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Java example source code file (Rfc3492Idn.java)

This example source code file (Rfc3492Idn.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java tags/keywords

a, ace_prefix, fixme, illegalargumentexception, immutable, rfc3492idn, string, stringbuilder, stringtokenizer, util

The Rfc3492Idn.java example source code

/*
 * $HeadURL$
 * $Revision$
 * $Date$
 *
 * ====================================================================
 *
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 *
 */

package org.apache.http.client.utils;

import java.util.StringTokenizer;

import org.apache.http.annotation.Immutable;

/**
 * Implementation from pseudo code in RFC 3492.
 *
 * @since 4.0
 */
@Immutable
public class Rfc3492Idn implements Idn {
    private static final int base = 36;
    private static final int tmin = 1;
    private static final int tmax = 26;
    private static final int skew = 38;
    private static final int damp = 700;
    private static final int initial_bias = 72;
    private static final int initial_n = 128;
    private static final char delimiter = '-';
    private static final String ACE_PREFIX = "xn--";
    
    private int adapt(int delta, int numpoints, boolean firsttime) {
        if (firsttime) delta = delta / damp;
        else delta = delta / 2;
        delta = delta + (delta / numpoints);
        int k = 0;
        while (delta > ((base - tmin) * tmax) / 2) {
          delta = delta / (base - tmin);
          k = k + base;
        }
        return k + (((base - tmin + 1) * delta) / (delta + skew));
    }
    
    private int digit(char c) {
        if ((c >= 'A') && (c <= 'Z')) return (c - 'A');
        if ((c >= 'a') && (c <= 'z')) return (c - 'a');
        if ((c >= '0') && (c <= '9')) return (c - '0') + 26;
        throw new IllegalArgumentException("illegal digit: "+ c);
    }

    public String toUnicode(String punycode) {
        StringBuilder unicode = new StringBuilder(punycode.length());
        StringTokenizer tok = new StringTokenizer(punycode, ".");
        while (tok.hasMoreTokens()) {
            String t = tok.nextToken();
            if (unicode.length() > 0) unicode.append('.');
            if (t.startsWith(ACE_PREFIX)) t = decode(t.substring(4));
            unicode.append(t);
        }
        return unicode.toString();
    }
    
    protected String decode(String input) {
        int n = initial_n;
        int i = 0;
        int bias = initial_bias;
        StringBuilder output = new StringBuilder(input.length());
        int lastdelim = input.lastIndexOf(delimiter);
        if (lastdelim != -1) {
            output.append(input.subSequence(0, lastdelim));
            input = input.substring(lastdelim + 1);
        }

        while (input.length() > 0) {
            int oldi = i;
            int w = 1;
            for (int k = base;; k += base) {
                if (input.length() == 0) break;
                char c = input.charAt(0);
                input = input.substring(1);
                int digit = digit(c);
                i = i + digit * w; // FIXME fail on overflow
                int t;
                if (k <= bias + tmin) {
                    t = tmin;
                } else if (k >= bias + tmax) {
                    t = tmax;
                } else {
                    t = k - bias;
                }
                if (digit < t) break;
                w = w * (base - t); // FIXME fail on overflow
            }
            bias = adapt(i - oldi, output.length() + 1, (oldi == 0));
            n = n + i / (output.length() + 1); // FIXME fail on overflow
            i = i % (output.length() + 1);
            // {if n is a basic code point then fail}
            output.insert(i, (char) n);
            i++;
        }
        return output.toString();
    }
    
}

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