[英]java.io.File(parent, child) does not work as expected
I am trying to construct a Java File object based on a user provided file name (could be absolute or relative) and a environment dependent base directory.我正在尝试根据用户提供的文件名(可以是绝对的或相对的)和依赖于环境的基目录构造一个 Java File 对象。 The java doc for java.io.File(File parent, String child) says the following:
java.io.File(File parent, String child) 的 java 文档说明如下:
If the child pathname string is absolute then it is converted into a relative pathname in a system-dependent way.
如果子路径名字符串是绝对的,那么它会以系统相关的方式转换为相对路径名。
That made me think that if I have the following code:这让我觉得如果我有以下代码:
public class TestClass {
public static void main(String[] args) throws IOException {
File file = new File(new File("C:/Temp"),"C:/Temp/file.txt");
System.out.println(file.getAbsolutePath());
}
}
the output would be输出将是
C:\Temp\file.txt
and then I'd be in business because it would not really matter anymore if the user provided an absolute or relative path.然后我会做生意,因为如果用户提供绝对路径或相对路径,这将不再重要。 But in fact, the output is
但实际上,输出是
C:\Temp\C:\Temp\file.txt
Which means I have to figure out the exact relative path (or at least test different options to see if the file exists).这意味着我必须找出确切的相对路径(或至少测试不同的选项以查看文件是否存在)。 Am I misunderstanding the JavaDoc?
我误解了 JavaDoc 吗?
If the child pathname string is absolute then it is converted into a relative pathname in a system-dependent way.
如果子路径名字符串是绝对的,那么它会以系统相关的方式转换为相对路径名。
I assume this means that even if you provide an absolute path, it will be converted to (in a system dependent way), and treated as, a relative path.我认为这意味着即使您提供了绝对路径,它也会被转换为(以依赖于系统的方式)并被视为相对路径。
Which means I have to figure out the exact relative path (or at least test different options to see if the file exists).
这意味着我必须找出确切的相对路径(或至少测试不同的选项以查看文件是否存在)。
Yes, I believe so.是的,我相信如此。
This could perhaps be easily done with这也许可以轻松完成
file.getAbsolutePath().startsWith(parent.getAbsolutePath());
to check if it is an absolute path to a directory in parent
, and检查它是否是
parent
目录中的绝对路径,以及
file.getAbsolutePath().substring(parent.getAbsolutePath().length());
to get the relative part.得到相对部分。
With your base directory expressed as a Path
, eg将您的基本目录表示为
Path
,例如
Path basePath = new File("C:/Temp").toPath();
you can use Path.resolve
to determine the Path
(or File
) for your fileName
, regardless of whether it is absolute or relative:您可以使用
Path.resolve
来确定您的fileName
的Path
(或File
),无论它是绝对的还是相对的:
Path path = basePath.resolve(fileName).normalize();
File file = path.toFile();
The additional normalize
here simply takes care of cleaning up any .
这里额外的
normalize
只负责清理任何.
or ..
from the path.或
..
从路径。
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