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Apache Commons Lang, a package of Java utility classes for the classes that are in java.lang's hierarchy, or are considered to be so standard as to justify existence in java.lang. The code is tested using the latest revision of the JDK for supported LTS releases: 8, 11, 17 and 21 currently. See https://github.com/apache/commons-lang/blob/master/.github/workflows/maven.yml Please ensure your build environment is up-to-date and kindly report any build issues.

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/*
 * 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.
 */
package org.apache.commons.lang3.text.translate;

import java.io.IOException;
import java.io.Writer;

/**
 * Translates escaped Unicode values of the form \\u+\d\d\d\d back to
 * Unicode. It supports multiple 'u' characters and will work with or
 * without the +.
 *
 * @since 3.0
 * @deprecated as of 3.6, use commons-text
 * 
 * UnicodeUnescaper instead
 */
@Deprecated
public class UnicodeUnescaper extends CharSequenceTranslator {

    /**
     * {@inheritDoc}
     */
    @Override
    public int translate(final CharSequence input, final int index, final Writer out) throws IOException {
        if (input.charAt(index) == '\\' && index + 1 < input.length() && input.charAt(index + 1) == 'u') {
            // consume optional additional 'u' chars
            int i = 2;
            while (index + i < input.length() && input.charAt(index + i) == 'u') {
                i++;
            }

            if (index + i < input.length() && input.charAt(index + i) == '+') {
                i++;
            }

            if (index + i + 4 <= input.length()) {
                // Get 4 hex digits
                final CharSequence unicode = input.subSequence(index + i, index + i + 4);

                try {
                    final int value = Integer.parseInt(unicode.toString(), 16);
                    out.write((char) value);
                } catch (final NumberFormatException nfe) {
                    throw new IllegalArgumentException("Unable to parse unicode value: " + unicode, nfe);
                }
                return i + 4;
            }
            throw new IllegalArgumentException("Less than 4 hex digits in unicode value: '" + input.subSequence(index, input.length())
                    + "' due to end of CharSequence");
        }
        return 0;
    }
}