jdbc操作mysql（二）：封装

案例四：封装共有操作

封装一个数据库的会话的类

import java.sql.*;

public class ConnectionUtil {
    /**
     * 获取连接对象的方法，返回一个Connection
     * 方法体中是共有操作：加载驱动，建立连接
     */
    public static Connection getConnection() {
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            String url = "jdbc:mysql://localhost:3306/jdbctest?serverTimezone=GMT";
            String user = "root";
            String password = "root";
            Connection connection = DriverManager.getConnection(url, user, password);
            return connection;
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * 关闭连接对象的方法，传入参数Connection对象
     * 方法体中是共有操作：判断该对象是否为连接状态，是则关闭
     */
    public static void close(Connection conn) {
        if(conn != null) {
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    /**
     * 关闭PreparedStatement对象的方法，传入参数为该对象
     * 方法体中是共有操作：判断该对象是否为连接状态，是则关闭
     */
    public static void close(PreparedStatement ps) {
        if(ps != null) {
            try {
                ps.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    /**
     * 关闭结果集对象的方法，传入参数为ResultSet对象
     * 方法体中是共有操作：判断该对象是否为连接状态，是则关闭
     */
    public static void close(ResultSet rs) {
        if(rs != null) {
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

封装对用户类的crud方法

import java.sql.Connection;
import java.sql.Date;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

public class UserManager {
    /**
     * 封装添加用户的方法
     */
    public void add(User user) {
        Connection conn = null;
        PreparedStatement ps = null;
        try {
            conn = ConnectionUtil.getConnection();
            String sql = "insert into t_user(username, age, sex, birthday) value(?, ?, ?, ?)";
            ps = conn.prepareStatement(sql);
            //setString 将指定的参数设置为给定的Java String值
            ps.setString(1, user.getUsername());  // 第一个占位符传入的参数
            ps.setInt(2, user.getAge());
            ps.setString(3, user.getSex());
            ps.setDate(4, new Date(user.getBirthday().getTime()), null);
            int rows = ps.executeUpdate();  // 受影响行
            System.out.println("->插入成功" + rows + "条信息");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            ConnectionUtil.close(ps);
            ConnectionUtil.close(conn);
        }
    }

    /**
     * 根据id删除用户
     */
    public void del(int id) {
        Connection conn = null;
        PreparedStatement ps = null;
        try {
            conn = ConnectionUtil.getConnection();
            String sql = "delete from t_user where id=?";
            ps = conn.prepareCall(sql);
            ps.setInt(1, id);
            int i = ps.executeUpdate();
            System.out.println("删除成功" + i + "条信息");
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            ConnectionUtil.close(ps);
            ConnectionUtil.close(conn);
        }
    }

    /**
     * 根据id查询用户信息
     */
    public User getUser(int id) {
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            conn = ConnectionUtil.getConnection();
            String sql = "select * from t_user where id=?";
            ps = conn.prepareStatement(sql);
            ps.setInt(1, id);
            rs = ps.executeQuery();
            while(rs.next()) {
                User u = new User();
                // getInt 检索的当前行中指定列的值
                u.setId(rs.getInt("id"));
                // getString 检索的当前行中指定列的值
                u.setUsername(rs.getString("username"));
                u.setAge(rs.getInt("age"));
                u.setBirthday(rs.getDate("birthday"));
                u.setSex(rs.getString("sex"));
                return u;
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            ConnectionUtil.close(rs);
            ConnectionUtil.close(ps);
            ConnectionUtil.close(conn);
        }
        return null;
    }

    /**
     * 查询所有用户的方法
     */
    public List<User> getAll() {
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            conn = ConnectionUtil.getConnection();
            String sql = "select * from t_user";
            ps = conn.prepareStatement(sql);
            // 返回结果集
            rs = ps.executeQuery();
            List<User> lists = new ArrayList<User>();
            while(rs.next()) {
                User u = new User();
                u.setId(rs.getInt("id"));
                u.setUsername(rs.getString("username"));
                u.setAge(rs.getInt("age"));
                u.setBirthday(rs.getDate("birthday"));
                u.setSex(rs.getString("sex"));
                lists.add(u);
            }
            return lists;
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            ConnectionUtil.close(rs);
            ConnectionUtil.close(ps);
            ConnectionUtil.close(conn);
        }
        return null;
    }

    /**
     * 更新用户信息的方法
     */
    public int update(User user){
        Connection conn = null;
        PreparedStatement ps = null;
        try {
            conn = ConnectionUtil.getConnection();
            String sql = "update t_user set age=?,username=?,sex=?,birthday=? where id=?";
            ps = conn.prepareCall(sql);
            ps.setInt(1, user.getAge());
            ps.setString(2, user.getUsername());
            ps.setString(3, user.getSex());
            ps.setDate(4, new Date(user.getBirthday().getTime()), null);
            ps.setInt(5, user.getId());
            int i = ps.executeUpdate();
            System.out.println("跟新成功" + i + "条信息");
        }catch (Exception e){
            e.printStackTrace();
        }finally {
            ConnectionUtil.close(ps);
            ConnectionUtil.close(conn);
        }
        return 0;
    }

}

测试

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.List;

public class UserTest {

    public static void main(String[] args) throws ParseException {
        UserManager um = new UserManager();
        User u = new User();
        u.setUsername("大力");
        u.setAge(20);
        u.setSex("男");
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        u.setBirthday(sdf.parse("1990-10-1"));
        //插入一条数据
        um.add(u);

        //查询id为1的用户信息
        User user = um.getUser(1);
        System.out.println("id=1 ->" + user.getUsername());

        //查询所有用户
        List<User> list = um.getAll();
        for(User u1 : list) {
            System.out.println("User ->" + u1.getUsername());
        }

        //更新id为1的用户信息
        User user1 = new User();
        user1.setId(1);
        user1.setUsername("狗剩");
        user1.setAge(15);
        user1.setSex("男");
        SimpleDateFormat sdf1 = new SimpleDateFormat("yyyy-MM-dd");
        user1.setBirthday(sdf1.parse("2021-1-1"));
        um.update(user1);

        //删除id为1的用户信息
        um.del(1);
    }

}

• 测试结果

->插入成功1条信息
id=1 ->小花
User ->小花
User ->大力
跟新成功1条信息
删除成功1条信息