why the isReachable() method always return "false"?

Question

I want to get the delay time between 2 PC by this way:

currentTime = System.currentTimeMillis();           
isPinged = InetAddress.getByName("192.168.6.18").isReachable(2000);                 
currentTime = System.currentTimeMillis() - currentTime;
System.out.println("----"+isPinged+":"+currentTime);

but the results always be "false" except "localhost",I tried change the getByName("192.168.6.18") to the PC of LAN ,or the website like "www.facebook.com",but it has no effect

Have you used something like `ping` to ensure that you actually *can* reach the host in question? — chrylis -cautiouslyoptimistic-, Sep 09 '13 at 03:22
please refer to this question : http://stackoverflow.com/questions/9922543/why-does-inetaddress-isreachable-return-false-when-i-can-ping-the-ip-address — Nikita Took, Sep 09 '13 at 03:29
possible duplicate of [Problem with isReachable in InetAddress class](http://stackoverflow.com/questions/4779367/problem-with-isreachable-in-inetaddress-class) — Stephen C, Sep 09 '13 at 03:44

score -3 · Answer 1 · edited May 23 '17 at 11:57

-3

Use this method for Windows PC

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.InetAddress;
import java.net.UnknownHostException;

public Boolean ping(String ipaddress)
{
    Runtime runtime = Runtime.getRuntime();
    String cmds = "ping "+ipaddress;
    System.out.println(cmds);
    Process proc;
    try {
         proc = runtime.exec(cmds);
        proc.getOutputStream().close();
        InputStream inputstream = proc.getInputStream();
        InputStreamReader inputstreamreader = new InputStreamReader(inputstream);
        BufferedReader bufferedreader = new BufferedReader(inputstreamreader);
        String line;
        while ((line = bufferedreader.readLine()) != null) {
            if(line.contains("Reply from "+ipaddress+":"))
                {
                return true;    
                }
            }
        }catch (IOException e) {
    e.printStackTrace();
    }
    return false;
 }

for more details see Ping class

For PC other than windows use

  public Boolean IsReachable(String ipaddress) {
    try {            
        final InetAddress host = InetAddress.getByName(ipaddress);

        try {
            return host.isReachable(3000);
        } catch (IOException e) {
            e.printStackTrace();
        }
    } catch (UnknownHostException e) {
        e.printStackTrace();
    }
    return false;
}

edited May 23 '17 at 11:57

Community

1
1

answered Apr 06 '14 at 18:25

prem30488

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And what if his OS has no `ping` command? And what if the result from the `ping` does not contain English text? This is not scalable solution. – qqilihq Apr 06 '14 at 18:32
This is not a good general solution. (1) The `ping` command may not exist. (2) The `ping` output may not be in that format - OS X will say `x bytes from`, and on non-English versions of Windows the messages will be translated into the local language. – nobody Apr 06 '14 at 18:33
Falling back to the same method that the OP says isn't working is not helpful. – nobody Apr 06 '14 at 18:51
1

Also, beware that some implementations of `ping` do not terminate (until you send a signal such as SIGINT). Heavy use of this could fill your process table and end up generating a *lot* of traffic. – nobody Apr 06 '14 at 18:56
I agree with your knowledge but it does not make sense to vote down my answer... it contains a solution. – prem30488 Apr 06 '14 at 18:58
It is a very low quality solution, for all the reasons I have listed. Down-voting is appropriate for low quality answers. – nobody Apr 06 '14 at 19:01

why the isReachable() method always return "false"?

1 Answers1