使用Java实现简单的局域网设备扫描

要实现局域网设备扫描，可以使用Java中的Socket类和InetAddress类。

首先，需要获取本地IP地址，并将其转换为InetAddress类型：

InetAddress myAddress = InetAddress.getLocalHost();

接着，可以获取子网掩码并计算出局域网IP地址范围：

byte[] addressBytes = myAddress.getAddress();
int subnetMaskLength = 24; // 子网掩码长度，一般为24位
int subnetMask = 0xffffffff << (32 - subnetMaskLength);
int networkAddress = Byte.toUnsignedInt(addressBytes[0]) << 24 |
                     Byte.toUnsignedInt(addressBytes[1]) << 16 |
                     Byte.toUnsignedInt(addressBytes[2]) << 8;
int startAddress = networkAddress & subnetMask;
int endAddress = startAddress | ~subnetMask;

然后，可以使用Socket类来扫描局域网内的设备。对于每个IP地址，可以创建一个Socket并尝试连接到一个已知的端口（如80或443）。如果连接成功，则说明该IP地址对应的设备存在。

for (int i = startAddress + 1; i < endAddress; i++) {
    String ipAddress = String.format("%d.%d.%d.%d", 
        (i >> 24) & 0xff, (i >> 16) & 0xff, (i >> 8) & 0xff, i & 0xff);
    try (Socket socket = new Socket()) {
        socket.connect(new InetSocketAddress(ipAddress, 80), 1000); // 尝试连接80端口
        System.out.println(ipAddress + " is up");
    } catch (IOException ex) {
        // 无法连接，说明设备不存在或不可达
    }
}

完整代码如下：

import java.io.IOException;
import java.net.InetAddress;
import java.net.InetSocketAddress;
import java.net.Socket;

public class DeviceScanner {
    public static void main(String[] args) throws IOException {
        InetAddress myAddress = InetAddress.getLocalHost();
        byte[] addressBytes = myAddress.getAddress();
        int subnetMaskLength = 24; // 子网掩码长度，一般为24位
        int subnetMask = 0xffffffff << (32 - subnetMaskLength);
        int networkAddress = Byte.toUnsignedInt(addressBytes[0]) << 24 |
                             Byte.toUnsignedInt(addressBytes[1]) << 16 |
                             Byte.toUnsignedInt(addressBytes[2]) << 8;
        int startAddress = networkAddress & subnetMask;
        int endAddress = startAddress | ~subnetMask;
        for (int i = startAddress + 1; i < endAddress; i++) {
            String ipAddress = String.format("%d.%d.%d.%d", 
                (i >> 24) & 0xff, (i >> 16) & 0xff, (i >> 8) & 0xff, i & 0xff);
            try (Socket socket = new Socket()) {
                socket.connect(new InetSocketAddress(ipAddress, 80), 1000); // 尝试连接80端口
                System.out.println(ipAddress + " is up");
            } catch (IOException ex) {
                // 无法连接，说明设备不存在或不可达
            }
        }
    }
}