统计本网段有多少可用IP地址

• 1.获取本机IP地址。
• 代码示例：

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("本机ip地址：" + ip);
    }
}

• 2.使用Java执行ping命令
• 代码示例：

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("本次指令返回的消息是：");
        System.out.println(sb.toString());
    }

}

• 3.为了提高效率，使用多线程方式同时ping。 但是如果开启255个线程，又会因为网络端口太拥挤，会被判定为无法ping通。所以本例使用java自带线程池，线程池的连接数还不能太大，启动了15个线程。 等待所有的线程结束后打印出ping通了的ip地址。
• 代码示例：

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("本机ip地址：" + ip);
        System.out.println("网段是: " + 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("找到可连接的ip地址：" + testIP);
                        ips.add(testIP);
   
                    synchronized (number) {
                        System.out.println("已经完成:" + number.incrementAndGet() + " 个 ip 测试");
                    }
                }
   
            });
   
        }
   
        // 等待所有线程结束的时候，就关闭线程池
        threadPool.shutdown();
        //等待线程池关闭，但是最多等待1个小时
        if (threadPool.awaitTermination(1, TimeUnit.HOURS)) {
            System.out.println("如下ip地址可以连接");
            for (String theip : ips) {
                System.out.println(theip);
            }
            System.out.println("总共有:" + ips.size() + " 个地址");
   
        }
    }
   
    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");
            }
   
            //当有TTL出现的时候，就表示连通了
            reachable = sb.toString().contains("TTL");
            br.close();
            return reachable;
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            return false;
        }
    }
   
}

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