从更长的文件路径中获取文件路径的一部分

Question

In my tool I let the user select a specific file. By calling getAbsolutePath() on that file I will get a String such as

C:\\folder\\folder\\folder\\dataset\\MainFolder\\folder\\folder\\folder\\myfile.xml

How can I the path of the "MainFolder" stored in a new String variable. What I want from the example above is

C:\\folder\\folder\\folder\\dataset\\MainFolder\\

The structure is always

Drive:\\random\\number\\of\\folders\\dataset\\main_folder_name\\folder1\\folder2\\folder3\\myfile.xml

The parent folder of the one I'm looking for always has the name "dataset". The one that follows that folder is the one i'm interested in.

Answer 1

I'd highly recommend using the File API rather than String manipulation, this isolates you from platform differences in forward vs backslashes or any other differences.

• keep "going up one", until you reach the root where getParentFile() returns null
• if you find the folder in you need along the way break out of the loop
• keep track of the last parent so you can refer to 'main_folder_name' after you've found 'dataset'

Code

String path = "C:\\random\\number\\of\\folders\\dataset\\main_folder_name\\folder1\\folder2\\folder3\\myfile.xml";
File search = new File(path);
File lastParent = search;
while (search != null) {
    if ("dataset".equals(search.getName())) {
        break;
    }
    lastParent = search;
    search = search.getParentFile();
}
if (lastParent != null) {
    System.out.println(lastParent.getCanonicalPath());
}

Output

C:\random\number\of\folders\dataset\main_folder_name

Answer 2

Use the below code in your program. This will solve your expectations :)

import java.util.StringTokenizer;

public class MainFolder {
    public static void main(String args[]) {
        String separator = "/";
        StringTokenizer st = new StringTokenizer("C:/folder/folder/folder/dataset/MainFolder/folder/folder/folder/myfile.xml",separator);
        String mainFolderPath = "";
        String searchWord = "dataset";
        while (st.hasMoreTokens()) {
            mainFolderPath = mainFolderPath + st.nextToken() + separator;
            if (mainFolderPath.contains(searchWord)) {
                mainFolderPath = mainFolderPath + st.nextToken() + separator;
                break;
            }
        }
        System.out.println(mainFolderPath);

    }

}

Answer 3

The URI class has a relativize, and File a toURI.

    String path = "C:\\folder\\folder\\folder\\dataset\\MainFolder\\folder\\folder\\folder\\myfile.xml";
    String base = "C:\\folder\\folder\\folder\\dataset\\MainFolder";
    File pathFile = new File(path);
    File baseFile = new File(base);
    URI pathURI = pathFile.toURI();
    URI baseURI = baseFile.toURI();

    URI relativeURI = baseURI.relativize(pathURI);
    System.out.println(relativeURI.toString());
    // folder/folder/folder/myfile.xml

    File relativeFile = new File(relativeURI.getPath());
    System.out.println(relativeFile.getPath());
    // folder\folder\folder\myfile.xml

Answer 4

It can be done by using only substring() and indexOf() method of String class. Code is:

    String path = "C:\\random\\number\\of\\folders\\dataset\\main_folder_name\\folder1\\folder2\\folder3\\myfile.xml";
    int indexOfFirstBkSlashB4Dataset = path.indexOf("\\dataset");
    String sub1 = path.substring(0,indexOfFirstBkSlashB4Dataset);
    String sub2 = "\\dataset\\";
    String sub3Intermediate = path.substring(indexOfFirstBkSlashB4Dataset+9,path.length());
    int index2 = sub3Intermediate.indexOf("\\");
    String sub4 = sub3Intermediate.substring(0,index2+1);
    String output = sub1+sub2+sub4;
    System.out.println(output);

Output is: C:\\random\\number\\of\\folders\\dataset\\main_folder_name\\