org.hibernate.AssertionFailure: possible non-threadsafe access to the session

Question

I am developing a web application with AngularJs as front-end and Spring+Hibernate as the service layer. Service Layer has a set of REST API's that are consumed by AngularJs. The front end of the application has no major issues. But in the service layer, I am facing some concurrency issues. For some scenarios, I have to make parallel Asychronous calls to same REST API's from the same http session. When I do that, there are times when I get the above error. Actually, the error keeps of changing everytime. Sometimes I also get NULLPointerException on Query.List() operation. Sometimes I get TransactionResourceAlreadyClosed exception. Various configurations and code snippets are attached below.

Web.xml

<context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>WEB-INF/config/fs-cxf-serverContext.xml,WEB-INF/config/fs-spring-jpa-config.xml,WEB-INF/config/security-beans.xml</param-value>
</context-param>

<listener>
    <listener-class>org.springframework.web.context.request.RequestContextListener</listener-class>
</listener>
<listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

<filter>
    <filter-name>CorsFilter</filter-name>
    <filter-class>org.apache.catalina.filters.CorsFilter</filter-class>
    <init-param>
        <param-name>cors.allowed.origins</param-name>
        <param-value>*</param-value>
    </init-param>
    <init-param>
        <param-name>cors.allowed.headers</param-name>
        <param-value>Content-Type,X-Requested-With,accept,Origin,Access-Control-Request-Method,Access-Control-Request-Headers,Access-Control-Allow-Origin</param-value>
    </init-param>
    <init-param>
        <param-name>cors.exposed.headers</param-name>
        <param-value>Access-Control-Allow-Origin</param-value>
    </init-param>
    <init-param>
        <param-name>cors.allowed.methods</param-name>
        <param-value>GET, POST, PUT, DELETE, OPTIONS, HEAD</param-value>
    </init-param>
</filter>
<filter-mapping>
    <filter-name>CorsFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

<filter>
    <filter-name>springSecurityFilterChain</filter-name>
    <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
</filter>
<filter-mapping>
    <filter-name>springSecurityFilterChain</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

<servlet>
    <description>Servlet to Initialize and shutdown the Scheduler</description>
    <servlet-name>QuartzInitializer</servlet-name>
    <servlet-class>org.quartz.ee.servlet.QuartzInitializerServlet</servlet-class>
    <init-param>
        <param-name>config-file</param-name>
        <param-value>quartz.properties</param-value>
    </init-param>
    <init-param>
        <param-name>shutdown-on-unload</param-name>
        <param-value>true</param-value>
    </init-param>
    <init-param>
        <param-name>start-scheduler-on-load</param-name>
        <param-value>true</param-value>
    </init-param>
    <load-on-startup>2</load-on-startup>
</servlet>
<servlet>
    <servlet-name>CXFServlet</servlet-name>
    <servlet-class>org.apache.cxf.transport.servlet.CXFServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
</servlet>

<servlet-mapping>
    <servlet-name>CXFServlet</servlet-name>
    <url-pattern>/services/*</url-pattern>
</servlet-mapping>

<resource-ref>
    <res-ref-name>jdbc/foodsafetyDS</res-ref-name>
    <res-type>javax.sql.DataSource</res-type>
    <res-auth>Container</res-auth>
    <res-sharing-scope>Shareable</res-sharing-scope>
</resource-ref>

JPA Configuration

<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
xmlns:tx="http://www.springframework.org/schema/tx"
xmlns:task="http://www.springframework.org/schema/task"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
    http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
    http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd
    http://www.springframework.org/schema/task http://www.springframework.org/schema/task/spring-task-3.2.xsd">

<!-- Hibernate session factory -->
<bean id="sessionFactory"
    class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
    <property name="configLocation" value="classpath:hibernate.cfg.xml" />
    <property name="entityInterceptor">
        <bean class="com.cts.foodSafety.interceptor.AuditLogInterceptor"/>
    </property>
</bean>

<bean id="transactionManager"
    class="org.springframework.orm.hibernate4.HibernateTransactionManager">
    <property name="sessionFactory" ref="sessionFactory" />
</bean>

<bean id="persistenceAnnotation"
    class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor" />

<tx:annotation-driven transaction-manager="transactionManager" />
<task:annotation-driven/>

Hibernate.cfg.xml

<hibernate-configuration>
<session-factory>
    <property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
    <property name="hibernate.dialect">org.hibernate.dialect.MySQLDialect</property>
    <property name="hibernate.connection.datasource">java:comp/env/jdbc/foodsafetyDS</property>
    <property name="hbm2ddl.auto">update</property>
    <property name="show_sql">false</property>

    <!-- Mapping with model class containing annotations -->

I have created a simple rest controller using CXF. REST end point is as below

@Path("/units")
@Produces(MediaType.APPLICATION_JSON)
public interface UnitService extends Serializable {

@GET
@Path("/getGraphData/{type}")
@Produces(MediaType.APPLICATION_JSON)
public UnitServiceBean getGraphData(@PathParam("type") String type)
        throws FoodSafetyException;

}

Implementation of the controller is as below

xxxServiceImpl.java

@Service("unit")
@Transactional
public class xxxServiceImpl implements xxxService {

private static final long serialVersionUID = 1L;

@Autowired
xxxDelegate xxxDelegate;

@Override
public UnitServiceBean getGraphData(String type) throws FoodSafetyException {
    UnitServiceBean bean = new UnitServiceBean();

    List<String[]> data = unitDelegate.getGraphData(type);
    ....
    ....
    return bean;
}

Delegate calls the DAO. (We haven't introduced the Business object as of now). Implementation of DAO is as below

@Component
public class UnitDAOImpl extends FoodSafetyDAO implements UnitDAO {
@Override
public List<String[]> getGraphData(String type) {
    List<String[]> data = new ArrayList<String[]>();
    Map<String, List<UnitReadingEntity>> readings = new HashMap<String, List<UnitReadingEntity>>();

    SimpleDateFormat df = CommonConstants.TIME_FORMATTER;

    // Get all the Units
    Query query = getSession().getNamedQuery(
            QueryConstants.FIND_UNITS_BY_TYPE);
    query.setParameter(QueryConstants.TYPE, type);
    List<UnitEntity> units = (List<UnitEntity>) query.list();
    if (units != null && units.size() != 0) {
        .....
        .....

        for (UnitEntity unit : units) {
            Calendar cal1 = Calendar.getInstance();
            cal1.add(Calendar.DAY_OF_YEAR, -1);
            query = getSession().getNamedQuery(
                    QueryConstants.FIND_READING_BY_UNIT_TIME).setLong(
                    QueryConstants.UNIT_ID, unit.getUnitId());

            List<UnitReadingEntity> rr = query.list();
            ...
            ...
        }
    }

    return data;
}

Now, when I call the REST service "getGraphData" once using POSTMAN etc. it works fine without any issue. But when I simulate concurrent call to this rest service using I get following error

Caused by: org.hibernate.AssertionFailure: possible non-threadsafe access to the session
at org.hibernate.engine.internal.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:130)
at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:1108)
at org.hibernate.loader.Loader.processResultSet(Loader.java:964)
at org.hibernate.loader.Loader.doQuery(Loader.java:911)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:342)
at org.hibernate.loader.Loader.doList(Loader.java:2526)
at org.hibernate.loader.Loader.doList(Loader.java:2512)
at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2342)
at org.hibernate.loader.Loader.list(Loader.java:2337)
at org.hibernate.loader.hql.QueryLoader.list(QueryLoader.java:495)
at org.hibernate.hql.internal.ast.QueryTranslatorImpl.list(QueryTranslatorImpl.java:356)
at org.hibernate.engine.query.spi.HQLQueryPlan.performList(HQLQueryPlan.java:195)
at org.hibernate.internal.SessionImpl.list(SessionImpl.java:1269)
at org.hibernate.internal.QueryImpl.list(QueryImpl.java:101)
at com.cts.foodSafety.model.dao.impl.UnitDAOImpl.getGraphData(UnitDAOImpl.java:255)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:317)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
at org.springframework.aop.framework.adapter.MethodBeforeAdviceInterceptor.invoke(MethodBeforeAdviceInterceptor.java:51)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.aspectj.AspectJAfterAdvice.invoke(AspectJAfterAdvice.java:42)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:91)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
at com.sun.proxy.$Proxy51.getGraphData(Unknown Source)
at com.cts.foodSafety.delegate.UnitDelegate.getGraphData(UnitDelegate.java:39)
at com.cts.foodSafety.delegate.UnitDelegate$$FastClassByCGLIB$$aac35d0d.invoke(<generated>)
at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:698)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
at org.springframework.aop.framework.adapter.MethodBeforeAdviceInterceptor.invoke(MethodBeforeAdviceInterceptor.java:51)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.aspectj.AspectJAfterAdvice.invoke(AspectJAfterAdvice.java:42)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:91)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:631)
at com.cts.foodSafety.delegate.UnitDelegate$$EnhancerByCGLIB$$75af66.getGraphData(<generated>)
at com.cts.foodSafety.service.impl.UnitServiceImpl.getGraphData(UnitServiceImpl.java:108)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:317)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
at org.springframework.aop.framework.adapter.MethodBeforeAdviceInterceptor.invoke(MethodBeforeAdviceInterceptor.java:51)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.aspectj.AspectJAfterAdvice.invoke(AspectJAfterAdvice.java:42)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.aspectj.AspectJAfterThrowingAdvice.invoke(AspectJAfterThrowingAdvice.java:55)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:96)
at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:260)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:94)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:91)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
at com.sun.proxy.$Proxy72.getGraphData(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.apache.cxf.service.invoker.AbstractInvoker.performInvocation(AbstractInvoker.java:180)
at org.apache.cxf.service.invoker.AbstractInvoker.invoke(AbstractInvoker.java:96)

Client that I used to make concurrent request is as below

public class RestClient implements Runnable{

private String i;

public RestClient(String x) {
    i=x;
}
public static void main(String[] args) {

    for(int i =1;i<=2;i++) {
        Thread t = new Thread(new RestClient(String.valueOf(i)));
        t.start();
    }
}

@Override
public void run() {
    System.out.println("started " + i);
      try {

            URL url = new URL(" http://localhost:8080/fs/services/units/getGraphData/Freezer");
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("GET");
            conn.setRequestProperty("Accept", "application/json");

            if (conn.getResponseCode() != 204) {
                throw new RuntimeException("Failed : HTTP error code : "
                        + conn.getResponseCode());
            }

Any pointers/suggestions ? I have gone through a lot of material on sessions and transaction management in Spring+hibernate. But I am not able to get my head around this problem.

Answer 1

I think, that if you use Hibernate like that, then you should acquire the session by calling getSession(false) instead so as to ensure you have the session bound to the transaction.

This is explained in chapter Implementing Spring-based DAOs without callbacks in Spring documentation : such code will usually pass false as the value of the getSession(..) methods allowCreate argument, to enforce running within a transaction (which avoids the need to close the returned Session, as its lifecycle is managed by the transaction).