致命异常：AsyncTask＃1 java.lang.RuntimeException：在执行doInBackground（）并将图像发送到服务器时发生错误

Question

Guys I am developing an application on android which will transfer an image from android application to the server. I have implemented the server in JAVA and so far the application is only for the internal network purpose. I am having an issue of FATAL Exception in my code of ASYNC class and I am not getting what I have done wrong. Kindly help me out plz I will be very thankful to you people.

Android Application Code

public class TakeImage extends ActionBarActivity {
Socket client;
DatagramSocket clientSocket;
byte[] image;
byte[] img;
private Bitmap bitmap;
private ImageButton camera;
private ImageButton gallery;
ImageView targetImage;
NotificationManager nm;
Uri fileUri = null;
private Button process;
private static int TAKE_PICTURE = 1;
private static int FROM_GALLERY = 2;
public static final int MEDIA_TYPE_IMAGE = 1;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_take_image);
    //Notification Code
    nm=(NotificationManager)getSystemService(NOTIFICATION_SERVICE);
    //
    targetImage=(ImageView)findViewById(R.id.setImage);
    process=(Button)findViewById(R.id.process);
    process.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            //bitmap=BitmapFactory.decodeResource(getResources(), R.id.setImage);
            BitmapDrawable bd=(BitmapDrawable)targetImage.getDrawable();
            bitmap=bd.getBitmap();
            ByteArrayOutputStream stream = new ByteArrayOutputStream();
            bitmap.compress(Bitmap.CompressFormat.PNG, 90, stream);
            image = stream.toByteArray();
            SendMessage sendMessageTask = new SendMessage();
            sendMessageTask.execute();
            Toast.makeText(getApplicationContext(),"Processing",Toast.LENGTH_LONG).show();
        }
    });
}
private class SendMessage extends AsyncTask<Void, Void, Void> {

    @Override
    protected Void doInBackground(Void... params) {
        try {
            int c=0;
            InetAddress inet=InetAddress.getByName("192.168.1.4");
            client = new Socket("192.168.1.4", 4000); // connect to the server
            for(int i=0;i<image.length;i++) {
                img[c] = image[i];
                c++;
                    DatagramPacket packet;
                    packet = new DatagramPacket(img,img.length,inet,4000);
                    img = new byte[1024];
                    c = 0;
                    clientSocket.send(packet);
                    System.out.println("sent a mini-packet");

            }
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return null;
    }

}

Server Side Code

public class Server {
private static ServerSocket serverSocket;
private static Socket clientSocket;
private static InputStreamReader inputStreamReader;
private static BufferedReader bufferedReader;
private static String message;

public static void main(String[] args) throws UnknownHostException {
    try {
        serverSocket = new ServerSocket(4000); // Server socket

    } catch (IOException e) {
        System.out.println("Could not listen on port: 4444");
    }
            System.out.println("Server started. Listening to the port 4444");

    while (true) {
        try {

            clientSocket = serverSocket.accept(); // accept the client connection
            inputStreamReader = new InputStreamReader(clientSocket.getInputStream());
            bufferedReader = new BufferedReader(inputStreamReader); // get the client message
            message = bufferedReader.readLine();

            System.out.println(message);
            inputStreamReader.close();
            clientSocket.close();

        } catch (IOException ex) {
            System.out.println("Problem in message reading");
        }
    }

}

I have only implemented the server for just recieving the bytes not for converting it to Image.

Log Cat

04-04 07:13:27.630      920-981/com.example.ali.cottondiseasedetection E/AndroidRuntime﹕ FATAL EXCEPTION: AsyncTask #1
java.lang.RuntimeException: An error occured while executing doInBackground()
        at android.os.AsyncTask$3.done(AsyncTask.java:299)
        at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
        at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
        at java.util.concurrent.FutureTask.run(FutureTask.java:239)
        at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
        at java.lang.Thread.run(Thread.java:856)
 Caused by: java.lang.NullPointerException
        at com.example.ali.cottondiseasedetection.TakeImage$SendMessage.doInBackground(TakeImage.java:151)
        at com.example.ali.cottondiseasedetection.TakeImage$SendMessage.doInBackground(TakeImage.java:135)
        at android.os.AsyncTask$2.call(AsyncTask.java:287)
        at java.util.concurrent.FutureTask.run(FutureTask.java:234)

Answer 1

You need to initialize the array img before you assign anything to it.

img = new byte[1024];    
for(int i=0;i<image.length;i++) {
        img[c] = image[i];
        c++;
        DatagramPacket packet;
        packet = new DatagramPacket(img,img.length,inet,4000);
        img = new byte[1024];
        c = 0;
        clientSocket.send(packet);
        System.out.println("sent a mini-packet");
}