TrieCache.java

package tv.dyndns.kishibe.qmaclone.server.relevance;

import java.io.File;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;

import com.google.common.base.Preconditions;
import com.google.common.base.Throwables;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import com.google.inject.Inject;

import tv.dyndns.kishibe.qmaclone.client.constant.Constant;

public class TrieCache {

  private static final File DICTIONARY_FILE = new File(
      Constant.FILE_PATH_BASE + "qmaclone/trie.bin");
  private static final Object STATIC_KEY = new Object();
  private final Dictionaries.Factory dictionariesFactory;
  private final Trie.Factory trieFactory;
  private final LoadingCache<Object, Trie> cache = CacheBuilder.newBuilder().concurrencyLevel(1)
      .expireAfterWrite(1, TimeUnit.DAYS).maximumSize(1).build(new CacheLoader<Object, Trie>() {
        @Override
        public Trie load(Object key) throws Exception {
          if (DICTIONARY_FILE.isFile() && System
              .currentTimeMillis() < DICTIONARY_FILE.lastModified() + 7L * 24 * 60 * 60 * 1000) {
            Trie trie = trieFactory.create();
            trie.load(DICTIONARY_FILE);
            return trie;
          }

          Trie trie = trieFactory.create();
          trie.build(dictionariesFactory.create().getWords());
          trie.save(DICTIONARY_FILE);
          return trie;
        }
      });

  @Inject
  public TrieCache(Dictionaries.Factory dictionariesFactory, Trie.Factory trieFactory) {
    this.dictionariesFactory = Preconditions.checkNotNull(dictionariesFactory);
    this.trieFactory = Preconditions.checkNotNull(trieFactory);
  }

  public Trie get() {
    try {
      return cache.get(STATIC_KEY);
    } catch (ExecutionException e) {
      throw Throwables.propagate(e);
    }
  }

}