Spring Validation实现原理分析

最近要做动态数据的提交解决，即需要分析提交数据字段定义信息后才可以明确对应的具体字段类型，进而做数据类型转换和字段有效性校验，而后做业务解决后提交数据库，自己开发一套校验逻辑的话周期太长，因而分析了Spring Validation的实现原理，复使用了其底层花样繁多的Validator，在此将分析Spring Validation原理的过程记录下，不深入细节

如何用Spring Validation

• Spring Bean初始化时校验Bean能否符合JSR-303规范
  1、手动增加BeanValidationPostProcessor Bean
  2、在model类中定义校验规则，如@Max、@Min、@NotEmpty
  3、公告Bean，综合代码如下：

@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内部有个boolean类型的属性afterInitialization，默认是false，假如是false，在postProcessBeforeInitialization过程中对bean进行验证，否则在postProcessAfterInitialization过程对bean进行验证
5、此种校验用了spring的BeanPostProcessor逻辑，可参考Spring Boot系列之一：如何快速熟习Spring技术栈
6、校验底层调使用了doValidate方法，进一步调使用validator.validate，默认validator为HibernateValidator，validation-api包为JAVA规范，Spring默认的规范实现为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默认调使用ValidatorFactoryImpl来生成validator，后面开展将ValidatorFactoryImpl

• 支持方法级别的JSR-303规范
  1、手动增加MethodValidationPostProcessor Bean
  2、类上加上@Validated注解（也支持自己设置注解，创立MethodValidationPostProcessor Bean时传入）
  3、在方法的参数中加上验证注解，比方@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内部用aop完成对方法的调使用

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、底层同样默认调使用ValidatorFactoryImpl来生成validator，由validator完成校验

• 直接编码调使用校验逻辑，如

public class Person {@NotNull(message = "性别不可以为空")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，默认调使用ValidatorFactoryImpl来生成validator，由validator完成具体校验

• 在Spring controller方法参数中用valid或者validated注解标注待校验参数
  1、先熟习下Spring的请求调使用流程
  image
  2、能看到在各种resolver解决请求参数的过程中做了参数校验
  3、底层统一调使用了DataBinder的validate方法
  4、DataBinder的作使用：Binder that allows for setting property values onto a target object, including support for validation and binding result analysis，也就是binder解决了request提交的字符串形式的参数，将其转换成服务端真正需要的类型，binder提供了对validation的支持，能存放校验结果
  5、DataBinder的validator默认在ConfigurableWebBindingInitializer中初始化，默认用OptionalValidatorFactoryBean，该Bean继承了LocalValidatorFactoryBean，LocalValidatorFactoryBean组合了ValidatorFactory、自己设置校验属性等各种校验会使用到的信息，默认用ValidatorFactoryImpl来获取validator

至此，所有的线索都指向了ValidatorFactoryImpl，下面分析下该类

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
在执行过程中封装了beanMetaDataManager、validationContext、valueContext等内容，都是校验时会使用到的上下文信息，如待校验bean的所有校验项（含父类和接口）、property、method parameter的校验信息，从ValidatorFactoryScopedContext继承过来的validator通使用的各种工具类（如message、script等的解决）等，内容比较复杂
2、分组（group）校验忽略，来到默认分组解决validateConstraintsForDefaultGroup->validateConstraintsForSingleDefaultGroupElement->validateMetaConstraint(注：metaConstraints维护了该bean类型及其父类、接口的所有校验，需要遍历调使用validateMetaConstraint)
3、继续调使用MetaConstraint的doValidateConstraint方法，根据不同的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、具体哪些走simple，哪些走composing暂且不论，由于二者都调使用了ConstraintTree的’getInitializedConstraintValidator’方法，该步使用来获取校验annotation（如DecimalMax、NotEmpty等）对应的validator并初始化validator
5、ConstraintHelper类维护了所有builtin的validator，并根据校验annotation（如DecimalMax）分类，validator的形容类中维护了该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) );

在获取具体bean类的validator时，先根据annotation获取所有的validator，对应方法是ConstraintManager.findMatchingValidatorDescriptor，而后根据被校验对象的类型获取唯一的validator
6、而后根据上下文信息initializeValidator，进而调使用validator的isValid方法校验

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