@RequestBody如何区分未发送的值和空值？ [英] @RequestBody how to differentiate an unsent value from a null value?

问题描述

@PatchMapping("/update")
HttpEntity<String> updateOnlyIfFieldIsPresent(@RequestBody Person person) {
    if(person.name!=null) //here
}

如何区分未发送的值和空值？如何检测客户端是否发送空或跳过字段？

how to differentiate an unsent value from a null value? How can I detect if client sent null or skipped field?

推荐答案

上述解决方案需要对方法签名进行一些更改才能克服请求体自动转换为POJO（即Person对象）。

The above solutions would require some change in the method signature to overcome the automatic conversion of request body to POJO (i.e. Person object).

方法1： -

您可以将对象作为Map接收，并检查是否存在密钥name，而不是将请求体转换为POJO类（Person）。

Instead of converting the request body to POJO class (Person), you can receive the object as Map and check for the existence of the key "name".

@PatchMapping("/update")
public String updateOnlyIfFieldIsPresent1(@RequestBody Map<String, Object> requestBody) {

    if (requestBody.get("name") != null) {
        return "Success" + requestBody.get("name"); 
    } else {
        return "Success" + "name attribute not present in request body";    
    }


}

方法2： -

以字符串形式接收请求正文并检查字符序列（即名称）。

Receive the request body as String and check for the character sequence (i.e. name).

@PatchMapping("/update")
public String updateOnlyIfFieldIsPresent(@RequestBody String requestString) throws JsonParseException, JsonMappingException, IOException {

    if (requestString.contains("\"name\"")) {
        ObjectMapper mapper = new ObjectMapper();
        Person person = mapper.readValue(requestString, Person.class);
        return "Success -" + person.getName();
    } else {
        return "Success - " + "name attribute not present in request body"; 
    }

}

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