1 概述
对于Web服务，需要对请求的参数进行校验，可以对不合法的参数进行提示，提高用户体验。也可以防止有人恶意用一些非法的参数对网站造成破坏。如果是对每个参数都写一段代码来判断值是否合法，那校验的代码就很多，也很繁琐。Spring提供了一套校验机制，先来了解一下。
2 原理
2.1 初始化mvcValidator
初始化mvcValidator，mvcValidator是一个SpringValidatorAdapter，其里面的targetValidator是真正执行validate校验的对象，初始化mvcValidator的主要目的就是要把targetValidator组装好。
// 源码位置：org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration.EnableWebMvcConfiguration
// EnableWebMvcConfiguration是带@Configuration注解的类，当开启了WebMvc就会加载
@Bean
public Validator mvcValidator() {if (!ClassUtils.isPresent("javax.validation.Validator", getClass().getClassLoader())) {return super.mvcValidator();}// 1. 调getValidator()获取Validator// EnableWebMvcConfiguration继承DelegatingWebMvcConfiguration，调的是DelegatingWebMvcConfiguration的getValidator()return ValidatorAdapter.get(getApplicationContext(), getValidator());
}// 源码位置：org.springframework.web.servlet.config.annotation.DelegatingWebMvcConfiguration
protected Validator getValidator() {// 2. configures就是平时熟悉的WebMvcConfigurer的封装(WebMvcConfigurerComposite)return this.configurers.getValidator();
}// 源码位置：org.springframework.web.servlet.config.annotation.WebMvcConfigurerComposite
public Validator getValidator() {Validator selected = null;for (WebMvcConfigurer configurer : this.delegates) {// 3. 如果定义了WebMvcConfigurer，则实际调WebMvcConfigurer的getValidator()// WebMvcConfigurer是Spring提供的常用的扩展方式，可通过它来增加Validator，此时没有定义返回的是nullValidator validator = configurer.getValidator();if (validator != null) {if (selected != null) {throw new IllegalStateException("No unique Validator found: {" +selected + ", " + validator + "}");}selected = validator;}}return selected;
}// 回到EnableWebMvcConfiguration的mvcValidator()，处理ValidatorAdapter.get()
// 源码位置：org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration.EnableWebMvcConfiguration
@Bean
public Validator mvcValidator() {if (!ClassUtils.isPresent("javax.validation.Validator", getClass().getClassLoader())) {return super.mvcValidator();}// 1. 调getValidator()获取Validator// 4. getValidator()获取的Validator作为默认的，继续由ValidatorAdapter.get()处理return ValidatorAdapter.get(getApplicationContext(), getValidator());
}// 源码位置：org.springframework.boot.autoconfigure.validation.ValidatorAdapter
public static Validator get(ApplicationContext applicationContext, Validator validator) {// 如果获取到了Validator，优先封装到ValidatorAdapter里面并返回ValidatorAdapter，这里主要看没有获取到Validator的场景if (validator != null) {return wrap(validator, false);}// 5. 获取一个存在的，如果没有就创建一个return getExistingOrCreate(applicationContext);
}
private static Validator getExistingOrCreate(ApplicationContext applicationContext) {// 6. 先获取已经存在的ValidatorValidator existing = getExisting(applicationContext);if (existing != null) {return wrap(existing, true);}return create(applicationContext);
}
private static Validator getExisting(ApplicationContext applicationContext) {try {// 7. 获取实现了org.springframework.validation.Validator接口的bean，这里主要看获取不到的场景，也就是Spring默认没有注入实现了该接口的beanjavax.validation.Validator validator = applicationContext.getBean(javax.validation.Validator.class);if (validator instanceof Validator) {return (Validator) validator;}return new SpringValidatorAdapter(validator);}catch (NoSuchBeanDefinitionException ex) {return null; // 获取不到从这里返回null}
}// 回到ValidatorAdapter的getExistingOrCreate()继续处理
// 源码位置：org.springframework.boot.autoconfigure.validation.ValidatorAdapter
private static Validator getExistingOrCreate(ApplicationContext applicationContext) {// 6. 先获取已经存在的ValidatorValidator existing = getExisting(applicationContext);if (existing != null) {return wrap(existing, true);}// 8. 没有存在的就创建一个return create(applicationContext);
}
private static Validator create(MessageSource messageSource) {// 9. 直接创建一个OptionalValidatorFactoryBean，它是Validator的一个工厂bean// 继承关系：OptionalValidatorFactoryBean < LocalValidatorFactoryBean < SpringValidatorAdapter < javax.validation.ValidatorOptionalValidatorFactoryBean validator = new OptionalValidatorFactoryBean();try {MessageInterpolatorFactory factory = new MessageInterpolatorFactory(messageSource);validator.setMessageInterpolator(factory.getObject());}catch (ValidationException ex) {}return wrap(validator, false);
}// 10. OptionalValidatorFactoryBean的父类SpringValidatorAdapter里有个关键的对象targetValidator，
// 实际的validate工作都是由它完成的，但上面OptionalValidatorFactoryBean()创建的时候使用的是无参构造，
// 则SpringValidatorAdapter里面的targetValidator也没有赋值，所以还做不了实际的validate工作
// 源码位置：org.springframework.validation.beanvalidation.SpringValidatorAdapter
public class SpringValidatorAdapter implements SmartValidator, javax.validation.Validator {private javax.validation.Validator targetValidator;public SpringValidatorAdapter(javax.validation.Validator targetValidator) {Assert.notNull(targetValidator, "Target Validator must not be null");this.targetValidator = targetValidator;}SpringValidatorAdapter() {}void setTargetValidator(javax.validation.Validator targetValidator) {this.targetValidator = targetValidator;}public void validate(Object target, Errors errors) {// 由targetValidator进行实际的validate工作if (this.targetValidator != null) {processConstraintViolations(this.targetValidator.validate(target), errors);}}// 省略其它代码
}// 回到ValidatorAdapter的create()继续处理
// 源码位置：org.springframework.boot.autoconfigure.validation.ValidatorAdapter
private static Validator create(MessageSource messageSource) {// 9. 直接创建一个OptionalValidatorFactoryBean，它是Validator的一个工厂beanOptionalValidatorFactoryBean validator = new OptionalValidatorFactoryBean();try {MessageInterpolatorFactory factory = new MessageInterpolatorFactory(messageSource);validator.setMessageInterpolator(factory.getObject());}catch (ValidationException ex) {}// 11. 把Validator包装到ValidatorAdapter返回return wrap(validator, false);
}// 源码位置：org.springframework.boot.autoconfigure.validation.ValidatorAdapter
private static Validator wrap(Validator validator, boolean existingBean) {if (validator instanceof javax.validation.Validator) {// 12. 从上面继承关系可以看到OptionalValidatorFactoryBean是SpringValidatorAdapter子类，if条件成立if (validator instanceof SpringValidatorAdapter) {return new ValidatorAdapter((SpringValidatorAdapter) validator, existingBean);}// 如果自定义提供一个实现了Validator接口且不是SpringValidatorAdapter子类的validator，则封装到SpringValidatorAdapter里return new ValidatorAdapter(new SpringValidatorAdapter((javax.validation.Validator) validator),existingBean);}// 使用WebMvcConfigurer提供的属于org.springframework.validation.Validator类型，不包装到SpringValidatorAdapter而直接作为mvcValidatorreturn validator;
}// 回到EnableWebMvcConfiguration的mvcValidator()
// 从这个过程看，目前只是创建了OptionalValidatorFactoryBean(包装到了ValidatorAdapter里)，还没有真正创建Validator，
// 这个ValidatorAdapter成为注入到Spring容器的bean，名称是mvcValidator
// 源码位置：org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration.EnableWebMvcConfiguration
@Bean
public Validator mvcValidator() {if (!ClassUtils.isPresent("javax.validation.Validator", getClass().getClassLoader())) {return super.mvcValidator();}// 1. 调getValidator()获取Validator// 4. getValidator()获取的Validator作为默认的，继续由ValidatorAdapter.get()处理// 13. 完成mvcValidator创建，mvcValidator实际是一个包装了OptionalValidatorFactoryBean的ValidatorAdapter// OptionalValidatorFactoryBean的父类LocalValidatorFactoryBean实现了InitializingBean接口会触发afterPropertiesSet()调用return ValidatorAdapter.get(getApplicationContext(), getValidator());
}// 源码位置：org.springframework.validation.beanvalidation.LocalValidatorFactoryBean
public void afterPropertiesSet() {Configuration<?> configuration;// 14. 如果提供了providerClass，则由providerClass来进行配置，否则加载classpath下services的ValidationProvider// 由于上面OptionalValidatorFactoryBean是直接new出来的，这个providerClass也没有赋值if (this.providerClass != null) {ProviderSpecificBootstrap bootstrap = Validation.byProvider(this.providerClass);if (this.validationProviderResolver != null) {bootstrap = bootstrap.providerResolver(this.validationProviderResolver);}configuration = bootstrap.configure();}else {GenericBootstrap bootstrap = Validation.byDefaultProvider();if (this.validationProviderResolver != null) {bootstrap = bootstrap.providerResolver(this.validationProviderResolver);}// 这里会加载classpath下services的ValidationProvider，如果引了hibernate-validator包就会有，// 如果没有引hibernate-validator包，这里会抛异常结束，即没有创建实际的Validatorconfiguration = bootstrap.configure();}// 省略部分代码try {// 实际的Validator要由validationProvider提供this.validatorFactory = configuration.buildValidatorFactory();setTargetValidator(this.validatorFactory.getValidator());}finally {closeMappingStreams(mappingStreams);}
}从上面代码看，如果希望mvcValidator里的targetValidator有值，有两个方法：
- 用WebMvcConfigurer提供一个实现了Validator接口且不是SpringValidatorAdapter子类的validator。
- 通过Services的方式提供。
2.2 设置mvcValidator
RequestMappingHandlerAdapter是SpringMVC处理http请求的关键类，在初始化的时候设置了WebBindingInitializer，而mvcValidator则设置到了WebBindingInitializer里，通过这种方式把mvcValidator组装到了RequestMappingHandlerAdapter里。
// 源码位置：org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration.EnableWebMvcConfiguration
@Bean
public RequestMappingHandlerAdapter requestMappingHandlerAdapter(@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager,@Qualifier("mvcConversionService") FormattingConversionService conversionService,@Qualifier("mvcValidator") Validator validator) {// 1. 初始化RequestMappingHandlerAdapter时，把mvcValidator设置到RequestMappingHandlerAdapterRequestMappingHandlerAdapter adapter = super.requestMappingHandlerAdapter(contentNegotiationManager, conversionService, validator);adapter.setIgnoreDefaultModelOnRedirect(this.mvcProperties == null || this.mvcProperties.isIgnoreDefaultModelOnRedirect());return adapter;
}// 源码位置：org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport
// 继承关系： EnableWebMvcConfiguration < DelegatingWebMvcConfiguration < WebMvcConfigurationSupport
@Bean
public RequestMappingHandlerAdapter requestMappingHandlerAdapter(@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager,@Qualifier("mvcConversionService") FormattingConversionService conversionService,@Qualifier("mvcValidator") Validator validator) {RequestMappingHandlerAdapter adapter = createRequestMappingHandlerAdapter();adapter.setContentNegotiationManager(contentNegotiationManager);adapter.setMessageConverters(getMessageConverters());// 2. mvcValidator实际是设置到了WebBindingInitializer，而WebBindingInitializer则设置到了RequestMappingHandlerAdapter里adapter.setWebBindingInitializer(getConfigurableWebBindingInitializer(conversionService, validator));adapter.setCustomArgumentResolvers(getArgumentResolvers());adapter.setCustomReturnValueHandlers(getReturnValueHandlers());if (jackson2Present) {adapter.setRequestBodyAdvice(Collections.singletonList(new JsonViewRequestBodyAdvice()));adapter.setResponseBodyAdvice(Collections.singletonList(new JsonViewResponseBodyAdvice()));}AsyncSupportConfigurer configurer = getAsyncSupportConfigurer();if (configurer.getTaskExecutor() != null) {adapter.setTaskExecutor(configurer.getTaskExecutor());}if (configurer.getTimeout() != null) {adapter.setAsyncRequestTimeout(configurer.getTimeout());}adapter.setCallableInterceptors(configurer.getCallableInterceptors());adapter.setDeferredResultInterceptors(configurer.getDeferredResultInterceptors());return adapter;
}// 源码位置：org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration.EnableWebMvcConfiguration
protected ConfigurableWebBindingInitializer getConfigurableWebBindingInitializer(FormattingConversionService mvcConversionService, Validator mvcValidator) {try {return this.beanFactory.getBean(ConfigurableWebBindingInitializer.class);}catch (NoSuchBeanDefinitionException ex) {// 3. 在父类设置return super.getConfigurableWebBindingInitializer(mvcConversionService, mvcValidator);}
}// 源码位置：org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport
protected ConfigurableWebBindingInitializer getConfigurableWebBindingInitializer(FormattingConversionService mvcConversionService, Validator mvcValidator) {// 4. 创建WebBindingInitializer(ConfigurableWebBindingInitializer)，并设置mvcValidatorConfigurableWebBindingInitializer initializer = new ConfigurableWebBindingInitializer();initializer.setConversionService(mvcConversionService);initializer.setValidator(mvcValidator);MessageCodesResolver messageCodesResolver = getMessageCodesResolver();if (messageCodesResolver != null) {initializer.setMessageCodesResolver(messageCodesResolver);}return initializer;
}2.3 请求参数校验
当发起HTTP请求的时候，SpringMVC会通过RequestMappingHandlerAdapter把mvcValidator设置到DataBinder(ExtendedServletRequestDataBinder)中，在对请求参数处理的时候，如果参数指定了需要校验的注解(如@Valid)，则在DataBinder里用Validator对参数进行校验，校验的结果放到BindingResult里。最后判断BindingResult里是否带了错误信息，如果带了则抛异常，如果抛异常则不会进入Controller的接口。
// BindingResult接口是Errors接口的子接口，它们是Spring的Validation机制的重要概念。
// Errors主要用于存储对象和对象方法的validation错误，前者用reject()接口，后者用rejectValue()接口。
// BindingResult则还记录了产生validation错误的对象
public interface BindingResult extends Errors {Object getTarget();// 省略其它接口
}
// 源码位置：org.springframework.validation.Errors
public interface Errors {void reject(String errorCode);void reject(String errorCode, String defaultMessage);void reject(String errorCode, @Nullable Object[] errorArgs, @Nullable String defaultMessage);void rejectValue(@Nullable String field, String errorCode);void rejectValue(@Nullable String field, String errorCode, String defaultMessage);void rejectValue(@Nullable String field, String errorCode, @Nullable Object[] errorArgs, @Nullable String defaultMessage);// 省略其它接口
}// RequestMappingHandlerAdapter处理http请求时，在匹配请求参数和Controller接口参数的时候，需要用到各种各样的MethodProcessor，
// 当参数类型属于自定义的类型，匹配到的处理类是ModelAttributeMethodProcessor；
// binderFactory为ServletRequestDataBinderFactory，里面带了ConfigurableWebBindingInitializer，WebBindingInitializer带了mvcValidator；
// binderFactory的ConfigurableWebBindingInitializer由RequestMappingHandlerAdapter提供。
// 源码位置：org.springframework.web.method.annotation.ModelAttributeMethodProcessor
public final Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {String name = ModelFactory.getNameForParameter(parameter);ModelAttribute ann = parameter.getParameterAnnotation(ModelAttribute.class);if (ann != null) {mavContainer.setBinding(name, ann.binding());}Object attribute = null;BindingResult bindingResult = null;if (mavContainer.containsAttribute(name)) {attribute = mavContainer.getModel().get(name);}else {try {// 1. 创建参数类型对应的对象，如例子里的GroupMemberattribute = createAttribute(name, parameter, binderFactory, webRequest);}catch (BindException ex) {if (isBindExceptionRequired(parameter)) {throw ex;}if (parameter.getParameterType() == Optional.class) {attribute = Optional.empty();}else {attribute = ex.getTarget();}bindingResult = ex.getBindingResult();}}if (bindingResult == null) {// 2. 创建一个WebDataBinder，由父类DefaultDataBinderFactory提供createBinder()方法WebDataBinder binder = binderFactory.createBinder()方法(webRequest, attribute, name);if (binder.getTarget() != null) {if (!mavContainer.isBindingDisabled(name)) {bindRequestParameters(binder, webRequest);}validateIfApplicable(binder, parameter);if (binder.getBindingResult().hasErrors() && isBindExceptionRequired(binder, parameter)) {throw new BindException(binder.getBindingResult());}}if (!parameter.getParameterType().isInstance(attribute)) {attribute = binder.convertIfNecessary(binder.getTarget(), parameter.getParameterType(), parameter);}bindingResult = binder.getBindingResult();}Map<String, Object> bindingResultModel = bindingResult.getModel();mavContainer.removeAttributes(bindingResultModel);mavContainer.addAllAttributes(bindingResultModel);return attribute;
}// 源码位置：org.springframework.web.bind.support.DefaultDataBinderFactory
public final WebDataBinder createBinder(NativeWebRequest webRequest, @Nullable Object target, String objectName) throws Exception {// 3. 调用ServletRequestDataBinderFactory的createBinderInstance()创建// 继承关系：ServletRequestDataBinderFactory < InitBinderDataBinderFactory < DefaultDataBinderFactoryWebDataBinder dataBinder = createBinderInstance(target, objectName, webRequest);if (this.initializer != null) {this.initializer.initBinder(dataBinder, webRequest);}initBinder(dataBinder, webRequest);return dataBinder;
}// 源码位置：org.springframework.web.servlet.mvc.method.annotation.ServletRequestDataBinderFactory
protected ServletRequestDataBinder createBinderInstance(@Nullable Object target, String objectName, NativeWebRequest request) throws Exception {// 4. 创建WebDataBinder对象return new ExtendedServletRequestDataBinder(target, objectName);
}// 回到DefaultDataBinderFactory的createBinder()继续处理
// 源码位置：org.springframework.web.bind.support.DefaultDataBinderFactory
public final WebDataBinder createBinder(NativeWebRequest webRequest, @Nullable Object target, String objectName) throws Exception {// 3. 调用ServletRequestDataBinderFactory的createBinderInstance()创建ExtendedServletRequestDataBinderWebDataBinder dataBinder = createBinderInstance(target, objectName, webRequest);if (this.initializer != null) {// 4. 初始化WebDataBinder// initializer为ConfigurableWebBindingInitializer，实现了WebBindingInitializer接口，initBinder()由接口提供this.initializer.initBinder(dataBinder, webRequest);}initBinder(dataBinder, webRequest);return dataBinder;
}// 源码位置：org.springframework.web.bind.support.WebBindingInitializer
default void initBinder(WebDataBinder binder, WebRequest request) {// 5. 调用子类方法初始化，子类为ConfigurableWebBindingInitializerinitBinder(binder);
}// 源码位置：org.springframework.web.bind.support.ConfigurableWebBindingInitializer
public void initBinder(WebDataBinder binder) {binder.setAutoGrowNestedPaths(this.autoGrowNestedPaths);if (this.directFieldAccess) {binder.initDirectFieldAccess();}if (this.messageCodesResolver != null) {binder.setMessageCodesResolver(this.messageCodesResolver);}if (this.bindingErrorProcessor != null) {binder.setBindingErrorProcessor(this.bindingErrorProcessor);}// 6. 把mvcValidator设置到WebDataBinder中，mvcValidator实际为SpringValidatorAdapterif (this.validator != null && binder.getTarget() != null && this.validator.supports(binder.getTarget().getClass())) {binder.setValidator(this.validator);}if (this.conversionService != null) {binder.setConversionService(this.conversionService);}if (this.propertyEditorRegistrars != null) {for (PropertyEditorRegistrar propertyEditorRegistrar : this.propertyEditorRegistrars) {propertyEditorRegistrar.registerCustomEditors(binder);}}
}// 回到ModelAttributeMethodProcessor继续处理
// 源码位置：org.springframework.web.method.annotation.ModelAttributeMethodProcessor
public final Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {// 省略部分代码if (bindingResult == null) {// 2. 创建一个WebDataBinder，由父类DefaultDataBinderFactory提供createBinder()方法WebDataBinder binder = binderFactory.createBinder()方法(webRequest, attribute, name);if (binder.getTarget() != null) {if (!mavContainer.isBindingDisabled(name)) {bindRequestParameters(binder, webRequest);}// 7. 校验参数值validateIfApplicable(binder, parameter);if (binder.getBindingResult().hasErrors() && isBindExceptionRequired(binder, parameter)) {throw new BindException(binder.getBindingResult());}}if (!parameter.getParameterType().isInstance(attribute)) {attribute = binder.convertIfNecessary(binder.getTarget(), parameter.getParameterType(), parameter);}bindingResult = binder.getBindingResult();}Map<String, Object> bindingResultModel = bindingResult.getModel();mavContainer.removeAttributes(bindingResultModel);mavContainer.addAllAttributes(bindingResultModel);return attribute;
}// 源码位置：org.springframework.web.method.annotation.ModelAttributeMethodProcessor
protected void validateIfApplicable(WebDataBinder binder, MethodParameter parameter) {for (Annotation ann : parameter.getParameterAnnotations()) {// 8. 把参数前指定的注解取出来，确定哪些是和validation有关的Object[] validationHints = ValidationAnnotationUtils.determineValidationHints(ann);if (validationHints != null) {binder.validate(validationHints);break;}}
}// 9. 一般要校验的参数前面要加上@Valid注解
// 从下面代码看不止这一种方式，还可以指定有值的@Validated注解，也可以自定义以Valid开头的注解等
// 源码位置：org.springframework.validation.annotation.ValidationAnnotationUtils
public static Object[] determineValidationHints(Annotation ann) {// 指定了注解@Validatedif (ann instanceof Validated) {return ((Validated) ann).value();}// 指定了注解@ValidClass<? extends Annotation> annotationType = ann.annotationType();if ("javax.validation.Valid".equals(annotationType.getName())) {return EMPTY_OBJECT_ARRAY;}// 注解间接指定了注解@ValidatedValidated validatedAnn = AnnotationUtils.getAnnotation(ann, Validated.class);if (validatedAnn != null) {return validatedAnn.value();}// 自定义注解是以Valid开头命名的if (annotationType.getSimpleName().startsWith("Valid")) {return convertValidationHints(AnnotationUtils.getValue(ann));}return null;
}// 回到ModelAttributeMethodProcessor的validateIfApplicable()继续处理
// 源码位置：org.springframework.web.method.annotation.ModelAttributeMethodProcessor
protected void validateIfApplicable(WebDataBinder binder, MethodParameter parameter) {for (Annotation ann : parameter.getParameterAnnotations()) {// 8. 把参数前指定的注解取出来，确定哪些是和validation有关的Object[] validationHints = ValidationAnnotationUtils.determineValidationHints(ann);if (validationHints != null) {// 如果匹配到了注解，则进行校验binder.validate(validationHints);break;}}
}// 源码位置：org.springframework.validation.DataBinder
public void validate(Object... validationHints) {Object target = getTarget();// 记录校验错误的BindingResult，一般为BeanPropertyBindingResultBindingResult bindingResult = getBindingResult();// 9. 获取到所有的Validator来校验，从前面看基本只有一个for (Validator validator : getValidators()) {if (!ObjectUtils.isEmpty(validationHints) && validator instanceof SmartValidator) {((SmartValidator) validator).validate(target, bindingResult, validationHints);}else if (validator != null) {// 10. 调用Validator的validate()方法进行校验，校验的结果要放到bindingResult中validator.validate(target, bindingResult);}}
}// 源码位置：org.springframework.web.method.annotation.ModelAttributeMethodProcessor
public final Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {// 省略部分代码if (bindingResult == null) {// 2. 创建一个WebDataBinder，由父类DefaultDataBinderFactory提供createBinder()方法WebDataBinder binder = binderFactory.createBinder()方法(webRequest, attribute, name);if (binder.getTarget() != null) {if (!mavContainer.isBindingDisabled(name)) {bindRequestParameters(binder, webRequest);}// 7. 校验参数值validateIfApplicable(binder, parameter);// 11. 如果有validation错误就抛异常if (binder.getBindingResult().hasErrors() && isBindExceptionRequired(binder, parameter)) {throw new BindException(binder.getBindingResult());}}if (!parameter.getParameterType().isInstance(attribute)) {attribute = binder.convertIfNecessary(binder.getTarget(), parameter.getParameterType(), parameter);}bindingResult = binder.getBindingResult();}Map<String, Object> bindingResultModel = bindingResult.getModel();mavContainer.removeAttributes(bindingResultModel);mavContainer.addAllAttributes(bindingResultModel);return attribute;
}2.4 Validation的使用
Spring提供的Validation模型为：
模型的核心部分是：
- Valid和Validated注解：主要是用来识别是否需要进行校验，如果不加这些注解，那么就相当于没有开启校验。注解由参数MethodParameter提供。
- Validator：主要实现校验逻辑。supports()用于识别参数的类型，validate()则完成具体的校验逻辑。
- Errors：用于存储校验的错误结果，分为整个对象的错误（如对象为null）和属性错误。ModelAttributeMethodProcessor等会从它里面获取错误进行处理。
- WebDataBinder用于组合Validator和Errors，完成整体的校验。
从上面看，要使用Spring提供的Validation对参数校验需要：
1) 自定义一个校验类，实现org.springframework.validation.Validator接口：
public interface Validator {boolean supports(Class<?> clazz);void validate(Object target, Errors errors);
}2) 把这个自定义类加到WebMvcConfigurer中
@Configuration
public class WebConfig implements WebMvcConfigurer {@Overridepublic Validator getValidator() {return new CustomValidator();}
}3) 在Validator的validate()校验到错误的时候，错误信息要加到Errors中
在support()里要定义好HTTP请求参数类型的匹配规则，这个方法的参数是HTTP请求参数对应的类。最直接的方式就是列出所有要支持校验的类，但这样扩展性就比较差，如果要扩展成一个框架，就得用其它方式，比如定义一些注解，通过这个类型来获取是否指定了注解，然后根据注解类做事情。
同理，validate()工作如果不是硬编码也不太容易。所以Spring提供的Validation有点比较原始，不方便直接使用。
3 架构一小步
使用Spring提供的@Valid注解标识Controller接口里接收的参数，增加扩展来支持校验（这个扩展有现成的hibernate-validator包)。
