public static final FileDescriptor in = standardStream(0);
public static final FileDescriptor out = standardStream(1);
public static final FileDescriptor err = standardStream(2); private static FileDescriptor standardStream(int fd) {FileDescriptor desc = new FileDescriptor();desc.handle = set(fd);return desc;
}
private static native long set(int d);

try {PrintWriter pw = new PrintWriter(new FileOutputStream(FileDescriptor.out)); pw.print("你好");pw.flush();pw.close();
} catch (Exception e) {
}

try {// 打开文件，获取文件描述符String fileName = "out.txt";FileOutputStream os = new FileOutputStream(fileName);FileDescriptor  fd = os.getFD();System.out.println("file name: " + fileName);//写数据入文件byte[] data = "你好".getBytes();os.write(data);System.out.println("data: " + data);// 刷新缓冲区,数据可能没有写入到磁盘 os.flush();// 阻塞直到数据缓冲区的数据全部写入磁盘,该方法返回后，数据已经写入到磁盘System.out.println("阻塞直到数据缓冲区的数据全部写入磁盘");fd.sync();// 关闭流
    os.close();
} catch (IOException e) {e.printStackTrace();
}

String fileName="file.txt";
try {  // 新建文件file.txt对应的FileOutputStream对象  FileOutputStream os1 = new FileOutputStream(fileName);  // 获取文件file.txt对应的FileDescriptor  FileDescriptor fd = os1.getFD();  // 根据FileDescriptor创建FileOutputStream对象  FileOutputStream os2 = new FileOutputStream(fd);  os1.write('a');    // 通过os1向file.txt中写入'a'  os2.write('b');    // 通过os1向file.txt中写入'b' if (fd!=null)  System.out.printf("fd(%s) is %s\n",fd, fd.valid()); System.out.println(os1.getFD()==os2.getFD()); //true
    os2.close();  os1.close();  } catch(IOException e) {  e.printStackTrace();
}

String fileName="file.txt";
try {  // 新建文件file.txt对应的FileOutputStream对象  FileOutputStream os1 = new FileOutputStream(fileName);           // 根据FileDescriptor创建FileOutputStream对象  FileOutputStream os2 = new FileOutputStream(fileName);  os1.write('a');    // 通过out1向file.txt中写入'a'  os2.write('b');   // 通过out1向file.txt中写入'b'
          System.out.println(os1.getFD()==os2.getFD());    //false
    os2.close();  os1.close();
} catch(IOException e) {  e.printStackTrace();
}