java-design-patterns/caching/src/main/java/com/iluwatar/caching/AppManager.java

/*
 * The MIT License
 * Copyright © 2014-2021 Ilkka Seppälä
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

package com.iluwatar.caching;

import com.iluwatar.caching.database.DbManager;

import java.util.Optional;

import lombok.extern.slf4j.Slf4j;

/**
 * AppManager helps to bridge the gap in communication between the main class
 * and the application's back-end. DB connection is initialized through this
 * class. The chosen  caching strategy/policy is also initialized here.
 * Before the cache can be used, the size of the  cache has to be set.
 * Depending on the chosen caching policy, AppManager will call the
 * appropriate function in the CacheStore class.
 */
@Slf4j
public class AppManager {
  /**
   * Caching Policy.
   */
  private CachingPolicy cachingPolicy;
  /**
   * Database Manager.
   */
  private final DbManager dbManager;
  /**
   * Cache Store.
   */
  private final CacheStore cacheStore;

  /**
   * Constructor.
   *
   * @param newDbManager database manager
   */
  public AppManager(final DbManager newDbManager) {
    this.dbManager = newDbManager;
    this.cacheStore = new CacheStore(newDbManager);
  }

  /**
   * Developer/Tester is able to choose whether the application should use
   * MongoDB as its underlying data storage or a simple Java data structure
   * to (temporarily) store the data/objects during runtime.
   */
  public void initDb() {
    dbManager.connect();
  }

  /**
   * Initialize caching policy.
   *
   * @param policy is a {@link CachingPolicy}
   */
  public void initCachingPolicy(final CachingPolicy policy) {
    cachingPolicy = policy;
    if (cachingPolicy == CachingPolicy.BEHIND) {
      Runtime.getRuntime().addShutdownHook(new Thread(cacheStore::flushCache));
    }
    cacheStore.clearCache();
  }

  /**
   * Find user account.
   *
   * @param userId String
   * @return {@link UserAccount}
   */
  public UserAccount find(final String userId) {
    LOGGER.info("Trying to find {} in cache", userId);
    if (cachingPolicy == CachingPolicy.THROUGH
            || cachingPolicy == CachingPolicy.AROUND) {
      return cacheStore.readThrough(userId);
    } else if (cachingPolicy == CachingPolicy.BEHIND) {
      return cacheStore.readThroughWithWriteBackPolicy(userId);
    } else if (cachingPolicy == CachingPolicy.ASIDE) {
      return findAside(userId);
    }
    return null;
  }

  /**
   * Save user account.
   *
   * @param userAccount {@link UserAccount}
   */
  public void save(final UserAccount userAccount) {
    LOGGER.info("Save record!");
    if (cachingPolicy == CachingPolicy.THROUGH) {
      cacheStore.writeThrough(userAccount);
    } else if (cachingPolicy == CachingPolicy.AROUND) {
      cacheStore.writeAround(userAccount);
    } else if (cachingPolicy == CachingPolicy.BEHIND) {
      cacheStore.writeBehind(userAccount);
    } else if (cachingPolicy == CachingPolicy.ASIDE) {
      saveAside(userAccount);
    }
  }

  /**
   * Returns String.
   *
   * @return String
   */
  public String printCacheContent() {
    return cacheStore.print();
  }

  /**
   * Cache-Aside save user account helper.
   *
   * @param userAccount {@link UserAccount}
   */
  private void saveAside(final UserAccount userAccount) {
    dbManager.updateDb(userAccount);
    cacheStore.invalidate(userAccount.getUserId());
  }

  /**
   * Cache-Aside find user account helper.
   *
   * @param userId String
   * @return {@link UserAccount}
   */
  private UserAccount findAside(final String userId) {
    return Optional.ofNullable(cacheStore.get(userId))
            .or(() -> {
              Optional<UserAccount> userAccount =
                      Optional.ofNullable(dbManager.readFromDb(userId));
              userAccount.ifPresent(account -> cacheStore.set(userId, account));
              return userAccount;
            })
            .orElse(null);
  }
}