Jar在FileOutputStream中找不到txt文件

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class Main {
    public static void main(String[] args) {
        String fileName = "example.txt"; // txt文件名
        InputStream inputStream = Main.class.getResourceAsStream(fileName);
        if (inputStream != null) {
            try {
                OutputStream outputStream = new FileOutputStream(fileName);
                byte[] buffer = new byte[1024];
                int length;
                while ((length = inputStream.read(buffer)) != -1) {
                    outputStream.write(buffer, 0, length);
                }
                outputStream.close();
                inputStream.close();
                System.out.println("文件写入成功！");
            } catch (IOException e) {
                e.printStackTrace();
            }
        } else {
            System.out.println("找不到txt文件！");
        }
    }
}