Spring的@RequestParam和Enum

Question

我有这个枚举：

public enum SortEnum {
    asc, desc;
}

我想用作rest请求的参数：

@RequestMapping(value = "/events", method = RequestMethod.GET, produces = MediaType.APPLICATION_JSON_VALUE)
public List<Event> getEvents(@RequestParam(name = "sort", required = false) SortEnum sort) {

当我发送这些请求时，它工作正常

/events 
/events?sort=asc
/events?sort=desc

但是当我发送：

/events?sort=somethingElse
我在控制台中收到500条响应和以下消息：

2019-09-29 17:20:51.600 DEBUG 5104 --- [  XNIO-2 task-6] com.myApp.aop.logging.LoggingAspect   : Enter: com.myApp.web.rest.errors.ExceptionTranslator.processRuntimeException() with argument[s] = [org.springframework.web.method.annotation.MethodArgumentTypeMismatchException: Failed to convert value of type [java.lang.String] to required type [com.myApp.common.SortEnum]; nested exception is org.springframework.core.convert.ConversionFailedException: Failed to convert from type [java.lang.String] to type [@org.springframework.web.bind.annotation.RequestParam com.myApp.common.SortEnum] for value 'somethingElse'; nested exception is java.lang.IllegalArgumentException: No enum constant com.myApp.common.SortEnum.somethingElse]
2019-09-29 17:20:51.600 DEBUG 5104 --- [  XNIO-2 task-6] com.myApp.aop.logging.LoggingAspect   : Exit: com.myApp.web.rest.errors.ExceptionTranslator.processRuntimeException() with result = <500 Internal Server Error,com.myApp.web.rest.errors.ErrorVM@1e3343c9,{}>
2019-09-29 17:20:51.601  WARN 5104 --- [  XNIO-2 task-6] .m.m.a.ExceptionHandlerExceptionResolver : Resolved exception caused by Handler execution: org.springframework.web.method.annotation.MethodArgumentTypeMismatchException: Failed to convert value of type [java.lang.String] to required type [com.myApp.common.SortEnum]; nested exception is org.springframework.core.convert.ConversionFailedException: Failed to convert from type [java.lang.String] to type [@org.springframework.web.bind.annotation.RequestParam com.myApp.common.SortEnum] for value 'somethingElse'; nested exception is java.lang.IllegalArgumentException: No enum constant com.myApp.common.SortEnum.somethingElse

有没有一种方法可以防止spring抛出这些异常并将enum设置为null？

编辑

Strelok接受的答案有效。但是，我决定处理MethodArgumentTypeMismatchException。

@ControllerAdvice
public class ExceptionTranslator {

    @ExceptionHandler(MethodArgumentTypeMismatchException.class)
    @ResponseBody
    public ResponseEntity<Object> handleMethodArgumentTypeMismatchException(MethodArgumentTypeMismatchException e) {
        Class<?> type = e.getRequiredType();
        String message;
        if(type.isEnum()){
            message = "The parameter " + e.getName() + " must have a value among : " + StringUtils.join(type.getEnumConstants(), ", ");
        }
        else{
            message = "The parameter " + e.getName() + " must be of type " + type.getTypeName();
        }
        return buildResponse(HttpStatus.UNPROCESSABLE_ENTITY, message);
    }

Answer 1

你可以创建一个自定义转换器，该转换器将null在提供无效值时返回而不是异常。

像这样：

@Configuration
public class MyConfig extends WebMvcConfigurationSupport {
   @Override
   public FormattingConversionService mvcConversionService() {
       FormattingConversionService f = super.mvcConversionService();
       f.addConverter(new MyCustomEnumConverter());
       return f;
   }
}

一个简单的转换器可能看起来像这样：

public class MyCustomEnumConverter implements Converter<String, SortEnum> {
    @Override
    public SortEnum convert(String source) {
       try {
          return SortEnum.valueOf(source);
       } catch(Exception e) {
          return null; // or SortEnum.asc
       }
    }
}