java学习笔记—JDBC5（20）

19 、连接池

创建Connection的过程是非常耗时的，为了保证Conection可以重用。应该将Connection进行池管理。

使用静态工厂方法管理一个唯一的连接：

package cn.itcast.utils;

import java.sql.Connection;
import java.sql.Driver;
import java.sql.DriverManager;
import java.util.Enumeration;

/**
 * 用静态工厂方法管理一个唯一的可重用的连接
 */
public class ConnUtils {
    private ConnUtils(){}
    private static Connection con;
    //在静态代码块中创建与数据库的连接
    static{
        try{
            Class.forName("com.mysql.jdbc.Driver");
            String url = "jdbc:mysql:///db909?characterEncoding=UTf8";
            con = DriverManager.getConnection(url,"root","1234");
        }catch(Exception e){
            throw new RuntimeException(e.getMessage(),e);
        }
    }
    //使用一个静态方法－静态工厂方法，返回connection实例
    public static Connection getCon(){   //静态工厂方法
        return con;
    }
}

2 连接池的实现

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为什么要有连接池

　１：维护多个连接。必须要保证每一个线程获取到的是不同的connection对象。

　２：提供一个方法可以回收连接。

以下是最基本的实现：

package cn.itcast.utils;
import java.sql.Connection;
import java.sql.DriverManager;
import java.util.ArrayList;
import java.util.List;
public class ConnUtils2 {
    //声明一个容器,放所有声明的连接Connection
    private static List<Connection> pool = new ArrayList<Connection>();
    static{
        try{
            Class.forName("com.mysql.jdbc.Driver");
            String url = "jdbc:mysql:///db909?characterEncoding=UTf8";
            for(int i=0;i<3;i++){
                //创建三个连接
                Connection con = DriverManager.getConnection(url,"root","1234");
                //将这个三个连接放到pool中去
                pool.add(con);
            }
            System.err.println("连接是:"+pool);
        }catch(Exception e){
            throw new RuntimeException(e.getMessage(),e);
        }
    }
    public static Connection getCon(){
        synchronized (pool) {
            Connection con = pool.remove(0);
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.err.println("还有："+pool.size());
            return con;
        }
    }
    //手工的还连接
    public static void back(Connection con){
        System.err.println("还连接："+con);
        pool.add(con);
    }
}

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为了回收连接。我们应该重写close方法。对close方法增强。

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