自定义JDBC工具类

因为数据库的连接代码都是固定的，为了将减少重复的代码的书写，可以将这些代码封装为一个工具类，获取数据库的连接对象。

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

 public final class JDBCUtils {// 不能被继承或重写
     private JDBCUtils() {
     }

     private static Connection con;

     static {
         try {
             Class.forName("com.mysql.jdbc.Driver");
             String url = "jdbc:mysql://localhost:3306/student mangement system";
             String username = "root";
             String password = "root";
             con = DriverManager.getConnection(url, username, password);
         } catch (Exception e) {
             e.printStackTrace();
             throw new RuntimeException(e + "数据库连接失败");
         }
     }

     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！");
             }
         }

     }
 }

测试工具类：

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
public class Test {
    public static void main(String[] args)throws Exception {
        Connection con = JDBCUtils.getConnection();
        PreparedStatement pst = con.prepareStatement("SELECT sname,studentno FROM student");
        ResultSet rs = pst.executeQuery();
        while(rs.next()){
            System.out.println(rs.getString("sname")+"   "+rs.getString("studentno"));
        }
        JDBCUtils.close(con, pst, rs);
    }
}