Get relative path of two URIs in Java

java, uri

Solution

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.

Problem

Original source

Related problems

• How to construct a relative path in Java from two absolute paths (or URLs)?
• How to construct a relative path in Java from two absolute paths (or URLs)?