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Validation Resource[] 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validator return 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#requestMappingHandlerAdapteradapter.setWebBindingInitializer(getConfigurableWebBindingInitializer()); 调用链3： EnableWebMvcConfiguration#ConfigurableWebBindingInitializersuper.getConfigurableWebBindingInitializer(); 调用链4： WebMvcConfigurationSupport#ConfigurableWebBindingInitializermvcValidator(),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#requestMappingHandlerAdapter RequestMappingHandlerAdapter 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#getConfigurableWebBindingInitializer adapter.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#getConfigurableWebBindingInitializer return 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#getValidator return 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。
转载于:https://www.cnblogs.com/liruiloveparents/p/9400426.html
