未能在升级App Engine Java SDK后打开写通道

Question

我试图升级我们用于Play的App Engine SDK的版本！ web应用程序从1.6.0到1.7.6。

升级之后，我们不再能够将文件写入本地开发服务器的blobstore。我们用下面的代码写入文件：

Image img = ImagesServiceFactory.makeImage(uploadedData); 

FileService fileService = FileServiceFactory.getFileService(); 
AppEngineFile file = fileService.createNewBlobFile("image/png", "__initial_data/" + vf.getName()); 

FileWriteChannel writeChannel = fileService.openWriteChannel(file, true); 
OutputStream output = Channels.newOutputStream(writeChannel); 

到fileService.openWriteChannel调用失败，出现以下堆栈跟踪：

Caused by: java.lang.NullPointerException 
    at com.google.appengine.tools.development.RequestEndListenerHelper.register(RequestEndListenerHelper.java:39) 
    at com.google.appengine.api.files.dev.LocalFileService.open(LocalFileService.java:247) 
    at com.google.appengine.tools.development.ApiProxyLocalImpl$AsyncApiCall.callInternal(ApiProxyLocalImpl.java:527) 
    at com.google.appengine.tools.development.ApiProxyLocalImpl$AsyncApiCall.call(ApiProxyLocalImpl.java:481) 
    at com.google.appengine.tools.development.ApiProxyLocalImpl$AsyncApiCall.call(ApiProxyLocalImpl.java:458) 
    at java.util.concurrent.Executors$PrivilegedCallable$1.run(Executors.java:461) 
    at java.security.AccessController.doPrivileged(Native Method) 
    at java.util.concurrent.Executors$PrivilegedCallable.call(Executors.java:458) 
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303) 
    at java.util.concurrent.FutureTask.run(FutureTask.java:138) 
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895) 
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918) 
    at java.lang.Thread.run(Thread.java:680) 

虽然应用程序引擎的SDK是开源的，我无法找到源用于这些特定于开发的类的文件，以查明内部发生了什么。

有谁知道从1.6.0版本开始，对象写入blobstore的实现细节是否发生了变化？

Answer 1

原来这是一个玩！具体问题。 play-gae模块实现了它自己的App Engine的LocalServerEnvironment，名为PlayDevEnvironment。这包含一个获取属性列表的方法。在App Engine的1.6.0和1.7.7版本之间进行了更改，需要返回其他属性。我们通过如下改变该类来解决它：

public class PlayDevEnvironment implements Environment, LocalServerEnvironment { 

    ... 

    @Override 
    public Map<String, Object> getAttributes() { 
     HashMap<String, Object> hashMap = new HashMap<String, Object>(); 
     hashMap.put(LocalEnvironment.REQUEST_END_LISTENERS, new ArrayList<RequestEndListener>()); 
     return hashMap; 
    } 
}