云端点更新方法在mgr.close()处崩溃

Question

我正在使用google作为iOS应用程序和android应用程序的后端。问题在于，update方法提供了一个空指针异常，而堆栈跟踪则指向mgr.close()方法。

我修改了原来的update方法，以创建一个为url服务的图像，其中包含在对象中传递的blobkey。

服务url被成功地创建并添加到对象中。

当我检查数据存储查看器时，该实体没有使用新信息进行更新，因此显然mgr.persist()方法失败了。我切换到了mgr.merge()方法，得到了相同的结果。

因此，当代码移动到try/catch语句以持久化或合并更新的对象时，它将失败，实体管理器将为空。然后，代码的下一行调用mgr.close()，并记录空指针异常。

下面是所讨论的方法：

    @ApiMethod(name = "updateParty")
    public Party updateParty(Party party) {
    if (party.getFlyerServingUrl() == null && party.getFlyerStr() != null) {
         blob = new BlobKey(party.getFlyerStr());        
            options = Builder.withBlobKey(blob);
            final String servingUrl = imagesService.getServingUrl(options);
            party.setFlyerServingUrl(servingUrl);
            if(party.getFlyerServingUrl() != null){
                log.info("Flyer serving url was generated and added to the party object.");
            }else{
                log.info("Flyer serving url was NOT generated.");
            }
            EntityManager mgr = getEntityManager();
            //update party with serving url             
            try {
                mgr.merge(party);           
            } finally {
                mgr.close();
            }
    }else{
        EntityManager mgr = getEntityManager();
        //update party with serving url             
        try {
            mgr.merge(party);           
        } finally {
            mgr.close();
        }

    }

    return party;
}

以下是日志信息：

com.google.api.server.spi.SystemService invokeServiceMethod: null
java.lang.NullPointerException
at com.google.appengine.api.datastore.KeyTranslator.convertToPb(KeyTranslator.java:49)
at com.google.appengine.api.datastore.EntityTranslator.convertToPb(EntityTranslator.java:50)
at com.google.appengine.api.datastore.AsyncDatastoreServiceImpl$4.toPb(AsyncDatastoreServiceImpl.java:203)
at com.google.appengine.api.datastore.AsyncDatastoreServiceImpl$4.toPb(AsyncDatastoreServiceImpl.java:180)
at com.google.appengine.api.datastore.Batcher$BatchIterator.<init>(Batcher.java:176)
at com.google.appengine.api.datastore.Batcher$2.<init>(Batcher.java:311)
at com.google.appengine.api.datastore.Batcher.getBatches(Batcher.java:311)
at com.google.appengine.api.datastore.AsyncDatastoreServiceImpl.doBatchPut(AsyncDatastoreServiceImpl.java:536)
at com.google.appengine.api.datastore.AsyncDatastoreServiceImpl.put(AsyncDatastoreServiceImpl.java:490)
at com.google.appengine.api.datastore.AsyncDatastoreServiceImpl.put(AsyncDatastoreServiceImpl.java:444)
at com.google.appengine.api.datastore.DatastoreServiceImpl.put(DatastoreServiceImpl.java:86)
at com.google.appengine.datanucleus.WrappedDatastoreService.put(WrappedDatastoreService.java:112)
at com.google.appengine.datanucleus.EntityUtils.putEntitiesIntoDatastore(EntityUtils.java:766)
at com.google.appengine.datanucleus.DatastorePersistenceHandler.insertObjectsInternal(DatastorePersistenceHandler.java:314)
at com.google.appengine.datanucleus.DatastorePersistenceHandler.insertObject(DatastorePersistenceHandler.java:218)
at org.datanucleus.state.JDOStateManager.internalMakePersistent(JDOStateManager.java:2381)
at org.datanucleus.state.JDOStateManager.flush(JDOStateManager.java:3778)
at org.datanucleus.ObjectManagerImpl.flushInternalWithOrdering(ObjectManagerImpl.java:3888)
at org.datanucleus.ObjectManagerImpl.flushInternal(ObjectManagerImpl.java:3811)
at org.datanucleus.ObjectManagerImpl.flush(ObjectManagerImpl.java:3751)
at org.datanucleus.ObjectManagerImpl.preCommit(ObjectManagerImpl.java:4141)
at org.datanucleus.ObjectManagerImpl.transactionPreCommit(ObjectManagerImpl.java:428)
at org.datanucleus.TransactionImpl.internalPreCommit(TransactionImpl.java:398)
at org.datanucleus.TransactionImpl.commit(TransactionImpl.java:287)
at org.datanucleus.ObjectManagerImpl.close(ObjectManagerImpl.java:1090)
at org.datanucleus.api.jpa.JPAEntityManager.close(JPAEntityManager.java:193)
at com.mastermindcode.theincrowd.PartyEndpoint.updateParty(PartyEndpoint.java:406)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:45)
at com.google.api.server.spi.SystemService.invokeServiceMethod(SystemService.java:359)
at com.google.api.server.spi.SystemServiceServlet.execute(SystemServiceServlet.java:124)
at com.google.api.server.spi.SystemServiceServlet.doPost(SystemServiceServlet.java:82)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
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 org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
at org.mortbay.jetty.servlet.ServletHandler$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 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$RequestHandler.headerComplete(HttpConnection.java:923)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
at com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:437)
at com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:444)
at com.google.tracing.CurrentContext.runInContext(CurrentContext.java:188)
at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:308)
at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:300)
at com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:441)
at java.lang.Thread.run(Thread.java:724)

Answer 1

刷新Manager以执行create/update语句。

try {
    mgr.merge(party);
    mgr.flush();           
} finally {
    mgr.close();
}

Answer 2

我自己解决了这个问题。问题在于云端点生成更新方法的方式。如果在数据存储中使用jpa，则需要对实体端点中的每个update方法进行这些更改。

下面是一些示例代码，展示了如何解决这个问题。

@ApiMethod(name = "updateMethod")
public Foo updateFoo(Foo foo) {
    EntityManager mgr = getEntityManager();
    EntityTransaction transaction = mgr.getTransaction(); //needed to get the object and change it.
    Foo updatedFoo = new Foo();
    try {
        transaction.begin();
        updatedFoo = mgr.find(Foo.class, foo.getKey().getId());
        updatedFoo.setFooProperty(foo.getFooProperty());//this is how you update the object's properties
        mgr.persist(updatedFoo);//persist the updated object
        transaction.commit();
        mgr.refresh(updatedFoo); //refresh the updated object in the datastore
    } finally {
        mgr.close();
    }
    return updatedFoo;
}