File.canWrite和Files.isWritable在Linux上未提供正确的值

我有一个测试java程序

import java.io.File;
import java.nio.file.FileSystems;
import java.nio.file.Files;

public class TestFileReadOnly
{    
    public static void main(String[] args)
    {
        String filePath = args[0];
        File f = new File(filePath);

        System.out.println("File.canWrite() for file: " + filePath + ", is: " + f.canWrite());
        System.out.println("Files.isWritable() for file: " + filePath + ", is: " + Files.isWritable(FileSystems.getDefault().getPath(f.getParent(), f.getName())));
    }
}  

我使用root登录Linux并创建两个文件。

echo "test file" > /root/ro.txt
echo "test file" > /root/rw.txt
chmod 444 /root/ro.txt
chmod 777 /root/rw.txt

当我以这种方式执行测试程序时,输出总是不正确的

[root@xxx ~]# /jdk1.8.0_31/bin/java TestFileReadOnly /root/ro.txt
File.canWrite() for file: /root/ro.txt, is: true
Files.isWritable() for file: /root/ro.txt, is: true
[root@xxx ~]# /jdk1.8.0_31/bin/java TestFileReadOnly /root/rw.txt
File.canWrite() for file: /root/rw.txt, is: true
Files.isWritable() for file: /root/rw.txt, is: true

我基本上在寻找java代码来验证文件是否是只读的,但我无法使用上面的方法来实现它。然而,这在Windows上运行良好。我尝试使用jdk1.7.0_07、jdk1.7.0 _75和jdk1.8.0_31编译和执行,但结果是相同的。我们非常感谢为解决这一问题提供的任何帮助。

解决方案: 使用@Matteo的建议将PosixFileAttributes用于类UNIX平台。工作代码如下:

private boolean isFileReadOnly(File file)
{
    boolean isReadOnly = false;
    if (System.getProperty("os.name").startsWith("Windows"))
    {
        // All Windows versions
        isReadOnly = !file.canWrite();
    }
    else
    {
        // All Unix-like OSes.
        Path path = Paths.get(file.getParent(), file.getName());
        PosixFileAttributes attributes = null;
        try
        {
            attributes = Files.getFileAttributeView(path, PosixFileAttributeView.class).readAttributes();
        }
        catch (java.io.IOException e)
        {
            // File presence is guaranteed. Ignore
            e.printStackTrace();
        }

        if (attributes != null)
        {
            // A file is read-only in Linux only when it has 0444 permissions.
            Set<PosixFilePermission> permissions = attributes.permissions();

            if (!permissions.contains(PosixFilePermission.OWNER_WRITE)
                && !permissions.contains(PosixFilePermission.OWNER_EXECUTE)
                && !permissions.contains(PosixFilePermission.GROUP_WRITE)
                && !permissions.contains(PosixFilePermission.GROUP_EXECUTE)
                && !permissions.contains(PosixFilePermission.OTHERS_WRITE)
                && !permissions.contains(PosixFilePermission.OTHERS_EXECUTE))
            {
                isReadOnly = true;
            }
        }
    }
    return isReadOnly;
}