提交时GAE Con​​currentModificationException

Question

我正在测试一个GAE应用程序，其中部署在localhost上的JPA由SDK提供的jetty（版本1.7.1）。 在每次提交时，框架都会引发ConcurrentModificationException，但该对象仍然存在于数据存储区中。 有什么我做错了吗？ Tnx提前

---

• 应用服务引擎的API-1.0-SDK-1.7.1
• DataNucleus将-API的JP-A-3.1.2
• datanucleus-core-3.1.2
• datanucleus-appengine-2.1.0-final

---

Transaction failed to commit
org.datanucleus.transaction.NucleusTransactionException: Transaction failed to commit
    at org.datanucleus.TransactionImpl.commit(TransactionImpl.java:365)
    at it.gustaff.core.PlaceRService.createPlace(PlaceRService.java:91)
    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 com.google.appengine.tools.development.agent.runtime.Runtime.invoke(Runtime.java:115)
    at com.sun.jersey.spi.container.JavaMethodInvokerFactory$1.invoke(JavaMethodInvokerFactory.java:60)
    at com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$TypeOutInvoker._dispatch(AbstractResourceMethodDispatchProvider.java:185)
    at com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:75)
    at com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:288)
    at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147)
    at com.sun.jersey.server.impl.uri.rules.ResourceClassRule.accept(ResourceClassRule.java:108)
    at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147)
    at com.sun.jersey.server.impl.uri.rules.RootResourceClassesRule.accept(RootResourceClassesRule.java:84)
    at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1469)
    at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1400)
    at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1349)
    at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1339)
    at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:416)
    at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:537)
    at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:708)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
    at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:35)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:60)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:125)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at com.google.appengine.tools.development.BackendServersFilter.doFilter(BackendServersFilter.java:97)
    at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
    at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
    at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
    at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
    at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
    at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
    at com.google.appengine.tools.development.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:94)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:370)
    at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
    at org.mortbay.jetty.Server.handle(Server.java:326)
    at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
    at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:938)
    at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:755)
    at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
    at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
    at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
    at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)
Caused by: java.util.ConcurrentModificationException
    at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
    at java.util.AbstractList$Itr.next(AbstractList.java:343)
    at com.google.appengine.datanucleus.DatastoreConnectionFactoryImpl$DatastoreManagedConnection.close(DatastoreConnectionFactoryImpl.java:146)
    at org.datanucleus.store.connection.ConnectionManagerImpl$2.transactionCommitted(ConnectionManagerImpl.java:296)
    at org.datanucleus.TransactionImpl.internalPostCommit(TransactionImpl.java:577)
    at org.datanucleus.TransactionImpl.commit(TransactionImpl.java:354)
    ... 51 more

---

<persistence-unit name="appengine-transactions-optional">
    <provider>org.datanucleus.api.jpa.PersistenceProviderImpl</provider>
    <class>it.gustaff.data.Place</class>
    <properties>
        <property name="datanucleus.NontransactionalRead" value="true"/>
        <property name="datanucleus.NontransactionalWrite" value="true"/>
        <property name="datanucleus.singletonEMFForName" value="true"/>
        <property name="datanucleus.ConnectionURL" value="appengine"/>
    </properties>
</persistence-unit>

---

public Place createPlace(Place p){

    EntityManager entityManager = EMF.get().createEntityManager();
    entityManager.getTransaction().begin();
    //avoid to persist a Place with an Id already set
    p.setId(null);
    entityManager.persist(p);
    ExecutionContext ec = (ExecutionContext) entityManager.getDelegate();
    ec.getTransaction().commit();
    entityManager.close();
    return p;
}

---

@Entity
public class Place {

    private String name;
    private String description;
    private String address;

    //omitted other getter/setter

    private com.google.appengine.api.datastore.Key id;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    public Key getId() {
        return id;
    }

    public void setId(Key id) {
        this.id = id;
    }
}

Answer 1

您不引用您的实体以及p.setId（null）正在执行的操作。除了你可以尝试的东西（找到真正的ConcurrentModificationException正在发生的地方）之外（类似的东西）用这个替换entityManager.getTransaction().commit()

ExecutionContext ec = (ExecutionContext)entityManager.getDelegate();
ec.getTransaction().commit();

如果抛出NucleusTransactionException然后打印出原因的堆栈跟踪并将其添加到您的问题中。原因在于真正的问题所在，如果它在GAE中出现问题则可以修复，否则如果它在您的代码中出现问题，那么您就知道它在哪里。