springboot情操陶冶-web配置(七)

参数校验通常是OpenApi必做的操作，其会对不合法的输入做统一的校验以防止恶意的请求。本文则对参数校验这方面作下简单的分析

spring.factories

读者应该对此文件加以深刻的印象，很多springboot整合第三方插件的方式均是从此配置文件去读取的，本文关注下检验方面的东西。在相应的文件搜索validation关键字，最终定位至ValidationAutoConfiguration类，笔者这就针对此类作主要的分析

ValidationAutoConfiguration

优先看下其头上的注解

@Configuration
@ConditionalOnClass(ExecutableValidator.class)
@ConditionalOnResource(resources = "classpath:META-INF/services/javax.validation.spi.ValidationProvider")
@Import(PrimaryDefaultValidatorPostProcessor.class)

使此类成功被注册的条件有两个，第一是当前环境下存在ExecutableValidator类，第二是当前类环境存在META-INF/services/javax.validation.spi.ValidationProvider文件。
通过查看maven依赖得知，其实springboot在引入starter-web板块便引入了hibernate-validator包，此包便满足了上述的两个要求。
笔者发现其也引入了PrimaryDefaultValidatorPostProcessor类，主要是判断当前的bean工厂是否已经包含了LocalValidatorFactoryBean和Validator对象，不影响大局。即使没有配置，下述的代码也是会注册的

	@Bean
	@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
	@ConditionalOnMissingBean(Validator.class)
	public static LocalValidatorFactoryBean defaultValidator() {
		LocalValidatorFactoryBean factoryBean = new LocalValidatorFactoryBean();
		MessageInterpolatorFactory interpolatorFactory = new MessageInterpolatorFactory();
		factoryBean.setMessageInterpolator(interpolatorFactory.getObject());
		return factoryBean;
	}

	@Bean
	@ConditionalOnMissingBean
	public static MethodValidationPostProcessor methodValidationPostProcessor(
			Environment environment, @Lazy Validator validator) {
		MethodValidationPostProcessor processor = new MethodValidationPostProcessor();
		boolean proxyTargetClass = environment
				.getProperty("spring.aop.proxy-target-class", Boolean.class, true);
		processor.setProxyTargetClass(proxyTargetClass);
		processor.setValidator(validator);
		return processor;
	}

通过查阅代码得知，使用注解式的校验方式是通过添加@Validated注解来实现的，但是其作用于参数上还是类上是有不同的操作逻辑的。笔者将之区分开，方便后续查阅。先附上@Validated注解源码

@Target({ElementType.TYPE, ElementType.METHOD, ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Validated {

	/**
	 * Specify one or more validation groups to apply to the validation step
	 * kicked off by this annotation.
	 * <p>JSR-303 defines validation groups as custom annotations which an application declares
	 * for the sole purpose of using them as type-safe group arguments, as implemented in
	 * {@link org.springframework.validation.beanvalidation.SpringValidatorAdapter}.
	 * <p>Other {@link org.springframework.validation.SmartValidator} implementations may
	 * support class arguments in other ways as well.
	 */
	Class<?>[] value() default {};

}

类级别的校验

即@Validated作用于类上，其相关的处理逻辑便是由MethodValidationPostProcessor来实现的，笔者稍微看下关键源码方法afterPropertiesSet()

	@Override
	public void afterPropertiesSet() {
		// 查找对应的类以及祖先类上是否含有@Validated注解
		Pointcut pointcut = new AnnotationMatchingPointcut(this.validatedAnnotationType, true);
		// 创建MethodValidationInterceptor处理类来处理具体的逻辑
		this.advisor = new DefaultPointcutAdvisor(pointcut, createMethodValidationAdvice(this.validator));
	}

上述的配置表明只要某个类上使用了@Validated注解，其相应的方法就会被校验相关的参数。笔者紧接着看下MethodValidationInterceptor#invoke()方法

	@Override
	@SuppressWarnings("unchecked")
	public Object invoke(MethodInvocation invocation) throws Throwable {
		// 读取相应方法上的@Validated的value属性，为空也是没问题的
		Class<?>[] groups = determineValidationGroups(invocation);

		// Standard Bean Validation 1.1 API
		ExecutableValidator execVal = this.validator.forExecutables();
		Method methodToValidate = invocation.getMethod();
		Set<ConstraintViolation<Object>> result;

		try {
			// ①校验参数
			result = execVal.validateParameters(
					invocation.getThis(), methodToValidate, invocation.getArguments(), groups);
		}
		catch (IllegalArgumentException ex) {
			// ②校验对应的桥接方法(兼容jdk1.5+后的泛型用法)的参数
			methodToValidate = BridgeMethodResolver.findBridgedMethod(
					ClassUtils.getMostSpecificMethod(invocation.getMethod(), invocation.getThis().getClass()));
			result = execVal.validateParameters(
					invocation.getThis(), methodToValidate, invocation.getArguments(), groups);
		}
		if (!result.isEmpty()) {
			throw new ConstraintViolationException(result);
		}
		// ③校验对应的返回值
		Object returnValue = invocation.proceed();

		result = execVal.validateReturnValue(invocation.getThis(), methodToValidate, returnValue, groups);
		if (!result.isEmpty()) {
			throw new ConstraintViolationException(result);
		}

		return returnValue;
	}

只要类上使用了@Validated注解，则其下的所有方法都会被校验。
检验规则如下：参数和返回值都会被校验，只要某一个没有通过，则会抛出ConstraintViolationException异常以示警告。
具体的参数校验属于hibernate-validator的范畴了，感兴趣的读者可自行分析~

参数级别的校验(推荐)

即@Validated注解作用于方法的参数上，其有关的校验则是被springmvc的参数校验器处理的。笔者在ModelAttributeMethodProcessor#resolveArgument()方法中查找到了相应的蛛丝马迹，列出关键的代码

	@Override
	@Nullable
	public final Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {

		....
		Object attribute = null;
		BindingResult bindingResult = null;

		if (mavContainer.containsAttribute(name)) {
			attribute = mavContainer.getModel().get(name);
		}
		else {
			// Create attribute instance
			try {
				attribute = createAttribute(name, parameter, binderFactory, webRequest);
			}
			catch (BindException ex) {
				.....
			}
		}

		if (bindingResult == null) {
			WebDataBinder binder = binderFactory.createBinder(webRequest, attribute, name);
			if (binder.getTarget() != null) {
				if (!mavContainer.isBindingDisabled(name)) {
					bindRequestParameters(binder, webRequest);
				}
				// 就是这里
				validateIfApplicable(binder, parameter);
				if (binder.getBindingResult().hasErrors() && isBindExceptionRequired(binder, parameter)) {
					throw new BindException(binder.getBindingResult());
				}
			}
			// Value type adaptation, also covering java.util.Optional
			if (!parameter.getParameterType().isInstance(attribute)) {
				attribute = binder.convertIfNecessary(binder.getTarget(), parameter.getParameterType(), parameter);
			}
			bindingResult = binder.getBindingResult();
		}

		....

		return attribute;
	}

我们继续看下其下的validateIfApplicable()方法

	protected void validateIfApplicable(WebDataBinder binder, MethodParameter parameter) {
		// 对参数上含有@Validated注解的进行校验器解析
		Annotation[] annotations = parameter.getParameterAnnotations();
		for (Annotation ann : annotations) {
			Validated validatedAnn = AnnotationUtils.getAnnotation(ann, Validated.class);
                        // 兼容@Valid注解方式
			if (validatedAnn != null || ann.annotationType().getSimpleName().startsWith("Valid")) {
				Object hints = (validatedAnn != null ? validatedAnn.value() : AnnotationUtils.getValue(ann));
				Object[] validationHints = (hints instanceof Object[] ? (Object[]) hints : new Object[] {hints});
				binder.validate(validationHints);
				break;
			}
		}
	}

上述的代码已经很简明概要了，笔者就不展开了。当然如果用户想要在出现异常的时候进行友好的返回，建议参考springboot情操陶冶-web配置(五)的异常机制文章便可迎刃而解

小结

参数的校验一般都是结合spring-context板块内的@Validated注解搭配hibernate的校验器便完成了相应的检测功能。
经过笔者的测试，发现在类上使用@Validated注释基本没啥用，还是会依赖在参数上添加@Validated注解方可生效。
如果大家对此有什么补充欢迎留言，在此希望此篇对大家有所帮助