Primary key factory tool class

1. Introduction :

    1. The composition of the primary key: the current time of the system is taken to milliseconds (15 digits) + the machine IP (6 digits) + the atomic self-increasing number (3 digits), a total of 24 digits

    2. Support to generate 1000*1000 per second

    3. Scalability: You can expand the number of self-increasing digits, and at this time, the number of primary keys generated per second will also increase automatically.

2. Code :

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;
    }

    /**
      * Get the specified number of ids
      * @param amount : the
 number of ids      */
 public static List<String> getIds( int amount) throws UnknownHostException {
         //Get the host IP, this block may throw exceptions,
 String ip = ip = InetAddress.getLocalHost (). getHostAddress ();            
        String[] ipArray = ip .split( " \\ ." );
         //The last six digits of the IP address
 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;
    }

    /**
      * Get the system time and format it as String, AtomicInteger guarantees non-repetitive self-increment within milliseconds
      * @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');
    }

}

3. Maven dependencies required by the code

<dependency>

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