jstorm源码之RotatingMap

一、作用
      基于LinkedList + HashMap<K,V>实现一个循环Map
二、源码
// 通过结合LinkedList 和 HashMap 构成一个循环Map数据结构
public class RotatingMap<K, V> {
    // this default ensures things expire at most 50% past the expiration time
    //  默认bucket数目为3
    private static final int DEFAULT_NUM_BUCKETS = 3;
   
    // 定义内部接口  key 到期的回调操作
    public static interface ExpiredCallback<K, V> {
        public void expire(K key, V val);
    }
    // 通过链表维护  一个 buckets 结构
    private LinkedList<HashMap<K, V>> _buckets;

    private ExpiredCallback _callback;
   //  构造RotationgMap的 bucket数目不能少于2
    public RotatingMap(int numBuckets, ExpiredCallback<K, V> callback) {
        if (numBuckets < 2) {
            throw new IllegalArgumentException("numBuckets must be >= 2");
        }
        _buckets = new LinkedList<HashMap<K, V>>();
        for (int i = 0; i < numBuckets; i++) {
            _buckets.add(new HashMap<K, V>());
        }

        _callback = callback;
    }

    public RotatingMap(ExpiredCallback<K, V> callback) {
        this(DEFAULT_NUM_BUCKETS, callback);
    }

    public RotatingMap(int numBuckets) {
        this(numBuckets, null);
    }
   
    // 执行rotate
    // 首先获取LinkedList 末尾元素
    //  其次在first位置 添加占位新元素
    //  结合expire的callback
    //  最末尾的batch多半是时间最久 极可能是超出有效期的
    public Map<K, V> rotate() {
        Map<K, V> dead = _buckets.removeLast();
        _buckets.addFirst(new HashMap<K, V>());
        if (_callback != null) {
            for (Entry<K, V> entry : dead.entrySet()) {
                _callback.expire(entry.getKey(), entry.getValue());
            }
        }
        return dead;
    }
   
    // 是否存在key
    public boolean containsKey(K key) {
        for (HashMap<K, V> bucket : _buckets) {
            if (bucket.containsKey(key)) {
                return true;
            }
        }
        return false;
    }

   // 获取value
    public V get(K key) {
        for (HashMap<K, V> bucket : _buckets) {
            if (bucket.containsKey(key)) {
                return bucket.get(key);
            }
        }
        return null;
    }

    // 添加item
    public void put(K key, V value) {
        Iterator<HashMap<K, V>> it = _buckets.iterator();
        HashMap<K, V> bucket = it.next();
        bucket.put(key, value);
        while (it.hasNext()) {
            bucket = it.next();
            bucket.remove(key);
        }
    }

    // 移除item
    public Object remove(K key) {
        for (HashMap<K, V> bucket : _buckets) {
            if (bucket.containsKey(key)) {
                return bucket.remove(key);
            }
        }
        return null;
    }

    // 总容量
    public int size() {
        int size = 0;
        for (HashMap<K, V> bucket : _buckets) {
            size += bucket.size();
        }
        return size;
    }
}