1.创建数据库配置文件
—文件名 jdbc_mysql.properties
—文件所在位置 如下图：

2.读取数据库配置文件类

package Connection.mysql;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.IOException;import java.io.InputStream;import java.util.Properties;public class Readconf extends base {    private final static String path ="./conf/jdbc_mysql.properties";         public static void main(String[] args)  {    }        public static String GetDriver(String path) {        String driver=null;        //文件路径        InputStream is;        try {            //获取配置路径流            is = new FileInputStream(path);            //new 读取配置文件对象            Properties p = new Properties();            try {                //加载配置文件                p.load(is);                //获取驱动名                driver = p.getProperty("driver");                       } catch (IOException e) {                System.out.println("没有找到");            }        } catch (FileNotFoundException e1) {            System.out.println("没有找到配置文件");        }        return driver;    }        public static String GetUrl(String path ,String dbname) throws FileNotFoundException{        String url =null;        //文件路径        InputStream is;        try {            //获取配置路径流            is = new FileInputStream(path);            //new 读取配置文件对象            Properties p = new Properties();            try {                //加载配置文件                p.load(is);                //获取驱动名                url = p.getProperty("url");                     } catch (IOException e) {                System.out.println("加载文件错误");            }        } catch (FileNotFoundException e1) {            System.out.println("没有找到配置文件");        }        return url+dbname+"?";    }        public static String Getuser(String path) throws FileNotFoundException{        String user =null;        //文件路径        InputStream is;        try {            //获取配置路径流            is = new FileInputStream(path);            //new 读取配置文件对象            Properties p = new Properties();            try {                //加载配置文件                p.load(is);                //获取驱动名                user = p.getProperty("user");                       } catch (IOException e) {                System.out.println("加载文件错误");            }        } catch (FileNotFoundException e1) {            System.out.println("没有找到配置文件");        }        return user;    }        public static String GetPass(String path) throws FileNotFoundException{        String pass =null;        //文件路径        InputStream is;        try {            //获取配置路径流            is = new FileInputStream(path);            //new 读取配置文件对象            Properties p = new Properties();            try {                //加载配置文件                p.load(is);                //获取驱动名                pass = p.getProperty("pass");                       } catch (IOException e) {                System.out.println("加载文件错误");            }        } catch (FileNotFoundException e1) {            System.out.println("没有找到配置文件");        }        return pass;    }}

3.创建连接数据库，以及执行sql语句的基类

package Connection.mysql;import java.io.FileNotFoundException;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.SQLException;import com.mysql.jdbc.Connection;import com.mysql.jdbc.PreparedStatement;public class Jdbc_base extends Readconf{    private final static String path ="./conf/jdbc_mysql.properties";  //配置文件路径    public static Connection conn = null; //连接服务器对象    public static PreparedStatement ps =null; //执行sql 对象    public static ResultSet  rs =null; //结果集对象        public static void main(String[] args) {//      boolean falg = Connection_db("demo");//      System.out.println(falg);    }        public static boolean Connection_db(String dbname)  {        boolean falg = false;                String driver = Readconf.GetDriver(path);        String url =null;        String user =null;        String pass =null;        try {            url  = Readconf.GetUrl(path, dbname);            user = Readconf.Getuser(path);            pass = Readconf.GetPass(path);        } catch (FileNotFoundException e) {            System.out.println("没有找到文件,错误在Readconf");        }        try {            //1.加载驱动            Class.forName(driver);            System.out.println("加载驱动成功");            //2.连接数据库            conn = (Connection) DriverManager.getConnection(url, user, pass);            //判断数据是否关闭着            boolean closed = conn.isClosed();            if(!closed){                System.out.println("数据库连接成功");                falg=true;            }else{                System.out.println("数据库连接失败");            }        } catch (ClassNotFoundException e) {            System.out.println("没有找到文件,错误在Readconf");        } catch (SQLException e) {            System.out.println("连接数据库失败");        }finally{//          try {//              conn.close();//          } catch (SQLException e) {//              System.out.println("关闭---Connection---错误");//          }        }        return falg;    }        public static ResultSet execute_sql(String dbname,String sql){        boolean falg = Connection_db(dbname);        if(falg){            try {                //预加载sql语句                ps = (PreparedStatement) conn.prepareStatement(sql);                //执行sql， 且获取返回值                rs = ps.executeQuery();            } catch (SQLException e) {                System.out.println("运行sql失败："+sql);            }finally{//              try {//                  ps.close();//              } catch (SQLException e) {//                  System.out.println("关闭---PreparedStatement---错误");//              }            }        }else{            System.out.println("没有连接上数据库");        }        return rs;    } }

4.调用基类，对数据库进行查询操作

package Connection.mysql;import java.sql.ResultSet;import java.sql.SQLException;public class Demo1 extends Jdbc_base{        public static void main(String[] args) {        select();    }    //执行查询    public static void select(){        //sql 语句 查询 id=1 的那一行的数据        String sql ="select * from user where id = '1'";        System.out.println(sql);        ResultSet rs = Jdbc_base.execute_sql("demo", sql);        try {            //测试部分            if(rs.next()){                //通过字段获取到 对应的值                 String username = rs.getString("username");                //打印数据库获取到的值                System.out.println("---------");                System.out.println("user:"+username);                System.out.println("---------");            }else{                System.out.println("kong");            }        } catch (SQLException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }finally{            try {                //关闭操作                rs.close();                Jdbc_base.ps.close();                Jdbc_base.conn.close();            } catch (SQLException e) {                // TODO Auto-generated catch block                e.printStackTrace();            }        }    }}