SQL注入攻击

1.sql注入攻击的演示

  • 在登录界面，输入一个错误的用户名或密码，也可以登录成功

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2.sql注入攻击的原理

  • 按照正常道理来说，我们在密码处输入的所有内容，都应该认为是密码的组成
  • 但是现在Statement对象在执行sql语句时，将一部分内容当做查询条件来执行了

3.PreparedStatement的介绍

  • 预编译sql语句的执行者对象。在执行sql语句之前，将sql语句进行提前编译。明确sql语句的格式后，就不会改变了。剩余的内容都会认为是参数！参数使用?作为占位符
  • 为参数赋值的方法：setXxx(参数1,参数2);
    • 参数1：?的位置编号(编号从1开始)
    • 参数2：?的实际参数
  • 执行sql语句的方法
    • 执行insert、update、delete语句：int executeUpdate();
    • 执行select语句：ResultSet executeQuery();

4.PreparedStatement的使用

  1. /*
  2.      使用PreparedStatement的登录方法，解决注入攻击
  3. */
  4. @Override
  5. public User findByLoginNameAndPassword(String loginName, String password) {
  6.     //定义必要信息
  7.     Connection conn = null;
  8.     PreparedStatement pstm = null;
  9.     ResultSet rs = null;
  10.     User user = null;
  11.     try {
  12.         //1.获取连接
  13.         conn = JDBCUtils.getConnection();
  14.         //2.创建操作SQL对象
  15.         String sql = "SELECT * FROM user WHERE loginname=? AND password=?";
  16.         pstm = conn.prepareStatement(sql);
  17.         //3.设置参数
  18.         pstm.setString(1,loginName);
  19.         pstm.setString(2,password);
  20.         System.out.println(sql);
  21.         //4.执行sql语句，获取结果集
  22.         rs = pstm.executeQuery();
  23.         //5.获取结果集
  24.         if (rs.next()) {
  25.             //6.封装
  26.             user = new User();
  27.             user.setUid(rs.getString("uid"));
  28.             user.setUcode(rs.getString("ucode"));
  29.             user.setUsername(rs.getString("username"));
  30.             user.setPassword(rs.getString("password"));
  31.             user.setGender(rs.getString("gender"));
  32.             user.setDutydate(rs.getDate("dutydate"));
  33.             user.setBirthday(rs.getDate("birthday"));
  34.             user.setLoginname(rs.getString("loginname"));
  35.         }
  36.         //7.返回
  37.         return user;
  38.     }catch (Exception e){
  39.         throw new RuntimeException(e);
  40.     }finally {
  41.         JDBCUtils.close(conn,pstm,rs);
  42.     }
  43. }

5.使用PreparedStatement优化student表的CRUD（作业）

public class StudentDaoImpl implements StudentDao {

    @Override
    public ArrayList<Student> findAll() {
        //定义必要信息
        Connection conn = null;
        PreparedStatement pstm = null;
        ResultSet rs = null;
        ArrayList<Student> students = null;
        try {
            //1.获取连接
            conn = JDBCUtils.getConnection();
            //2.获取操作对象
            pstm = conn.prepareStatement("select * from student");
            //3.执行sql语句，获取结果集
            rs = pstm.executeQuery();
            //4.遍历结果集
            students = new ArrayList<Student>();
            while (rs.next()) {
                //5.封装
                Student student = new Student();
                student.setSid(rs.getInt("sid"));
                student.setName(rs.getString("name"));
                student.setAge(rs.getInt("age"));
                student.setBirthday(rs.getDate("birthday"));
                //加入到集合中
                students.add(student);
            }
            //6.返回
            return students;
        }catch (Exception e){
            throw new RuntimeException(e);
        }finally {
            JDBCUtils.close(conn,pstm,rs);
        }
    }

    @Override
    public Student findById(Integer sid) {
        //定义必要信息
        Connection conn = null;
        PreparedStatement pstm = null;
        ResultSet rs = null;
        Student student = null;
        try {
            //1.获取连接
            conn = JDBCUtils.getConnection();
            //2.获取操作对象
            pstm = conn.prepareStatement("select * from student where sid = ? ");
            pstm.setInt(1,sid);
            //3.执行sql语句，获取结果集
            rs = pstm.executeQuery();
            //4.遍历结果集
            if (rs.next()) {
                //5.封装
                student = new Student();
                student.setSid(rs.getInt("sid"));
                student.setName(rs.getString("name"));
                student.setAge(rs.getInt("age"));
                student.setBirthday(rs.getDate("birthday"));
            }
            //6.返回
            return student;
        }catch (Exception e){
            throw new RuntimeException(e);
        }finally {
            JDBCUtils.close(conn,pstm,rs);
        }
    }

    @Override
    public int insert(Student student) {
        //定义必要信息
        Connection conn = null;
        PreparedStatement pstm = null;
        int result = 0;
        try {
            //1.获取连接
            conn = JDBCUtils.getConnection();
            //2.获取操作对象
            pstm = conn.prepareStatement("insert into student(sid,name,age,birthday)values(null,?,?,?)");
            //3.设置参数
            //pstm.setInt(1,null);
            pstm.setString(1,student.getName());
            pstm.setInt(2,student.getAge());
            pstm.setDate(3,new Date(student.getBirthday().getTime()));
            //4.执行sql语句
            result = pstm.executeUpdate();
        }catch (Exception e){
            throw new RuntimeException(e);
        }finally {
            JDBCUtils.close(conn,pstm);
        }
        return result;
    }

    @Override
    public int update(Student student) {
        //定义必要信息
        Connection conn = null;
        PreparedStatement pstm = null;
        int result = 0;
        try {
            //1.获取连接
            conn = JDBCUtils.getConnection();
            //2.获取操作对象
            pstm = conn.prepareStatement("update student set name=?,age=?,birthday=? where sid=? ");
            //3.设置参数
            pstm.setString(1,student.getName());
            pstm.setInt(2,student.getAge());
            pstm.setDate(3,new Date(student.getBirthday().getTime()));
            pstm.setInt(4,student.getSid());
            //4.执行sql语句
            result = pstm.executeUpdate();
        }catch (Exception e){
            throw new RuntimeException(e);
        }finally {
            JDBCUtils.close(conn,pstm);
        }
        return result;
    }

    @Override
    public int delete(Integer sid) {
        //定义必要信息
        Connection conn = null;
        PreparedStatement pstm = null;
        int result = 0;
        try {
            //1.获取连接
            conn = JDBCUtils.getConnection();
            //2.获取操作对象
            pstm = conn.prepareStatement("delete from student where sid=? ");
            //3.设置参数
            pstm.setInt(1,sid);
            //4.执行sql语句
            result = pstm.executeUpdate();
        }catch (Exception e){
            throw new RuntimeException(e);
        }finally {
            JDBCUtils.close(conn,pstm);
        }
        return result;
    }
}