public static String findUrl(PsiFile file, int offset, String uri) {
    final PsiElement currentElement = file.findElementAt(offset);
    final XmlAttribute attribute = PsiTreeUtil.getParentOfType(currentElement, XmlAttribute.class);

    if (attribute != null) {
      final XmlTag tag = PsiTreeUtil.getParentOfType(currentElement, XmlTag.class);

      if (tag != null) {
        final String prefix = tag.getPrefixByNamespace(XmlUtil.XML_SCHEMA_INSTANCE_URI);
        if (prefix != null) {
          final String attrValue = tag.getAttributeValue(XmlUtil.SCHEMA_LOCATION_ATT, XmlUtil.XML_SCHEMA_INSTANCE_URI);
          if (attrValue != null) {
            final StringTokenizer tokenizer = new StringTokenizer(attrValue);

            while (tokenizer.hasMoreElements()) {
              if (uri.equals(tokenizer.nextToken())) {
                if (!tokenizer.hasMoreElements()) return uri;
                final String url = tokenizer.nextToken();

                return url.startsWith(HTTP_PROTOCOL) ? url : uri;
              }

              if (!tokenizer.hasMoreElements()) return uri;
              tokenizer.nextToken(); // skip file location
            }
          }
        }
      }
    }
    return uri;
  }
public static String findUrl(PsiFile file, int offset, String uri)