JDBC技术进阶:

抽取JDBC工具类：JDBCutils

目的：简化书写
分析：
1.注册驱动抽取
2.抽取一个方法获取连接对象
*需求：不想传递参数（麻烦），还得保证工具类的通用性。
*解决：配置文件

代码：

配置文件：jdbc . properties

url=jdbc:mysql:///Test
user=root
password=123456
Driver=com.mysql.cj.jdbc.Driver

工具类：JDBCutils

package com.idea.Test;

import java.io.FileReader;
import java.io.IOException;
import java.net.URL;
import java.sql.*;
import java.util.Properties;

public class JDBCutils {
    private static String url;
    private static String user;
    private static String password;
    private static String Driver;
    
    //获取properties配置文件的内容
   static {
       try {
           Properties pro = new Properties();
           ClassLoader classLoader = JDBCutils.class.getClassLoader();
           URL resource = classLoader.getResource("pro.properties");
           String path = resource.getPath();
           pro.load(new FileReader(path));
           url = pro.getProperty("url");
           user = pro.getProperty("user");
           password = pro.getProperty("password");
           Driver = pro.getProperty("Driver");
           try {
               Class.forName(Driver);
           } catch (ClassNotFoundException e) {
               e.printStackTrace();
           }
       } catch (IOException e) {
           e.printStackTrace();
       }
   }
   //获取连接方法
   public static Connection getConnection() throws SQLException {
       return DriverManager.getConnection(url,user,password);
   }
   //释放资源方法
    public static void close(ResultSet rs,Statement stmt,Connection conn){
        if (rs != null){
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (stmt != null){
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
    //释放资源方法重载
    public static void close(Statement stmt,Connection conn){
        if (stmt != null){
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

}

测试类：

package com.idea.Test;

import java.sql.*;
import java.util.ArrayList;
import java.util.List;

public class JDBC {
    public static void main(String[] args) {
        List<Emp> list = findAll();
        System.out.println(list);
    }
    public static List<Emp> findAll(){
        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;
        List<Emp> list = null;
        try {
            conn = JDBCutils.getConnection();
            String sql = "select * from emp";
            stmt = conn.createStatement();
            rs = stmt.executeQuery(sql);
            Emp emp = null;
            list = new ArrayList<>();
            while (rs.next()){
                int id = rs.getInt(1);
                String name = rs.getString("name");
                int salary = rs.getInt(3);
                Date join_date = rs.getDate(4);
                emp = new Emp();
                emp.setId(id);
                emp.setName(name);
                emp.setSalary(salary);
                emp.setJoin_time(join_date);
                //装载集合
                list.add(emp);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            JDBCutils.close(rs,stmt,conn);
        }
        return list;
    }
}

运行结果：