这段代码将现有文件的权限转换为完全权限0777：

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.attribute.PosixFilePermissions;

public class testFile {
    public static void main(String[] args) throws SecurityException, IOException {
        String dir= "path to your file/test.txt";  
        Path path = Paths.get(dir);
        try {
            // permission 0777 
            Files.setPosixFilePermissions(path, PosixFilePermissions.fromString("rwxrwxrwx"));
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }