Spring stomp socket - ios客户端实现

Question

我正在创建一个可以与Spring stomp websocket交互的ios应用程序，但我无法这样做。

Java代码：

配置：

Process: com.example.newtable.newtable, PID: 5668


java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.newtable.newtable/com.example.newtable.newtable.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference
                                                                                 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2416)
                                                                                 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
                                                                                 at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                                 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
                                                                                 at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                                 at android.os.Looper.loop(Looper.java:148)
                                                                                 at android.app.ActivityThread.main(ActivityThread.java:5417)
                                                                                 at java.lang.reflect.Method.invoke(Native Method)
                                                                                 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                                 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                                              Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.lang.String.length()' on a null object reference
                                                                                 at org.json.JSONTokener.nextCleanInternal(JSONTokener.java:116)
                                                                                 at org.json.JSONTokener.nextValue(JSONTokener.java:94)
                                                                                 at org.json.JSONArray.<init>(JSONArray.java:92)
                                                                                 at org.json.JSONArray.<init>(JSONArray.java:108)
                                                                                 at com.example.newtable.newtable.MainActivity.onCreate(MainActivity.java:65)
                                                                                 at android.app.Activity.performCreate(Activity.java:6237)
                                                                                 at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1107)
                                                                                 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2369)
                                                                                 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
                                                                                 at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                                                                                 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
                                                                                 at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                                 at android.os.Looper.loop(Looper.java:148) 
                                                                                 at android.app.ActivityThread.main(ActivityThread.java:5417) 
                                                                                 at java.lang.reflect.Method.invoke(Native Method) 
                                                                                 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                                                                                 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

控制器：

<websocket:message-broker application-destination-prefix="/app">
    <websocket:stomp-endpoint path="/ws">
    </websocket:stomp-endpoint>
    <websocket:simple-broker prefix="/topic"/>
  </websocket:message-broker>