android项目中的J2ME类

Question

I copied my port scanner class to my android project without changing anything in source code. Eclipse didn't complain about code, but my code just doesnt seem to work correctly in android. Here is my whole portscanner code.

import java.net.InetSocketAddress;
import java.net.Socket;
import java.util.ArrayList;
import java.util.Collection;
import java.util.LinkedList;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;


public class PortScanner {

    private final String ip;
    private final int sPort, ePort, timeout, poolSize;
    private ArrayList<Integer> openPorts = new ArrayList();
    private final ExecutorService es;
    private Collection<Future<?>> futures = new LinkedList<>();


    public PortScanner(String ip, int sPort, int ePort, int timeout, int poolSize) {
        this.ip = ip;
        this.sPort = sPort;
        this.ePort = ePort;
        this.timeout = timeout;
        this.poolSize = poolSize;
        es = Executors.newFixedThreadPool(this.poolSize);

    }

    public ArrayList<Integer> getPorts() {
        return openPorts;
    }

    public void runScanner() {

        for (int startPort = sPort; startPort <= ePort; startPort++) {
            futures.add(es.submit(new Check(ip, startPort, timeout)));
        }

        es.shutdown();

    }

    private class Check implements Runnable { //  BEGININ OF INNER CLASS

        private String ip;
        private int port, timeout;

        private Check(String ip, int port, int timeout) {
            this.ip = ip;
            this.port = port;
            this.timeout = timeout;
        }

        @Override
        public void run() {

            try {
                Socket socket = new Socket();
                socket.connect(new InetSocketAddress(ip, port), timeout);
                socket.close();
                openPorts.add(port);
            } catch (Exception ex) {
            }
        }
    }                                       // END OF INNER CLASS
}

I tested my code in several different ways, and its sure that only thing that doesnt work correctly is inner classes run method, because when i add some ports manually to array list they do print, but when I lat my scanner add them it return always empty. Same port scan code works perfect on desktop. Does anyone know what am I doing wrong?

Answer 1

Not sure if it's the problem you have, but you're adding things to an ArrayList, which is not thread-safe, from multiple threads, without any kind of synchronization. This will lead to erratic behavior.

Also, you don't show how and when you display the content of this list. Calling code has no way to know when the scanning ends, so if you ask for the list right after the runScanner() has been called, there's a good chance that none of the scanning task has finished executing yet. BTW, why add futures to a list of futures if you never use this list?

Answer 2

Have you checked the exceptions? If exception threw before the socket added to openPorts, you will get an empty array list. And you didn't print the exception stack when the exception caught -- I also meet the similar problem when I forget to print an error log in the exception -catch.

        try {
            Socket socket = new Socket();
            socket.connect(new InetSocketAddress(ip, port), timeout);
            socket.close();
            openPorts.add(port);
        } catch (Exception ex) {
            //It's better to do something at least print an error log
            ex.printStackTrace();
        }