主键工厂工具类

一.介绍：

    1.主键的组成： 系统当前时间取至毫秒（15位） + 机器IP（6位） + 原子性自增涨数字（3位） 共24位

    2.支持每秒产生1000*1000个

    3.扩展性：可以将自增涨数字位数扩大，这时每秒产生的主键也会自变多

二.代码：

import org.apache.commons.lang.StringUtils;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.locks.ReentrantLock;


/**
 * @describe: 主键工厂
 * @author:houkai
 * @Date: 2018/3/5 9:47
 */
public class IdFactoryUtil {

    private static HashMap<String, AtomicInteger> cache  = new HashMap<String, AtomicInteger>(1);
    private static final ReentrantLock lock = new ReentrantLock();
    private static final SimpleDateFormat sdf = new SimpleDateFormat("yyMMddHHmmssSSS");

    /**
     * 获取主键
     * @return
     * @throws Exception
     */
    public static String getId() throws UnknownHostException {
        String ip = null;
        ip = InetAddress.getLocalHost().getHostAddress();
        String[] ipArray = ip.split("\\.");

        final String lastTwoPhaseIp = StringUtils.rightPad(ipArray[2], 3, '0') + StringUtils.leftPad(ipArray[3], 3, '0');
        String tss = getTimeStampSequence();
        String id = tss + lastTwoPhaseIp;
        return id;
    }

    /**
     * 获取指定数量的id
     * @param amount : id数量
     */
    public static List<String> getIds(int amount) throws UnknownHostException {
        //获取主机IP ，这块可能会有异常抛出，
        String ip = ip = InetAddress.getLocalHost().getHostAddress();
        String[] ipArray = ip.split("\\.");
        //IP地址后六位
        final String lastTwoPhaseIp = StringUtils.rightPad(ipArray[2], 3, '0') + StringUtils.leftPad(ipArray[3], 3, '0');

        List<String> list = new ArrayList<>(amount);
        for (int i = 0; i < amount; i++){
            String tss = getTimeStampSequence();
            String id = tss + lastTwoPhaseIp;
            list.add(id);
        }
        return list;
    }

    /**
     * 获取系统时间且格式化为String，AtomicInteger保证毫秒内不重复的自增
     * @return
     */
    private static String getTimeStampSequence() {
        String timestamp = null;
        String inc = null;
        lock.lock();
        try {
            timestamp = sdf.format(new Date());
            AtomicInteger value = cache.get(timestamp);
            if(value == null) {
                cache.clear();
                int defaultStartValue = 0;
                cache.put(timestamp, new AtomicInteger(defaultStartValue));
                inc = String.valueOf(defaultStartValue);
            } else {
                inc = String.valueOf(value.addAndGet(1));
            }
        } finally {
            lock.unlock();
        }
        return timestamp + StringUtils.leftPad(inc, 4, '0');
    }

}

三. 代码需要的maven依赖

<groupId>org.apache.commons</groupId>
<artifactId>commons-lang3</artifactId>
<version>3.4</version>
</dependency>

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