这会与Pro卫兵有关吗？--在查询数据存储时神秘的"NullPonterException“，还有”缺失“类。

Question

我开发了一个简单的应用程序来将数据保存到google应用引擎的数据存储中，然后调用数据存储并列出所有实体。

虽然我能够将数据存储在数据存储中，但我无法“查询”数据存储。

当我试图构建我的查询时，我会得到一个错误："java.lang.NullPointerException:没有为这个线程注册任何API环境。“

这发生在这一行上，不管我把它放在哪里：

Query query = new Query("myStoredBean");

注意:在调用上面的代码行之前，我确实验证了数据存储连接是打开的和有效的。

此外，除了nullpointerexception之外，我的logcat还报告了一些奇怪的问题，我不知道如何解决这些问题：

10-01 18:11:38.884  32537-32537/com.myApp.MyModule W/dalvikvm﹕ Link of class 'Lcom/google/appengine/repackaged/com/google/io/protocol/ProtocolMessage;' failed
10-01 18:11:38.884  32537-32537/com.myApp.MyModule W/dalvikvm﹕ Unable to resolve superclass of Lcom/google/apphosting/api/DatastorePb$Transaction; (2168)
10-01 18:11:38.884  32537-32537/com.myApp.MyModule W/dalvikvm﹕ Link of class 'Lcom/google/apphosting/api/DatastorePb$Transaction;' failed
10-01 18:11:38.884  32537-32537/com.myApp.MyModule E/dalvikvm﹕ Could not find class 'com.google.apphosting.api.DatastorePb$Transaction', referenced from method com.google.appengine.api.datastore.BaseDatastoreServiceImpl.a
10-01 18:11:38.884  32537-32537/com.myApp.MyModule W/dalvikvm﹕ VFY: unable to resolve new-instance 2597 (Lcom/google/apphosting/api/DatastorePb$Transaction;) in Lcom/google/appengine/api/datastore/BaseDatastoreServiceImpl;
10-01 18:11:38.884  32537-32537/com.myApp.MyModule W/dalvikvm﹕ Link of class 'Lcom/google/appengine/repackaged/com/google/io/protocol/ProtocolMessage;' failed
10-01 18:11:38.884  32537-32537/com.myApp.MyModule W/dalvikvm﹕ Unable to resolve superclass of Lcom/google/apphosting/api/DatastorePb$Transaction; (2168)
10-01 18:11:38.884  32537-32537/com.myApp.MyModule W/dalvikvm﹕ Link of class 'Lcom/google/apphosting/api/DatastorePb$Transaction;' failed
10-01 18:11:38.884  32537-32537/com.myApp.MyModule W/dalvikvm﹕ Link of class 'Lcom/google/appengine/repackaged/com/google/io/protocol/ProtocolMessage;' failed
10-01 18:11:38.884  32537-32537/com.myApp.MyModule W/dalvikvm﹕ Unable to resolve superclass of Lcom/google/apphosting/api/DatastorePb$PutRequest; (2168)
10-01 18:11:38.884  32537-32537/com.myApp.MyModule W/dalvikvm﹕ Link of class 'Lcom/google/apphosting/api/DatastorePb$PutRequest;' failed
10-01 18:11:38.884  32537-32537/com.myApp.MyModule E/dalvikvm﹕ Could not find class 'com.google.apphosting.api.DatastorePb$PutRequest', referenced from method com.google.appengine.api.datastore.AsyncDatastoreServiceImpl.a
10-01 18:11:38.884  32537-32537/com.myApp.MyModule W/dalvikvm﹕ VFY: unable to resolve new-instance 2568 (Lcom/google/apphosting/api/DatastorePb$PutRequest;) in Lcom/google/appengine/api/datastore/AsyncDatastoreServiceImpl;
10-01 18:11:38.884  32537-32537/com.myApp.MyModule W/dalvikvm﹕ Link of class 'Lcom/google/appengine/repackaged/com/google/io/protocol/ProtocolMessage;' failed
10-01 18:11:38.884  32537-32537/com.myApp.MyModule W/dalvikvm﹕ Unable to resolve superclass of Lcom/google/apphosting/api/DatastorePb$PutRequest; (2168)
10-01 18:11:38.884  32537-32537/com.myApp.MyModule W/dalvikvm﹕ Link of class 'Lcom/google/apphosting/api/DatastorePb$PutRequest;' failed
10-01 18:11:38.884  32537-32537/com.myApp.MyModule W/dalvikvm﹕ Link of class 'Lcom/google/appengine/repackaged/com/google/io/protocol/ProtocolMessage;' failed
10-01 18:11:38.884  32537-32537/com.myApp.MyModule W/dalvikvm﹕ VFY: unable to find class referenced in signature (Lcom/google/appengine/repackaged/com/google/io/protocol/ProtocolMessage;)
10-01 18:11:38.884  32537-32537/com.myApp.MyModule W/dalvikvm﹕ Link of class 'Lcom/google/appengine/repackaged/com/google/io/protocol/ProtocolMessage;' failed
10-01 18:11:38.884  32537-32537/com.myApp.MyModule W/dalvikvm﹕ Unable to resolve superclass of Lcom/google/apphosting/api/DatastorePb$DeleteRequest; (2168)
10-01 18:11:38.884  32537-32537/com.myApp.MyModule W/dalvikvm﹕ Link of class 'Lcom/google/apphosting/api/DatastorePb$DeleteRequest;' failed
10-01 18:11:38.884  32537-32537/com.myApp.MyModule E/dalvikvm﹕ Could not find class 'com.google.apphosting.api.DatastorePb$DeleteRequest', referenced from method com.google.appengine.api.datastore.AsyncDatastoreServiceImpl$1.a

知道怎么解决这个问题吗？我正在使用android和最新的应用程序引擎api。

此外，我有一个核心应用程序中断错误出现在上面，所引用的行是当我初始化“查询”对象时：

10-03 10:25:17.844  16385-16385/com.myapp.myModule E/AndroidRuntime﹕ FATAL EXCEPTION: main
    Process: com.myapp.myModule, PID: 16385
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.myapp.myModule/com.myapp.myModule.MainActivityWithSwipeableTabs}: java.lang.NullPointerException
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2585)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2641)
            at android.app.ActivityThread.access$800(ActivityThread.java:156)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1355)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:157)
            at android.app.ActivityThread.main(ActivityThread.java:5867)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:674)
            at dalvik.system.NativeStart.main(Native Method)
     Caused by: java.lang.NullPointerException
            at com.myapp.myModule.MainActivityWithSwipeableTabs.onCreate(SourceFile:66)
            at android.app.Activity.performCreate(Activity.java:5312)
            at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1111)
            at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2541)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2641)
            at android.app.ActivityThread.access$800(ActivityThread.java:156)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1355)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:157)
            at android.app.ActivityThread.main(ActivityThread.java:5867)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:674)
            at dalvik.system.NativeStart.main(Native Method)

我还试图定位android的“订单和导出”功能，我认为它现在基本上位于项目结构部分。我不知道里面有什么会影响这个错误..。

Answer 1

我有一个像这样的应用程序曾经工作过。下面是我的Endpoint类中用于查询数据存储的API方法。

     @Api(name = "myendpoint", namespace = @ApiNamespace(ownerDomain = "domain.com", ownerName =                    "domain.com.com", packagePath = "myPackage"))
 public class MyEndpoint {

    /**
     * This method lists all the entities inserted in datastore.
      * It uses HTTP GET method and paging support.
 *
 * @return A CollectionResponse class containing the list of all entities
 * persisted and a cursor to the next page.
 */
@SuppressWarnings({ "unchecked", "unused" })
@ApiMethod(name = "listStuff")
public CollectionResponse<Stuff> listStuff(
        @Nullable @Named("cursor") String cursorString,
        @Nullable @Named("limit") Integer limit) {

    EntityManager mgr = null;
    Cursor cursor = null;
    List<Stuff> execute = null;

    try {
        mgr = getEntityManager();
        Query query = mgr
                .createQuery("select from Stuff as Stuff");
        if (cursorString != null && cursorString != "") {
            cursor = Cursor.fromWebSafeString(cursorString);
            query.setHint(JPACursorHelper.CURSOR_HINT, cursor);
        }

        if (limit != null) {
            query.setFirstResult(0);
            query.setMaxResults(limit);
        }

        execute = (List<Stuff>) query.getResultList();
        cursor = JPACursorHelper.getCursor(execute);
        if (cursor != null)
            cursorString = cursor.toWebSafeString();

        // Tight loop for fetching all entities from datastore and accomodate
        // for lazy fetch.
        for (Stuff obj : execute)
            ;
    } finally {
        mgr.close();
    }

    return CollectionResponse.<Stuff> builder().setItems(execute)
            .setNextPageToken(cursorString).build();
}

我用这个代码从一个AsyncTask调用了这个方法。

Myendpoint.Builder endpointBuilder = new Myendpoint.Builder(
                AndroidHttp.newCompatibleTransport(), new JacksonFactory(),
                null);
        endpointBuilder =     CloudEndpointUtils.updateBuilder(endpointBuilder).setApplicationName(MainActivity.APPLICATION_NAME);

        endpoint = endpointBuilder.build();

        try {
             result = endpoint.listStuff().execute();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            // SynchKey = 0;
            // result = null;
        }

        return result;

Answer 2

据这一讨论称，

You MUST run the application as a Web Application to be able to activate the App Engine environment with the Datastore that you need for JDO.

你能试试看它是否有效吗？