What is the purpose of the change

• fix expire cache bug
• Optimize code

public static void main(String[] args) {
	Map<String, String> map = new ConcurrentHashMap<>();
	map.put("cache.seconds", "10");
	map.put("cache.interval", "10");
	URL url = new URL("", "", "", "", 8888, "", map);
	ExpiringCache cache = new ExpiringCache(url);

	long start = System.currentTimeMillis();
	boolean in = false;
	boolean out10 = false;
	boolean out20 = false;
	while (true) {
		long end = System.currentTimeMillis();
		// put k,v in 5s when the programmer start
		if (!in && (end - start) > 5 * 1000) {
			cache.put("aaa", "aaa");
			cache.put("bbb", "bbb");
			log.info("put val");
			in = true;
		}
		// get value after expire time(10s)
		// but I get can get the value where is no null. wrong
		if (!out10 && (end - start) > 16 * 1000) {
			log.info("val = {}", cache.get("aaa"));
			out10 = true;
		}

		// second thread clean。this is null, currect
		if (!out20 && (end - start) > 21 * 1000) {
			log.info("val = {}", cache.get("bbb"));
			out20 = true;
		}
	}
}

Let's look at this piece of code. Set the expiration time to 10s and clear the cache every 10s. At the 5s, we put "aaa" and "bbb" into memory. In theory, after 15s, he should be cleared. When we took the aaa-key in 16s, he was still in memory. And when we took the bbb-key in 21s, he was null. At this time we The bug can be located.

Brief changelog

fix expire cache map

Verifying this change

XXXXX

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