数据库连接池的基本使用

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首先创建一个类管理连接池,对连接进行获取以及分配

ConnectionPool.java

package jdbc;import java.sql.Connection;import java.sql.DriverManager;import java.sql.SQLException;import java.util.ArrayList;import java.util.List;public class ConnectionPool {        List<Connection> connections=new ArrayList<Connection>();    int size;//连接池容量    public ConnectionPool(int size) {        this.size=size;        init();    }            private void init() {        // 不能使用try-with-resource的方式创建连接,因为这些连接要放到连接池中备用        try {            Class.forName("com.mysql.jdbc.Driver");            for(int i=0; i<size;i++) {                Connection connection=DriverManager.getConnection                        ("jdbc:mysql://127.0.0.1:3306/study?characterEncoding=UTF-8", "root", "joey");                connections.add(connection);            }        } catch (ClassNotFoundException e) {            e.printStackTrace();        } catch (SQLException e) {            e.printStackTrace();        }    }        /**     * 从连接池中获取连接     * @return     */    public synchronized Connection getConnection() {        while(connections.isEmpty()) {            // 如果连接池中没有可用连接, 让线程等待            try {                this.wait();            } catch (InterruptedException e) {                e.printStackTrace();            }        }        // 从连接池中获取一个连接        Connection connection=connections.remove(0);        return connection;    }        /**     * 返回连接给连接池,并通知其它线程(有可用连接)     * @param connection     */    public synchronized void returnConnection(Connection connection) {        connections.add(connection);        this.notifyAll();    }}

测试类中创建多线程虚拟任务,利用连接池中的连接完成

ConnectionPoolTest.java

package jdbc;import java.sql.Connection;import java.sql.DriverManager;import java.sql.SQLException;import java.sql.Statement;public class ConnectionPoolTest {    public static void main(String[] args) {        long start = System.currentTimeMillis();                // 通过连接池的管理,让多线程任务可以循环利用连接资源        ConnectionPool connectionPool = new ConnectionPool(10);        for (int i = 0; i < 100; i++) {            new WorkingThread("working thread" + i, connectionPool).start();        }        // 直接发起多线程任务/*        for (int i = 0; i < 100; i++) {            new WorkingThread2("working thread" + i).start();        }*/                long end = System.currentTimeMillis();        System.out.println("耗时: " + (end - start));    }}class WorkingThread extends Thread {    private ConnectionPool connectionPool;    public WorkingThread(String name, ConnectionPool connectionPool) {        super(name);        this.connectionPool = connectionPool;    }    @Override    public void run() {        Connection connection = connectionPool.getConnection();        System.out.println(this.getName() + ":\t获取了一个连接,并开始工作");        try (Statement statement = connection.createStatement()) {            // 模拟耗时一秒的数据库SQL语句            Thread.sleep(1000);            statement.execute("select * from employee;");        } catch (SQLException e) {            e.printStackTrace();        } catch (InterruptedException e) {            e.printStackTrace();        }        connectionPool.returnConnection(connection);        System.out.println(this.getName() + ":\t结束工作,并返回连接");    }}class WorkingThread2 extends Thread {    public WorkingThread2(String name) {        super(name);    }    @Override    public void run() {        System.out.println(this.getName() + ":\t获取了一个连接,并开始工作");        try (Connection connection = DriverManager                .getConnection("jdbc:mysql://127.0.0.1:3306/study?characterEncoding=UTF-8", "root", "joey");                Statement statement = connection.createStatement()) {            // 模拟耗时一秒的数据库SQL语句            Thread.sleep(1000);            statement.execute("select * from employee;");        } catch (SQLException e) {            e.printStackTrace();        } catch (InterruptedException e) {            e.printStackTrace();        }        System.out.println(this.getName() + ":\t结束工作,并返回连接");    }}

--主线程中的耗时计算不准确??

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