File.getCanonicalPath()和File.toPath().toRealPath()是否会产生不同的结果?它们似乎都做类似的事情,但文档从未明确说明它们应该做相同的事情。是否有一些边界情况我可以更倾向于使用其中一种方法?而File.getAbsolutePath()与Path.toAbsolutePath()又是如何运作的,它们是否应该以相同的方式工作?
File.getCanonicalPath()和File.toPath().toRealPath()是否会产生不同的结果?它们似乎都做类似的事情,但文档从未明确说明它们应该做相同的事情。是否有一些边界情况我可以更倾向于使用其中一种方法?而File.getAbsolutePath()与Path.toAbsolutePath()又是如何运作的,它们是否应该以相同的方式工作?
getAbsolutePath
和 getPath
没有验证,因此永远不会失败getCanonicalPath
当驱动器字母无效或与当前文件夹不同时,可能会得出无效结果toPath().toRealPath()
是在检查有效性,但是需要文件存在并且可以遵循或不遵循符号链接toPath()
足够安全,不需要文件存在.toPath().toAbsolutePath().normalize()
是最好的,而且不需要文件存在我在Windows中进行了类似于@John的测试。
@Test
public void testCanonical() throws IOException {
test("d:tarGet\\..\\Target", "File exist and drive letter is on the current one");
test("d:tarGet\\..\\Target\\.\\..\\", "File exist and drive letter is on the current one, but parent of current drive should exist");
test("d:tarGet\\non-existent\\..\\..\\Target\\.\\..\\", "Relative path contains non-existent file");
test("d:target\\\\file", "Double slash");
test("c:tarGet\\..\\Target\\.", "File doesn't exist and drive letter is on different drive than the current one");
test("l:tarGet\\..\\Target\\.\\..\\", "Drive letter doesn't exist");
test("za:tarGet\\..\\Target\\.\\..\\", "Drive letter is double so not valid");
test("d:tarGet|Suffix", "Path contains invalid chars in windows (|)");
test("d:tarGet\u0000Suffix", "Path contains invalid chars in both linux and windows (\\0)");
}
private void test(String filename, String message) throws IOException {
java.io.File file = new java.io.File(filename);
System.out.println("Use: " + filename + " -> " + message);
System.out.println("F-GET: " + Try.of(() -> file.getPath()));
System.out.println("F-ABS: " + Try.of(() -> file.getAbsolutePath()));
System.out.println("F-CAN: " + Try.of(() -> file.getCanonicalPath()));
System.out.println("P-TO: " + Try.of(() -> file.toPath()));
System.out.println("P-ABS: " + Try.of(() -> file.toPath().toAbsolutePath()));
System.out.println("P-NOR: " + Try.of(() -> file.toPath().normalize()));
System.out.println("P-NOR-ABS: " + Try.of(() -> file.toPath().normalize().toAbsolutePath()));
System.out.println("P-ABS-NOR: " + Try.of(() -> file.toPath().toAbsolutePath().normalize()));
System.out.println("P-REAL: " + Try.of(() -> file.toPath().toRealPath()));
System.out.println("");
}
Use: d:tarGet\..\Target -> File exist and drive letter is on the current one
F-GET: Success(d:tarGet\..\Target)
F-ABS: Success(d:\home\raiser\work\restfs\tarGet\..\Target)
F-CAN: Success(D:\home\raiser\work\restfs\target)
P-TO: Success(d:tarGet\..\Target)
P-ABS: Success(D:\home\raiser\work\restfs\tarGet\..\Target)
P-NOR: Success(d:Target)
P-NOR-ABS: Success(D:\home\raiser\work\restfs\Target)
P-ABS-NOR: Success(D:\home\raiser\work\restfs\Target)
P-REAL: Success(D:\home\raiser\work\restfs\target)
Use: d:tarGet\..\Target\.\..\ -> File exist and drive letter is on the current one, but parent of current drive should exist
F-GET: Success(d:tarGet\..\Target\.\..)
F-ABS: Success(d:\home\raiser\work\restfs\tarGet\..\Target\.\..)
F-CAN: Success(D:\home\raiser\work\restfs)
P-TO: Success(d:tarGet\..\Target\.\..)
P-ABS: Success(D:\home\raiser\work\restfs\tarGet\..\Target\.\..)
P-NOR: Success(d:)
P-NOR-ABS: Success(D:\home\raiser\work\restfs\)
P-ABS-NOR: Success(D:\home\raiser\work\restfs)
P-REAL: Success(D:\home\raiser\work\restfs)
Use: d:tarGet\non-existent\..\..\Target\.\..\ -> Relative path contains non-existent file
F-GET: Success(d:tarGet\non-existent\..\..\Target\.\..)
F-ABS: Success(d:\home\raiser\work\restfs\tarGet\non-existent\..\..\Target\.\..)
F-CAN: Success(D:\home\raiser\work\restfs)
P-TO: Success(d:tarGet\non-existent\..\..\Target\.\..)
P-ABS: Success(D:\home\raiser\work\restfs\tarGet\non-existent\..\..\Target\.\..)
P-NOR: Success(d:)
P-NOR-ABS: Success(D:\home\raiser\work\restfs\)
P-ABS-NOR: Success(D:\home\raiser\work\restfs)
P-REAL: Success(D:\home\raiser\work\restfs)
Use: d:target\\file -> Double slash
F-GET: Success(d:target\file)
F-ABS: Success(d:\home\raiser\work\restfs\target\file)
F-CAN: Success(D:\home\raiser\work\restfs\target\file)
P-TO: Success(d:target\file)
P-ABS: Success(D:\home\raiser\work\restfs\target\file)
P-NOR: Success(d:target\file)
P-NOR-ABS: Success(D:\home\raiser\work\restfs\target\file)
P-ABS-NOR: Success(D:\home\raiser\work\restfs\target\file)
P-REAL: Failure(java.nio.file.NoSuchFileException: D:\home\raiser\work\restfs\target\file)
Use: c:tarGet\..\Target\. -> File doesn't exist and drive letter is on different drive than the current one
F-GET: Success(c:tarGet\..\Target\.)
F-ABS: Success(c:\\tarGet\..\Target\.)
F-CAN: Success(C:\Target)
P-TO: Success(c:tarGet\..\Target\.)
P-ABS: Success(C:\tarGet\..\Target\.)
P-NOR: Success(c:Target)
P-NOR-ABS: Success(C:\Target)
P-ABS-NOR: Success(C:\Target)
P-REAL: Failure(java.nio.file.NoSuchFileException: C:\Target)
Use: l:tarGet\..\Target\.\..\ -> Drive letter doesn't exist
F-GET: Success(l:tarGet\..\Target\.\..)
F-ABS: Success(l:\tarGet\..\Target\.\..)
F-CAN: Success(L:\)
P-TO: Success(l:tarGet\..\Target\.\..)
P-ABS: Failure(java.io.IOError: java.io.IOException: Unable to get working directory of drive 'L')
P-NOR: Success(l:)
P-NOR-ABS: Failure(java.io.IOError: java.io.IOException: Unable to get working directory of drive 'L')
P-ABS-NOR: Failure(java.io.IOError: java.io.IOException: Unable to get working directory of drive 'L')
P-REAL: Failure(java.io.IOException: Unable to get working directory of drive 'L')
Use: za:tarGet\..\Target\.\..\ -> Drive letter is double so not valid
F-GET: Success(za:tarGet\..\Target\.\..)
F-ABS: Success(D:\home\raiser\work\restfs\za:tarGet\..\Target\.\..)
F-CAN: Success(D:\home\raiser\work\restfs)
P-TO: Failure(java.nio.file.InvalidPathException: Illegal char <:> at index 2: za:tarGet\..\Target\.\..)
P-ABS: Failure(java.nio.file.InvalidPathException: Illegal char <:> at index 2: za:tarGet\..\Target\.\..)
P-NOR: Failure(java.nio.file.InvalidPathException: Illegal char <:> at index 2: za:tarGet\..\Target\.\..)
P-NOR-ABS: Failure(java.nio.file.InvalidPathException: Illegal char <:> at index 2: za:tarGet\..\Target\.\..)
P-ABS-NOR: Failure(java.nio.file.InvalidPathException: Illegal char <:> at index 2: za:tarGet\..\Target\.\..)
P-REAL: Failure(java.nio.file.InvalidPathException: Illegal char <:> at index 2: za:tarGet\..\Target\.\..)
Use: d:tarGet|Suffix -> Path contains invalid chars in windows (|)
F-GET: Success(d:tarGet|Suffix)
F-ABS: Success(d:\home\raiser\work\restfs\tarGet|Suffix)
F-CAN: Failure(java.io.IOException: The filename, directory name, or volume label syntax is incorrect)
P-TO: Failure(java.nio.file.InvalidPathException: Illegal char <|> at index 8: d:tarGet|Suffix)
P-ABS: Failure(java.nio.file.InvalidPathException: Illegal char <|> at index 8: d:tarGet|Suffix)
P-NOR: Failure(java.nio.file.InvalidPathException: Illegal char <|> at index 8: d:tarGet|Suffix)
P-NOR-ABS: Failure(java.nio.file.InvalidPathException: Illegal char <|> at index 8: d:tarGet|Suffix)
P-ABS-NOR: Failure(java.nio.file.InvalidPathException: Illegal char <|> at index 8: d:tarGet|Suffix)
P-REAL: Failure(java.nio.file.InvalidPathException: Illegal char <|> at index 8: d:tarGet|Suffix)
一个规范路径是绝对且唯一的, 但在不同的系统上具有不同的含义。
一个规范路径名既是绝对的又是唯一的。规范形式的精确定义取决于系统。
真实路径是相对于系统而言的实际路径。您还必须传递是否处理符号链接,其中使用canonicalPath
隐式处理。
所以,是的,这两种方法可以返回不同的结果,但这实际上取决于你的系统。如果你需要一个唯一的东西,那么该方法的精确定义取决于实现,但通常它从此路径派生出一个绝对路径,该路径定位与此路径相同的文件,但名称元素表示目录和文件的实际名称。例如,如果文件系统上的文件名比较不区分大小写,则名称元素表示名称的实际大小写。此外,结果路径已删除冗余名称元素。
canonicalPath
是你最安全的选择,即使它不是一个Path
。import java.io.File;
public class FileExample {
public static void main(String[] args) throws Exception {
File file = new File("/TEMP/../TEMP/myfile.txt");
System.out.println("ABS: " + file.getAbsolutePath());
System.out.println(" TO: " + file.toPath());
System.out.println("GET: " + file.getPath());
System.out.println("CAN: " + file.getCanonicalPath());
}
}
ABS: C:\TEMP\..\TEMP\myfile.txt
TO: \TEMP\..\TEMP\myfile.txt
GET: \TEMP\..\TEMP\myfile.txt
CAN: C:\TEMP\myfile.txt
File file = new File("../test.txt"); // execute from /tmp/java/example
file.getAbsolutePath(); // evaluates to /tmp/java/example/../test.txt
file.getCanonicalPath(); // evaluates to /tmp/java/test.txt