JDBC模拟连接池、C3P0获取链接和最终的JdbcUtils工具类的版本

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一丶模拟连接池获取连接：

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package jdbc_util;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;
//模式连接池的操作
public class JdbcUtil02 {
    private static String driver = null;
    private static String url = null;
    private static String username = null;
    private static String password = null;
    private static int Normal = 10; //初始化连接数
    private static int MAX = 20; //最大的连接数
    private static int MIN = 5; //最小的连接数
    @SuppressWarnings("unused")
    private static int NUM = 0; //当前连接数

    //使用集合 模式连接池
    private static List<Connection> pool = new ArrayList<Connection>();
    //初始化连接池
    static{
        //读取参数
        Properties p = new Properties();
        try {
            FileInputStream fis = new FileInputStream(new File("src//jdbc.properties"));
            p.load(fis);
            driver = p.getProperty("driver");
            url = p.getProperty("url");
            username = p.getProperty("username");
            password = p.getProperty("password");

            //加载驱动
            Class.forName(driver);

            //初始化连接池
            for(int i = 0; i < Normal; i++){                
                pool.add(createConnection());
                NUM++;
            }
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }       
    }

    //从数据库中获取物理链接
    private static Connection createConnection(){
        Connection conn = null;
        try {
            conn = DriverManager.getConnection(url, username, password);
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return conn;
    }

    //获取链接的方法
    public static Connection getConnection(){
        if(pool.size() > MIN){
            return pool.remove(0);
        }else{
            if(pool.size() <= MAX){
                Connection conn = createConnection();
                NUM++;
                return conn;
            }else{
                throw new RuntimeException("链接已经用完，请等待...");
            }
        }   
    }

    public static void close(Connection conn,Statement stat, ResultSet rs){
        if(conn != null){
            //关闭  实际上是将连接 放回到连接池中
            pool.add(conn);
        }
        try {
            if(stat != null){
                stat.close();
            }
            if(rs != null){
                rs.close();
            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

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properties文件的情况：

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二丶使用C3P0获取连接

1.首先加载C3P0的驱动包，

2.再将C3P0的配置文件放在src的目录下，

3.改配置文件里面的密码，和需要访问数据库的名字

代码如下：

package jdbc_util;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import javax.sql.DataSource;

import com.mchange.v2.c3p0.ComboPooledDataSource;

public class JdbcUtil03 {
    private static DataSource ds ; //数据源
    //加载驱动
    static{
        //读配置文件
        ds = new ComboPooledDataSource();
    }
    public static Connection getConnection(){
        Connection conn = null;
        try {
            conn = ds.getConnection();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return conn;    
    }

    public static void close(Connection conn,Statement stat,ResultSet rs){
        if(conn != null){
            try {
                conn.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        if(stat != null){
            try {
                stat.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        if(rs != null){
            try {
                rs.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}

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三丶最终的JDBCUtil工具类

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需要加载的jar的包有一下：