    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      https://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.text.translate;
    018
    019import java.io.IOException;
    020import java.io.Writer;
    021
    022/**
    023 * Translates escaped Unicode values of the form \\u+\d\d\d\d back to
    024 * Unicode. It supports multiple 'u' characters and will work with or
    025 * without the +.
    026 *
    027 * @since 1.0
    028 */
    029public class UnicodeUnescaper extends CharSequenceTranslator {
    030
    031    /**
    032     * Constructs a new instance.
    033     */
    034    public UnicodeUnescaper() {
    035        // empty
    036    }
    037
    038    /**
    039     * {@inheritDoc}
    040     */
    041    @Override
    042    public int translate(final CharSequence input, final int index, final Writer writer) throws IOException {
    043        if (input.charAt(index) == '\\' && index + 1 < input.length() && input.charAt(index + 1) == 'u') {
    044            // consume optional additional 'u' chars
    045            int i = 2;
    046            while (index + i < input.length() && input.charAt(index + i) == 'u') {
    047                i++;
    048            }
    049
    050            if (index + i < input.length() && input.charAt(index + i) == '+') {
    051                i++;
    052            }
    053
    054            if (index + i + 4 <= input.length()) {
    055                // Get 4 hex digits
    056                final CharSequence unicode = input.subSequence(index + i, index + i + 4);
    057
    058                try {
    059                    final int value = Integer.parseInt(unicode.toString(), 16);
    060                    writer.write((char) value);
    061                } catch (final NumberFormatException nfe) {
    062                    throw new IllegalArgumentException("Unable to parse unicode value: " + unicode, nfe);
    063                }
    064                return i + 4;
    065            }
    066            throw new IllegalArgumentException("Less than 4 hex digits in unicode value: '"
    067                    + input.subSequence(index, input.length())
    068                    + "' due to end of CharSequence");
    069        }
    070        return 0;
    071    }
    072}