Question

以下代码不会在相应的表中插入一行。我已经测试了数据库连接并在数据库中运行了查询，两者均已通过，但是当我通过.jsp表单添加输入时，值仍未插入。

<script type="text/javascript">
    var myArray = 
        ['<a href="https://ceiti.md/">CEITI</a>', 
        ['<a href="#">Inner Value 1</a>', 
        '<a href="#">Inner Value 2</a>', 
        '<a href="#">Inner Value 3</a>',
        '<a href="#">Inner Value 4</a>'], 
        '<a href="#">Value 2</a>',
        '<a href="#">Value 3</a>',
        '<a href="#">Value 4</a>',
        '<a href="#">Value 5</a>',
        '<a href="#">Value 6</a>'];
    function iter(target) {
        var ul = document.createElement('ul'),
            li;
            ul.setAttribute('class','lifin');
        target.appendChild(ul);
            return function (a) {
            if (Array.isArray(a)) {

                                if (!li) {
                                    li = document.createElement('li');
                                    ul.appendChild(li);
                                }
                                a.forEach(iter(li));
                                ul.setAttribute('id','proList');
                                li.setAttribute('id','pList');
                                return;
                            }
                            li = document.createElement('li');
                            li.setAttribute('id','Mon');
                            li.appendChild(document.createTextNode(a));
                            ul.appendChild(li);
                        };
    }
    myArray.forEach(iter(document.getElementById('myList')));

    </script>

}

作为参考，这是我的servlet类和.jsp文件的外观：

public class UserDao {

public String registerUser(User user){
    String username = user.getUsername();
    String email = user.getEmail();
    String password = user.getPassword();

    Connection con;
    con = DBConnection.createConnection();

    PreparedStatement preparedStatement;

    try{
        con.setAutoCommit(false);

        String query = ("INSERT INTO user (username, email, password, user_id) VALUES(?, ?, ?, ?)");
        preparedStatement = con.prepareStatement(query);
        preparedStatement.setString(1, username);
        preparedStatement.setString(2, email);
        preparedStatement.setString(3, password);
        preparedStatement.setString(4,null);

        int i = preparedStatement.executeUpdate();
        con.commit();
        preparedStatement.close();
        con.close();

        if(i !=0 ){
            return "SUCCESS";
        }
    }catch(SQLException e){
      throw new RuntimeException(e);

    }

    return "Something is wrong!";
}

}

public class UserRegistrationServlet extends HttpServlet {

public UserRegistrationServlet(){}
/**
 * Handles the HTTP <code>POST</code> method.
 *
 * @param request servlet request
 * @param response servlet response
 * @throws ServletException if a servlet-specific error occurs
 * @throws IOException if an I/O error occurs
 */
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException {

    String userName = request.getParameter("username");
    String email = request.getParameter("email");
    String password = request.getParameter("password");
    User user = new User();
    user.setUsername(userName);
    user.setEmail(email);
    user.setPassword(password);
    UserDao userDao = new UserDao();
    String userRegistered = userDao.registerUser(user);
    if(userRegistered.equals("SUCCESS")){
        request.getRequestDispatcher("test.jsp").forward(request, response);

    }else{
        request.setAttribute("error", userRegistered);
        request.getRequestDispatcher("/UserRegistration.jsp").forward(request, response);
    }
}

不确定我的代码中的错误在哪里，因此任何建议都将非常有帮助。谢谢

更新：

[！[引发运行时异常之后] [2]] [2]

Answer 1

您正在将user_id设置为null，数据库抱怨该列不能为null。我假设您没有直接将null传递给针对DB进行测试的语句，因此您正在设置一个空字符串（或者该表将设置默认值或自动生成的值，以防丢失）

如果有默认值或自动生成的值，则只需在插入语句中省略user_id，它就可以工作。

JDBC插入查询不会更新mysql数据库

1 个答案: