对于非字符串类型的字段，Spring Boot 无法从 POST 请求将 JSON 转换为 pojo

Question

 public class Dog {
   private String name;
   private int weight;
     //...getters and
    //setters and constructor 
 }

Controller:

 @RequestMapping(value = "/dogs", method = RequestMethod.POST, 
 produces = "application/json")
 public void createDog(Dog dog) {
    dr.save(dog); 
 }

How come when I call the endpoint with json {"name":"bark", "weight":50} I get an error:

Failed to convert value of type 'null' to required type 'int'; nested exception is org.springframework.core.convert.ConversionFailedException: Failed to convert from type [null] to type [int] for value 'null'; nested exception is java.lang.IllegalArgumentException: A null value cannot be assigned to a primitive type", "objectName": "dog", "field": "weight", "rejectedValue": null, "bindingFailure": true, "code": "typeMismatch"

"message": "Validation failed for object='dog'. Error count: 1

edit: I get the same issue with booleans and doubles. I guess I have to use objects not primitives?

Answer 1

在你的create方法中将注解@RequestBody添加到 param dog

Answer 2

Need to specify the @RequestBody annotation to specify we are sending DOG object as part of request body:

@RequestMapping(value = "/dogs", method = RequestMethod.POST, produces = "application/json") 
public void createDog((**@RequestBody** Dog dog) { dr.save(dog); }

Answer 3

仅适用于对象，因此请使用 Integer 而不是 int。

Answer 4

If exist possibility object receive null, you can't use type primitives, same int, char, boolean.

private int weight

Use type objects same Integer, Boolean ... for one type primitive has a Object, then can receive null value.