一、需求

今天在搭建Springboot框架的时候，又遇到一个需求：在多模块系统中，有些模块想自己管理BeanValidation的资源文件（默认是启动项目claspath下的 ValidationMessages.properties）。刚开始还天真地认为springboot会不会帮我们做了，结果并没有，于是就是撸源码了。

以下是我的实现和实现原理

二、实现

@Configuration
public class MyWebMvcConfigurer implements WebMvcConfigurer {
/*** 当有异常时返回默认的验证器* @return 返回的是org.springframework.validation.Validator,不是javax.validation.Validator* 所以返回时要适配一下*/
@Override
public Validator getValidator() {//路径匹配PathMatchingResourcePatternResolver resourcePatternResolver =new PathMatchingResourcePatternResolver(MyWebMvcConfigurer.class.getClassLoader());try {//匹配属性文件，有个限制，资源文件名称必须包含ValidationResource[] resources = resourcePatternResolver.getResources("classpath*:*Validation*.properties");List<String> files = Arrays.stream(resources).filter(resource -> StringUtils.isNotBlank(resource.getFilename())).map(resource -> {String fileName = resource.getFilename();return fileName.substring(0, fileName.indexOf("."));}).collect(Collectors.toList());javax.validation.Validator validator = Validation.byDefaultProvider().configure()//这里可以加载多个文件.messageInterpolator(new ResourceBundleMessageInterpolator(new AggregateResourceBundleLocator(files))).buildValidatorFactory().getValidator();//适配return new SpringValidatorAdapter(validator);} catch (IOException e) {//发生异常，返回null，springboot框架会采用默认的validatorreturn null;}
}

三、实现原理

源码分析

1、定位Bean在什么地方验证的

DispatcherServlet验证Bean的主要源码路径

• RequestResponseBodyMethodProcessor#resolveArgument
  • AbstractMessageConverterMethodArgumentResolver#validateIfApplicable
    • DataBinder#validate（核心）

源码：

/*** 该方法定位：org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor#resolveArgument* Throws MethodArgumentNotValidException if validation fails.* @throws HttpMessageNotReadableException if {@link RequestBody#required()}* is {@code true} and there is no body content or if there is no suitable* converter to read the content with.*/
@Override
public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {parameter = parameter.nestedIfOptional();Object arg = readWithMessageConverters(webRequest, parameter, parameter.getNestedGenericParameterType());String name = Conventions.getVariableNameForParameter(parameter);if (binderFactory != null) {WebDataBinder binder = binderFactory.createBinder(webRequest, arg, name);if (arg != null) {//*******校验方法参数是否符合要求*******//调用链：也就是验证器被调用的地方validateIfApplicable(binder, parameter);if (binder.getBindingResult().hasErrors() && isBindExceptionRequired(binder, parameter)) {throw new MethodArgumentNotValidException(parameter, binder.getBindingResult());}}if (mavContainer != null) {mavContainer.addAttribute(BindingResult.MODEL_KEY_PREFIX + name, binder.getBindingResult());}}return adaptArgumentIfNecessary(arg, parameter);
}/*** 该方法定位：org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodArgumentResolver#validateIfApplicable*  * Validate the binding target if applicable.* <p>The default implementation checks for {@code @javax.validation.Valid},* Spring's {@link org.springframework.validation.annotation.Validated},* and custom annotations whose name starts with "Valid".* @param binder the DataBinder to be used* @param parameter the method parameter descriptor* @since 4.1.5* @see #isBindExceptionRequired*/
protected void validateIfApplicable(WebDataBinder binder, MethodParameter parameter) {Annotation[] annotations = parameter.getParameterAnnotations();for (Annotation ann : annotations) {Validated validatedAnn = AnnotationUtils.getAnnotation(ann, Validated.class);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});//调用链binder.validate(validationHints);break;}}
}/*** 该方法定位：org.springframework.validation.DataBinder#validate(java.lang.Object...)** Invoke the specified Validators, if any, with the given validation hints.* <p>Note: Validation hints may get ignored by the actual target Validator.* @param validationHints one or more hint objects to be passed to a {@link SmartValidator}* @see #setValidator(Validator)* @see SmartValidator#validate(Object, Errors, Object...)* 核心方法*/
public void validate(Object... validationHints) {for (Validator validator : getValidators()) {if (!ObjectUtils.isEmpty(validationHints) && validator instanceof SmartValidator) {((SmartValidator) validator).validate(getTarget(), getBindingResult(), validationHints);}else if (validator != null) {validator.validate(getTarget(), getBindingResult());}}
}
/*** 获取验证器（关键就在：this.validators怎么初始化的？）*/
public List<Validator> getValidators() {return Collections.unmodifiableList(this.validators);
}

发现：在DataBinder#validate中有验证Bean的核心代码validator.validate(...)

分析到这里关键就是validator在哪赋值的？

2、validators赋值

• DataBinder属性validators赋值
  private final List validators = new ArrayList<>();

  //断点跟踪发现：
  public void setValidator(@Nullable Validator validator) {assertValidators(validator);this.validators.clear();if (validator != null) {this.validators.add(validator);}}

  • DataBinder#setValidator被调用的位置
    • org.springframework.web.bind.support.ConfigurableWebBindingInitializer#initBinder

    源码：

    @Override
    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);}if (this.validator != null && binder.getTarget() != null &&this.validator.supports(binder.getTarget().getClass())) {//发现是在这里调用的，下面的问题就是ConfigurableWebBindingInitializer//中的validator属性在哪初始化的？//在对应的setValidator方法打断点binder.setValidator(this.validator);}if (this.conversionService != null) {binder.setConversionService(this.conversionService);}if (this.propertyEditorRegistrars != null) {for (PropertyEditorRegistrar propertyEditorRegistrar :         this.propertyEditorRegistrars) {propertyEditorRegistrar.registerCustomEditors(binder);}}
    }

  • ConfigurableWebBindingInitializer#initBinder被调用的位置
    研究发现：ConfigurableWebBindingInitializer#initBinder是在springboot初始化时被调用的
    调用链如下：
    调用链1：初始化springmvc的requestMappingHandlerAdapter
    EnableWebMvcConfiguration#requestMappingHandlerAdapter
    • super.requestMappingHandlerAdapter();—>WebMvcConfigurationSupport
      调用链2：
      WebMvcConfigurationSupport#requestMappingHandlerAdapter
    • adapter.setWebBindingInitializer(getConfigurableWebBindingInitializer());
      调用链3：
      EnableWebMvcConfiguration#ConfigurableWebBindingInitializer
    • super.getConfigurableWebBindingInitializer();
      调用链4：
      WebMvcConfigurationSupport#ConfigurableWebBindingInitializer
    • mvcValidator(),这个是核心

    源码：

    /*** @see org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration.* EnableWebMvcConfiguration#requestMappingHandlerAdapter*/
    @Bean
    @Override
    public RequestMappingHandlerAdapter requestMappingHandlerAdapter() {//调用链1：调用父类WebMvcConfigurationSupport#requestMappingHandlerAdapterRequestMappingHandlerAdapter adapter = super.requestMappingHandlerAdapter();adapter.setIgnoreDefaultModelOnRedirect(this.mvcProperties == null|| this.mvcProperties.isIgnoreDefaultModelOnRedirect());return adapter;
    }/*** @seeorg.springframework.web.servlet.config.annotation.* WebMvcConfigurationSupport#requestMappingHandlerAdapter**/
    public RequestMappingHandlerAdapter requestMappingHandlerAdapter() {RequestMappingHandlerAdapter adapter = createRequestMappingHandlerAdapter();adapter.setContentNegotiationManager(mvcContentNegotiationManager());adapter.setMessageConverters(getMessageConverters());//调用链2：EnableWebMvcConfiguration#getConfigurableWebBindingInitializeradapter.setWebBindingInitializer(getConfigurableWebBindingInitializer());adapter.setCustomArgumentResolvers(getArgumentResolvers());adapter.setCustomReturnValueHandlers(getReturnValueHandlers());...
    }/*** @see springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration.* EnableWebMvcConfiguration#getConfigurableWebBindingInitializer**/
    @Override
    protected ConfigurableWebBindingInitializer getConfigurableWebBindingInitializer() {try {//这里是不存在实例，报异常return this.beanFactory.getBean(ConfigurableWebBindingInitializer.class);}catch (NoSuchBeanDefinitionException ex) {//调用链3：WebMvcConfigurationSupport#getConfigurableWebBindingInitializerreturn super.getConfigurableWebBindingInitializer();}
    }/*** @seespringframework.web.servlet.config.annotation.WebMvcConfigurationSupport* #getConfigurableWebBindingInitializer**/
    protected ConfigurableWebBindingInitializer getConfigurableWebBindingInitializer() {ConfigurableWebBindingInitializer initializer = new ConfigurableWebBindingInitializer();initializer.setConversionService(mvcConversionService());//调用链4：核心方法mvcValidator()initializer.setValidator(mvcValidator());MessageCodesResolver messageCodesResolver = getMessageCodesResolver();if (messageCodesResolver != null) {initializer.setMessageCodesResolver(messageCodesResolver);}return initializer;
    }

3、validator是什么

通过源码分析，找到了关键点就是mvcValidator()，现在对其分析，找出其返回的validator到底是什么？

断点调试时发现mvcValidator()进入了

org.springframework.context.annotation.ConfigurationClassEnhancer.BeanMethodInterceptor#intercept

• org.springframework.context.annotation.ConfigurationClassEnhancer.BeanMethodInterceptor#resolveBeanReference
  resolveBeanReference方法里有个关键的代码

  //关键在于 beanFactory.getBean(beanName)，name = "mvcValidator"，创建该实例
  //从而会找到EnableWebMvcConfiguration的mvcValidator方法
  //（因为mvcValidator方法上有@Bean,方法名称又与beanName相同，故调用）
  Object beanInstance = (useArgs ? beanFactory.getBean(beanName, beanMethodArgs) :beanFactory.getBean(beanName));

• org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration.EnableWebMvcConfiguration#mvcValidator
  终于找到创建validator对象的点了，以下就是如何自己扩展？
  继续研究创建validator的源码，寻找关键点

  @Bean
  @Override
  public Validator mvcValidator() {if (!ClassUtils.isPresent("javax.validation.Validator",getClass().getClassLoader())) {return super.mvcValidator();}//关键在于getValidator()方法//真正调用的是父类DelegatingWebMvcConfiguration#getValidatorreturn ValidatorAdapter.get(getApplicationContext(), getValidator());
  }

4、关键点：分析getValidator()方法

注意：这里就是我们可以扩展的地方

/*** springframework.web.servlet.config.annotation.DelegatingWebMvcConfiguration#getValidator*/
@Override
@Nullable
protected Validator getValidator() {//configurers属性是WebMvcConfigurerComposite的对象return this.configurers.getValidator();
}/***@see springframework.web.servlet.config.annotation.WebMvcConfigurerComposite#getValidator*/
@Override
public Validator getValidator() {Validator selected = null;//看到WebMvcConfigurer这个东西，我是很激动呀！终于看到曙光了,激动半天//于是我就自定义了MyWebMvcConfigurer实现WebMvcConfigurer，并重写//其中的getValidator方法，哈哈，终于找到扩展点了for (WebMvcConfigurer configurer : this.delegates) {Validator validator = configurer.getValidator();if (validator != null) {if (selected != null) {throw new IllegalStateException("No unique Validator found: {" +selected + ", " + validator + "}");}selected = validator;}}return selected;
}

通过getValidator()获取自定义的validator后

ValidatorAdapter.get(getApplicationContext(), getValidator());对其包装如下：

/*** @see springframework.boot.autoconfigure.validation.ValidatorAdapter#get*/
public static Validator get(ApplicationContext applicationContext,Validator validator) {//如果为null（自定义的validator发生异常），返回默认的if (validator != null) {//因为非空，会执行该行代码return wrap(validator, false);}return getExistingOrCreate(applicationContext);
}private static Validator wrap(Validator validator, boolean existingBean) {if (validator instanceof javax.validation.Validator) {//执行该代码if (validator instanceof SpringValidatorAdapter) {return new ValidatorAdapter((SpringValidatorAdapter) validator,existingBean);}return new ValidatorAdapter(new SpringValidatorAdapter((javax.validation.Validator) validator),existingBean);}return validator;
}

总结：在分析源码的过程中犯了最大的错误就是：总想什么都搞明白，跟踪每个源码的实现，结果发现还是没搞懂，白白浪费了很多时间。其实在分析源码的过程中，不需要钻牛角尖，把每个都搞懂。你要搞明白你的“关注点“在哪？，不要走着走着就走偏了。很多源码“观其大意”就行，没必要深究，不然就呵呵了。