Trie

public class Trie
{
  private class TrieNode
  {
    public TrieNode[] children;
    public ArrayList<String> words;

    public TrieNode()
    {
      children = new TrieNode[26];
      words = new ArrayList<String>();
    }
  }

  private TrieNode root;

  public Trie(String file)
  {
    root = new TrieNode();

    BufferedReader in = new BufferedReader(new FileReader(file));
    String str;
    while ((str = in.readLine()) != null)
    {
      char[] chars = str.toCharArray();
      Arrays.sort(chars);
      insert(root, chars, 0);
    }
    in.close();
  }

  private void insert(TrieNode node, char[] chars, int x)
  {
    if (x >= chars.length)
    {
      node.words.add(new String(chars));
      return;
    }

    if(node.children[chars[x]-'a'] == null)
      node.children[chars[x]-'a'] = new TrieNode();

    insert(node.children[chars[x]-'a'], chars, x+1);
  }

  public ArrayList<String> getPermutations(String s)
  {
    char[] chars = s.toCharArray();
    Arrays.sort(chars);

    TrieNode current = root;
    for (int i=0; i < chars.length && current != null; i++)
      current = current.children[chars[i]-'a']

    return (current == null) ? new ArrayList<String>() : current.words.clone();
  }
}

public static void main(String[] args)
{
  Trie dict = new Trie("c://scrabbledictionary.txt");
  ArrayList<String> words = dict.getPermutations("infantry");
}