The Java server gets the client MAC address (only valid within the same network segment)

method one

Get client MAC address by executing CMD command

nbtstat -a 172.16.30.4

import java.io.IOException;
import java.io.InputStreamReader;
import java.io.LineNumberReader;

public class RemoteMacTest {
    public static String getMACAddress(String ip) {
        String str = "";
        String macAddress = "";
        try {
            Process p = Runtime.getRuntime().exec("nbtstat -a " + ip);
            InputStreamReader ir = new InputStreamReader(p.getInputStream());
            LineNumberReader input = new LineNumberReader(ir);
            for (int i = 1; i < 100; i++) {
                str = input.readLine();
                if (str != null) {
                    // if (str.indexOf("MAC Address") > 1) {
                    if (str.indexOf("MAC") > 1) {
                        macAddress = str.substring(str.indexOf("=") + 2, str.length());
                        break;
                    }
                }
            }
        } catch (IOException e) {
            e.printStackTrace(System.out);
        }
        return macAddress;
    }

    public static void main(String[] args) {
        System.out.println(getMACAddress("172.16.30.2"));
    }
}

Method Two

Obtain the MAC address based on the NetBIOS name service, send a UDP request to the client through the server, and parse the information returned by the client.
UDP/TCP port 137 provides NetBIOS name service to realize the mapping between computer name and IP address

import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;

/**
 * 主机A向主机B发送“UDP－NetBIOS－NS”询问包，即向主机B的137端口，发Query包来询问主机B的NetBIOS Names信息。 其 * 次，主机B接收到“UDP－NetBIOS－NS”询问包，假设主机B正确安装了NetBIOS服务........... 而且137端口开放， 则主机B会向主机A发送一个“UDP－NetBIOS－NS”应答包，即发Answer包给主机A。 并利用UDP(NetBIOS Name Service)来快速获取远程主机MAC地址的方法
 * @author WINDY
 */

public class RemoteMacTest {
    private String sRemoteAddr;
    private int iRemotePort = 137;
    private byte[] buffer = new byte[1024];
    private DatagramSocket ds = null;

    public RemoteMacTest(String strAddr) throws Exception {
        sRemoteAddr = strAddr;
        ds = new DatagramSocket();
    }

    protected final DatagramPacket send(final byte[] bytes) throws IOException {
        DatagramPacket dp = new DatagramPacket(bytes, bytes.length, InetAddress.getByName(sRemoteAddr), iRemotePort);
        ds.send(dp);
        return dp;
    }

    protected final DatagramPacket receive() throws Exception {
        DatagramPacket dp = new DatagramPacket(buffer, buffer.length);
        ds.receive(dp);
        return dp;
    }

    // 询问包结构:
    // Transaction ID 两字节（16位） 0x00 0x00
    // Flags 两字节（16位） 0x00 0x10
    // Questions 两字节（16位） 0x00 0x01
    // AnswerRRs 两字节（16位） 0x00 0x00
    // AuthorityRRs 两字节（16位） 0x00 0x00
    // AdditionalRRs 两字节（16位） 0x00 0x00
    // Name:array [1..34] 0x20 0x43 0x4B 0x41(30个) 0x00 ;
    // Type:NBSTAT 两字节 0x00 0x21
    // Class:INET 两字节（16位）0x00 0x01
    protected byte[] GetQueryCmd() throws Exception {
        byte[] t_ns = new byte[50];
        t_ns[0] = 0x00;
        t_ns[1] = 0x00;
        t_ns[2] = 0x00;
        t_ns[3] = 0x10;
        t_ns[4] = 0x00;
        t_ns[5] = 0x01;
        t_ns[6] = 0x00;
        t_ns[7] = 0x00;
        t_ns[8] = 0x00;
        t_ns[9] = 0x00;
        t_ns[10] = 0x00;
        t_ns[11] = 0x00;
        t_ns[12] = 0x20;
        t_ns[13] = 0x43;
        t_ns[14] = 0x4B;

        for (int i = 15; i < 45; i++) {
            t_ns[i] = 0x41;
        }

        t_ns[45] = 0x00;
        t_ns[46] = 0x00;
        t_ns[47] = 0x21;
        t_ns[48] = 0x00;
        t_ns[49] = 0x01;
        return t_ns;
    }

    // 表1 “UDP－NetBIOS－NS”应答包的结构及主要字段一览表
    // 序号 字段名 长度
    // 1 Transaction ID 两字节（16位）
    // 2 Flags 两字节（16位）
    // 3 Questions 两字节（16位）
    // 4 AnswerRRs 两字节（16位）
    // 5 AuthorityRRs 两字节（16位）
    // 6 AdditionalRRs 两字节（16位）
    // 7 Name<Workstation/Redirector> 34字节（272位）
    // 8 Type:NBSTAT 两字节（16位）
    // 9 Class:INET 两字节（16位）
    // 10 Time To Live 四字节（32位）
    // 11 Length 两字节（16位）
    // 12 Number of name 一个字节（8位）
    // NetBIOS Name Info 18×Number Of Name字节
    // Unit ID 6字节（48位
    protected final String GetMacAddr(byte[] brevdata) throws Exception {
        // 获取计算机名
        int i = brevdata[56] * 18 + 56;
        String sAddr = "";
        StringBuffer sb = new StringBuffer(17);
        // 先从第56字节位置，读出Number Of Names（NetBIOS名字的个数，其中每个NetBIOS Names Info部分占18个字节）
        // 然后可计算出“Unit ID”字段的位置＝56＋Number Of Names×18，最后从该位置起连续读取6个字节，就是目的主机的MAC地址。
        for (int j = 1; j < 7; j++) {
            sAddr = Integer.toHexString(0xFF & brevdata[i + j]);
            if (sAddr.length() < 2) {
                sb.append(0);
            }
            sb.append(sAddr.toUpperCase());
            if (j < 6) sb.append(':');
        }
        return sb.toString();
    }

    public final void close() {
        try {
            ds.close();
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    public final String GetRemoteMacAddr() throws Exception {
        byte[] bqcmd = GetQueryCmd();
        send(bqcmd);
        DatagramPacket dp = receive();
        String smac = GetMacAddr(dp.getData());
        close();

        return smac;
    }
    public static void main(String[] args) {
        try {
            RemoteMacTest test = new RemoteMacTest("172.16.30.2");
            System.out.println(test.GetRemoteMacAddr());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

refer to

Three methods of Java/JSP to obtain the MAC address of the client network card Analysis
of the principle and implementation of obtaining the MAC address based on the NetBIOS name service