Spring Validation方法實現(xiàn)原理分析

更新時間：2018年07月10日 08:39:43 作者：68號小喇叭

這篇文章主要介紹了Spring Validation實現(xiàn)原理分析，小編覺得挺不錯的，現(xiàn)在分享給大家，也給大家做個參考。一起跟隨小編過來看看吧

最近要做動態(tài)數(shù)據(jù)的提交處理，即需要分析提交數(shù)據(jù)字段定義信息后才能明確對應(yīng)的具體字段類型，進而做數(shù)據(jù)類型轉(zhuǎn)換和字段有效性校驗，然后做業(yè)務(wù)處理后提交數(shù)據(jù)庫，自己開發(fā)一套校驗邏輯的話周期太長，因此分析了Spring Validation的實現(xiàn)原理，復(fù)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(jié)

如何使用Spring Validation

Spring Bean初始化時校驗Bean是否符合JSR-303規(guī)范

1、手動添加BeanValidationPostProcessor Bean

2、在model類中定義校驗規(guī)則，如@Max、@Min、@NotEmpty

3、聲明Bean，綜合代碼如下：

@Bean
public BeanPostProcessor beanValidationPostProcessor() {
  return new BeanValidationPostProcessor();
}

@Bean
public UserModel getUserModel() {
  UserModel userModel = new UserModel();
  userModel.setUsername(null);
  userModel.setPassword("123");
  return userModel;
}

@Data
class 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(nèi)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(diào)用了doValidate方法，進一步調(diào)用validator.validate，默認validator為HibernateValidator，validation-api包為JAVA規(guī)范，Spring默認的規(guī)范實現(xiàn)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(diào)用ValidatorFactoryImpl來生成validator，后面展開將ValidatorFactoryImpl

支持方法級別的JSR-303規(guī)范

1、手動添加MethodValidationPostProcessor Bean

2、類上加上@Validated注解（也支持自定義注解，創(chuàng)建MethodValidationPostProcessor Bean時傳入）

3、在方法的參數(shù)中加上驗證注解，比如@Max、@Min、@NotEmpty、@NotNull等，如

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

4、MethodValidationPostProcessor內(nèi)部使用aop完成對方法的調(diào)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(diào)用ValidatorFactoryImpl來生成validator，由validator完成校驗

直接編碼調(diào)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(diào)用ValidatorFactoryImpl來生成validator，由validator完成具體校驗

在Spring controller方法參數(shù)中使用valid或validated注解標(biāo)注待校驗參數(shù)

1、先熟悉下Spring的請求調(diào)用流程

2、可以看到在各種resolver處理請求參數(shù)的過程中做了參數(shù)校驗

3、底層統(tǒng)一調(diào)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(shù)，將其轉(zhuǎn)換成服務(wù)端真正需要的類型，binder提供了對validation的支持，可以存放校驗結(jié)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(zhí)行過程中封裝了beanMetaDataManager、validationContext、valueContext等內(nèi)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(nèi)容比較復(fù)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(diào)用validateMetaConstraint)

3、繼續(xù)調(diào)用MetaConstraint的doValidateConstraint方法，根據(jù)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(diào)用了ConstraintTree的'getInitializedConstraintValidator'方法，該步用來獲取校驗annotation（如DecimalMax、NotEmpty等）對應(yīng)的validator并初始化validator

5、 ConstraintHelper 類維護了所有builtin的validator，并根據(jù)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(jù)annotation獲取所有的validator，對應(yīng)方法是ConstraintManager.findMatchingValidatorDescriptor，然后根據(jù)被校驗對象的類型獲取唯一的validator

6、然后根據(jù)上下文信息initializeValidator，進而調(diào)用validator的isValid方法校驗

以上就是本文的全部內(nèi)容，希望對大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。

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