Question

我有一个静态HTML文档，它将表单发布到Java servlet。然后，servlet获取表单的值并将它们转发到SQL数据库。但是，问题是当我确定该值不为null时，数据库声明值为null。

以下是表格：

<form method="post" action="Handler" target="_blank" enctype="multipart/form-data">
  <div class="row uniform 50%">
    <div class="6u 12u(mobilep)">
      <input type="text" name="name" id="name" placeholder="Username" />
    </div>
    <div class="6u 12u(mobilep)">
      <input type="email" name="email" id="email" placeholder="Email" />
    </div>
  </div>
  <div class="row uniform 50%">
    <div class="6u 12u(mobilep)">
      <input type="password" name="password" id="password" placeholder="Password" />
    </div>
  </div>
  <div class="row uniform 50%">
    <div class="12u">
      <textarea name="bio" id="bio" placeholder="Describe yourself" maxlength="200" rows="3"></textarea>
    </div>
  </div>
  <div class="row uniform">
    <div class="12u">
      <ul class="actions align-center">
        <li><input type="submit" value="Send Message" /></li>
      </ul>
    </div>
  </div>
</form>

这是servlet代码：

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // TODO Auto-generated method stub
    Connection c = null;
    PrintWriter op = response.getWriter();
    response.setContentType("text/html");

    try{
        Class.forName("com.mysql.jdbc.Driver");
        c = DriverManager.getConnection(DB_URL, "root", "root");
    }catch(Exception s){
        op.println("<html>");
        op.println("<body><h1><strong>"+ "Error: "+ s +"</strong></h1></body>");
        op.println("</html>");
    }

    String username = request.getParameter("name");
    String email = request.getParameter("email");
    String pass = request.getParameter("password");
    String bio = request.getParameter("bio");
    String proPicName = "false";
    Long time = System.currentTimeMillis();
    String sysTime = time.toString();

    Statement stmt = null;

    try{
        stmt = c.createStatement();
        stmt.execute("USE dvlpr;");
        stmt.execute("INSERT INTO user_tbl (username, email, password, bio, pro_pic, last_on, date_created)" + " VALUES ("+username+", "+email+", "+pass+", "+bio+", "+proPicName+", "+sysTime+", "+sysTime+");");


        op.println("<html>");
        op.println("<body><h1><strong>Connection made! Username: " + username+ " Email: " + email+ " Your account has been created. We'll keep your password private, too. Thanks!</strong></h1>");
        op.println("</body>");
        op.println("</html>");
    }catch(Exception s){
        op.println("<html>");
        op.println("<body><h1><strong>"+ "Error: "+ s +"</strong></h1></body>");
        op.println("</html>");
    }

}

错误代码如下：

错误：com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException：列'username'不能为null

为什么返回null？

Answer 1

参数很好。由于语法原因，查询未正确执行。值本身需要用引号括起来，所以看起来应该是这样的：

VALUES('"+username+"',....

正如您所看到的，我在双引号之前添加了一个'，之后添加了一个'，因此VALUES('MyUsername', 'MyPassword',...);将成为结果字符串的一部分。就像在任何其他SQL插入中一样，您可以执行stmt.execute("USE dvlpr; INSERT INTO....");。

此外，您可能希望使用一个执行方法而不是2，因此它将是：

此外，" VALUES

之前不需要

class Choices(models.Model):
choices = models.CharField(max_length=70)

def __unicode__(self):
    return self.choices

class UserProfile(models.Model):
    user = models.OneToOneField(MyUser)
    about_me = models.TextField(max_length=2000, null=True, blank=True)
    country = models.CharField(max_length=100,null=True, blank=True)
    choices = models.ManyToManyField(Choices, blank=True)

为什么request.getParameter（）方法返回null？

1 个答案: