发送 json 数据时的空指针
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【中文标题】发送 json 数据时的空指针【英文标题】：nullpointer in sending json data 【发布时间】：2018-11-08 00:32:52 【问题描述】：我在将 json 数据从前端引导程序发送到 express servlet 时遇到问题。这是我尝试过的。我使用 ajax 将数据从我的表单发送到带有 json 的 servlet 类。请帮我解决这个问题。这是我的学生注册表格：
<html>
<head>
<link rel="stylesheet" type="text/css" href="resources/css/bootstrap.min.css">
<script type="text/javascript" src="resources/js/jquery.min.js"></script>
<script type="text/javascript" src="resources/js/bootstrap.min.js"> </script>
<script type="text/javascript">
function registerStudent()
var firstName = $("#firstName").val();
var lastname = $("#lastname").val();
var phone = $("#phone").val();
var email = $("#email").val();
var studentCode = $("#studentCode").val();
$.ajax(
type : "POST",
url : "/RegisterStudent",
data :data: "firstName=" + firstName + "lastname=" + lastname + " phone=" + phone + "email=" + email+"studentCode"+studentCode,
success : function(data)
var ht = data.msg;
$("#resp").html(ht);
,
error : function(data)
alert("Some error occured.");
);
</script>
</head>
<body>
<div class="container">
<div class="card " style="width:750px;margin:0px auto">
<div class="card-header">Student Register</div>
<div class="card-body">
<form data-toggle="validator" role="form" method="post" >
<div class="form-group">
<label class="control-label" for="firstName">Name</label>
<input class="form-control" data-error="Please enter name field." id="firstName" placeholder="Name" type="text" required />
<div class="help-block with-errors"></div>
</div>
<div class="form-group">
<label for="lastname" class="control-label">lastname</label>
<input type="text" class="form-control" id="lastname" placeholder="lastname" required>
<div class="help-block with-errors"></div>
</div>
<div class="form-group">
<label for="phone" class="control-label">phone</label>
<div class="form-group">
<input type="text" data-minlength="5" class="form-control" id="phone" data-error="fill your phone" placeholder="phone" required>
<div class="help-block with-errors"></div>
</div>
</div>
<div class="form-group">
<label class="control-label" for="email">email</label>
<textarea class="form-control" data-error="Please enter email field." id="email" placeholder="email" required=""></textarea>
<div class="help-block with-errors"></div>
</div>
<div class="form-group">
<label for="studentCode" class="control-label">studentCode</label>
<div class="form-group">
<input type="text" class="form-control" id="studentCode" data-error="fill your studentCode" placeholder="studentCode" required>
<div class="help-block with-errors"></div>
</div>
</div>
</form>
</div>
<button onclick="registerStudent();" type="button" class="btn btn-success btn-block">Register</button>
<div class="text-center" id="resp" style="margin-top: 14px;"></div>
</div>
</div>
这是我将数据发送到数据库的 servlet 类。
@WebServlet(urlPatterns = "/RegisterStudent")
public class RegisterStudentController extends HttpServlet
StudentServiceInter service = new StudentServiceImpl();
ObjectMapper mapper = new ObjectMapper();
String json = "";
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
Student student = new Student();
req.getSession().setAttribute("student", student);
resp.sendRedirect("/addStudent.jsp");
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
String jsonData = req.getParameter("data");
resp.setContentType("application/json");
PrintWriter out = resp.getWriter();
out.println(jsonData);
out.close();
【问题讨论】：
您是否收到此警报（“发生了一些错误。”）；？如果没有，你能检查一下你是否要去那个网址吗？ @BILALMALIK 是的，我收到了这个警报 【参考方案1】：试试这个...
$.ajax(
type: 'GET',
url: '<?php echo base_url(); ?>"/RegisterStudent"', // your syntax
data:
'firstName ': firstName ,
'lastName' :lastname,
'phone': phone,
'email' : email,
'studentCode' : studentCode,
,
success : function(data)
var ht = data.msg;
$("#resp").html(ht);
,
error : function(data)
alert("Some error occured.");
);
【讨论】：
【参考方案2】：一个问题是，客户端，您没有创建 json，而服务器端您尝试解析 json。 Json 格式没有equal (=) 符号。
一个有效的对象是：
data =
data:
firstName: 'Name',
lastName: 'Surname',
phone: '123-4456',
email: 'a@b.c',
studentCode: 12345
;
在发送之前你应该做JSON.stringify(data)。
【讨论】：
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