Java EE WEB工程师培训-JDBC+Servlet+JSP整合开发之02.JDBC Connection

本季我们来学习下JDBC Connection连接、获得数据连接Connection及获得一个可配置的连接

Connection简介

（1）获得数据库连接是操作数据库的第一步，是应用程序和数据库的一个“握手”过程
（2）数据库打开的连接数是有限的，所以连接使用完成需要关闭

获得数据连接Connection

–获得数据库连接的步骤
• Class.forName加载驱动
–Class.forName("com.mysql.jdbc.Driver");
• DriverManager获得连接
–DriverManager是获得数据连接的一个工厂（实例化的作用）
» DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbc_db", "root", "mysqladmin");

Class.forName("com.mysql.jdbc.Driver");    
Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/michael_db", "root", "mysqladmin");

ConnectionUtil.java

package com.michael.jdbc;    

import java.sql.Connection;    
import java.sql.DriverManager;    

public class ConnectionUtil {    

        /**    
         * @param args    
         */    
        public Connection getConnection(){    
                Connection conn = null;    
                try {    
                        //Class.forName加载驱动    
                        Class.forName("com.mysql.jdbc.Driver");    
                        //DriverManager获得连接    
                        conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbc_db","root","mysqladmin");    
                        return conn;    
                } catch (Exception e) {    
                        e.printStackTrace();    
                }    
                return null;    
        }    

}

Main.java

package com.michael.main;    

import com.michael.jdbc.ConnectionUtil;    

public class Main {    

        /**    
         * @param args    
         */    
        public static void main(String[] args) {    
                ConnectionUtil cu = new ConnectionUtil();    
                System.out.print(cu.getConnection());    
        }    

}

测试结果：

下面我们来看下第二种写法哈~

ConnectionUtil.java

package com.michael.jdbc;    

import java.sql.Connection;    
import java.sql.DriverManager;    

public class ConnectionUtil {    
        //第一种方法    
        public Connection getConnection(){    
                Connection conn = null;    
                try {    
                        //Class.forName加载驱动    
                        Class.forName("com.mysql.jdbc.Driver");    
                        //DriverManager获得连接    
                        conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbc_db","root","mysqladmin");    
                        return conn;    
                } catch (Exception e) {    
                        e.printStackTrace();    
                }    
                return null;    
        }    
        //第二种方法    
        public Connection getConnection(String driver,String url,String user,String password){    
                Connection conn = null;    
                try {    
                        //Class.forName加载驱动    
                        Class.forName(driver);    
                        //DriverManager获得连接    
                        conn = DriverManager.getConnection(url,user,password);    
                        return conn;    
                } catch (Exception e) {    
                        e.printStackTrace();    
                }    
                return null;    
        }    

}

Main.java

package com.michael.main;    

import com.michael.jdbc.ConnectionUtil;    

public class Main {    

        /**    
         * @param args    
         */    
        public static void main(String[] args) {    
                ConnectionUtil cu = new ConnectionUtil();    
                //第一种方法    
                System.out.println(cu.getConnection());    
                //第二种方法    
                System.out.println(cu.getConnection("com.mysql.jdbc.Driver","jdbc:mysql://localhost:3306/jdbc_db","root","mysqladmin"));    
        }    

}

测试结果：

获得一个可配置的连接

数据库的连接参数会经常改变哈~我们可以将连接参数写在配置文件当中,这也是第三种获取数据连接的方法，可以不修改源程序哈~

DBConfig.properties

driver=com.mysql.jdbc.Driver    
url=jdbc:mysql://localhost:3306/jdbc_db    
user=root    
password=mysqladmin

  

ConnectionUtil.java

package com.michael.jdbc;    

import java.sql.Connection;    
import java.sql.DriverManager;    
import java.util.Properties;    

public class ConnectionUtil {    
        //第一种方法    
        public Connection getConnection(){    
                Connection conn = null;    
                try {    
                        //Class.forName加载驱动    
                        Class.forName("com.mysql.jdbc.Driver");    
                        //DriverManager获得连接    
                        conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/jdbc_db","root","mysqladmin");    
                        return conn;    
                } catch (Exception e) {    
                        e.printStackTrace();    
                }    
                return null;    
        }    
        //第二种方法    
        public Connection getConnection(String driver,String url,String user,String password){    
                Connection conn = null;    
                try {    
                        //Class.forName加载驱动    
                        Class.forName(driver);    
                        //DriverManager获得连接    
                        conn = DriverManager.getConnection(url,user,password);    
                        return conn;    
                } catch (Exception e) {    
                        e.printStackTrace();    
                }    
                return null;    
        }    
        //第三种方法    
        public Connection openConnection(){    
                String driver = "";    
                String url = "";    
                String user = "";    
                String password = "";    
                Properties prop = new Properties();    
                Connection conn = null;    
                try {    
                        //加载属性文件    
                        prop.load(this.getClass().getClassLoader().getResourceAsStream("DBConfig.properties"));    
                        driver = prop.getProperty("driver");    
                        url = prop.getProperty("url");    
                        user = prop.getProperty("user");    
                        password = prop.getProperty("password");    
                        //Class.forName加载驱动    
                        Class.forName(driver);    
                        //DriverManager获得连接    
                        conn = DriverManager.getConnection(url,user,password);    
                        return conn;    
                } catch (Exception e) {    
                        e.printStackTrace();    
                }    
                return null;    
        }    

}

Main.java

package com.michael.main;    

import com.michael.jdbc.ConnectionUtil;    

public class Main {    

        /**    
         * @param args    
         */    
        public static void main(String[] args) {    
                ConnectionUtil cu = new ConnectionUtil();    
                //第一种方法    
                System.out.println("第一种方法:"+cu.getConnection());    
                //第二种方法    
                System.out.println("第二种方法:"+cu.getConnection("com.mysql.jdbc.Driver","jdbc:mysql://localhost:3306/jdbc_db","root","mysqladmin"));    
                //第三种方法    
                System.out.println("第三种方法:"+cu.openConnection());    
        }    

}

测试结果：

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