发现一个API报了错：
javax.validation.UnexpectedTypeException: HV000030: No validator could be found for constraint 'javax.validation.constraints.NotEmpty' validating type 'java.lang.String'. Check configuration for 'cancelReason' at org.hibernate.validator.internal.engine.constraintvalidation.ConstraintTree.throwExceptionForNullValidator(ConstraintTree.java:229) ~[hibernate-validator-5.3.6.Final.jar:5.3.6.Final] at org.hibernate.validator.internal.engine.constraintvalidation.ConstraintTree.getConstraintValidatorNoUnwrapping(ConstraintTree.java:310) ~[hibernate-validator-5.3.6.Final.jar:5.3.6.Final] at org.hibernate.validator.internal.engine.constraintvalidation.ConstraintTree.getConstraintValidatorInstanceForAutomaticUnwrapping(ConstraintTree.java:244) ~[hibernate-validator-5.3.6.Final.jar:5.3.6.Final] at org.hibernate.validator.internal.engine.constraintvalidation.ConstraintTree.getInitializedConstraintValidator(ConstraintTree.java:163) ~[hibernate-validator-5.3.6.Final.jar:5.3.6.Final] at org.hibernate.validator.internal.engine.constraintvalidation.ConstraintTree.validateConstraints(ConstraintTree.java:116) ~[hibernate-validator-5.3.6.Final.jar:5.3.6.Final] at org.hibernate.validator.internal.engine.constraintvalidation.ConstraintTree.validateConstraints(ConstraintTree.java:87) ~[hibernate-validator-5.3.6.Final.jar:5.3.6.Final] at org.hibernate.validator.internal.metadata.core.MetaConstraint.validateConstraint(MetaConstraint.java:73) ~[hibernate-validator-5.3.6.Final.jar:5.3.6.Final] at org.hibernate.validator.internal.engine.ValidatorImpl.validateMetaConstraint(ValidatorImpl.java:621) ~[hibernate-validator-5.3.6.Final.jar:5.3.6.Final] at org.hibernate.validator.internal.engine.ValidatorImpl.validateConstraint(ValidatorImpl.java:584) ~[hibernate-validator-5.3.6.Final.jar:5.3.6.Final] at org.hibernate.validator.internal.engine.ValidatorImpl.validateConstraintsForSingleDefaultGroupElement(ValidatorImpl.java:528) ~[hibernate-validator-5.3.6.Final.jar:5.3.6.Final] at org.hibernate.validator.internal.engine.ValidatorImpl.validateConstraintsForDefaultGroup(ValidatorImpl.java:496) ~[hibernate-validator-5.3.6.Final.jar:5.3.6.Final] at org.hibernate.validator.internal.engine.ValidatorImpl.validateConstraintsForCurrentGroup(ValidatorImpl.java:461) ~[hibernate-validator-5.3.6.Final.jar:5.3.6.Final] at org.hibernate.validator.internal.engine.ValidatorImpl.validateInContext(ValidatorImpl.java:411) ~[hibernate-validator-5.3.6.Final.jar:5.3.6.Final] at org.hibernate.validator.internal.engine.ValidatorImpl.validate(ValidatorImpl.java:208) ~[hibernate-validator-5.3.6.Final.jar:5.3.6.Final] at org.springframework.validation.beanvalidation.SpringValidatorAdapter.validate(SpringValidatorAdapter.java:103) ~[spring-context-4.3.17.RELEASE.jar:4.3.17.RELEASE] at org.springframework.boot.autoconfigure.web.WebMvcValidator.validate(WebMvcValidator.java:64) ~[spring-boot-autoconfigure-1.5.13.RELEASE.jar:1.5.13.RELEASE] at org.springframework.validation.DataBinder.validate(DataBinder.java:895) ~[spring-context-4.3.17.RELEASE.jar:4.3.17.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodArgumentResolver.validateIfApplicable(AbstractMessageConverterMethodArgumentResolver.java:270) ~[spring-webmvc-4.3.17.RELEASE.jar:4.3.17.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.resolveArgument(RequestResponseBodyMethodProcessor.java:133) ~[spring-webmvc-4.3.17.RELEASE.jar:4.3.17.RELEASE] at org.springframework.web.method.support.HandlerMethodArgumentResolverComposite.resolveArgument(HandlerMethodArgumentResolverComposite.java:121) ~[spring-web-4.3.17.RELEASE.jar:4.3.17.RELEASE] at org.springframework.web.method.support.InvocableHandlerMethod.getMethodArgumentValues(InvocableHandlerMethod.java:158) ~[spring-web-4.3.17.RELEASE.jar:4.3.17.RELEASE] at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:128) ~[spring-web-4.3.17.RELEASE.jar:4.3.17.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:97) ~[spring-webmvc-4.3.17.RELEASE.jar:4.3.17.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:827) ~[spring-webmvc-4.3.17.RELEASE.jar:4.3.17.RELEASE] at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:738) ~[spring-webmvc-4.3.17.RELEASE.jar:4.3.17.RELEASE] at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85) ~[spring-webmvc-4.3.17.RELEASE.jar:4.3.17.RELEASE] at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:967) ~[spring-webmvc-4.3.17.RELEASE.jar:4.3.17.RELEASE] at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901) ~[spring-webmvc-4.3.17.RELEASE.jar:4.3.17.RELEASE] at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) [spring-webmvc-4.3.17.RELEASE.jar:4.3.17.RELEASE] at org.springframework.web.servlet.FrameworkServlet.doPut(FrameworkServlet.java:883) [spring-webmvc-4.3.17.RELEASE.jar:4.3.17.RELEASE]
一、HV000030: No validator
报这个错，一般有两种情况：
（1）约束与对象属性不匹配，譬如在String 上使用javax.validation.constraints.Future就会报这个错
（2）真的是没有相关的Validator
一下子觉得很奇怪，难道javax.validation.constraints.NotEmpty不能用在java.lang.String??
这有什么错呢!!
真的是没有Validator?
如果有，会是这样的，以javax.validation.constraints.Future为例：
还真没有！！但是@NotEmpty是有两个的
看了下线上在跑的的API，发现使用的是org.hibernate.validator.constraints.NotEmpty。
刚才也看到了，也是没有对应Validator
但是有一些与javax.validation.constraints.NotEmpty不一样的地方：使用了两个元约束@NotNull和@Size(min=1)
也就是一个校验不需要一个专门的Validator也是可以的？
二、ComposingConstraints【组合约束】
打断点看了下,hibernate-validator在处理约束时，使用组合约束的概念【可扩展性好强】。
具体工作流程如下：
（1）先递归校验组合约束。譬如javax.validation.constraints.NotEmpty中的@NotNull和@Size(min=1)
（2）校验主约束，如果有则校验；否则，跳过。譬如javax.validation.constraints.NotEmpty
（3）处理组合约束的校验结果。有三种策略：OR,AND,ALL_FALSE
org.hibernate.validator.internal.engine.constraintvalidation.ConstraintTree#validateConstraints(org.hibernate.validator.internal.engine.ValidationContext<T>, org.hibernate.validator.internal.engine.ValueContext<?,V>, java.util.Set<javax.validation.ConstraintViolation<T>>)
org.hibernate.validator.internal.engine.constraintvalidation.ConstraintTree#validateComposingConstraints
三、为什么会有这个一定会报错的javax.validation.constraints.NotEmpty呢？
大家都知道Spring Boot帮助我们做了一件脏活、累活【感恩】：依赖包的版本管理。难道此处有bug?
使用IDEA中的Maven Helper插件看一下：
Jump to Source，原来是pom.xml中显式引入2.0.1.Final的validator-api
Spring Boot1.5.13中使用的是1.1.0.Final
问了下当时添加此依赖的同学，反馈是从老项目中继承过来的，当时是为了解决JPA的一个问题。不过现在已经全部改用Mybatis，那么这个是可以去掉的。
把项目所有的微服务check了一遍，发现只有这个项目有。
去掉并回归了下，相关接口并没有受到影响。OK,收工