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A set of utilities and tools to speed up and ease programming in Java.
There is a newer version: 0.5
/*
 * (c) 2005 David B. Bracewell
 *
 * 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 com.davidbracewell.cache;

import com.davidbracewell.config.Config;
import com.davidbracewell.conversion.Cast;
import com.davidbracewell.reflection.Reflect;
import com.davidbracewell.reflection.ReflectionException;
import com.davidbracewell.string.StringUtils;
import com.google.common.base.Strings;
import com.google.common.base.Throwables;

import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

/**
 * Manages the creation and retrieval of caches. Caches are defined as specification {@link CacheSpec}. Additionally,
 * there can be cacheSpecClass configuration setting if a special CacheSpec needs to be used
 * to parse the string specification.
 *
 * @author David Bracewell
 */
public final class CacheManager {

  /**
   * The name of the global cache.
   */
  public static final String GLOBAL_CACHE = "com.davidbracewell.cache.globalCache";
  private static volatile CacheManager INSTANCE = null;
  private volatile Map> caches = new ConcurrentHashMap<>();


  private CacheManager() {

  }

  /**
   * Creates an object that automatically caches results for methods annotated with the @Cached
   * annotation.
   *
   * @param     The type of the object
   * @param object The object, which must implement an interface,  that we are wrapping
   * @return The Proxy object
   */
  public static  T cacheObject(T object) {
    return CacheProxy.cache(object);
  }

  /**
   * Gets instance.
   *
   * @return The CacheManager instance
   */
  public static CacheManager getInstance() {
    if (INSTANCE == null) {
      synchronized (CacheManager.class) {
        if (INSTANCE == null) {
          INSTANCE = new CacheManager();
        }
      }
    }
    return INSTANCE;
  }

  /**
   * Determines if a cache with a given name has been created
   *
   * @param name The cache name
   * @return True if the cache has been created, false if not.
   */
  public boolean contains(String name) {
    return caches.containsKey(name);
  }

  /**
   * Gets the cache associated with the given name. If the name is not known, i.e. the associated cache has not been
   * defined, a no operation cache (no cache) is returned.
   *
   * @param   the type parameter
   * @param   the type parameter
   * @param name The name of the cache
   * @return A cache
   */
  public  Cache get(String name) {
    if (StringUtils.isNullOrBlank(name)) {
      throw new IllegalArgumentException("Cache name must not be null or blank.");
    }

    if (GLOBAL_CACHE.equals(name)) {
      return Cast.as(getGlobalCache());
    } else if (caches.containsKey(name)) {
      return Cast.as(caches.get(name));
    } else if (Config.hasProperty(name) && caches.containsKey(Config.get(name).asString())) {
      return Cast.as(caches.get(Config.get(name).asString()));
    }

    return register(this.getCacheSpec(name));
  }

  /**
   * Gets cache names.
   *
   * @return The names of all of the initialized caches.
   */
  public Set getCacheNames() {
    return caches.keySet();
  }

  private  CacheSpec getCacheSpec(String property) {

    //Sanity check for the global cache. If one is not defined in the configuration create a default with max size 1,000
    if (GLOBAL_CACHE.equals(property) && !Config.hasProperty(property)) {
      return new CacheSpec().name(GLOBAL_CACHE).maxSize(1000);
    }

    String specString = Config.get(property).asString();

    //Make sure the cache is defined
    if (Strings.isNullOrEmpty(specString)) {
      throw new IllegalArgumentException(property + " is not a known cache and is not defined via a config file.");
    }

    CacheSpec spec;
    //See if there is special implementation of the cache spec class
    if (Config.hasProperty(property + ".cacheSpecClass")) {
      try {
        spec = Reflect.onClass(Config.get(property + ".cacheSpecClass").asClass()).create().get();
      } catch (ReflectionException e) {
        throw Throwables.propagate(e);
      }
    } else {
      spec = new CacheSpec<>();
    }

    try {
      spec.fromString(specString);
      if (!specString.contains("name:")) {
        spec.name(property);
      }
    } catch (Exception e) {
      throw new IllegalStateException(specString + " is an invalid specification string.");
    }

    return spec;
  }

  /**
   * Gets global cache.
   *
   * @return The global cache
   */
  public  Cache getGlobalCache() {
    if (caches.containsKey(GLOBAL_CACHE)) {
      return Cast.as(caches.get(GLOBAL_CACHE));
    }
    Cache cache = Cast.as(register(getCacheSpec(GLOBAL_CACHE)));
    caches.put(GLOBAL_CACHE, cache);
    return cache;
  }

  /**
   * Creates a cache for a given cache specification. If the name in the specification is a known cache, then
   * it will return that cache.
   *
   * @param            The key type
   * @param            The value type
   * @param specification The specification
   * @return A cache for the specification
   */
  public  Cache register(CacheSpec specification) {
    if (!caches.containsKey(specification.getName())) {
      Cache cache = specification.getEngine().create(specification);
      caches.putIfAbsent(cache.getName(), cache);
    }
    return Cast.as(caches.get(specification.getName()));
  }

}//END OF CacheManager