java.util.ConcurrentModificationException

java.util.ConcurrentModificationException

多線程情況下出錯，具體如下：

java.util.ConcurrentModificationException
	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:909)
	at java.util.ArrayList$Itr.next(ArrayList.java:859)
	at com.gmweb.web.controller.message.EmailUtil$1.run(EmailUtil.java:131)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)
[2018-11-20 15:16:15 ERROR] [pool-1-thread-10] EmailUtil.run(227) | 發送郵件出錯：
java.util.ConcurrentModificationException
	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:909)
	at java.util.ArrayList$Itr.next(ArrayList.java:859)
	at com.gmweb.web.controller.message.EmailUtil$1.run(EmailUtil.java:131)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at java.lang.Thread.run(Thread.java:748)

解決辦法：有2種

　　1）在使用iterator迭代的時候使用synchronized或者Lock進行同步；

　　2）使用併發容器CopyOnWriteArrayList代替ArrayList和Vector。