https://blog.csdn.net/qq\_16038125/article/details/80180941

池：同一类对象集合

连接池的作用 
1． 资源重用 
由于数据库连接得到重用，避免了频繁创建、释放连接引起的大量性能开销。在减少系统消耗的基础上，另一方面也增进了系统运行环境的平稳性（减少内存碎片以及数据库临时进程/线程的数量）。 
2． 更快的系统响应速度 
数据库连接池在初始化过程中，往往已经创建了若干数据库连接置于池中备用。此时连接的初始化工作均已完成。对于业务请求处理而言，直接利用现有可用连接，避免了数据库连接初始化和释放过程的时间开销，从而缩减了系统整体响应时间。 
3． 新的资源分配手段 
对于多应用共享同一数据库的系统而言，可在应用层通过数据库连接的配置，使用数据库连接池技术。设置某一应用最大可用数据库连接数，避免某一应用独占所有数据库资源。 
4． 统一的连接管理，避免数据库连接泄漏 
在较为完备的数据库连接池实现中，可根据预先设定的连接占用超时时间，强制收回被超时占用的连接。从而避免了常规数据库连接操作中可能出现的资源泄漏（当程序存在缺陷时，申请的连接忘记关闭，这时候，就存在连接泄漏了）。

示例

配置文件

jdbcDriver=com.mysql.jdbc.Driver
jdbcurl=jdbc:mysql://localhost:3306/mybatis userName=root password=root initCount=10 stepSize=4 poolMaxSize=150

数据库连接封装

public class PooledConnection {
    private boolean isBusy = false; private Connection connection; public Connection getConnection() { return connection; } public void setConnection(Connection connection) { this.connection = connection; } public boolean isBusy() { return isBusy; } public void setBusy(boolean isBusy) { this.isBusy = isBusy; } public PooledConnection(Connection connection, boolean isBusy) { this.connection = connection; this.isBusy = isBusy; } public void close() { this.isBusy = false; } public ResultSet queryBysql(String sql) { Statement sm = null; java.sql.ResultSet rs = null; try { sm = connection.createStatement(); rs = sm.executeQuery(sql); } catch (SQLException e) { e.printStackTrace(); } return rs; } } 

连接池接口

public interface IMyPool {

    PooledConnection getConnection();

    void createConnection(int count);
}

实现

import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.Driver;
import java.sql.DriverManager; import java.sql.SQLException; import java.util.Properties; import java.util.Vector; public class MyPoolImpl implements IMyPool { private static String jdbcDriver = null; private static String jdbcUrl = null; private static String userName = null; private static String password = null; private static int initCount; private static int stepSize; private static int poolMaxSize; private static Vector<PooledConnection> pooledConnections = new Vector<>(); public MyPoolImpl() { init(); } private void init() { InputStream inputStream = this.getClass().getClassLoader().getResourceAsStream("jdbc.properties"); //字节信息 key value 形式化 Properties pro = new Properties(); try { pro.load(inputStream); } catch (IOException e) { e.printStackTrace(); } jdbcDriver = pro.getProperty("jdbcDriver"); jdbcUrl = pro.getProperty("jdbcurl"); userName = pro.getProperty("userName"); password = pro.getProperty("password"); initCount = Integer.valueOf(pro.getProperty("initCount")); stepSize = Integer.valueOf(pro.getProperty("stepSize")); poolMaxSize = Integer.valueOf(pro.getProperty("poolMaxSize")); try { Driver mysqlDriver = (Driver) Class.forName(jdbcDriver).newInstance(); DriverManager.registerDriver(mysqlDriver); createConnection(initCount); } catch (IllegalAccessException e) { e.printStackTrace(); } catch (InstantiationException e) { e.printStackTrace(); } catch (SQLException e) { e.printStackTrace(); } catch (ClassNotFoundException e) { e.printStackTrace(); } } public PooledConnection getConnection() { if (pooledConnections.size() == 0) { System.out.println("获取链接管道失败，原因是连接池中没有可用管道"); throw new RuntimeException("创建管道对象失败，原因是即将超过最大上限值"); } //连接池中的管道是没有超时 没有其他线程占用 PooledConnection connection = getRealConnection(); while (connection == null) { createConnection(stepSize); connection = getRealConnection(); try { Thread.sleep(300); } catch (InterruptedException e) { e.printStackTrace(); } } return connection; } @Override public void createConnection(int count) { if (poolMaxSize > 0 && pooledConnections.size() + count > poolMaxSize) { System.out.println("创建管道对象失败，原因是即将超过最大上限值"); throw new RuntimeException("创建管道对象失败，原因是即将超过最大上限值"); } for (int i = 0; i < count; i++) { try { Connection conn = DriverManager.getConnection(jdbcUrl, userName, password); PooledConnection pooledConnection = new PooledConnection(conn, false); pooledConnections.add(pooledConnection); } catch (SQLException e) { e.printStackTrace(); } } } private synchronized PooledConnection getRealConnection() { for (PooledConnection conn : pooledConnections) { if (!conn.isBusy()) { Connection connection = conn.getConnection(); try { //发送一个信息给数据库 2000毫秒内 收到返回信息 认为 这个管道没有超时 if (!connection.isValid(2000)) { Connection validConn = DriverManager.getConnection(jdbcUrl, userName, password); conn.setConnection(validConn); } } catch (SQLException e) { e.printStackTrace(); } conn.setBusy(true); return conn; } } return null; } }

连接池管理

public class PoolManager {

    private static class createPool { private static MyPoolImpl poolImpl = new MyPoolImpl(); } /** * 内部类单利模式产生使用对象 * @return */ public static MyPoolImpl getInstance() { return createPool.poolImpl; } }

测试类

import java.sql.ResultSet;
import java.sql.SQLException;

public class MypoolTest {

    private static MyPoolImpl poolImpl = PoolManager.getInstance();

    public synchronized static void selctData() { PooledConnection connection = poolImpl.getConnection(); ResultSet rs = connection.queryBysql("SELECT * FROM user"); try { while (rs.next()) { System.out.println(rs.getString("ID") + "\t\t"); System.out.println(rs.getString("USERNAME") + "\t\t"); System.out.println(rs.getString("PASSWORD") + "\t\t"); System.out.println(); } rs.close(); connection.close(); } catch (SQLException e) { e.printStackTrace(); } } public static void main(String[] args) { for (int i = 0; i < 1500; i++) { new Thread(new Runnable() { @Override public void run() { selctData(); } }).start(); } } }