云端点更新方法在 mgr.close() 处崩溃

Question

我使用 google app engine for java 作为 android 应用程序和 iOS 应用程序的后端。问题是更新方法给出了一个空指针异常，而堆栈跟踪指向了 mgr.close() 方法。

我改变了原来的更新方法，用对象中传递的 blobkey 创建了一个图像服务 url。

服务 url 已成功创建并添加到对象中。

当我检查数据存储查看器时，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() 方法并得到了相同的结果。

所以当代码移动到 try/catch 语句以持久化或合并更新的对象时，它会失败并且实体管理器变为空。然后代码的下一行调用 mgr.close() 并记录空指针异常。

这里是有问题的方法：

    @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;
}

这里是日志信息：

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

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。如果您在数据存储中使用 jpa，则需要对实体端点中的每个更新方法进行这些更改。

这里是一些示例代码，展示了如何解决问题。

@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;
}

Answer 2

刷新管理器以执行创建/更新语句。

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