4.JDBC编程

/*
 * 1.注册驱动
 * 2.获取连接
 * 3.获取SQL执行器
 * 4.执行SQL，并获取结果集(查询)
 * 5.解析结果集
 * 6.关闭资源
 */
public class Demo {
    public static void main(String[] args) throws Exception {
        //1.注册驱动     // 数据库.jdbc.驱动
        Class.forName("com.mysql.jdbc.Driver");
        //2.获取连接
        Connection conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/testdb_1", "root", "root");
        //3.获取SQL执行器
        Statement stmt = conn.createStatement();
        //4.执行SQL，并获取结果集(查询)
        String sql = "select * from product";
        ResultSet rs = stmt.executeQuery(sql);
        //5.解析结果集
        while(rs.next()){
            System.out.println(rs.getInt("pid") + "\t" +
                                rs.getString("pname") + "\t" +
                                rs.getInt("price") + "\t" +
                                rs.getInt("cid"));
        }
        //6.关闭资源
        rs.close();
        stmt.close();
        conn.close();
    }
    @Test
    public void delete() throws Exception{
        Class.forName("com.mysql.jdbc.Driver");
        Connection conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/testdb_1","root","root");
        Statement stmt = conn.createStatement();
        String sql = "delete from product where pid = 6";
        int row = stmt.executeUpdate(sql);
        System.out.println("删除影响的行数：" + row);
        stmt.close();
        conn.close();
    }
}

public class Demo {
　　 @Test
    public void add() throws Exception{
        //1.注册驱动
        Class.forName("com.mysql.jdbc.Driver");
        //2.获取连接
        Connection conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/testdb_1","root","root");
        //3.获取SQL执行器
        Statement stmt = conn.createStatement();
        //4.执行SQL语句
        String sql = "insert into product values(null,‘钢琴‘,28000,1)";
        int row = stmt.executeUpdate(sql);
        System.out.println("添加影响的行数：" + row);
        //5.释放资源
        stmt.close();
        conn.close();
    }
　　 @Test
    public void update() throws Exception{
        //1.注册驱动
        Class.forName("com.mysql.jdbc.Driver");
        //2.获取连接
        Connection conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/testdb_1","root","root");
        //3.获取SQL执行器
        Statement stmt = conn.createStatement();
        //4.执行SQL
        String sql = "update product set price = 38000 where pid = 7";
        int row = stmt.executeUpdate(sql);
        System.out.println("修改影响的行数：" + row);
        //5.释放资源
        stmt.close();
        conn.close();
    }
　　 @Test
    public void delete() throws Exception{
        Class.forName("com.mysql.jdbc.Driver");
        Connection conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/testdb_1","root","root");
        Statement stmt = conn.createStatement();
        String sql = "delete from product where pid = 7";
        int row = stmt.executeUpdate(sql);
        System.out.println("删除影响的行数：" + row);
        stmt.close();
        conn.close();
    }
    @Test
    public void findAll() throws Exception{
        Class.forName("com.mysql.jdbc.Driver");
        Connection conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/testdb_1","root","root");
        Statement stmt = conn.createStatement();
        String sql = "select * from product";
        ResultSet rs = stmt.executeQuery(sql);
        while(rs.next()){
            System.out.println(rs.getInt("pid") + "\t" +
                                rs.getString("pname") + "\t" +
                                rs.getInt("price") + "\t" +
                                rs.getInt("cid"));
        }
        rs.close();
        stmt.close();
        conn.close();
    }
}

    public class JDBCUtils {
        //1.获取Connection对象--代码重用的目的 --静态方法
        public static Connection getConnection() throws Exception{     //前两步 定义了一个静态方法
            Class.forName("com.mysql.jdbc.Driver");
            Connection conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/testdb_1","root","root");
            return conn;
        }
        //2.关闭资源
        public static void closeAll(ResultSet rs,Statement stmt,Connection conn) throws SQLException{
            if(rs != null){
                rs.close();
            }
            if(stmt != null){
                stmt.close();
            }
            if(conn != null){
                conn.close();
            }
        }
    }

import导包;
//定义一个数据库工具类JdbcUtil，用来简化数据库操作出现的重复代码。
//创建类JdbcUtil包含3个方法：
//1) 可以把几个字符串定义成常量
//2) public static Connection getConnection() 得到数据库的连接
//3) 在静态代码块中注册驱动，只需注册一次即可。无需放在getConnection()方法中
//4) public static void close(Connection conn,Statement stmt,ResultSet rs) 关闭所有打开的资源
//5)public static void close(Connection conn,Statement stmt) 关闭没有结果集的资源，可以调用上面的方法。
public class JDBCUtils {
     private static String driver = "com.mysql.jdbc.Driver";
     private static String url = "jdbc:mysql:///testdb2";
     private static String user = "root";
     private static String password = "root";
     static{
           try {
                Class.forName(driver);
           } catch (Exception e) {
                throw new RuntimeException(e) ;
           }
     }
     public static Connection getConnection() throws Exception{
           Connection conn = DriverManager.getConnection(url, user, password);
           return conn;
     }
     public static void close(Connection conn,Statement stmt,ResultSet rs){
           if (rs != null) {
                try {
                     rs.close();
                } catch (SQLException e) {
                }
           }
           if (stmt != null) {
                try {
                     stmt.close();
                } catch (SQLException e) {
                }
           }
           if (conn != null) {
                try {
                     conn.close();
                } catch (SQLException e) {
                }
           }
     }
     public static void close(Connection conn,Statement stmt){
           if (stmt != null) {
                try {
                     stmt.close();
                } catch (SQLException e) {
                }
           }
           if (conn != null) {
                try {
                     conn.close();
                } catch (SQLException e) {
                }
           }
     }
}

    public class Demo {
        public static void main(String[] args) throws Exception {
            Scanner sc = new Scanner(System.in);
            System.out.println("请输入商品名称：");
            String pname = sc.next();//海尔冰柜
            System.out.println("价格：");
            int price = sc.nextInt();//2300
            System.out.println("类别ID:");
            int cid = sc.nextInt();//1

            //1.获取连接对象
            Connection conn = JDBCUtils.getConnection();
            //2.获取SQL执行器
            Statement stmt = conn.createStatement();
            //3.【封装SQL语句】
            //先想象，封装后的SQL语句："insert into product values(null,‘海尔冰柜‘,2300,1)"
            String sql = "insert into product values(null,‘" + pname +
                                "‘," + price + "," +
                                cid + ")";
            System.out.println(sql);

            //4.执行SQL语句
            int row = stmt.executeUpdate(sql);
            System.out.println("添加影响的行数：" + row);
            //5.释放资源
            JDBCUtils.closeAll(null, stmt, conn);
        }
    }

import 导包;
public class Demo {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入登录名：");     //sfasdfg
        String loginName = sc.nextLine();       
        System.out.println("输入密码：");        //asfsadf ‘ or ‘1=1    //(后者1=1 恒成立,显示登录成功,所以有bug)
        String loginPwd = sc.nextLine();
        //1.获取连接对象
        Connection conn = JDBCUtils.getConnection();
        Statement stmt = conn.createStatement();
        String sql = "select * from users where uname = ‘" + loginName +
                        "‘ and password = ‘" + loginPwd + "‘";
        System.out.println(sql);
        ResultSet rs = stmt.executeQuery(sql);
        if(rs.next()){
            System.out.println("欢迎：" + loginName + " 登录系统！");
        }else{
            System.out.println("用户名或密码错误！！");
        }
        //2.释放资源
        JDBCUtils.closeAll(rs, stmt, conn);
    }
}

    Scanner sc = new Scanner(System.in);
    System.out.println("请输入登录名：");
    String loginName = sc.nextLine();
    System.out.println("输入密码：");
    String loginPwd = sc.nextLine();

    Connection conn = JDBCUtils.getConnection();
    //1.先封装SQL语句，数据部分要用?号占位，任何数据类型不需要单引号
    String sql = "select * from users where uname = ? and password = ?";             //红色 就是改过的区别
    //2.获取PreparedStatemet对象
    PreparedStatement ps = conn.prepareStatement(sql);
    //3.填充数据
    ps.setString(1, loginName);     //这个1代表第一个?号
    ps.setString(2, loginPwd);       //这个2代表第二个?号

    //4.执行
    ResultSet rs = ps.executeQuery();//注意：不要再传SQL语句了，因为之前已经有SQL语句了（ps中已传入数据了）
    if(rs.next()){
        System.out.println("欢迎：" + loginName + " 登录系统！");
    }else{
        System.out.println("用户名或密码错误！！");
    }
    //2.释放资源
    JDBCUtils.closeAll(rs, ps, conn);

  public void add() throws Exception{
        //1.获取连接对象
        Connection conn = JDBCUtils.getConnection();
        //2.获取预处理对象
        String sql = "insert into product values(null,?,?,?)";
        PreparedStatement ps = conn.prepareStatement(sql);
        //3.填充数据
        ps.setString(1, "奔驰");
        ps.setInt(2, 440000);
        ps.setInt(3, 1);
        //4.执行SQL
        int row = ps.executeUpdate();
        System.out.println("添加影响的行数：" + row);
        //5.释放资源
        JDBCUtils.closeAll(null, ps, conn);          //记得,别忘了关闭资源
    }
    public void update() throws Exception{
        //1.获取连接对象
        Connection conn = JDBCUtils.getConnection();
        //2.获取预处理对象
        String sql = "update product set pname = ? , price = ? where pid = ?";     //所以的数据都 用? 替换掉(set在表名后)
        PreparedStatement ps = conn.prepareStatement(sql);
        //3.填充数据
        ps.setString(1, "奔驰E级");
        ps.setInt(2, 420000);
        ps.setInt(3, 9);
        //4.执行SQL
        int row = ps.executeUpdate();
        System.out.println("修改影响的行数："  + row);
        //5.释放资源
        JDBCUtils.closeAll(null, ps, conn);
    }
    public void delete() throws Exception{
        Connection conn = JDBCUtils.getConnection();
        String sql = "delete from product where pid = ?";          //删除没有 * 号,切记
        PreparedStatement ps = conn.prepareStatement(sql);
        ps.setInt(1, 9);
        int row = ps.executeUpdate();
        System.out.println("删除影响的行数：" + row);
        JDBCUtils.closeAll(null, ps, conn);
    }
    public void findAll() throws Exception{          //查找所有 ,不需要填充数据
        Connection conn = JDBCUtils.getConnection();
        String sql = "select * from product";
        PreparedStatement ps = conn.prepareStatement(sql);

        ResultSet rs = ps.executeQuery();
        while(rs.next()){                                   //查询所有用 while
            System.out.println(rs.getInt("pid") + "\t" + rs.getString("pname") + "\t"
                            + rs.getInt("price") + "\t" + rs.getInt("cid"));
        }
        JDBCUtils.closeAll(rs, ps, conn);
    }
    @Test
    public void findById() throws Exception{
        Connection conn = JDBCUtils.getConnection();
        String sql = "select * from product where pid = ?";
        PreparedStatement ps = conn.prepareStatement(sql);
        ps.setInt(1, 1);

        ResultSet rs = ps.executeQuery();
        if(rs.next()){                    //切记查找一个,需要用if
            System.out.println(rs.getInt("pid") + "\t" + rs.getString("pname") + "\t"
                                        + rs.getInt("price") + "\t" + rs.getInt("cid"));
        }

        JDBCUtils.closeAll(rs, ps, conn);

    }