JsonMappingException：无法从 START_OBJECT 令牌反序列化 java.lang.Integer 的实例
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JsonMappingException: Can not deserialize instance of java.lang.Integer out of START_OBJECT token
提问by user2581426
I wanted to write a small and simple REST service using Spring Boot. Here is the REST service code:
我想使用 Spring Boot 编写一个小而简单的 REST 服务。这是 REST 服务代码：
@Async
@RequestMapping(value = "/getuser", method = POST, consumes = "application/json", produces = "application/json")
public @ResponseBody Record getRecord(@RequestBody Integer userId) {
Record result = null;
// Omitted logic
return result;
}
The JSON object I sent is the following:
我发送的 JSON 对象如下：
{
"userId": 3
}
And here is the exception I got:
这是我得到的例外：
WARN 964 --- [ XNIO-2 task-7] .w.s.m.s.DefaultHandlerExceptionResolver : Failed to read HTTP message: org.springframework.http.converter.HttpMessageNotReadableException: Could not read document: Can not deserialize instance of java.lang.Integer out of START_OBJECT token at [Source: java.io.PushbackInputStream@12e7333c; line: 1, column: 1]; nested exception is com.fasterxml.Hymanson.databind.JsonMappingException: Can not deserialize instance of java.lang.Integer out of START_OBJECT token at [Source: java.io.PushbackInputStream@12e7333c; line: 1, column: 1]
警告 964 --- [XNIO-2 task-7] .wsmsDefaultHandlerExceptionResolver：无法读取 HTTP 消息：org.springframework.http.converter.HttpMessageNotReadableException：无法读取文档：无法从 START_OBJECT 中反序列化 java.lang.Integer 的实例[来源：java.io.PushbackInputStream@12e7333c; 行：1，列：1]；嵌套异常是 com.fasterxml.Hymanson.databind.JsonMappingException：无法从 [来源：java.io.PushbackInputStream@12e7333c; 的 START_OBJECT 令牌中反序列化 java.lang.Integer 的实例；行：1，列：1]
采纳答案by Ali Dehghani
Obviously Hymanson can not deserialize the passed JSON into an Integer. If you insist to send a JSON representation of a Userthrough the request body, you should encapsulate the userIdin another bean like the following:
显然 Hymanson 无法将传递的 JSON 反序列化为Integer. 如果您坚持通过请求正文发送用户的 JSON 表示，则应将其封装userId在另一个 bean 中，如下所示：
public class User {
private Integer userId;
// getters and setters
}
Then use that bean as your handler method argument:
然后使用该 bean 作为您的处理程序方法参数：
@RequestMapping(...)
public @ResponseBody Record getRecord(@RequestBody User user) { ... }
If you don't like the overhead of creating another bean, you could pass the userIdas part of Path Variable, e.g. /getuser/15. In order to do that:
如果您不喜欢创建另一个 bean 的开销，您可以将其userId作为Path Variable 的一部分传递，例如/getuser/15. 为了做到这一点：
@RequestMapping(value = "/getuser/{userId}", method = POST, produces = "application/json")
public @ResponseBody Record getRecord(@PathVariable Integer userId) { ... }
Since you no longer send a JSON in the request body, you should remove that consumesattribute.
由于您不再在请求正文中发送 JSON，您应该删除该consumes属性。
回答by Javier Sanchez C
Perhaps you are trying to send a request with JSON text in its body from a Postman client or something similar like this:
也许您正在尝试从 Postman 客户端或类似的东西发送一个在其正文中包含 JSON 文本的请求：
{
"userId": 3
}
This cannot be deserialized by Hymanson since this is not an Integer (it seems to be, but it isn't). An Integer object from java.lang Integer is a little more complex.
这不能被Hyman逊反序列化，因为这不是一个整数（似乎是，但实际上不是）。来自 java.lang Integer 的 Integer 对象稍微复杂一些。
For your Postman request to work, simply put (without curly braces { }):
为了让您的 Postman 请求工作，只需输入（不带花括号 { }）：
3
