How to automatically group image files based on file name prefix

need

A lot of files (such as pictures) are piled up in a directory, and their naming rules follow a certain format, and it is difficult to manage when mixed together. It needs to be automatically sorted through code. Automatically group image files based on file name prefix, creating a folder for each group to archive.

background

A batch of picture files with the following naming format:

A_20241021
A_20241021
A_20241022
A_20241023

The previous parts are consistent. Files with the same prefix belong to the same group. Based on this prefix, divide them into their respective "folders".

Analytical ideas

Extract file name prefix: separate with -number, remove the suffix name, and take the first half as the basis for grouping.

Use Map to store grouping results: key is the prefix and value is the corresponding file list.

Output or move to the corresponding folder.

Implement code

Here is the complete sample code, focusing on how to extract prefixes and group them:

import .*;

public class FileGrouper {
    public static void main(String[] args) {
        // List of example file names        List<String> fileNames = (
            "A_20241021",
            "A_20241021",
            "A_20241022",
            "A_20241023"
        );

        //Storing the grouped file name        Map<String, List<String>> groupedFiles = new HashMap<>();

        for (String fileName : fileNames) {
            // Extract the prefix part as key            String prefix = getPrefix(fileName);

            // Add to the corresponding group            (prefix, k -> new ArrayList<>()).add(fileName);
        }

        // Output grouping results        for (<String, List<String>> entry : ()) {
            ("Folder: " + ());
            for (String file : ()) {
                ("  " + file);
            }
        }
    }

    /**
      * Get the file name prefix (remove the `-number` and extension)
      */
    private static String getPrefix(String fileName) {
        int lastDashIndex = ('-');
        if (lastDashIndex != -1) {
            return (0, lastDashIndex);
        }
        return fileName;
    }
}

Output result

After running, you will get the following output:

Folder: A_20241021
  A_20241021
  A_20241021
Folder: A_20241022
  A_20241022
Folder: A_20241023
  A_20241023

The grouping was successful and a "folder name" was generated for each group.

Knowledge extension

Java Find files based on file name prefix

In Java, we can find files by prefixing the file name. This process is mainly divided into the following steps: reading the file directory, filtering the file name, matching the prefix, and finding the target file.

Detailed steps

Step 1: Read the file directory

First, we need to get a list of all file names in the target folder.

// Specify the destination folder pathFile folder = new File("path/to/folder");
// Get all files in the target folderFile[] listOfFiles = ();

Step 2: Filter the file name

Next, we need to filter out the target file name.

List<String> fileNames = new ArrayList<>();
for (File file : listOfFiles) {
    if (()) {
        (());
    }
}

Step 3: Match the prefix

Then, we need to match the file name prefix and find the target file.

String targetPrefix = "prefix";
String targetFile = null;
for (String fileName : fileNames) {
    if ((targetPrefix)) {
        targetFile = fileName;
        break;
    }
}

Step 4: Find the target file

Finally, we can find the target file based on the target file name.

File file = new File(() +  + targetFile);
// Perform subsequent operations, such as reading file content

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