A Joda time zone provider based on the JVM's TimeZone implementation, instead of Joda's Olson database. This can reduce Joda's initialization time (during class loading) by several seconds on Android. Inspired by http://stackoverflow.com/a/6298241/37020, but implemented from scratch. Requires Guava, for ImmutableSet.

JdkBasedTimeZoneProvider.java

/*
 * Copyright (C) 2013 Onavo Inc.
 *
 * Licensed 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 com.example;

import com.google.common.collect.ImmutableSet;

import org.joda.time.DateTimeZone;
import org.joda.time.tz.Provider;

import java.util.Set;
import java.util.TimeZone;

/**
 * A Joda time zone provider based on the JVM's TimeZone implementation, instead of Joda's Olson database.
 * <p/>
 * This can reduce Joda's initialization time (during class loading) by several seconds on Android.
 * To wire it up, add this to your Application subclass's onCreate():
 * {@code System.setProperty("org.joda.time.DateTimeZone.Provider", JdkBasedTimeZoneProvider.class.getCanonicalName());}
 * <p/>
 * Inspired by http://stackoverflow.com/a/6298241/37020, but implemented from scratch.
 * Requires Guava for ImmutableSet.
 */
public class JdkBasedTimeZoneProvider implements Provider {
    private static Set<String> availableIds = ImmutableSet.copyOf(TimeZone.getAvailableIDs());

    public Set<String> getAvailableIDs() {
        return availableIds;
    }

    public DateTimeZone getZone(final String id) {
        if (id == null) {
            return null;
        }

        return DateTimeZone.forOffsetMillis(TimeZone.getTimeZone(id).getOffset(System.currentTimeMillis()));
    }
}