, Object mutex) {this.c = Objects.requireNonNull(c);this.mutex = Objects.requireNonNull(mutex);}public int size() {synchronized (mutex) {return c.size();}}public boolean isEmpty() {synchronized (mutex) {return c.isEmpty();}}public boolean contains(Object o) {synchronized (mutex) {return c.contains(o);}}public Object[] toArray() {synchronized (mutex) {return c.toArray();}}public <T> T[] toArray(T[] a) {synchronized (mutex) {return c.toArray(a);}}public Iterator<E> iterator() {return c.iterator(); // Must be manually synched by user!}public boolean add(E e) {synchronized (mutex) {return c.add(e);}}public boolean remove(Object o) {synchronized (mutex) {return c.remove(o);}}public boolean containsAll(Collection<?> coll) {synchronized (mutex) {return c.containsAll(coll);}}public boolean addAll(Collection<? extends E> coll) {synchronized (mutex) {return c.addAll(coll);}}public boolean removeAll(Collection<?> coll) {synchronized (mutex) {return c.removeAll(coll);}}public boolean retainAll(Collection<?> coll) {synchronized (mutex) {return c.retainAll(coll);}}public void clear() {synchronized (mutex) {c.clear();}}public String toString() {synchronized (mutex) {return c.toString();}}// Override default methods in Collection@Overridepublic void forEach(Consumer<? super E> consumer) {synchronized (mutex) {c.forEach(consumer);}}@Overridepublic boolean removeIf(Predicate<? super E> filter) {synchronized (mutex) {return c.removeIf(filter);}}@Overridepublic Spliterator<E> spliterator() {return c.spliterator(); // Must be manually synched by user!}@Overridepublic Stream<E> stream() {return c.stream(); // Must be manually synched by user!}@Overridepublic Stream<E> parallelStream() {return c.parallelStream(); // Must be manually synched by user!}private void writeObject(ObjectOutputStream s) throws IOException {synchronized (mutex) {s.defaultWriteObject();}}
}

可以这么理解，Collections的synchronizedList实现的功能就是在封装List的public时多加了synchronized锁操作。

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Java多线程篇之List与Collections集合工具类

Java多线程篇之List与Collections集合工具类

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