Java: Check if path is parent of a file

问题

I cant seem to find a solution.

I have two paths, like:

D:/Views/me/a.b AND D:/Views/me/a

D:/Views/me/a.b AND D:/Views/me/a.b/x/y

I have to ensure, that one file/directory is not a child of the other. I have tried Contains but it does not work for me in this case?

回答1:

Try using startsWith api of String:

String str1 = "D:/Views/me/a.b";
String str2 = "D:/Views/me/a";
if (str1.startsWith(str2 + ".") || str1.startsWith(str2 + "/")) {
    System.out.println("Yes it is");
}
str1 = "D:/Views/me/a/c/d";
str2 = "D:/Views/me/a";
if (str1.startsWith(str2 + ".") || str1.startsWith(str2 + "/")) {
     System.out.println("Yes it is");
}
Output:
Yes it is
Yes it is

回答2:

I think Path and Paths from java.nio.file can be useful here (if you have at least Java 7).

public static void main(String[] args) {
    Path p1 = Paths.get("D:/Views/me/a.b");
    Path p2 = Paths.get("D:/Views/me/a");
    System.out.println(isChild(p1, p2));
    System.out.println(isChild(p2, p1));

    Path p3 = Paths.get("D:/Views/me/a.b");
    Path p4 = Paths.get("D:/Views/me/a.b/x/y");
    System.out.println(isChild(p3, p4));
    System.out.println(isChild(p4, p3));
}

//Check if childCandidate is child of path
public static boolean isChild(Path path, Path childCandidate) {
    return childCandidate.startsWith(path);
}

You might consider using toAbsolutePath() or toRealPath() on the paths before the check depending on your needs.

Here's the the official Java tutorial for Path Operations.

回答3:

    String path = "D:/Views/me/a.b";
    String path2 = "D:/Views/me/a";
    File file = new File(path);
    if(file.getParentFile().getAbsolutePath().equals("path2")){
    System.out.println("file is parent");
    }else{
        System.out.println("file is not parent");
    }

回答4:

Surprisingly there is no simple, yet functional solution.

Here is one using java.nio.file.Path API only:

static boolean isChildPath(Path parent, Path child){
      Path pn = parent.normalize();
      Path cn = child.normalize();
      return cn.getNameCount() > pn.getNameCount() && cn.startsWith(pn);
}

Test cases:

 @Test
public void testChildPath() {
      assertThat(isChildPath(Paths.get("/FolderA/FolderB/F"), Paths.get("/FolderA/FolderB/F"))).isFalse();
      assertThat(isChildPath(Paths.get("/FolderA/FolderB/F"), Paths.get("/FolderA/FolderB/F/A"))).isTrue();
      assertThat(isChildPath(Paths.get("/FolderA/FolderB/F"), Paths.get("/FolderA/FolderB/F/A.txt"))).isTrue();

      assertThat(isChildPath(Paths.get("/FolderA/FolderB/F"), Paths.get("/FolderA/FolderB/F/../A"))).isFalse();
      assertThat(isChildPath(Paths.get("/FolderA/FolderB/F"), Paths.get("/FolderA/FolderB/FA"))).isFalse();

      assertThat(isChildPath(Paths.get("FolderA"), Paths.get("FolderA"))).isFalse();
      assertThat(isChildPath(Paths.get("FolderA"), Paths.get("FolderA/B"))).isTrue();
      assertThat(isChildPath(Paths.get("FolderA"), Paths.get("FolderA/B"))).isTrue();
      assertThat(isChildPath(Paths.get("FolderA"), Paths.get("FolderAB"))).isFalse();
      assertThat(isChildPath(Paths.get("/FolderA/FolderB/F"), Paths.get("/FolderA/FolderB/F/Z/X/../A"))).isTrue();
}

来源：https://stackoverflow.com/questions/28698125/java-check-if-path-is-parent-of-a-file

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java

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filepath