基本使用

package cn.itcast.jdbc;

import java.sql.*;

/*
 * DDL语句
 * */
public class JdbcDemo6 {
    public static void main(String[] args) {
        //声明数据库连接对象
        Connection conn = null;
        //声明数据库执行对象
        Statement stmt = null;
        //声明结果集对象
        ResultSet rs = null;
        try {
            //1.注册驱动
            Class.forName("com.mysql.jdbc.Driver");
            //2.获取数据库连接对象
            conn = DriverManager.getConnection("jdbc:mysql:///myemployees", "root", "ROOT");
            //3.定义SQL
            String sql ="select * from job_grades;";
            //4.获取执行SQL的对象
            stmt = conn.createStatement();
            //5.执行SQL
            rs= stmt.executeQuery(sql);
            //6.处理返回结果
            //6.1让游标向下移动一行
            rs.next();
            //6.2获取数据
            String str = rs.getString(1);
            int i = rs.getInt(2);
            double d = rs.getDouble(3);
            System.out.println(str+" "+i+" "+d);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            //7.释放资源,最后用的最先释放
            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();
                }
            }
        }
    }
}

 正确使用

package cn.itcast.jdbc;

import java.sql.*;

public class JdbcDemo7 {
    public static void main(String[] args) {
        //声明数据库连接对象
        Connection conn = null;
        //声明数据库执行对象
        Statement stmt = null;
        //声明结果集对象
        ResultSet rs = null;
        try {
            //1.注册驱动
            Class.forName("com.mysql.jdbc.Driver");
            //2.获取数据库连接对象
            conn = DriverManager.getConnection("jdbc:mysql:///myemployees", "root", "ROOT");
            //3.定义SQL
            String sql ="select * from job_grades;";
            //4.获取执行SQL的对象
            stmt = conn.createStatement();
            //5.执行SQL
            rs= stmt.executeQuery(sql);
            //6.处理返回结果
                //循环判断游标是否是最后一行末尾
            while (rs.next()){
                //获取数据
                String str = rs.getString(1);
                int i = rs.getInt(2);
                double d = rs.getDouble(3);
                System.out.println(str+" "+i+" "+d);
            }

        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            //7.释放资源,最后用的最先释放
            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();
                }
            }
        }
    }
}

 练习

package cn.itcast.domain;

import java.util.Date;

/*
* 封装Beauty表数据的JavaBean类
* */
public class Beauty {
    private int id;
    private String name;
    private char sex;
    private Date borndate;
    private double phone;
    private int boyfriend_id;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public char getSex() {
        return sex;
    }

    public void setSex(char sex) {
        this.sex = sex;
    }

    public Date getBorndate() {
        return borndate;
    }

    public void setBorndate(Date borndate) {
        this.borndate = borndate;
    }

    public double getPhone() {
        return phone;
    }

    public void setPhone(int phone) {
        this.phone = phone;
    }

    public int getBoyfriend_id() {
        return boyfriend_id;
    }

    public void setBoyfriend_id(int boyfriend_id) {
        this.boyfriend_id = boyfriend_id;
    }

    @Override
    public String toString() {
        return "Beauty{" +
                "id=" + id +
                ", name=‘" + name + ‘\‘‘ +
                ", sex=" + sex +
                ", borndate=" + borndate +
                ", phone=" + phone +
                ", boyfriend_id=" + boyfriend_id +
                ‘}‘;
    }
}

 封装类用的util包下的date

 项目中返回的sql下的date

 sql下的date是util下date的子类，父类可以接受子类对象。直接封装就行了

package cn.itcast.jdbc;

import cn.itcast.domain.Beauty;

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

/**
 * 定义一个方法，查询beauty表的数据将其封装为对象，然后装载集合返回
 */
public class JDBCDemo8 {
    public static void main(String[] args) {
        List<Beauty> list = new JDBCDemo8().findAll();
        System.out.println(list);
        System.out.println(list.size());
    }
    /**
     * 查询所有beauty对象
     */
    public List<Beauty> findAll() {
        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;
        List<Beauty> list = null;
        try {
            //1.注册驱动
            Class.forName("com.mysql.jdbc.Driver");
            //2.获取连接
            conn = DriverManager.getConnection("jdbc:mysql:///girls", "root", "ROOT");
            //3.第一SQL
            String sql = "select * from beauty";
            //4.获取执行SQL的对象
            stmt = conn.createStatement();
            //5.执行SQL
            rs = stmt.executeQuery(sql);
            //7.封装对象
            Beauty beauty = null;
            //6.遍历结果集，封装对象，装载集合
            list = new ArrayList<Beauty>();
            while (rs.next()) {//判断是否有下一行，有就执行，没有就结束执行下面的语句
                //获取数据

                //名字要和数据库保持一致，和封装类没有关系
                int id = rs.getInt("id");
                String name = rs.getString("name");
                Date borndate = rs.getDate("borndate");
                int boyfriend_id = rs.getInt("boyfriend_id");

//                Beauty beauty = new Beauty();
                /*
                 * 如果写在这就会占用很多栈内存（new的对象都在栈内存）
                 * 写在第七步的位置
                 * */

                //创建对象并赋值
                beauty = new Beauty();
                beauty.setId(id);
                beauty.setName(name);
                beauty.setBorndate(borndate);
                beauty.setBoyfriend_id(boyfriend_id);

                //装载集合
                list.add(beauty);
            }

        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            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();
                }
            }
        }
        return list;
    }
}

JDBC——ResultSet结果集对象

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