并发修改异常

Question

My following code is throwing concurrent modification exception and I am not able to solve it. Help!

  {
    long now = new Date().getTime();
    Set<String> keyset = requests.keySet();
    Iterator<String> iterator = keyset.iterator();

    while (iterator.hasNext()) {
        String packetId = iterator.next();
        RequestHolder entry = requests.get(packetId);
        if (entry.isExpired(now)) {
            entry.getListener().onTimeout(packetId);
            iterator.remove();
        }
    }
  }

Answer 1

Replace your code by

long now = new Date().getTime();
Iterator<Map.Entry<String, RequestHolder>> iterator = requests.entrySet().iterator();

while (iterator.hasNext()) {
    Map.Entry<String, RequestHolder> entry = iterator.next();
    String packetId = entry.getKey();
    RequestHolder requestHolder = entry.getValue();
    if (requestHolder.isExpired(now)) {
        requestHolder.getListener().onTimeout(packetId);
        iterator.remove();
    }
}

The solution is to iterate over the whole collection and not over the key set, using the key set iterator to access entries from the collection again and removing entries from the key set

Answer 2

Replace your while loop with this one ...

for (Entry<String, RequestHolder> entryElem : requests.keySet()) {
            String packetId = entryElem.getValue();
        RequestHolder entry = requests.getValue.get(packetId);
        if (entry.isExpired(now)) {
            entry.getListener().onTimeout(packetId);
            iterator.remove();
        }
    }