1. import java.io.File;
  2. import java.util.ArrayList;
  3. import java.util.HashMap;
  4. import java.util.List;
  5. import java.util.Map;
  7. public class DirectoryGrouper {
  9. /**
  10. * Groups entries of directories based on their file extensions.
  11. * Handles edge cases like empty directories and directories with no files.
  12. *
  13. * @param rootDir The root directory to process.
  14. * @return A map where keys are file extensions (e.g., ".txt") and values
  15. * are lists of file paths with that extension. Returns an empty
  16. * map if the root directory doesn't exist.
  17. */
  18. public static Map<String, List<String>> groupEntriesByExtension(String rootDir) {
  19. File root = new File(rootDir);
  21. if (!root.exists()) {
  22. System.err.println("Error: Root directory does not exist: " + rootDir);
  23. return new HashMap<>(); // Return empty map if root doesn't exist
  24. }
  26. Map<String, List<String>> groupedFiles = new HashMap<>();
  28. if (!root.isDirectory()) {
  29. System.err.println("Error: Root is not a directory: " + rootDir);
  30. return new HashMap<>();
  31. }
  33. File[] files = root.listFiles();
  35. if (files == null) {
  36. System.err.println("Error: Could not list files in: " + rootDir);
  37. return new HashMap<>();
  38. }
  40. for (File file : files) {
  41. if (file.isFile()) {
  42. String extension = file.getName().split("\\.")[file.getName().split("\\.").length - 1]; // Extract extension
  43. if (!extension.isEmpty()) {
  44. groupedFiles.computeIfAbsent(extension, k -> new ArrayList<>()).add(file.getAbsolutePath());
  45. }
  46. } else if (file.isDirectory()) {
  47. // Recursive call to handle subdirectories (optional, can be removed for one-off)
  48. //groupEntriesByExtension(file.getAbsolutePath());
  49. }
  50. }
  52. return groupedFiles;
  53. }
  55. public static void main(String[] args) {
  56. // Example usage:
  57. String rootDirectory = "test_dir"; //Replace with your directory
  58. File testDir = new File(rootDirectory);
  60. if (!testDir.exists()) {
  61. testDir.mkdir();
  62. File file1 = new File(testDir, "file1.txt");
  63. file1.createNewFile();
  64. File file2 = new File(testDir, "file2.java");
  65. file2.createNewFile();
  66. File subdir = new File(testDir, "subdir");
  67. subdir.mkdir();
  68. File file3 = new File(subdir, "file3.txt");
  69. file3.createNewFile();
  70. }
  72. Map<String, List<String>> grouped = groupEntriesByExtension(rootDirectory);
  74. for (Map.Entry<String, List<String>> entry : grouped.entrySet()) {
  75. System.out.println(entry.getKey() + ": " + entry.getValue());
  76. }
  78. }
  79. }

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