池以及barrier简单

用了下CyclicBarrier，注意线程池中的线程数量设置，还有就是DB连接的时候，需要考虑单个DB能承受的最大连接数目和每个连接上能同时打开的cursor等限制，需要时可以通过jstack查看堆栈中关于等待锁的信息，同时注意在线程数/连接池中连接数以及任务数中找到性能平衡点

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ConPoolTest {
    public static void main(String[] args) throws InterruptedException, BrokenBarrierException {
        long start = System.currentTimeMillis();
        ExecutorService exec = Executors.newFixedThreadPool(5000);
        CyclicBarrier barrier = new CyclicBarrier(5001);
        for (int i = 0; i < 5000; i++) {
            exec.execute(new TaskRun(barrier));
        }
        barrier.await();
        System.out.println(ConnectionPool.connCnt);
        ConnectionPool.cleanAll();
        System.out.println(ConnectionPool.connCnt);
        System.out.println(System.currentTimeMillis() - start);
        exec.shutdown();
    }
}

class TaskRun implements Runnable {
    CyclicBarrier barrier = null;

    TaskRun(CyclicBarrier barrier) {
        this.barrier = barrier;
    }

    @Override
    public void run() {
        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;
        try {
            conn = ConnectionPool.getConnect();
            stmt = conn.createStatement();
            rs = stmt.executeQuery("select * from t");
            while (rs.next()) {
                System.out.println(Thread.currentThread().getName() + " ...  " + rs.getString(1));
            }
        } catch (ClassNotFoundException | SQLException e) {
            e.printStackTrace();
        } finally {
            try {
                if (stmt != null) 
                stmt.close();
                if (rs != null) 
                rs.close();
                try {
                    barrier.await();
                } catch (InterruptedException | BrokenBarrierException e) {
                    e.printStackTrace();
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
import java.util.Random;
import java.util.TreeMap;

//简单初始化固定数目的链接，需要用的时候过来随机拿一个
public class ConnectionPool {
    private static List<Connection> connList = new ArrayList<Connection>();
    static TreeMap<Integer, Integer> connCnt = new TreeMap<Integer, Integer>(new Comparator<Integer>() {
        public int compare(Integer o1, Integer o2) {
            return o2.compareTo(o1); 
        }
    });
    static {
        int i = 0;
        while (i++ < 100) {
            try {
                Class.forName("oracle.jdbc.driver.OracleDriver");
                Connection conn = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:orcl", "system",
                        "*****");
                connList.add(conn);
            } catch (SQLException | ClassNotFoundException e) {
                e.printStackTrace();
            }
        }
    }

    public static synchronized Connection getConnect() throws ClassNotFoundException, SQLException {
        Random random = new Random();
        int idx = random.nextInt(100);
        boolean isContains = connCnt.containsKey(idx);
        if (isContains) {
            int cnt = connCnt.get(idx);
            connCnt.put(idx, cnt + 1);
        } else {
            connCnt.put(idx, 1);
        }
        return connList.get(idx);
    }

    public static synchronized void cleanAll() {
        for (Connection conn : connList) {
            try {
                conn.close();
                connCnt.clear();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}