Spring controller校验入参的方法详解

@RestController
@RequestMapping("/demo")
public class DemoController {
    @Override
    @PostMapping("/user")
    public CreateUserRsp createUser(
        @NotNull @Size(min = 1, max = 64) @RequestHeader(value = "token") String token,
        @NotNull @Valid @RequestBody CreateUserReq createUserReq) {
        // 业务逻辑
    }
}

public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer, NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {
	parameter = parameter.nestedIfOptional();
	Object arg = this.readWithMessageConverters(webRequest, parameter, parameter.getNestedGenericParameterType());
	String name = Conventions.getVariableNameForParameter(parameter);
	if (binderFactory != null) {
		WebDataBinder binder = binderFactory.createBinder(webRequest, arg, name);
		if (arg != null) {
                // 重点
			this.validateIfApplicable(binder, parameter);
			if (binder.getBindingResult().hasErrors() && this.isBindExceptionRequired(binder, parameter)) {
				throw new MethodArgumentNotValidException(parameter, binder.getBindingResult());
			}
		}

		if (mavContainer != null) {
			mavContainer.addAttribute(BindingResult.MODEL_KEY_PREFIX + name, binder.getBindingResult());
		}
	}

	return this.adaptArgumentIfNecessary(arg, parameter);
}

protected void validateIfApplicable(WebDataBinder binder, MethodParameter parameter) {
	Annotation[] annotations = parameter.getParameterAnnotations();
	Annotation[] var4 = annotations;
	int var5 = annotations.length;

	for(int var6 = 0; var6 < var5; ++var6) {
		Annotation ann = var4[var6];
        // 重点，解析参数的注解
		Object[] validationHints = ValidationAnnotationUtils.determineValidationHints(ann);
		if (validationHints != null) {
            // 执行校验
			binder.validate(validationHints);
			break;
		}
	}

}

public static Object[] determineValidationHints(Annotation ann) {
	if (ann instanceof Validated) {
		return ((Validated)ann).value();
	} else {
		Class<? extends Annotation> annotationType = ann.annotationType();
		if ("javax.validation.Valid".equals(annotationType.getName())) {
			return EMPTY_OBJECT_ARRAY;
		} else {
			Validated validatedAnn = (Validated)AnnotationUtils.getAnnotation(ann, Validated.class);
			if (validatedAnn != null) {
				return validatedAnn.value();
			} else {
				return annotationType.getSimpleName().startsWith("Valid") ? convertValidationHints(AnnotationUtils.getValue(ann)) : null;
			}
		}
	}
}

<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-validation</artifactId>
</dependency>

public class MethodValidationPostProcessor extends AbstractBeanFactoryAwareAdvisingPostProcessor implements InitializingBean {
    private Class<? extends Annotation> validatedAnnotationType = Validated.class;
	public void afterPropertiesSet() {
		Pointcut pointcut = new AnnotationMatchingPointcut(this.validatedAnnotationType, true);
		this.advisor = new DefaultPointcutAdvisor(pointcut, this.createMethodValidationAdvice(this.validator));
	}

	protected Advice createMethodValidationAdvice(@Nullable Validator validator) {
		return validator != null ? new MethodValidationInterceptor(validator) : new MethodValidationInterceptor();
	}
}

public Object invoke(MethodInvocation invocation) throws Throwable {
	if (this.isFactoryBeanMetadataMethod(invocation.getMethod())) {
		return invocation.proceed();
	} else {
        // 方法和类上有没有@Validated
		Class<?>[] groups = this.determineValidationGroups(invocation);
		ExecutableValidator execVal = this.validator.forExecutables();
		Method methodToValidate = invocation.getMethod();
		Object target = invocation.getThis();
		Assert.state(target != null, "Target must not be null");

		Set result;
		try {
            // 校验
			result = execVal.validateParameters(target, methodToValidate, invocation.getArguments(), groups);
		} catch (IllegalArgumentException var8) {
			methodToValidate = BridgeMethodResolver.findBridgedMethod(ClassUtils.getMostSpecificMethod(invocation.getMethod(), target.getClass()));
			result = execVal.validateParameters(target, methodToValidate, invocation.getArguments(), groups);
		}

		if (!result.isEmpty()) {
            // 校验失败的异常
			throw new ConstraintViolationException(result);
		} else {
			Object returnValue = invocation.proceed();
			result = execVal.validateReturnValue(target, methodToValidate, returnValue, groups);
			if (!result.isEmpty()) {
				throw new ConstraintViolationException(result);
			} else {
				return returnValue;
			}
		}
	}
}

private void validateMetaConstraints(BaseBeanValidationContext<?> validationContext, ValueContext<?, Object> valueContext, Object parent, Iterable<MetaConstraint<?>> constraints) {
	Iterator var5 = constraints.iterator();

	while(var5.hasNext()) {
		MetaConstraint<?> metaConstraint = (MetaConstraint)var5.next();
		this.validateMetaConstraint(validationContext, valueContext, parent, metaConstraint);
		if (this.shouldFailFast(validationContext)) {
			break;
		}
	}

}