Java：如何从保存在路径中的多个文件夹中提取最大名称到文件夹名称都是数字的变量中？

Question

There is a directory which has many folders. The folder names are all numeric. How to extract the folder name which has the greatest value into an integer variable in java?

For example: Lets say directory .../home/user has following folders:

.../home/user/19620918

.../home/user/19620919

.../home/user/19620920

How to get x = 19620920 , where x is lets say the integer variable, using the simplest and most efficient code?

Answer 1

Using a Files.list() , you can use the following approach:

public static OptionalInt getMaxNumericFilename(Path path) {
    try (Stream<Path> files = Files.list(path)) {
        return files
            .filter(Files::isDirectory)
            .map(Path::getFileName)
            .map(Path::toString)
            .mapToInt(Integer::parseInt)
            .max();
    } catch (IOException e) {
        return OptionalInt.empty();
    }
}

Example usage:

Path path = Path.of(".../home/user");

OptionalInt max = getMaxNumericFilename(path);
System.out.println(max.getAsInt());

If the OptionalInt is empty, there are no present directories. If you want to add additional resiliency, you can filter if the filename is an int before parsing with Integer::parseInt which can throw an exception.

This solution will work for filename numbers up to Integer.MAX_VALUE (2.147.483.647). Consider using long or BigDecimal if required.