最近要做动态数据的提交处理，即需要分析提交数据字段定义信息后才能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，然后做业务处理后提交数据库，自己开发一套校验逻辑的话周期太长，因此分析了Spring Validation的实现原理，复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
如何使用Spring Validation
Spring Bean初始化时校验Bean是否符合JSR-303规范
1、手动添加BeanValidationPostProcessor Bean
2、在model类中定义校验规则，如@Max、@Min、@NotEmpty
3、声明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，如果是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、此种校验使用了spring的BeanPostProcessor逻辑，可参考Spring Boot系列之一：如何快速熟悉Spring技术栈
6、校验底层调用了doValidate方法，进一步调用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默认调用ValidatorFactoryImpl来生成validator，后面展开将ValidatorFactoryImpl
支持方法级别的JSR-303规范
1、手动添加MethodValidationPostProcessor Bean
2、类上加上@Validated注解（也支持自定义注解，创建MethodValidationPostProcessor Bean时传入）
3、在方法的参数中加上验证注解，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内部使用aop完成对方法的调用
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、底层同样默认调用ValidatorFactoryImpl来生成validator，由validator完成校验
直接编码调用校验逻辑，如
public class Person {@NotNull(message = "性别不能为空")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，默认调用ValidatorFactoryImpl来生成validator，由validator完成具体校验
在Spring controller方法参数中使用
valid或validated注解标注待校验参数
1、先熟悉下Spring的请求调用流程image
2、可以看到在各种resolver处理请求参数的过程中做了参数校验
3、底层统一调用了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处理了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，可以存放校验结果
5、DataBinder的validator默认在ConfigurableWebBindingInitializer中初始化，默认使用OptionalValidatorFactoryBean，该Bean继承了LocalValidatorFactoryBean，LocalValidatorFactoryBean组合了ValidatorFactory、自定义校验属性等各种校验会用到的信息，默认使用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通用的各种工具类（如message、script等的处理）等，内容比较复杂
2、分组（group）校验忽略，来到默认分组处理validateConstraintsForDefaultGroup->validateConstraintsForSingleDefaultGroupElement->validateMetaConstraint(注：metaConstraints维护了该bean类型及其父类、接口的所有校验，需要遍历调用validateMetaConstraint)
3、继续调用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暂且不管，因为二者都调用了ConstraintTree的'getInitializedConstraintValidator'方法，该步用来获取校验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的描述类中维护了该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，然后根据被校验对象的类型获取唯一的validator
6、然后根据上下文信息initializeValidator，进而调用validator的isValid方法校验
作者：68号小喇叭
链接：https://www.jianshu.com/p/5ac6bf554aaa
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