Get relative path of two URIs in Java

Question

I have these two URIs:

http://www.google.de/blank.gif

http://www.google.de/sub/

I want the relative path from http://www.google.de/sub/ to http://www.google.de/blank.gif so that the result is ../blank.gif

URI.relativize() does not work here :/

Thanks!

This is [known bug](http://bugs.sun.com/view_bug.do?bug_id=6226081). I think you need to find different library or write it yourself. — Piotr Praszmo, May 29 '12 at 14:57

score 6 · Accepted Answer · answered May 29 '12 at 15:28

The Apache URIUtils should work. If you don't want to pull in an external library, here's a simple implementation of a method that should correctly resolve relative URIs for the case that java.net.URI can't handle (i.e. where the base URI path is not a prefix of the child URI path).

public static URI relativize(URI base, URI child) {
  // Normalize paths to remove . and .. segments
  base = base.normalize();
  child = child.normalize();

  // Split paths into segments
  String[] bParts = base.getPath().split("\\/");
  String[] cParts = child.getPath().split("\\/");

  // Discard trailing segment of base path
  if (bParts.length > 0 && !base.getPath().endsWith("/")) {
    bParts = Arrays.copyOf(bParts, bParts.length - 1);
  }

  // Remove common prefix segments
  int i = 0;
  while (i < bParts.length && i < cParts.length && bParts[i].equals(cParts[i])) {
    i++;
  }

  // Construct the relative path
  StringBuilder sb = new StringBuilder();
  for (int j = 0; j < (bParts.length - i); j++) {
    sb.append("../");
  }
  for (int j = i; j < cParts.length; j++) {
    if (j != i) {
      sb.append("/");
    }
    sb.append(cParts[j]);
  }

  return URI.create(sb.toString());
}

Note that this doesn't enforce that the base and child have the same scheme and authority -- you'll have to add that if you want it to handle the general case. This might not work against all boundary cases, but it works against you example.

Thanks, but you have to compare both host names `if (!base.getHost().equalsIgnoreCase(child.getHost())) { return child; }` — Heiko, Jun 01 '12 at 12:23

score 4 · Answer 2 · answered May 29 '12 at 14:59

I think you can use Apache URIUtils

http://hc.apache.org/httpcomponents-client-ga/httpclient/apidocs/org/apache/http/client/utils/URIUtils.html#resolve%28java.net.URI,%20java.net.URI%29

resolve

public static URI resolve(URI baseURI, URI reference)

Resolves a URI reference against a base URI. Work-around for bugs in java.net.URI (e.g. )

Parameters:
    baseURI - the base URI
    reference - the URI reference 
Returns:
    the resulting URI

Example:

http://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk/httpclient/src/test/java/org/apache/http/client/utils/TestURIUtils.java

Get relative path of two URIs in Java

2 Answers2