I have created this method which firsts checks if a URL is valid, and then checks if it links to an image or if it is a youtube video. My program fails when it gets to the 

```
String contentType = connection.getHeaderField("Content-Type"); 

```

portion of the method. Why is this happening?

Also, is it extraneous to check if its a valid URL using URLUtil.isValidUrl() as well as creating a connection and attempting to open that connection.

```
private boolean checkContent() {
    //check if valid image
    boolean img = false;
    boolean youtube = false;
    if(URLUtil.isValidUrl(imageAddress)) {
        URLConnection connection = null;
        try {
            connection = new URL(imageAddress).openConnection();
        } catch (IOException e) {
            e.printStackTrace();
        }
        String contentType = connection.getHeaderField("Content-Type");
        img = contentType.startsWith("image/");

        if(!img) {
            // Check host of url if youtube exists
            Uri uri = Uri.parse(imageAddress);
            if ("www.youtube.com".equals(uri.getHost()))
                youtube = true;
        }
    }
    return img || youtube;
}

```

I have internet permissions in my Manifest!!!

```
Process: com.example.robert.demo, PID: 11504
java.lang.IllegalStateException: Could not execute method of the activity
        at android.view.View$1.onClick(View.java:4020)
        at android.view.View.performClick(View.java:4780)
        at android.view.View$PerformClick.run(View.java:19866)
        at android.os.Handler.handleCallback(Handler.java:739)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:135)
        at android.app.ActivityThread.main(ActivityThread.java:5257)
        at java.lang.reflect.Method.invoke(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:372)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

java.lang.reflect.InvocationTargetException
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at android.view.View$1.onClick(View.java:4015)
            at android.view.View.performClick(View.java:4780)
            at android.view.View$PerformClick.run(View.java:19866)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5257)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
     Caused by: android.os.NetworkOnMainThreadException
            at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1147)
            at java.net.InetAddress.lookupHostByName(InetAddress.java:418)
            at java.net.InetAddress.getAllByNameImpl(InetAddress.java:252)
            at java.net.InetAddress.getAllByName(InetAddress.java:215)
            at com.android.okhttp.HostResolver$1.getAllByName(HostResolver.java:29)
            at com.android.okhttp.internal.http.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:232)
            at com.android.okhttp.internal.http.RouteSelector.next(RouteSelector.java:124)
            at com.android.okhttp.internal.http.HttpEngine.connect(HttpEngine.java:272)
            at com.android.okhttp.internal.http.HttpEngine.sendRequest(HttpEngine.java:211)
            at com.android.okhttp.internal.http.HttpURLConnectionImpl.execute(HttpURLConnectionImpl.java:382)
            at com.android.okhttp.internal.http.HttpURLConnectionImpl.getResponse(HttpURLConnectionImpl.java:332)
            at com.android.okhttp.internal.http.HttpURLConnectionImpl.getHeaderField(HttpURLConnectionImpl.java:161)
            at com.example.robert.demo.Demo.checkContent(Demo.java:110)
            at com.example.robert.demo.Demo.submitFile(Demo.java:89)
            at com.example.robert.demo.Demo.submitClick(Demo.java:65)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at android.view.View$1.onClick(View.java:4015)
            at android.view.View.performClick(View.java:4780)
            at android.view.View$PerformClick.run(View.java:19866)
            at android.os.Handler.handleCallback(Handler.java:739)
            at android.os.Handler.dispatchMessage(Handler.java:95)
            at android.os.Looper.loop(Looper.java:135)
            at android.app.ActivityThread.main(ActivityThread.java:5257)
            at java.lang.reflect.Method.invoke(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:372)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)

```