How to List Folders with 6 Digits in Their Names Using Java

Learn how to filter folders in Java to only display those with `6 digits` in their names. Use regex and the Java File API.
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This video is based on the question https://stackoverflow.com/q/66407117/ asked by the user 'MMMMS' ( https://stackoverflow.com/u/3766129/ ) and on the answer https://stackoverflow.com/a/66407211/ provided by the user 'Sergey Afinogenov' ( https://stackoverflow.com/u/13415164/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to List Folders with 6 Digits in Their Names Using Java

When working with file systems in Java, there might be situations where you need to retrieve specific directories based on their names. One common requirement is to list only the folders that contain a specific pattern in their names, like 6 digits. This article will guide you through the solution, helping you create a Java program that efficiently filters folders by their name structure.

The Problem

You want to list only those folders that have names consisting entirely of 6 digits. For instance, in a directory containing various folders, you may have the following:

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From this example, the desired output should only include the folder C:\war\032678 since it is the only folder that meets the 6 digits criteria. The challenge is to effectively filter directories using Java's file handling capabilities.

The Solution

To achieve this, you can utilize a regular expression to match folder names that consist of exactly 6 digits. The Java File API is quite flexible, and you can filter directories with the help of a lambda expression and the listFiles method.

Step-by-Step Implementation

Here’s how you can implement this solution in a few clear steps:

Setup Your Project: Ensure that you have Java setup on your machine. You will be working with Java's File and Paths classes.

Create Your File Filter: Use a filter within the listFiles method to check directory names against a regex pattern.

Implement the Code: The following code snippet illustrates this solution:

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Breaking Down the Code

File Class: new File("F:\war"): This creates a File object that points to your target directory.

listFiles Method: This method returns an array of File objects representing the directories that match the specified filter.

Lambda Expression: file -> file.isDirectory() && file.getName().matches("[0-9]{6}"). This checks two conditions:

file.isDirectory(): Ensures that the file is indeed a directory.

file.getName().matches("[0-9]{6}"): Uses a regular expression to check if the directory name consists of exactly 6 digits.

Resulting Output

When you run the code provided above, the output will filter out all directories and only display those that match the 6 digit criteria:

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Conclusion

Filtering folders by their names can be easily achieved in Java with the combination of the File API and regular expressions. By using the listFiles method with a custom filter, you can selectively retrieve folders based solely on their names. This approach not only saves you time but also ensures that you get exactly what you need, making your file handling tasks more efficient.

Feel free to integrate this approach in your projects and enhance your directory management capabilities with Java!