mysql语句的注入错误是什么？

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sql注入式错误(SQL injection)

危害
攻击者利用它来读取、修改或者删除数据库内的数据，获得数据库中用户资料和密码等信息，更严重的就是获得管理员的权限。

例子

复制代码 //注入式错误
    public static void test3(String name,String passward){
        Connection connection = null;
        Statement st = null;
        ResultSet rs = null;
        try {
            // 加载JDBC 驱动
            Class.forName("com.mysql.jdbc.Driver");
            // 获得JDBC 连接
            String url = "jdbc:mysql://localhost:3306/tulun";
            connection = DriverManager.getConnection(url,"root","123456");
            //创建一个查询语句
            st = connection.createStatement();
            //sql语句
            String sql = "select * from student where name = '"+ name+"' and passward = '"+passward+"'";
            rs = st.executeQuery(sql);

            if(rs.next()){
                System.out.println("登录成功。");
            }else{
                System.out.println("登录失败。");
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    public static void main(String[] args) {
       
        test3("wjm3' or '1 = 1","151515");

    }1
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//注入式错误
    public static void test3(String name,String passward){
        Connection connection = null;
        Statement st = null;
        ResultSet rs = null;
        try {
            // 加载JDBC 驱动
            Class.forName("com.mysql.jdbc.Driver");
            // 获得JDBC 连接
            String url = "jdbc:mysql://localhost:3306/tulun";
            connection = DriverManager.getConnection(url,"root","123456");
            //创建一个查询语句
            st = connection.createStatement();
            //sql语句
            String sql = "select * from student where name = '"+ name+"' and passward = '"+passward+"'";
            rs = st.executeQuery(sql);

            if(rs.next()){
                System.out.println("登录成功。");
            }else{
                System.out.println("登录失败。");
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
    public static void main(String[] args) {
       
        test3("wjm3' or '1 = 1","151515");

    }
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数据库信息
在这里插入图片描述
如上面的代码所示，用户名为wjm3’ or '1 = 1，密码为151515，从数据库中可以看出我们没有这样的用户，本来应该显示登录失败，但是结果却是登陆成功，因为or '1 = 1 已经不是用户名里面的内容了，它现在为SQL 语句里面的内容，不论如何，结果都为true,等于不用输密码都可以登录。这里就产生了安全问题。

解决方法

1. PrepareStatement

复制代码 //注入式错误
    public static void test3(String name,String passward){
        Connection connection = null;
        PreparedStatement st = null;
        ResultSet rs = null;
        try {
            // 加载JDBC 驱动
            Class.forName("com.mysql.jdbc.Driver");
            // 获得JDBC 连接
            String url = "jdbc:mysql://localhost:3306/tulun";
            connection = DriverManager.getConnection(url,"root","123456");
            //创建一个查询语句
            String sql1 =  "select * from student where name = ? and passward = ?";
            st = connection.prepareStatement(sql1);
           st.setString(1,name);
           st.setString(2,passward);
            //sql语句
            //String sql = "select * from student where name = '"+ name+"' and passward = '"+passward+"'";
            rs = st.executeQuery();

            if(rs.next()){
                System.out.println("登录成功。");
            }else{
                System.out.println("登录失败。");
            }

        } catch (Exception e) {
            e.printStackTrace();
        }finally{
            try {
                connection.close();
                st.close();
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
     public static void main(String[] args) {
        test3("wjm3' or '1 = 1","151515");
    }1
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//注入式错误
    public static void test3(String name,String passward){
        Connection connection = null;
        PreparedStatement st = null;
        ResultSet rs = null;
        try {
            // 加载JDBC 驱动
            Class.forName("com.mysql.jdbc.Driver");
            // 获得JDBC 连接
            String url = "jdbc:mysql://localhost:3306/tulun";
            connection = DriverManager.getConnection(url,"root","123456");
            //创建一个查询语句
            String sql1 =  "select * from student where name = ? and passward = ?";
            st = connection.prepareStatement(sql1);
           st.setString(1,name);
           st.setString(2,passward);
            //sql语句
            //String sql = "select * from student where name = '"+ name+"' and passward = '"+passward+"'";
            rs = st.executeQuery();

            if(rs.next()){
                System.out.println("登录成功。");
            }else{
                System.out.println("登录失败。");
            }

        } catch (Exception e) {
            e.printStackTrace();
        }finally{
            try {
                connection.close();
                st.close();
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
     public static void main(String[] args) {
        test3("wjm3' or '1 = 1","151515");
    }
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