• 1.獲取本機IP地址。
• 程式碼示例：

package socket;

import java.net.InetAddress;
import java.net.UnknownHostException;

public class TestSocket {

    public static void main(String[] args) throws UnknownHostException {
        InetAddress host = InetAddress.getLocalHost();
        String ip =host.getHostAddress();
        System.out.println("本機ip地址：" + ip);
    }
}

• 2.使用Java執行ping命令
• 程式碼示例：

package socket;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class TestSocket {

    public static void main(String[] args) throws IOException {

        Process p = Runtime.getRuntime().exec("ping " + "192.168.2.106");
        BufferedReader br = new BufferedReader(new InputStreamReader(p.getInputStream()));
        String line = null;
        StringBuilder sb = new StringBuilder();
        while ((line = br.readLine()) != null) {
            if (line.length() != 0)
                sb.append(line + "\r\n");
        }
        System.out.println("本次指令返回的訊息是：");
        System.out.println(sb.toString());
    }

}

• 3.為了提高效率，使用多執行緒方式同時ping。 但是如果開啟255個執行緒，又會因為網路埠太擁擠，會被判定為無法ping通。所以本例使用java自帶執行緒池，執行緒池的連線數還不能太大，啟動了15個執行緒。 等待所有的執行緒結束後打印出ping通了的ip地址。
• 程式碼示例：

package socket;
   
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.InetAddress;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
   
public class TestSocket {
   
    public static void main(String[] args) throws IOException, InterruptedException {
        InetAddress host = InetAddress.getLocalHost();
        String ip = host.getHostAddress();
        String ipRange = ip.substring(0, ip.lastIndexOf('.'));
        System.out.println("本機ip地址：" + ip);
        System.out.println("網段是: " + ipRange);
   
        List<String> ips = Collections.synchronizedList(new ArrayList<>());
        ThreadPoolExecutor threadPool = new ThreadPoolExecutor(10, 15, 60, TimeUnit.SECONDS,
                new LinkedBlockingQueue<Runnable>());
        AtomicInteger number = new AtomicInteger();
        for (int i = 0; i < 255; i++) {
            String testIP = ipRange + "." + (i + 1);
            threadPool.execute(new Runnable() {
                @Override
                public void run() {
                    boolean reachable = isReachable(testIP);
                    if (reachable)
                        // System.out.println("找到可連線的ip地址：" + testIP);
                        ips.add(testIP);
   
                    synchronized (number) {
                        System.out.println("已經完成:" + number.incrementAndGet() + " 個 ip 測試");
                    }
                }
   
            });
   
        }
   
        // 等待所有執行緒結束的時候，就關閉執行緒池
        threadPool.shutdown();
        //等待執行緒池關閉，但是最多等待1個小時
        if (threadPool.awaitTermination(1, TimeUnit.HOURS)) {
            System.out.println("如下ip地址可以連線");
            for (String theip : ips) {
                System.out.println(theip);
            }
            System.out.println("總共有:" + ips.size() + " 個地址");
   
        }
    }
   
    private static boolean isReachable(String ip) {
        try {
            boolean reachable = false;
   
            Process p = Runtime.getRuntime().exec("ping -n 1 " + ip);
            BufferedReader br = new BufferedReader(new InputStreamReader(p.getInputStream()));
            String line = null;
            StringBuilder sb = new StringBuilder();
            while ((line = br.readLine()) != null) {
                if (line.length() != 0)
                    sb.append(line + "\r\n");
            }
   
            //當有TTL出現的時候，就表示連通了
            reachable = sb.toString().contains("TTL");
            br.close();
            return reachable;
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            return false;
        }
    }
   
}