生成整数自增ID(集群主键生成服务)

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class SeqGenerator {
    private static ExecutorService singleThreadExecutor = Executors.newSingleThreadExecutor();

    private static int currentVal = -1;
    private static int maxVal = -1;
    private static int fetchSize = 10000;//每次生成一万个id

    static{
        try {
            fetchFromDB();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
    
    public static int getSeq() throws InterruptedException, ExecutionException {
        Callable<Integer> c = new Callable<Integer>() {
            @Override
            public Integer call() throws Exception {
                int result = currentVal;
                if (currentVal > maxVal) {//如果当前值>数据库最大值，重新生成id
                    fetchFromDB();
                    result = currentVal;
                }
                currentVal++;
                return result;

            }
        };
        Future<Integer> task = singleThreadExecutor.submit(c);
        return task.get().intValue();
    }

    private static void fetchFromDB() throws Exception {
        Class.forName("com.mysql.jdbc.Driver");
        Connection connection = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/test", "xx", "xx");
        connection.setAutoCommit(false);
        Statement st = connection.createStatement();
        ResultSet rs = st.executeQuery("select * from test for update");
        rs.next();
        currentVal = rs.getInt(1) + 1;//当前值
        rs.close();
        st.executeUpdate("update test set id=id+" + fetchSize);//更新db中最大值
        rs = st.executeQuery("select * from test for update");
        rs.next();
        maxVal = rs.getInt(1);//最大值
        connection.commit();
        rs.close();
        st.close();
        connection.close();
    }

    public static void main(String[] args) throws Exception {
        int i = 1000000;
        long start = System.currentTimeMillis();

        while (i > 0) {
            System.out.println(SeqGenerator.getSeq());
            i--;
        }
        long end = System.currentTimeMillis();
        System.out.println(end - start);
    }
}