On a recent project I need to find all the possible permutations of a given URL. Stripping off subdomains, paths, and query parameters. Here is the first part of the solution. A method which takes a string and strips it down based on a given divider in a given direction at a given interval.

Here’s the code:

private static String[] getPermutations(String whole, String divider, int lim, int dir) {
	   String[] chunks = whole.split((divider.matches("\\.") ? "\\" : "")+divider);
	   System.out.println("chunks.length: "+chunks.length);

	   if(chunks.length <= lim) {
		   System.out.println("return whole: "+whole);
		   return new String[]{whole};
	   }

	   String[] permutations = new String[chunks.length-lim];

	   if(dir == 1) {
		   	permutations[0] = whole;
   		    System.out.println("permutations[0]: "+permutations[0]);
			for(int i = 1; i < chunks.length-lim; i++) {
			   String permutation = "";
			   for(int o = i; o < chunks.length; o++) {
				   permutation += (o == i ? "" : divider) + chunks[o];
			   }
			   permutations[i] = permutation;
			   System.out.println("permutations["+i+"]: "+permutations[i]);
			}
	   } else if(dir == -1) {
		   for(int i = 0; i < chunks.length-lim; i++) {
			   String permutation = "";
	 		   for(int o = 0; o < chunks.length-i; o++) {
				   permutation += (o == 0 ? "" : divider) + chunks[o];
			   }
			   permutations[i] = permutation;
			   System.out.println("permutations["+i+"]: "+permutations[i]);
			}
	   }

	   return permutations;
   }

Here is an example of it being used.

Input:

      getPermutations("com",".",1, 1);
      getPermutations("google.com",".",1, 1);
      getPermutations("a.b.c.d.e.cool.google.com",".",1, 1);
      getPermutations("/path/asdf/a/b/c/d/e/f","/",0, -1);
      getPermutations("a=b&c=d&e=f","&",0, -1);

Output:

$ javac Runme.java && java Runme
chunks.length: 1
return whole: com
chunks.length: 2
permutations[0]: google.com
chunks.length: 8
permutations[0]: a.b.c.d.e.cool.google.com
permutations[1]: b.c.d.e.cool.google.com
permutations[2]: c.d.e.cool.google.com
permutations[3]: d.e.cool.google.com
permutations[4]: e.cool.google.com
permutations[5]: cool.google.com
permutations[6]: google.com
chunks.length: 9
permutations[0]: /path/asdf/a/b/c/d/e/f
permutations[1]: /path/asdf/a/b/c/d/e
permutations[2]: /path/asdf/a/b/c/d
permutations[3]: /path/asdf/a/b/c
permutations[4]: /path/asdf/a/b
permutations[5]: /path/asdf/a
permutations[6]: /path/asdf
permutations[7]: /path
permutations[8]:
chunks.length: 3
permutations[0]: a=b&c=d&e=f
permutations[1]: a=b&c=d
permutations[2]: a=b

Next I’ll need to combine the URL components to get a list of valid URLs..