编写一段java代码，实现在linux和Windows操作系统下计算本系统的网络带宽占有率，不使用Android包

下面是一段Java代码，用于计算Linux和Windows操作系统下的网络带宽占用率：

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

public class NetworkBandwidth {

    public static void main(String[] args) throws IOException {
        String os = System.getProperty("os.name");
        if (os.startsWith("Windows")) {
            // Windows系统下的网络带宽占用率计算
            ProcessBuilder builder = new ProcessBuilder("netstat", "-e");
            Process process = builder.start();
            BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
            String line;
            while ((line = reader.readLine()) != null) {
                if (line.startsWith("Bytes")) {
                    String[] tokens = line.split("\\s+");
                    long sent = Long.parseLong(tokens[1]);
                    long received = Long.parseLong(tokens[4]);
                    System.out.println("Sent: " + sent + " bytes, Received: " + received + " bytes");
                    break;
                }
            }
            process.destroy();
        } else if (os.startsWith("Linux")) {
            // Linux系统下的网络带宽占用率计算
            ProcessBuilder builder = new ProcessBuilder("cat", "/proc/net/dev");
            Process process = builder.start();
            BufferedReader reader = new BufferedReader(new InputStreamReader(process.getInputStream()));
            String line;
            while ((line = reader.readLine()) != null) {
                if (line.contains(":") && !line.contains("lo:")) {
                    String[] tokens = line.trim().split("\\s+");
                    long received = Long.parseLong(tokens[1]);
                    long sent = Long.parseLong(tokens[9]);
                    System.out.println("Received: " + received + " bytes, Sent: " + sent + " bytes");
                }
            }
            process.destroy();
        } else {
            // 不支持其他操作系统
            System.out.println("不支持的操作系统");
        }
    }
}

该代码使用了不同的命令行工具来获取网络统计信息，并解析出发送和接收的字节数。在Windows下，使用了`netstat -e`命令，而在Linux下，使用了`cat /proc/net/dev`命令。我们可以根据不同的操作系统来执行相应的命令，并计算出网络带宽占用率。