Edit. This post is made obsolete by https://jakut.is/2013/08/06/a-java-program-to-list-all-duplicates-update.


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69</td>
import java.io.File; import java.io.FileInputStream; import java.io.IOException; import java.math.BigInteger; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; import java.util.HashMap; import java.util.LinkedList; import java.util.List; import java.util.Map; public class FindDuplicates { private static MessageDigest md; static { try { md = MessageDigest.getInstance("SHA-512"); } catch (NoSuchAlgorithmException e) { throw new RuntimeException("cannot initialize SHA-512 hash function", e); } } public static void find(Map<String, List<String>> lists, File directory) { for (File child : directory.listFiles()) { if (child.isDirectory()) { find(lists, child); } else { try { FileInputStream fin = new FileInputStream(child); byte data[] = new byte[(int) child.length()]; fin.read(data); fin.close(); String hash = new BigInteger(1, md.digest(data)).toString(16); List<String> list = lists.get(hash); if (list == null) { list = new LinkedList<String>(); lists.put(hash, list); } list.add(child.getAbsolutePath()); } catch (IOException e) { throw new RuntimeException("cannot read file " + child.getAbsolutePath(), e); } } } } public static void main(String[] args) { if (args.length < 1) { System.out.println("Please supply a path to directory to find duplicate files in."); return; } File dir = new File(args[0]); if (!dir.isDirectory()) { System.out.println("Supplied directory does not exist."); return; } Map<String, List<String>> lists = new HashMap<String, List<String>>(); FindDuplicates.find(lists, dir); for (List<String> list : lists.values()) { if (list.size() > 1) { System.out.println("--"); for (String file : list) { System.out.println(file); } } } System.out.println("--"); } } </pre></div>