Concurrent Modification exception while evicting cache in Hibernate

Question

My application maintains a cache of list of users and it is evicted when any new user is created. I am getting Concurrent Modification exception while evicting the cache.

Stack trace :

java.util.ConcurrentModificationException: null
    at java.util.HashMap.forEach(HashMap.java:1292)
    at org.hibernate.resource.jdbc.internal.ResourceRegistryStandardImpl.releaseResources(ResourceRegistryStandardImpl.java:323)
    at org.hibernate.resource.jdbc.internal.AbstractLogicalConnectionImplementor.afterTransaction(AbstractLogicalConnectionImplementor.java:60)
    at org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.afterTransaction(LogicalConnectionManagedImpl.java:167)
    at org.hibernate.resource.jdbc.internal.LogicalConnectionManagedImpl.afterCompletion(LogicalConnectionManagedImpl.java:291)
    at org.hibernate.resource.jdbc.internal.AbstractLogicalConnectionImplementor.commit(AbstractLogicalConnectionImplementor.java:95)
    at org.hibernate.resource.transaction.backend.jdbc.internal.JdbcResourceLocalTransactionCoordinatorImpl$TransactionDriverControlImpl.commit(JdbcResourceLocalTransactionCoordinatorImpl.java:282)
    at org.hibernate.engine.transaction.internal.TransactionImpl.commit(TransactionImpl.java:101)
    at org.springframework.orm.hibernate5.HibernateTransactionManager.doCommit(HibernateTransactionManager.java:627)
    at org.springframework.transaction.support.AbstractPlatformTransactionManager.processCommit(AbstractPlatformTransactionManager.java:743)
    at org.springframework.transaction.support.AbstractPlatformTransactionManager.commit(AbstractPlatformTransactionManager.java:711)
    at org.springframework.transaction.interceptor.TransactionAspectSupport.commitTransactionAfterReturning(TransactionAspectSupport.java:633)
    at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:386)
    at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:118)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:749)
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:95)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:749)
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:691)
    at com.mytestapp.service.impl.MyCacheManager$$EnhancerBySpringCGLIB$$6a5d7f13.resetTeamListCache(<generated>)
    at 
com.mytestapp.webapp.listener.StartupListener.refreshContext(StartupListener.java:199)
    at com.mytestapp..webapp.controller.admin.SystemUserManagementController.saveSystemUserData(SystemUserManagementController.java:529)

In my controller the code is as follows :

systemUserProfileManager.saveSystemUserProfile(userBasicInfo); // async call
StartupListener.refreshContext(request.getSession().getServletContext()); // cache evict

refreshContextMethod in StartupListener :

public static void refreshContext(ServletContext context) {
        ApplicationContext ctx = WebApplicationContextUtils
                .getRequiredWebApplicationContext(context);
        MyCacheManager myCacheManager = (MyCacheManager) ctx
                .getBean(myCacheManager);
        
        LOG.debug("Processing started for refreshing Servlet Context/ Cache!");
        // RESET All Cache
        myCacheManager.resetTeamListCache();
        LOG.debug("Processing completed for refreshing Servlet Context/ Cache!");
    }

resetTeamListCache method in MyCacheManager :

@CacheEvict(value = CacheConstants.SALES_TEAM_LIST, allEntries = true)
public void resetTeamListCache() {
    // Intentionally blank
}

Answer 1

The error suggests that you are using the same Hibernate Session in multiple threads concurrently. The hash map, which according to the exception is iterated, does not change within the process of iteration, so the only way this can happen is if you have a concurrency problem in your application.