java.util.ConcurrentModificationException的异常

[potahai]

	public final static int MAP_INIT_CAPACITY = 100000;
	public static Map<Integer, Integer> productViewCount = new HashMap<Integer, Integer>(MAP_INIT_CAPACITY);
	public static Map<Integer, Integer> providerViewCount = new HashMap<Integer, Integer>(MAP_INIT_CAPACITY);
//每一分钟调用一次flush()
public static void flush() {
		ViewCountLogic viewCountLogic = new ViewCountLogic();
		
		Iterator productViewCountIter = productViewCount.keySet().iterator();
		while(productViewCountIter.hasNext()) {
			
			Integer productId = (Integer)productViewCountIter.next();//这里抛出异常
			Integer viewCount = productViewCount.get(productId);
			viewCountLogic.incProductViewCount(productId, viewCount);
			
			
			ProductLogic productLogic=new ProductLogic();
			Product product = productLogic.getProductAllById(productId);
			int userId = product.getUserId();
			int uViewCount = viewCount;
			if(providerViewCount.containsKey(userId)) {
				uViewCount += providerViewCount.get(userId);
			}
			providerViewCount.put(userId, uViewCount);
		}
		
		
		Iterator userViewCountIter = providerViewCount.keySet().iterator();
		while(userViewCountIter.hasNext()) {
			Integer userId = (Integer)userViewCountIter.next();
			Integer viewCount = providerViewCount.get(userId);
			viewCountLogic.incUserViewCount(userId, viewCount);
		}
		
		productViewCount.clear();
		providerViewCount.clear();
		productViewCount = new HashMap<Integer, Integer>(MAP_INIT_CAPACITY);
		providerViewCount = new HashMap<Integer, Integer>(MAP_INIT_CAPACITY);
	}

查了一些资料，这种时候会抛出java.util.ConcurrentModificationException的异常

Iterator<MonthlyStatData> it = papers.iterator();
        while (it.hasNext()) {
            MonthlyStatData data = it.next();
            if (data.getValue == 0 ) {
                papers.remove(data);
            }
        }



上面的代码是说有个月统计的List, 里面有部分统计数据是0, 不想让出现,于是就迭代遍历,删除统计数据是0的数据. 但是上面的代码会导致ConcurrentModificationException, 正确的应该是:

Iterator<MonthlyStatData> it = papers.iterator();
        while (it.hasNext()) {
            MonthlyStatData data = it.next();
            if (data.getValue == 0 ) {
                it.remove();
                papers.remove(data);
            }
        }

但是我的代码中并没有去remove什么 直接都是重新获得一个Iterator，不知道为什么会出现这种问题。
请大家帮忙分析分析

[potahai]

public final static int MAP_INIT_CAPACITY = 100000;
	public static Map<Integer, Integer> productViewCount = new HashMap<Integer, Integer>(MAP_INIT_CAPACITY);
	public static Map<Integer, Integer> providerViewCount = new HashMap<Integer, Integer>(MAP_INIT_CAPACITY);

	/*
	 * 
	 */
	public static void incProductViewCount(int productId) {
		if(productViewCount.containsKey(productId)) {
			int viewCount = productViewCount.get(productId) + 1;
			productViewCount.put(productId, viewCount);
		} else {
			productViewCount.put(productId, 1);
		}
	}

	/*
	 * 
	 */
	public static void incProviderViewCount(int userId) {
		if(providerViewCount.containsKey(userId)) {
			int viewCount = providerViewCount.get(userId) + 1;
			providerViewCount.put(userId, viewCount);
		} else {
			providerViewCount.put(userId, 1);
		}
	}
	
	/*
	 * 
	 */
	public static void flush() {
		ViewCountLogic viewCountLogic = new ViewCountLogic();
		
		Iterator productViewCountIter = productViewCount.keySet().iterator();
		while(productViewCountIter.hasNext()) {
			
			Integer productId = (Integer)productViewCountIter.next();
			Integer viewCount = productViewCount.get(productId);
			viewCountLogic.incProductViewCount(productId, viewCount);
			
			
			ProductLogic productLogic=new ProductLogic();
			Product product = productLogic.getProductAllById(productId);
			int userId = product.getUserId();
			int uViewCount = viewCount;
			if(providerViewCount.containsKey(userId)) {
				uViewCount += providerViewCount.get(userId);
			}
			providerViewCount.put(userId, uViewCount);
		}
		
		
		Iterator userViewCountIter = providerViewCount.keySet().iterator();
		while(userViewCountIter.hasNext()) {
			Integer userId = (Integer)userViewCountIter.next();
			Integer viewCount = providerViewCount.get(userId);
			viewCountLogic.incUserViewCount(userId, viewCount);
		}
		
		productViewCount.clear();
		providerViewCount.clear();
		productViewCount = new HashMap<Integer, Integer>(MAP_INIT_CAPACITY);
		providerViewCount = new HashMap<Integer, Integer>(MAP_INIT_CAPACITY);
	}

这些方法和变量中都需要在哪里加synchronized？ 请指点1，2

[potahai]

不要沉啊

[龙四]

有没有其他线程操作了你的productViewCount？

[龙四]

我看你最后些了providerViewCount.put(userId, uViewCount);了

那么我猜想你在遍历provier的时候是不是remove了productViewCount

[potahai]

	public static void incProductViewCount(int productId) {
		if(productViewCount.containsKey(productId)) {
			int viewCount = productViewCount.get(productId) + 1;
			productViewCount.put(productId, viewCount);
		} else {
			productViewCount.put(productId, 1);
		}
	}


	public static void incProviderViewCount(int userId) {
		if(providerViewCount.containsKey(userId)) {
			int viewCount = providerViewCount.get(userId) + 1;
			providerViewCount.put(userId, viewCount);
		} else {
			providerViewCount.put(userId, 1);
		}
	}

这个在页面上随时都会被调用，而flush（）方法只有一个线程在定时调用

[potahai]

[Quote=引用 2 楼 ticmy 的回复:]

我看你最后些了providerViewCount.put(userId, uViewCount);了

那么我猜想你在遍历provier的时候是不是remove了productViewCount
[/Quote]

我的代码里没有调用remove方法
只有清空MAP的clear（）方法

[龙四]

可能就是因为你遍历的时候另一个线程调用了productViewCount.put的原因

[龙四]

你的例子好比就是以下代码


Map<String, String> map = new HashMap<String, String>();
map.put("1", "1");
Iterator<Map.Entry<String, String>> iterator = map.entrySet().iterator();
Map.Entry<String, String> entry = null;
while((entry = iterator.next()) != null) {
map.put("2", "2");
}

[potahai]

public static synchronized Map<Integer, Integer> productViewCount = new HashMap<Integer, Integer>(MAP_INIT_CAPACITY);
    public static synchronized Map<Integer, Integer> providerViewCount = new HashMap<Integer, Integer>(MAP_INIT_CAPACITY);

那意思是说这样可以解决问题吗？ 还是需要在那里枷锁呢？

[potahai]

我对该在哪个地方枷锁比较茫然！！！！

[龙四]

显然是不行的。。。。。


凡是用到productViewCount 的时候都同步
synchronized(productViewCount ) {
//操作
}

[Quote=引用 7 楼 potahai 的回复:]

Java code
public static synchronized Map<Integer, Integer> productViewCount = new HashMap<Integer, Integer>(MAP_INIT_CAPACITY);
public static synchronized Map<Integer, Integer> providerViewCount……
[/Quote]

[potahai]

晕了，为什么只有一个人