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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.time;

import java.util.TimeZone;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Faster methods to produce custom time zones.
 *
 * @since 3.7
 */
public class FastTimeZone {

    private static final Pattern GMT_PATTERN = Pattern.compile("^(?:(?i)GMT)?([+-])?(\\d\\d?)?(:?(\\d\\d?))?$");

    private static final TimeZone GREENWICH = new GmtTimeZone(false, 0, 0);

    /**
     * Gets the GMT TimeZone.
     * @return A TimeZone with a raw offset of zero.
     */
    public static TimeZone getGmtTimeZone() {
        return GREENWICH;
    }

    /**
     * Gets a TimeZone with GMT offsets.  A GMT offset must be either 'Z', or 'UTC', or match
     * (GMT)? hh?(:?mm?)?, where h and m are digits representing hours and minutes.
     *
     * @param pattern The GMT offset
     * @return A TimeZone with offset from GMT or null, if pattern does not match.
     */
    public static TimeZone getGmtTimeZone(final String pattern) {
        if ("Z".equals(pattern) || "UTC".equals(pattern)) {
            return GREENWICH;
        }

        final Matcher m = GMT_PATTERN.matcher(pattern);
        if (m.matches()) {
            final int hours = parseInt(m.group(2));
            final int minutes = parseInt(m.group(4));
            if (hours == 0 && minutes == 0) {
                return GREENWICH;
            }
            return new GmtTimeZone(parseSign(m.group(1)), hours, minutes);
        }
        return null;
    }

    /**
     * Gets a TimeZone, looking first for GMT custom ids, then falling back to Olson ids.
     * A GMT custom id can be 'Z', or 'UTC', or has an optional prefix of GMT,
     * followed by sign, hours digit(s), optional colon(':'), and optional minutes digits.
     * i.e. [GMT] (+|-) Hours [[:] Minutes]
     *
     * @param id A GMT custom id (or Olson id
     * @return A time zone
     */
    public static TimeZone getTimeZone(final String id) {
        final TimeZone tz = getGmtTimeZone(id);
        if (tz != null) {
            return tz;
        }
        return TimeZone.getTimeZone(id);
    }

    private static int parseInt(final String group) {
        return group != null ? Integer.parseInt(group) : 0;
    }

    private static boolean parseSign(final String group) {
        return group != null && group.charAt(0) == '-';
    }

    // do not instantiate
    private FastTimeZone() {
    }

}




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