自定义JDBC工具类（配置文件）

 import java.io.IOException;
 import java.io.InputStream;
 import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.Properties;

 public class JDBCUtils {
     private static Connection con;
     private static String driver;
     private static String url;
     private static String username;
     private static String password;

     static {// 静态代码块只执行一次，获取一次信息即可
         try {
             readConfig();
             Class.forName(driver);
             con = DriverManager.getConnection(url, username, password);
         } catch (Exception ex) {
             throw new RuntimeException("数据库连接失败");
         }
     }
 /*
  * getClassLoader();返回该类的加载器
  * getResourceAsStream();查找具有给定名称的资源
  */
     private static void readConfig() {
         InputStream in = JDBCUtils.class.getClassLoader().getResourceAsStream("JDBC.properties");
         Properties pro = new Properties();
         try {
             pro.load(in);
         } catch (IOException e) {
             e.printStackTrace();
         }
         driver = pro.getProperty("driver");
         url = pro.getProperty("url");
         username = pro.getProperty("username");
         password = pro.getProperty("password");
     }

     public static Connection getConnection() {
         return con;
     }
     public static void close(Connection con, Statement stat) {

         if (stat != null) {
             try {
                 stat.close();
             } catch (SQLException e) {
                 e.printStackTrace();
                 System.out.println("stat流关闭异常！");
             }
         }

         if (con != null) {
             try {
                 con.close();
             } catch (SQLException e) {
                 e.printStackTrace();
                 System.out.println("con流关闭异常！");
             }
         }

     }

     public static void close(Connection con, Statement stat, ResultSet rs) {
         if (rs != null) {
             try {
                 rs.close();
             } catch (SQLException e) {
                 e.printStackTrace();
                 System.out.println("rs流关闭异常！");
             }
         }

         if (stat != null) {
             try {
                 stat.close();
             } catch (SQLException e) {
                 e.printStackTrace();
                 System.out.println("stat流关闭异常！");
             }
         }

         if (con != null) {
             try {
                 con.close();
             } catch (SQLException e) {
                 e.printStackTrace();
                 System.out.println("con流关闭异常！");
             }
         }

 }
 }

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

public class Test {
    public static void main(String[] args) {

        ResultSet rs = null;
        PreparedStatement pst = null;

        Connection con = JDBCUtils.getConnection();
        try {
            pst = con.prepareStatement("SELECT sname,studentno FROM student");
            rs = pst.executeQuery();
            while (rs.next()) {
                System.out.println(rs.getString("sname") + "   "
                        + rs.getString("studentno"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        JDBCUtils.close(con, pst, rs);
    }
}

配置文件：

这样在以后更换数据库后，只需更改配置文件即可，不用再修改程序里面的内容。

利用Properties类，读取配置文件中的信息，通过键获取值。

类加载器getClassLoader（）负责读取 Java 字节代码，因为在实际情况下，用户得到的项目没有sre文件夹，只能在bin目录下读取文件。