libphonenumber/src/com/google/i18n/phonenumbers/RegexCache.java

/*
 * Copyright (C) 2010 The Libphonenumber Authors
 *
 * 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.google.i18n.phonenumbers;

import java.util.LinkedHashMap;
import java.util.Map;
import java.util.regex.Pattern;

/**
 * LRU Cache for compiled regular expressions used by the libphonenumbers libary.
 *
 * @author Shaopeng Jia
 */
public class RegexCache {
  private LRUCache<String, Pattern> cache;

  public RegexCache(int size) {
    cache = new LRUCache<String, Pattern>(size);
  }

  public Pattern getPatternForRegex(String regex) {
    Pattern pattern = cache.get(regex);
    if (pattern == null) {
      pattern = Pattern.compile(regex);
      cache.put(regex, pattern);
    }
    return pattern;
  }

  // This method is used for testing.
  boolean containsRegex(String regex) {
    return cache.containsKey(regex);
  }

  private static class LRUCache<K, V> {
    // LinkedHashMap offers a straightforward implementation of LRU cache.
    private LinkedHashMap<K, V> map;
    private int size;

    @SuppressWarnings("serial")
    public LRUCache(int size) {
      this.size = size;
      map = new LinkedHashMap<K, V>(size * 4 / 3 + 1, 0.75f, true) {
        @Override
        protected boolean removeEldestEntry(Map.Entry<K, V> eldest) {
          return size() > LRUCache.this.size;
        }
      };
    }

    public synchronized V get(K key) {
      return map.get(key);
    }

    public synchronized void put(K key, V value) {
      map.put(key, value);
    }

    public synchronized boolean containsKey(K key) {
      return map.containsKey(key);
    }
  }
}