Spring 6.1.x如何从HandlerMethodValidationException的ParameterValidationResult获取ConstraintViolation？

目前Spring 6.1.x的HandlerMethodValidationException本身持有原始的ConstraintViolation集合，但ParameterValidationResult仅暴露DefaultMessageSourceResolvable，无法直接获取。可以通过以下两种方式解决：

方式一：反射获取内部的ConstraintViolation集合 #

直接通过反射访问HandlerMethodValidationException的私有violations字段，获取原始验证信息。这种方式实现简单，但依赖Spring内部字段结构，后续版本若字段变更可能失效。

示例代码：

@ExceptionHandler(HandlerMethodValidationException.class)
public ResponseEntity<Object> handleValidationException(HandlerMethodValidationException ex) {
    try {
        Field violationsField = HandlerMethodValidationException.class.getDeclaredField("violations");
        violationsField.setAccessible(true);
        @SuppressWarnings("unchecked")
        List<ConstraintViolation<?>> violations = (List<ConstraintViolation<?>>) violationsField.get(ex);
        
        // 此处可处理原始ConstraintViolation，比如提取约束类型、属性名等
        List<String> errorDetails = violations.stream()
                .map(v -> String.format("参数[%s]违反约束[%s]：%s", 
                        v.getPropertyPath(), 
                        v.getConstraintDescriptor().getAnnotation().annotationType().getSimpleName(),
                        v.getMessage()))
                .toList();
                
        return ResponseEntity.badRequest().body(errorDetails);
    } catch (NoSuchFieldException | IllegalAccessException e) {
        // 反射失败时降级处理，使用默认错误信息
        List<String> defaultErrors = ex.getValidationResult().getResolvableErrors().stream()
                .map(DefaultMessageSourceResolvable::getDefaultMessage)
                .toList();
        return ResponseEntity.badRequest().body(defaultErrors);
    }
}

方式二：自定义验证适配器，扩展验证结果结构 #

通过扩展Spring的MethodValidationAdapter，将原始ConstraintViolation封装到自定义的MessageSourceResolvable实现中，让ParameterValidationResult携带完整的验证信息。这种方式更稳定，不依赖内部字段。

步骤1：自定义ResolvableError类 #

实现MessageSourceResolvable，同时持有原始ConstraintViolation：

public class ConstraintViolationResolvableError implements MessageSourceResolvable {
    private final ConstraintViolation<?> violation;

    public ConstraintViolationResolvableError(ConstraintViolation<?> violation) {
        this.violation = violation;
    }

    @Override
    public String[] getCodes() {
        return new String[]{violation.getMessageTemplate()};
    }

    @Override
    public Object[] getArguments() {
        return violation.getConstraintDescriptor().getAttributes().values().toArray();
    }

    @Override
    public String getDefaultMessage() {
        return violation.getMessage();
    }

    public ConstraintViolation<?> getViolation() {
        return violation;
    }
}

步骤2：自定义MethodValidationAdapter #

重写验证逻辑，将自定义的ResolvableError传入ParameterValidationResult：

@Component
public class CustomMethodValidationAdapter extends MethodValidationAdapter {
    @Override
    public void validateMethodParameters(Object target, Method method, Object[] arguments, Class<?>[] groups) {
        Set<ConstraintViolation<Object>> violations = getValidator().forExecutables()
                .validateParameters(target, method, arguments, groups);
        
        if (!violations.isEmpty()) {
            MethodParameter[] parameters = getMethodParameters(method);
            Map<MethodParameter, List<ConstraintViolation<Object>>> paramViolationsMap = violations.stream()
                    .collect(Collectors.groupingBy(v -> findMatchingParameter(parameters, v)));
            
            List<HandlerMethodValidationException> exceptions = new ArrayList<>();
            for (Map.Entry<MethodParameter, List<ConstraintViolation<Object>>> entry : paramViolationsMap.entrySet()) {
                MethodParameter param = entry.getKey();
                List<ConstraintViolation<Object>> paramViolations = entry.getValue();
                
                List<ConstraintViolationResolvableError> resolvableErrors = paramViolations.stream()
                        .map(ConstraintViolationResolvableError::new)
                        .collect(Collectors.toList());
                
                ParameterValidationResult validationResult = ParameterValidationResult.forValidationErrors(param, resolvableErrors);
                exceptions.add(new HandlerMethodValidationException(param, paramViolations, validationResult));
            }
            throw new MethodValidationException(exceptions);
        }
    }

    // 根据ConstraintViolation找到对应的MethodParameter
    private MethodParameter findMatchingParameter(MethodParameter[] parameters, ConstraintViolation<Object> violation) {
        String paramName = violation.getPropertyPath().iterator().next().getName();
        return Arrays.stream(parameters)
                .filter(p -> paramName.equals(p.getParameterName()))
                .findFirst()
                .orElseThrow(() -> new IllegalArgumentException("未找到匹配的参数：" + paramName));
    }
}

步骤3：在异常处理器中获取原始ConstraintViolation #

@ExceptionHandler(HandlerMethodValidationException.class)
public ResponseEntity<Object> handleValidationException(HandlerMethodValidationException ex) {
    List<ConstraintViolation<?>> originalViolations = ex.getValidationResult().getResolvableErrors().stream()
            .filter(error -> error instanceof ConstraintViolationResolvableError)
            .map(error -> ((ConstraintViolationResolvableError) error).getViolation())
            .toList();
            
    // 处理原始验证信息
    List<String> errorDetails = originalViolations.stream()
            .map(v -> String.format("参数[%s]违反%s约束：%s",
                    v.getPropertyPath(),
                    v.getConstraintDescriptor().getAnnotation().annotationType().getSimpleName(),
                    v.getMessage()))
            .toList();
            
    return ResponseEntity.badRequest().body(errorDetails);
}

内容的提问来源于stack exchange，提问作者Kiwon Seo