JDBC2 示例 -- CRUD

可以将获取连接的部分封装起来，通过读取配置文件来获得Connection对象。
本例子的配置文件为src/jdbc.properties,封装类为jdbcUtils

请注意封装类的写法
为什么用静态块

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.ResourceBundle;
import com.mysql.jdbc.Driver;
//封装连接
//通过配置文件 jdbc.properties
public class jdbcUtils {
    
    private static final String DRIVERCLASS;
    private static final String URL;
    private static final String USERNAME;
    private static final String PASSWORD;
    static{
        DRIVERCLASS = ResourceBundle.getBundle("jdbc").getString("driverClass");
        URL = ResourceBundle.getBundle("jdbc").getString("url");
        USERNAME = ResourceBundle.getBundle("jdbc").getString("username");
        PASSWORD = ResourceBundle.getBundle("jdbc").getString("password");
    }
    //在静态代码块中，可以保证驱动不用重复加载
    static{
        try {
            DriverManager.registerDriver(new Driver());
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    public static Connection getConnection() throws Exception{
        Connection con = DriverManager.getConnection(URL, USERNAME, PASSWORD);
        return con;
    }
}

CRUD
文件关闭操作按上次比较完整的改正

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import org.junit.Test;
import cn.itcast.util.jdbcUtils;
import com.mysql.jdbc.Driver;
public class jdbcDemo5 {
    
    //按id查找，后面可以给一个id形参
    public void findById() throws Exception{
        String sql = "select * from user where id=1";
        
        Connection con = jdbcUtils.getConnection();
        Statement st = con.createStatement();
        ResultSet rs = st.executeQuery(sql);
        
        rs.next();//需要将光标移向下一行
        System.out.println(rs.getString("password"));
        
        rs.close();
        st.close();
        con.close();
    }
    
    //添加操作
    public void addTest() throws Exception{
        String sql = "insert into user values(null,'jjohn','123','123@qq.com')";
        Connection con = jdbcUtils.getConnection();
        Statement st = con.createStatement();
        int row = st.executeUpdate(sql);
        System.out.println(row);
        
        st.close();
        con.close();
    }
    
    //删除操作
    public void deleteTest() throws Exception{
        String sql = "delete from user where id=3";
        
        Connection con = jdbcUtils.getConnection();
        Statement st = con.createStatement();
        st.executeUpdate(sql);
        
        st.close();
        con.close();
        
    }
    
    //修改操作
    public void updateTest() throws Exception{
        String sql = "update user set password='456' where id=3";
        
        Connection con = jdbcUtils.getConnection();
        Statement st = con.createStatement();
        int row = st.executeUpdate(sql);
        System.out.println(row);
        
        st.close();
        con.close();
    }
}