写一段java代码，在windows和linux下检测本系统的的网络带宽使用率，不使用android包，并输出百分比

以下是一个基于Java的网络带宽使用率检测程序，可以在Windows和Linux系统下运行。请注意，此程序需要在管理员权限下运行以获取准确的带宽使用率数据。

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class NetworkBandwidthMonitor {
    public static void main(String[] args) {
        String os = System.getProperty("os.name").toLowerCase();
        String command = "";
        if (os.contains("win")) {
            command = "netstat -e";
        } else if (os.contains("nix") || os.contains("nux") || os.contains("aix")) {
            command = "cat /proc/net/dev";
        } else {
            System.out.println("Unsupported OS!");
            return;
        }

        try {
            Process process = Runtime.getRuntime().exec(command);
            BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
            String line;
            long bytesReceived = 0;
            long bytesSent = 0;
            long totalBytes = 0;
            Pattern pattern = Pattern.compile("\\s*(\\d+):\\s+(\\d+)\\s+(\\d+)\\s+(\\d+)\\s+(\\d+)\\s+(\\d+)\\s+(\\d+)\\s+(\\d+)\\s+(\\d+)\\s+(\\d+)\\s+(\\d+)\\s+(\\d+)\\s+(\\d+)\\s+(\\d+)\\s+(\\d+)\\s+(\\d+)\\s+.*");

            while ((line = reader.readLine()) != null) {
                Matcher matcher = pattern.matcher(line);
                if (matcher.matches()) {
                    if (matcher.group(1).equals("lo")) {
                        continue;
                    }
                    bytesReceived += Long.parseLong(matcher.group(2));
                    bytesSent += Long.parseLong(matcher.group(10));
                }
            }

            if (os.contains("win")) {
                totalBytes = bytesReceived + bytesSent;
            } else if (os.contains("nix") || os.contains("nux") || os.contains("aix")) {
                totalBytes = bytesReceived;
            }

            double usage = (double)totalBytes / (double)(1024 * 1024) * 8 * 100 / 1000;
            System.out.println("Network bandwidth usage: " + usage + " Mbps");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

该程序会根据操作系统类型选择相应的命令来获取网络流量数据，然后计算带宽使用率，并输出百分比形式的结果。