SelectMessageQueueByHash.java

/**
 * Copyright (C) 2010-2013 Alibaba Group Holding Limited
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.alibaba.rocketmq.client.producer.selector;

import java.util.List;

import com.alibaba.rocketmq.client.producer.MessageQueueSelector;
import com.alibaba.rocketmq.common.message.Message;
import com.alibaba.rocketmq.common.message.MessageQueue;


/**
 * 使用哈希算法来选择队列，顺序消息通常都这样做<br>
 * 
 * @author shijia.wxr<vintage.wang@gmail.com>
 * @since 2013-6-27
 */
public class SelectMessageQueueByHash implements MessageQueueSelector {

    @Override
    public MessageQueue select(List<MessageQueue> mqs, Message msg, Object arg) {
        int value = arg.hashCode();
        if (value < 0) {
            value = Math.abs(value);
        }

        value = value % mqs.size();
        return mqs.get(value);
    }
}