原文地址：启用dubbo validation后hessian反序列化异常解决方案
现象
启用dubbo参数验证，当在provider端开启验证validation="true"。调用接口时，若接口参数为对象类型，对象属性验证失败，客户端会报如下异常。
2019-04-25T09:57:18.544+0800 [ERROR] business-service o.a.c.c.C.[.[.[.[dispatcherServlet] - - Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is java.lang.reflect.UndeclaredThrowableException] with root cause
com.alibaba.dubbo.remoting.RemotingException: com.alibaba.com.caucho.hessian.io.HessianFieldException: org.hibernate.validator.internal.engine.ConstraintViolationImpl.constraintDescriptor: 'org.hibernate.validator.internal.metadata.descriptor.ConstraintDescriptorImpl' could not be instantiated
com.alibaba.com.caucho.hessian.io.HessianFieldException: org.hibernate.validator.internal.engine.ConstraintViolationImpl.constraintDescriptor: 'org.hibernate.validator.internal.metadata.descriptor.ConstraintDescriptorImpl' could not be instantiated
at com.alibaba.com.caucho.hessian.io.JavaDeserializer.logDeserializeError(JavaDeserializer.java:167)
at com.alibaba.com.caucho.hessian.io.JavaDeserializer$ObjectFieldDeserializer.deserialize(JavaDeserializer.java:410)
at com.alibaba.com.caucho.hessian.io.JavaDeserializer.readObject(JavaDeserializer.java:276)
at com.alibaba.com.caucho.hessian.io.JavaDeserializer.readObject(JavaDeserializer.java:203)
at com.alibaba.com.caucho.hessian.io.SerializerFactory.readObject(SerializerFactory.java:526)
... more
Caused by: com.alibaba.com.caucho.hessian.io.HessianProtocolException: 'org.hibernate.validator.internal.metadata.descriptor.ConstraintDescriptorImpl' could not be instantiated
at com.alibaba.com.caucho.hessian.io.JavaDeserializer.instantiate(JavaDeserializer.java:316)
at com.alibaba.com.caucho.hessian.io.JavaDeserializer.readObject(JavaDeserializer.java:201)
at com.alibaba.com.caucho.hessian.io.Hessian2Input.readObjectInstance(Hessian2Input.java:2818)
at com.alibaba.com.caucho.hessian.io.Hessian2Input.readObject(Hessian2Input.java:2145)
at com.alibaba.com.caucho.hessian.io.Hessian2Input.readObject(Hessian2Input.java:2074)
at com.alibaba.com.caucho.hessian.io.Hessian2Input.readObject(Hessian2Input.java:2118)
at com.alibaba.com.caucho.hessian.io.Hessian2Input.readObject(Hessian2Input.java:2074)
at com.alibaba.com.caucho.hessian.io.JavaDeserializer$ObjectFieldDeserializer.deserialize(JavaDeserializer.java:406)
... 41 more
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at com.alibaba.com.caucho.hessian.io.JavaDeserializer.instantiate(JavaDeserializer.java:312)
... 48 more
Caused by: java.lang.NullPointerException
at org.hibernate.validator.internal.metadata.descriptor.ConstraintDescriptorImpl.(ConstraintDescriptorImpl.java:176)
at org.hibernate.validator.internal.metadata.descriptor.ConstraintDescriptorImpl.(ConstraintDescriptorImpl.java:233)
... more
版本
org.apache.dubbo
dubbo
2.7.1
同时测试了2.6.5也有同样的问题。
分析
异常表象为'org.hibernate.validator.internal.metadata.descriptor.ConstraintDescriptorImpl' could not be instantiated，在继续跟踪栈信息是在下面的地方抛出了NullPointerException异常。
Caused by: java.lang.NullPointerException
at org.hibernate.validator.internal.metadata.descriptor.ConstraintDescriptorImpl.(ConstraintDescriptorImpl.java:176)
at org.hibernate.validator.internal.metadata.descriptor.ConstraintDescriptorImpl.(ConstraintDescriptorImpl.java:233)
进入ConstraintDescriptorImpl.java:176行看下，代码如下：
public ConstraintDescriptorImpl(ConstraintHelper constraintHelper,
Member member,
ConstraintAnnotationDescriptor annotationDescriptor,
ElementType type,
Class implicitGroup,
ConstraintOrigin definedOn,
ConstraintType externalConstraintType) {
this.annotationDescriptor = annotationDescriptor;
this.elementType = type;
this.definedOn = definedOn;
this.isReportAsSingleInvalidConstraint = annotationDescriptor.getType().isAnnotationPresent(ReportAsSingleViolation.class);
... more
报空指针的位置就是
this.isReportAsSingleInvalidConstraint = annotationDescriptor.getType().isAnnotationPresent(ReportAsSingleViolation.class);
结论
dubbo使用默认序列化协议hessian，在反序列化时根据构造函数参数个数优先级来取参数最少的构造器，由于ConstraintDescriptorImpl该类只一个构造器，debug进入发现在初始化时传入的参数全部为null，这就造成了NullPointerException异常，导致序列化失败。
从ConstraintViolationException继承结构可以看到其继承自ValidationException，并增加了一个参数private final Set
屏幕快照 2019-04-25 下午3.17.42.png
解决方案
知道了问题出在哪里，那解决起来还是很方便的。既然Set
使用dubbo验证扩展自定义一个validation。
具体实现如下：
实现一个Validation接口，返回一个自定义的Validator
package com.example.demo.dubbo.validation;
import org.apache.dubbo.common.URL;
import org.apache.dubbo.validation.Validation;
import org.apache.dubbo.validation.Validator;
/**
* @ClassName CustomValidation
* @Description
* @Author lixin
* @Date 2019-04-23 17:34
*/
public class CustomValidation implements Validation{
@Override
public Validator getValidator(URL url) {
return new CustomValidator(url);
}
}
CustomValidation实现，这里只需要简单的捕获一下ConstraintViolationException异常，将violations取出重新格式化即可，同时还保持了dubbo validation的原生逻辑支持
package com.example.demo.dubbo.validation;
import org.apache.dubbo.common.URL;
import org.apache.dubbo.common.json.JSONArray;
import org.apache.dubbo.common.json.JSONObject;
import org.apache.dubbo.common.utils.ReflectUtils;
import org.apache.dubbo.validation.support.jvalidation.JValidator;
import org.apache.dubbo.validation.Validator;
import javax.validation.*;
import java.util.*;
/**
* 继承自{@link JValidator}保证了dubbo原生的vidation逻辑。
* 修改点：1、捕获ConstraintViolationException异常，将验证未通过异常改为ValidationException，解决dubbo hessian反序列化失败问题
* 2、格式化验证提示，使用json格式响应
*
* @Author lixin
* @Date 2019-04-23 17:35
*/
public class CustomValidator extends JValidator implements Validator {
private final Class clazz;
@SuppressWarnings({"unchecked", "rawtypes"})
public CustomValidator(URL url) {
super(url);
this.clazz = ReflectUtils.forName(url.getServiceInterface());
}
@Override
public void validate(String methodName, Class[] parameterTypes, Object[] arguments) throws Exception {
try{
super.validate(methodName,parameterTypes,arguments);
}catch (ConstraintViolationException e){
throw new ValidationException(constraintMessage(clazz.getName(),methodName,e.getConstraintViolations()));
}
}
private String constraintMessage(String className,String methodName,Set> violations){
JSONObject json = new JSONObject();
json.put("service",className);
json.put("method",methodName);
JSONArray details = new JSONArray();
for(ConstraintViolation violation : violations){
JSONObject detail = new JSONObject();
detail.put("bean",violation.getRootBean().getClass().getName());
detail.put("property",violation.getPropertyPath().toString());
detail.put("message",violation.getMessage());
details.add(detail);
}
json.put("details",details);
return json.toString();
}
}
使用方式
provider端启用(注解方式)
@Service(validation = "xxx")
consumer端启用(注解方式)
@Reference(validation = "xxx")
建议
1、在consumer端开启验证，以减少无用的请求打到provider端。
2、自定义的model类，增加默认构造器。