如何从本机Android连接到AMF web服务？

正在尝试使用本机Android应用程序中的一些旧AMF Web服务。 我包括了库：flex-messaging-core.jar和flex-messaging-common.jar

Android活动中的代码：

    AMFConnection amfConnection = new AMFConnection();
    try{
        String url = "http://example.com/cc/messagebroker/amf";
        amfConnection.connect(url);

        Object result = amfConnection.call("exampleService","foo", "bar");
        textView.setText(result.toString());
    } catch (Exception e) {
        Log.e(TAG, e.getMessage(),e);
    }
    amfConnection.close();

同样的amf连接在JavaSE中工作，可以得到正确的响应。但在安卓系统中，我有一个例外：

 java.lang.NullPointerException
 at com.android.okhttp.internal.http.HttpEngine.readResponse(HttpEngine.java:632)
 at com.android.okhttp.internal.http.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:347)
 at com.android.okhttp.internal.http.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:296)
 at com.android.okhttp.internal.http.HttpURLConnectionImpl.getResponseCode(HttpURLConnectionImpl.java:503)
 at flex.messaging.io.amf.client.AMFConnection.generateHttpResponseInfo(AMFConnection.java:633)
 at flex.messaging.io.amf.client.AMFConnection.call(AMFConnection.java:532)
 at com.example.jamesjin.myapplication2.MainActivity.tryAMF(MainActivity.java:42)
 at com.example.jamesjin.myapplication2.MainActivity.onCreate(MainActivity.java:33)
 at android.app.Activity.performCreate(Activity.java:5451)
 at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1093)
 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2392)
 at android.app.ActivityThread.access$900(ActivityThread.java:169)
 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1280)
 at android.os.Handler.dispatchMessage(Handler.java:102)
 at android.os.Looper.loop(Looper.java:146)
 at android.app.ActivityThread.main(ActivityThread.java:5487)
 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:1283)
 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1099)
 at dalvik.system.NativeStart.main(Native Method)

我也尝试了library，给出了相同的例外

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那么，如何解决此异常并从本机Android应用程序连接AMF Web服务？

此错误是因为我没有在AsyncTask中执行Web服务请求