code: /*
  Copyright (c) 2001, 2002 Thai Open Source Software Center Ltd
  All rights reserved.
  
  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions are
  met:
  
      Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.
  
      Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in
      the documentation and/or other materials provided with the
      distribution.
  
      Neither the name of the Thai Open Source Software Center Ltd nor
      the names of its contributors may be used to endorse or promote
      products derived from this software without specific prior written
      permission.
  
  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR
  CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
  LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
  package com.sun.xml.xsom.impl.util;
  
  import java.io.IOException;
  import java.io.UnsupportedEncodingException;
  import java.net.URL;
  
  public class Uri {
    private static String utf8 = "UTF-8";
  
    public static boolean isValid(String s) {
      return isValidPercent(s) && isValidFragment(s) && isValidScheme(s);
    }
  
    private static final String HEX_DIGITS = "0123456789abcdef";
  
    public static String escapeDisallowedChars(String s) {
      StringBuffer buf = null;
      int len = s.length();
      int done = 0;
      for (;;) {
        int i = done;
        for (;;) {
          if (i == len) {
            if (done == 0)
              return s;
            break;
          }
          if (isExcluded(s.charAt(i)))
            break;
          i++;
        }
        if (buf == null)
          buf = new StringBuffer();
        if (i > done) {
          buf.append(s.substring(done, i));
          done = i;
        }
        if (i == len)
          break;
        for (i++; i < len && isExcluded(s.charAt(i)); i++)
          ;
        String tem = s.substring(done, i);
        byte[] bytes;
        try {
          bytes = tem.getBytes(utf8);
        }
        catch (UnsupportedEncodingException e) {
          utf8 = "UTF8";
          try {
            bytes = tem.getBytes(utf8);
          }
          catch (UnsupportedEncodingException e2) {
            // Give up
            return s;
          }
        }
        for (int j = 0; j < bytes.length; j++) {
          buf.append('%');
          buf.append(HEX_DIGITS.charAt((bytes[j] & 0xFF) >> 4));
          buf.append(HEX_DIGITS.charAt(bytes[j] & 0xF));
        }
        done = i;
      }
      return buf.toString();
    }
  
    private static String excluded = "<>\"{}|\\^`";
  
    private static boolean isExcluded(char c) {
      return c <= 0x20 || c >= 0x7F || excluded.indexOf(c) >= 0;
    }
  
    private static boolean isAlpha(char c) {
      return ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z');
    }
  
    private static boolean isHexDigit(char c) {
      return ('a' <= c && c <= 'f') || ('A' <= c && c <= 'F') || isDigit(c);
    }
  
    private static boolean isDigit(char c) {
      return '0' <= c && c <= '9';
    }
    
    private static boolean isSchemeChar(char c) {
      return isAlpha(c) || isDigit(c) || c == '+' || c == '-' || c =='.';
    }
  
    private static boolean isValidPercent(String s) {
      int len = s.length();
      for (int i = 0; i < len; i++)
        if (s.charAt(i) == '%') {
          if (i + 2 >= len)
            return false;
          else if (!isHexDigit(s.charAt(i + 1))
               || !isHexDigit(s.charAt(i + 2)))
            return false;
        }
      return true;
    }
  
    private static boolean isValidFragment(String s) {
      int i = s.indexOf('#');
      return i < 0 || s.indexOf('#', i + 1) < 0;
    }
  
    private static boolean isValidScheme(String s) {
      if (!isAbsolute(s))
        return true;
      int i = s.indexOf(':');
      if (i == 0
      || i + 1 == s.length()
      || !isAlpha(s.charAt(0)))
        return false;
      while (--i > 0)
        if (!isSchemeChar(s.charAt(i)))
      return false;
      return true;
    }
  
      public static String resolve(String baseUri, String uriReference) throws IOException {
          if (isAbsolute(uriReference))
              return uriReference;
  
          if(baseUri==null)
              throw new IOException("Unable to resolve relative URI "+uriReference+" without a base URI");
  
          if(!isAbsolute(baseUri))
              throw new IOException("Unable to resolve relative URI "+uriReference+" because base URI is not absolute: "+baseUri);
  
          return new URL(new URL(baseUri), uriReference).toString();
      }
  
      public static boolean hasFragmentId(String uri) {
      return uri.indexOf('#') >= 0;
    }
  
    public static boolean isAbsolute(String uri) {
      int i = uri.indexOf(':');
      if (i < 0)
        return false;
      while (--i >= 0) {
        switch (uri.charAt(i)) {
        case '#':
        case '/':
        case '?':
      return false;
        }
      }
      return true;
    }
  }
  