Android with websocket communication (Node Websocket server and Android Java Client). Dosen't work on Android 4

I tried to use as a Android client Websocket - weberknecht with a thread to send every second a message to a Nodejs Websocket (js): Node WebSocket Server

It work fine on android 2 or 2.3.3, but when i trie on android 4 i get an error on websocket.connect();

Do you know why or what i am doing wrong?

My code is:

public class MainThread extends Thread {

    private boolean is_running;
    private URI url = null;
    private de.roderick.weberknecht.WebSocket websocket = null;

    public MainThread() {
        this.is_running = false;
        try {
            url = new URI("ws://192.168.1.88:8088/");
            websocket = new WebSocketConnection(url);

            websocket.setEventHandler(new WebSocketEventHandler() {
                public void onOpen(){
                    System.out.println("--open");
                }
                public void onMessage(WebSocketMessage message){
                    System.out.println("--received message: " + message.getText());
                }
                public void onClose(){
                    System.out.println("--close");
                }
            });
        } catch (WebSocketException wse) {
            wse.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
        } catch (URISyntaxException use) {
            use.printStackTrace();  //To change body of catch statement use File | Settings | File Templates.
        }

    }
    @Override
    public void run() {
        while(is_running){
            try {
                websocket.send("hello world");
                Thread.sleep(10000);
            }
            catch (WebSocketException wse) {
                wse.printStackTrace();
            } catch (InterruptedException e) {
                e.printStackTrace();  
            }

        }
    }

    public void set_running(boolean is_running) {
        if(is_running == true)
            try {
                websocket.connect();
                this.is_running = is_running;
            } catch (WebSocketException e) {
                System.out.println(e.toString());
                //e.printStackTrace();  
            }
    }
}

and the error I get on android 4:

ERROR/AndroidRuntime(562): FATAL EXCEPTION: main
        java.lang.RuntimeException: Unable to start activity ComponentInfo{com.biskis.test.websocket/com.biskis.test.websocket.GameActivity}: android.os.NetworkOnMainThreadException
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
        at android.app.ActivityThread.access$600(ActivityThread.java:123)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:4424)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
        at dalvik.system.NativeStart.main(Native Method)
        Caused by: android.os.NetworkOnMainThreadException
        at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1099)
        at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:84)
        at libcore.io.IoBridge.connectErrno(IoBridge.java:127)
        at libcore.io.IoBridge.connect(IoBridge.java:112)
        at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:192)
        at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:172)
        at java.net.Socket.startupSocket(Socket.java:566)
        at java.net.Socket.tryAllAddresses(Socket.java:127)
        at java.net.Socket.<init>(Socket.java:177)
        at java.net.Socket.<init>(Socket.java:149)
        at de.roderick.weberknecht.WebSocketConnection.createSocket(WebSocketConnection.java:238)
        at de.roderick.weberknecht.WebSocketConnection.connect(WebSocketConnection.java:83)
        at com.biskis.test.websocket.MainThread.set_running(MainThread.java:76)
        at com.biskis.test.websocket.GameActivity.onCreate(GameActivity.java:20)
        at android.app.Activity.performCreate(Activity.java:4465)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
        ... 11 more

Or do you know how to implement this in a better way to comunicate a client (java, android) to a server (nodejs, websocket) ?

Thank you.