1 jdbc连接池原理

package com.msb.dao;

import com.msb.util.PropertiesUtil;
import org.apache.log4j.Logger;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.LinkedList;


public class MyConnectionPool {
    private static String driver;
    private static String url;
    private static String user;
    private static String password;
    private static int initSize;
    private static int maxSize;
    private static Logger logger;
    private static LinkedList<Connection> pool;

    static{
        logger=Logger.getLogger(MyConnectionPool.class);
        // 初始化参数
        PropertiesUtil propertiesUtil=new PropertiesUtil("/jdbc.properties");
        driver=propertiesUtil.getProperties("driver");
        url=propertiesUtil.getProperties("url");
        user=propertiesUtil.getProperties("user");
        password=propertiesUtil.getProperties("password");
        initSize=Integer.parseInt(propertiesUtil.getProperties("initSize"));
        maxSize=Integer.parseInt(propertiesUtil.getProperties("maxSize"));
        // 加载驱动
        try {
            Class.forName(driver);
        } catch (ClassNotFoundException e) {
            logger.fatal("找不到数据库驱动类"+driver,e);
        }
        // 初始化pool
        pool=new LinkedList<Connection>();
        // 创建5个链接对象
        for (int i = 0; i <initSize ; i++) {
            Connection connection = initConnection();
            if(null != connection){
                pool.add(connection);
                logger.info("初始化连接"+connection.hashCode()+"放入连接池");

            }
        }
    }

    // 私有的初始化一个链接对象的方法
    private static Connection initConnection(){
        try {
            return DriverManager.getConnection(url,user,password);
        } catch (SQLException e) {
            logger.fatal("初始化连接异常",e);
        }
        return null;
    }
    // 共有的向外界提供链接对象的
    public static Connection getConnection(){
        Connection connection =null;
        if(pool.size()>0){
            connection= pool.removeFirst();// 移除集合中的第一个元素
            logger.info("连接池中还有连接:"+connection.hashCode());
        }else{
            connection = initConnection();
            logger.info("连接池空,创建新连接:"+connection.hashCode());
        }
        return connection;
    }

    // 共有的向连接池归还连接对象的方法
    public static void returnConnection(Connection connection){
        if(null != connection){
            try {
                if(!connection.isClosed()){

                    if(pool.size()<maxSize){
                        try {
                            connection.setAutoCommit(true);// 调整事务状态
                            logger.debug("设置连接:"+connection.hashCode()+"自动提交为true");
                        } catch (SQLException e) {
                            e.printStackTrace();
                        }
                        pool.addLast(connection);
                        logger.info("连接池未满,归还连接:"+connection.hashCode());
                    }else{
                        try {
                            connection.close();
                           logger.info("连接池满了,关闭连接:"+connection.hashCode());
                        } catch (SQLException e) {
                            e.printStackTrace();
                        }
                    }
                }else{
                   logger.info("连接:"+connection.hashCode()+"已经关闭,无需归还");
                }
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }else{
           logger.warn("传入的连接为null,不可归还");
        }
    }

}

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package com.msb.util;

import java.io.IOException;
import java.io.InputStream;
import java.util.Properties;

public class PropertiesUtil {
    private Properties properties;

    public PropertiesUtil(String path){
        properties=new Properties();
        InputStream inputStream = this.getClass().getResourceAsStream(path);
        try {
            properties.load(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public String getProperties(String key){
        return properties.getProperty(key);
    }

}

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提前创建的多个连接池connection对象放在队列中