BytesKey以及其他一些代码细节

byte数组如何作为key？下面是一个实现。

public class BytesKey implements Serializable {
	/**
	 * serialVersionUID
	 */
	private static final long serialVersionUID = -6296965387124592707L;

	private byte[] data;
	
	public BytesKey(byte[] data) {
		this.data = data;
	}

	/**
	 * @return the data
	 */
	public byte[] getData() {
		return data;
	}

	/**
	 * @param data the data to set
	 */
	public void setData(byte[] data) {
		this.data = data;
	}
	
	@Override
	public int hashCode() {
		int h = 0;
		if (null != this.data) {
	        for (int i = 0; i < this.data.length; i++) {
	            h = 31*h + data[i++];
	        }
		}
        return h;
	}
	
	@Override
	public boolean equals(Object o) {
		if (null == o || !(o instanceof BytesKey)) {
			return false;
		}
		BytesKey k = (BytesKey)o;
		if (null == k.getData() && null == this.getData()) {
			return true;
		}
		if (null == k.getData() || null == this.getData()) {
			return false;
		}
		if (k.getData().length != this.getData().length) {
			return false;
		}
		for (int i = 0; i < this.data.length; ++i) {
			if (this.data[i] != k.getData()[i]) {
				return false;
			}
		}
		return true;
	}
}

顺带使用BytesKey实现的简单Memory KV缓存

public class MemStore implements Store {
    private Map<BytesKey, byte[]> datas = new ConcurrentHashMap<BytesKey, byte[]>();


    /*
     * (non-Javadoc)
     * 
     * @see com.taobao.common.store.Store#add(byte[], byte[])
     */
    public void add(byte[] key, byte[] data) throws IOException {
        datas.put(new BytesKey(key), data);
    }


    /*
     * (non-Javadoc)
     * 
     * @see com.taobao.common.store.Store#get(byte[])
     */
    public byte[] get(byte[] key) throws IOException {
        return datas.get(new BytesKey(key));
    }


    /*
     * (non-Javadoc)
     * 
     * @see com.taobao.common.store.Store#iterator()
     */
    public Iterator<byte[]> iterator() throws IOException {
        final Iterator<BytesKey> it = datas.keySet().iterator();
        return new Iterator<byte[]>() {
            public boolean hasNext() {
                return it.hasNext();
            }


            public byte[] next() {
                BytesKey key = it.next();
                if (null == key) {
                    return null;
                }
                return key.getData();
            }


            public void remove() {
                it.remove();
            }
        };
    }


    /*
     * (non-Javadoc)
     * 
     * @see com.taobao.common.store.Store#remove(byte[])
     */
    public boolean remove(byte[] key) throws IOException {
        return null != datas.remove(new BytesKey(key));
    }


    /*
     * (non-Javadoc)
     * 
     * @see com.taobao.common.store.Store#size()
     */
    public int size() {
        return datas.size();
    }


    /*
     * (non-Javadoc)
     * 
     * @see com.taobao.common.store.Store#update(byte[], byte[])
     */
    public boolean update(byte[] key, byte[] data) throws IOException {
        datas.put(new BytesKey(key), data);
        return true;
    }


    public void close() throws IOException {
        // nodo
    }


    public long getMaxFileCount() {
        return Long.MAX_VALUE;
    }


    public void setMaxFileCount(long maxFileCount) {
    }
}

使用双重hash算key,

 private int hash(int keyHash, int i) {
        return abs(hash1(keyHash) + i * hash2(keyHash)) % table.length; // 双重散列
    }

使用BitSet进行快速判定key是否存在,存在的话进行下一轮的双重hash算key

 while (this.table[j] != null && !isEntryDeleted(j) && this.bitSet.get(offset) && i < m) {
            j = hash(keyHash, i++);
            offset = calcOffset(j);
        }