Spring Validation方法實現原理分析

最近要做動態數據的提交處理，即需要分析提交數據字段定義信息後才能明確對應的具體字段類型，進而做數據類型轉換和字段有效性校驗，然後做業務處理後提交數據庫，自己開發一套校驗邏輯的話週期太長，因此分析了Spring Validation的實現原理，復用了其底層花樣繁多的Validator，在此將分析Spring Validation原理的過程記錄下，不深入細節

如何使用Spring Validation

Spring Bean初始化時校驗Bean是否符合JSR-303規範

1、手動添加BeanValidationPostProcessor Bean

2、在model類中定義校驗規則，如@Max、@Min、@NotEmpty

3、聲明Bean，綜合代碼如下：

 @Beanpublic BeanPostProcessor beanValidationPostProcessor() { return new BeanValidationPostProcessor();}@Beanpublic UserModel getUserModel() { UserModel userModel = new UserModel(); userModel.setUsername(null); userModel.setPassword("123"); return userModel;}@Dataclass UserModel { @NotNull(message = "username can not be null") @Pattern(regexp = "[a-zA-Z0-9_]{5,10}", message = "username is illegal") private String username; @Size(min = 5, max = 10, message = "password's length is illegal") private String password;}

4、BeanValidationPostProcessor Bean內部有個boolean類型的屬性afterInitialization，默認是false，如果是false，在postProcessBeforeInitialization過程中對bean進行驗證，否則在postProcessAfterInitialization過程對bean進行驗證

5、此種校驗使用了spring的BeanPostProcessor邏輯

6、校驗底層調用了doValidate方法，進一步調用validator.validate，默認validator為HibernateValidator，validation-api包為JAVA規範，Spring默認的規範實現為hibernate-validator包，此hibernate非ORM框架Hibernate

 protected void doValidate(Object bean) { Assert.state(this.validator != null, "No Validator set"); Set<ConstraintViolation<Object>> result = this.validator.validate(bean);

7、HibernateValidator默認調用ValidatorFactoryImpl來生成validator，後面展開將ValidatorFactoryImpl

支持方法級別的JSR-303規範

1、手動添加MethodValidationPostProcessor Bean

2、類上加上@Validated註解（也支持自定義註解，創建MethodValidationPostProcessor Bean時傳入）

3、在方法的參數中加上驗證註解，比如@Max、@Min、@NotEmpty、@NotNull等，如

@Component@Validatedpublic class BeanForMethodValidation { public void validate(@NotEmpty String name, @Min(10) int age) { System.out.println("validate, name: " + name + ", age: " + age); }}

4、MethodValidationPostProcessor內部使用aop完成對方法的調用

public void afterPropertiesSet() { Pointcut pointcut = new `AnnotationMatchingPointcut`(this.validatedAnnotationType, true); this.advisor = new `DefaultPointcutAdvisor`(pointcut, createMethodValidationAdvice(this.validator));}protected Advice createMethodValidationAdvice(@Nullable Validator validator) { return (validator != null ? new `MethodValidationInterceptor`(validator) : new MethodValidationInterceptor());}

5、底層同樣默認調用ValidatorFactoryImpl來生成validator，由validator完成校驗

直接編碼調用校驗邏輯，如

public class Person {@NotNull(message = "性別不能為空")private Gender gender;@Min(10)private Integer age;...}ValidatorFactory validatorFactory = Validation.buildDefaultValidatorFactory();Validator validator = validatorFactory.getValidator();Person person = new Person();person.setGender(Gender.Man);validator.validate(person);

同上，默認調用ValidatorFactoryImpl來生成validator，由validator完成具體校驗

在Spring controller方法參數中使用valid或validated註解標註待校驗參數

1、先熟悉下Spring的請求調用流程

2、可以看到在各種resolver處理請求參數的過程中做了參數校驗

3、底層統一調用了DataBinder的validate方法

4、DataBinder的作用：Binder that allows for setting property values onto a target object, including support for validation and binding result analysis，也就是binder處理了request提交的字符串形式的參數，將其轉換成服務端真正需要的類型，binder提供了對validation的支持，可以存放校驗結果

5、DataBinder的validator默認在ConfigurableWebBindingInitializer中初始化，默認使用OptionalValidatorFactoryBean，該Bean繼承了LocalValidatorFactoryBean，LocalValidatorFactoryBean組合了ValidatorFactory、自定義校驗屬性等各種校驗會用到的信息，默認使用ValidatorFactoryImpl來獲取validator

至此，所有的線索都指向了ValidatorFactoryImpl，下面分析下該類

public Validator `getValidator`() { return `createValidator`( constraintValidatorManager.getDefaultConstraintValidatorFactory(), valueExtractorManager, validatorFactoryScopedContext, methodValidationConfiguration );}Validator `createValidator`(ConstraintValidatorFactory constraintValidatorFactory, ValueExtractorManager valueExtractorManager, ValidatorFactoryScopedContext validatorFactoryScopedContext, MethodValidationConfiguration methodValidationConfiguration) { BeanMetaDataManager beanMetaDataManager = beanMetaDataManagers.computeIfAbsent( new BeanMetaDataManagerKey( validatorFactoryScopedContext.getParameterNameProvider(), valueExtractorManager, methodValidationConfiguration ), key -> new BeanMetaDataManager( `constraintHelper`, executableHelper, typeResolutionHelper, validatorFactoryScopedContext.getParameterNameProvider(), valueExtractorManager, validationOrderGenerator, buildDataProviders(), methodValidationConfiguration ) ); return `new ValidatorImpl`( constraintValidatorFactory, beanMetaDataManager, valueExtractorManager, constraintValidatorManager, validationOrderGenerator, validatorFactoryScopedContext );}public final <T> Set<ConstraintViolation<T>> validate(T object, Class<?>... groups) { Contracts.assertNotNull( object, MESSAGES.validatedObjectMustNotBeNull() ); sanityCheckGroups( groups ); ValidationContext<T> validationContext = `getValidationContextBuilder().forValidate( object )`; if ( !validationContext.getRootBeanMetaData().hasConstraints() ) { return Collections.emptySet(); } ValidationOrder validationOrder = determineGroupValidationOrder( groups ); ValueContext<?, Object> valueContext = `ValueContext.getLocalExecutionContext`( validatorScopedContext.getParameterNameProvider(), object, validationContext.getRootBeanMetaData(), PathImpl.createRootPath() ); return validateInContext( validationContext, valueContext, validationOrder );}

1、getValidator->createValidator->ValidatorImpl->validate

在執行過程中封裝了beanMetaDataManager、validationContext、valueContext等內容，都是校驗時會用到的上下文信息，如待校驗bean的所有校驗項（含父類和接口）、property、method parameter的校驗信息，從ValidatorFactoryScopedContext繼承過來的validator通用的各種工具類（如message、script等的處理）等，內容比較複雜

2、分組（group）校驗忽略，來到默認分組處理validateConstraintsForDefaultGroup->validateConstraintsForSingleDefaultGroupElement->validateMetaConstraint(注：metaConstraints維護了該bean類型及其父類、接口的所有校驗，需要遍歷調用validateMetaConstraint)

3、繼續調用MetaConstraint的doValidateConstraint方法，根據不同的annotation type走不同的ConstraintTree

 public static <U extends Annotation> ConstraintTree<U> of(ConstraintDescriptorImpl<U> composingDescriptor, Type validatedValueType) { if ( composingDescriptor.getComposingConstraintImpls().isEmpty() ) { return new SimpleConstraintTree<>( composingDescriptor, validatedValueType ); } else { return new ComposingConstraintTree<>( composingDescriptor, validatedValueType ); }}

4、具體哪些走simple，哪些走composing暫且不管，因為二者都調用了ConstraintTree的'getInitializedConstraintValidator'方法，該步用來獲取校驗annotation（如DecimalMax、NotEmpty等）對應的validator並初始化validator

5、 ConstraintHelper類維護了所有builtin的validator，並根據校驗annotation（如DecimalMax）分類，validator的描述類中維護了該validator的泛型模板（如BigDecimal），如下：

 putConstraints( tmpConstraints, DecimalMax.class, Arrays.asList( DecimalMaxValidatorForBigDecimal.class, DecimalMaxValidatorForBigInteger.class, DecimalMaxValidatorForDouble.class, DecimalMaxValidatorForFloat.class, DecimalMaxValidatorForLong.class, DecimalMaxValidatorForNumber.class, DecimalMaxValidatorForCharSequence.class, DecimalMaxValidatorForMonetaryAmount.class) );

在獲取具體bean類的validator時，先根據annotation獲取所有的validator，對應方法是ConstraintManager.findMatchingValidatorDescriptor，然後根據被校驗對象的類型獲取唯一的validator

6、然後根據上下文信息initializeValidator，進而調用validator的isValid方法校驗

以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持武林網。