java实现ping功能，是否到达地址的返回值为什么总是false？

Question

这是测试代码：
import java.io.IOException;
import java.net.InetAddress;
import java.net.UnknownHostException;
public class TestPing {

/**
 * @param args
 */
public static void main(String[] args) {
    // TODO Auto-generated method stub
    String host = "www.baidu.com";
    int timeOut = 3000;
    try {
        boolean statu = InetAddress.getByName(host).isReachable(timeOut);
        System.out.println(statu);
    } catch (UnknownHostException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

}

Answer 1

换种方式实现吧，代码如下：
[quote]

/*
* * 能否ping通IP地址
*
* @param server IP地址
*
* @param timeout 超时时长(毫秒)
*
* @return true能ping通
*/
public static boolean pingServer(String server, int timeout)
{
BufferedReader in = null;
Runtime r = Runtime.getRuntime();

    String pingCommand = "ping " + server + " -n 1 -w " + timeout;
    try
    {
        Process p = r.exec(pingCommand);
        if (p == null)
        {
            return false;
        }
        in = new BufferedReader(new InputStreamReader(p.getInputStream()));
        String line = null;
        while ((line = in.readLine()) != null)
        {
            if (line.startsWith("Reply from"))
            {
                return true;
            }
        }

    }
    catch (Exception ex)
    {
        ex.printStackTrace();
        return false;
    }
    finally
    {
        try
        {
            in.close();
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
    }
    return false;
}

[/quote]