中阶d03.1 JDBCDemo

1. jdbc使用查看驱动的doc文档《connector-j.html》

2.代码实现：1. 注册驱动---2. 建立连接---3. 创建statement ，跟数据库打交道---

　　　　　　---4. 执行sql，得到ResultSet---5. 遍历结果 ---6. 释放资源

package zj_1_JDBC;

import java.sql.*;

public class MainTest {
    public static void main(String[] args) throws ClassNotFoundException {
        //注册驱动
        Class.forName("com.mysql.jdbc.Driver"); //注册驱动这步可以写也可以不用写

      
        String url = "jdbc:mysql://localhost/student";
        String username = "root";
        String password = "root";
        Connection conn = null;
        Statement st = null;
        ResultSet rs = null;

        try {
　　　　　　　　//建立连接
            conn = DriverManager.getConnection(url,username,password);
            // 创建statement
            st = conn.createStatement();//创建statement ，跟数据库打交道，一定需要这个对象

            // 执行sql，得到ResultSet
            String sql = "SELECT * FROM users WHERE name = '小明'";
            rs = st.executeQuery(sql);

            // 遍历结果 
            while (rs.next()) { //rs.next() 当读到行末尾时会返回false，下一行有数据则返回true
                int id = rs.getInt("id");
                String name = rs.getString("name");
                int age = rs.getInt("age");

                System.out.println(id+""+name+","+age);
            }

        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            // 释放资源
            JDBCUtil.release(conn,st,rs);
           /* try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }

            try {
                st.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }

            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }*/
        }

    }
}

工具类，整合释放资源方法

package zj_1_JDBC;

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

public class JDBCUtil {
    Connection conn = null;
    Statement st = null;
    ResultSet rs = null;

    public static void release(Connection conn, Statement st, ResultSet rs) {
        closeRs(rs);
        closeSt(st);
        closeConn(conn);
    }

    private static void closeRs(ResultSet rs){
        try {
            if(rs != null){
                rs.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally{
            rs = null;
        }
    }

    private static void closeSt(Statement st) {
        try {
            if(st != null) {
                st.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            st = null;
        }
    }

    private static void closeConn(Connection conn) {
        try {
            if(conn != null) {
                conn.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            conn = null;
        }
    }
}