ArrayList 上的 java.util.ConcurrentModificationException

Question

我有一个 Server 类和一个 Timer，它应该清除死掉的客户端(崩溃的客户端)。我按照下面的示例在 Timer 遍历用户时锁定集合，但我仍然遇到此异常(在我使连接的客户端崩溃之后)。

http://www.javaperformancetuning.com/articles/fastfail2.shtml

List<User> users;
List<User> connectedUsers;
ConcurrentMap<User, IClient> clients;

...

users = Collections.synchronizedList(new ArrayList<User>());
connectedUsers = new ArrayList<User>();
clients = new ConcurrentHashMap<User, IClient>();
timer = new Timer();
timer.schedule(new ClearDeadClients(), 5000, 5000);

...

class ClearDeadClients extends TimerTask {
    public void run() {
        synchronized (users) {
            Iterator<User> it = users.iterator();
            while (it.hasNext()) {
                User user = it.next(); // Throws exception
                if (!connectedUsers.contains(user)) {
                    users.remove(user);
                    clients.remove(user);
                }
            }
        }       

        connectedUsers.clear();
    }
}

Answer 1

您需要从迭代器而不是集合中移除。它看起来像这样:

Iterator<User> it = users.iterator();
while (it.hasNext()) {
    User user = it.next(); 
    if (!connectedUsers.contains(user)) {
         it.remove();
         clients.remove(user);
     }
}