Spring Boot使用bean validation驗證失敗時，預設會返回HTTP Status: 400 Bad Request及訊息。
例如下面為@Size驗證傳入參數失敗的預設回應訊息。
{
"timestamp": "2020-05-30T05:20:24.417+0000",
"status": 400,
"error": "Bad Request",
"errors": [
{
"codes": [
"Size.demoRequest.password",
"Size.password",
"Size.java.lang.String",
"Size"
],
"arguments": [
{
"codes": [
"demoRequest.password",
"password"
],
"arguments": null,
"defaultMessage": "password",
"code": "password"
},
10,
5
],
"defaultMessage": "size must be between 5 and 10",
"objectName": "demoRequest",
"field": "password",
"rejectedValue": "1234",
"bindingFailure": false,
"code": "Size"
}
],
"message": "Validation failed for object='demoRequest'. Error count: 1",
"path": "/demo/send"
}
若要自訂的返回的訊息格式或HTTP Status狀態碼，可利用@ControllerAdvice捕捉MethodArgumentNotValidException。
例如下面為bean validation驗證失敗要返回的自訂訊息類別。
DemoResponse
package com.abc.demo.controller.response;
public class DemoResponse {
private String code;
private String message;
// getters and setters
}
接著建立一個掛有@ControllerAdvice的DemoExceptionHandler類別來自訂回應訊息。
package com.abc.demo.exception.handler;
import com.abc.demo.controller.response.DemoResponse;
import org.springframework.http.HttpStatus;
import org.springframework.web.bind.MethodArgumentNotValidException;
import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.bind.annotation.ResponseStatus;
@ControllerAdvice
public class DemoExceptionHandler {
@ExceptionHandler(MethodArgumentNotValidException.class)
@ResponseStatus(HttpStatus.BAD_REQUEST)
@ResponseBody
public DemoResponse handleBeanValidationFail(MethodArgumentNotValidException e) {
DemoResponse demoResponse = new DemoResponse();
demoResponse.setCode("9999");
demoResponse.setMessage("Invalid input");
return demoResponse;
}
}
在處理方法前加上@ExceptionHandler(MethodArgumentNotValidException.class)處理bean validation驗證失敗時拋出的例外。
利用@ResponseStatus定義返回時的HTTP狀態碼，例如HttpStatus.BAD_REQUEST(400)或HttpStatus.OK(200)。
由於DemoResponse為回應主體，所以方法前加上@ResponseBody才能將其轉為json，否則Spring Boot會以ViewResolver處理。（@ControllerAdvice改用@RestControllerAdvice即可，就不用自行撰寫ResponseEntity<T>的包裝邏輯。）
設定完以上後驗證失敗時的回應訊息如下，HTTP Statu:400，也就是在DemoExceptionHandler.handleBeanValidationFail()中自訂的訊息內容。
{
"code": "9999",
"message": "Invalid input"
}
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