Java实现一个简单的缓存方法

Posted 2020-10-27 For_elegant

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缓存是在web开发中经常用到的，将程序经常使用到或调用到的对象存在内存中，或者是耗时较长但又不具有实时性的查询数据放入内存中，在一定程度上可以提高性能和效率。下面我实现了一个简单的缓存，步骤如下。

创建缓存对象EntityCache.java

public class EntityCache {
  /**
   * 保存的数据
   */
  private Object datas;
 
  /**
   * 设置数据失效时间,为0表示永不失效
   */
  private long timeOut;
 
  /**
   * 最后刷新时间
   */
  private long lastRefeshTime;
 
  public EntityCache(Object datas, long timeOut, long lastRefeshTime) {
    this.datas = datas;
    this.timeOut = timeOut;
    this.lastRefeshTime = lastRefeshTime;
  }
  public Object getDatas() {
    return datas;
  }
  public void setDatas(Object datas) {
    this.datas = datas;
  }
  public long getTimeOut() {
    return timeOut;
  }
  public void setTimeOut(long timeOut) {
    this.timeOut = timeOut;
  }
  public long getLastRefeshTime() {
    return lastRefeshTime;
  }
  public void setLastRefeshTime(long lastRefeshTime) {
    this.lastRefeshTime = lastRefeshTime;
  }
 
 
}
定义缓存操作接口，ICacheManager.java
public interface ICacheManager {
  /**
   * 存入缓存
   * @param key
   * @param cache
   */
  void putCache(String key, EntityCache cache);
 
  /**
   * 存入缓存
   * @param key
   * @param cache
   */
  void putCache(String key, Object datas, long timeOut);
 
  /**
   * 获取对应缓存
   * @param key
   * @return
   */
  EntityCache getCacheByKey(String key);
 
  /**
   * 获取对应缓存
   * @param key
   * @return
   */
  Object getCacheDataByKey(String key);
 
  /**
   * 获取所有缓存
   * @param key
   * @return
   */
  Map<String, EntityCache> getCacheAll();
 
  /**
   * 判断是否在缓存中
   * @param key
   * @return
   */
  boolean isContains(String key);
 
  /**
   * 清除所有缓存
   */
  void clearAll();
 
  /**
   * 清除对应缓存
   * @param key
   */
  void clearByKey(String key);
 
  /**
   * 缓存是否超时失效
   * @param key
   * @return
   */
  boolean isTimeOut(String key);
 
  /**
   * 获取所有key
   * @return
   */
  Set<String> getAllKeys();
}
实现接口ICacheManager，CacheManagerImpl.java
这里我使用了ConcurrentHashMap来保存缓存，本来以为这样就是线程安全的，其实不然，在后面的测试中会发现它并不是线程安全的。
public class CacheManagerImpl implements ICacheManager {
  private static Map<String, EntityCache> caches = new ConcurrentHashMap<String, EntityCache>();
 
  /**
   * 存入缓存
   * @param key
   * @param cache
   */
  public void putCache(String key, EntityCache cache) {
    caches.put(key, cache);
  }
 
  /**
   * 存入缓存
   * @param key
   * @param cache
   */
  public void putCache(String key, Object datas, long timeOut) {
    timeOut = timeOut > 0 ? timeOut : 0L;
    putCache(key, new EntityCache(datas, timeOut, System.currentTimeMillis()));
  }
 
  /**
   * 获取对应缓存
   * @param key
   * @return
   */
  public EntityCache getCacheByKey(String key) {
    if (this.isContains(key)) {
      return caches.get(key);
    }
    return null;
  }
 
  /**
   * 获取对应缓存
   * @param key
   * @return
   */
  public Object getCacheDataByKey(String key) {
    if (this.isContains(key)) {
      return caches.get(key).getDatas();
    }
    return null;
  }
 
  /**
   * 获取所有缓存
   * @param key
   * @return
   */
  public Map<String, EntityCache> getCacheAll() {
    return caches;
  }
 
  /**
   * 判断是否在缓存中
   * @param key
   * @return
   */
  public boolean isContains(String key) {
    return caches.containsKey(key);
  }
 
  /**
   * 清除所有缓存
   */
  public void clearAll() {
    caches.clear();
  }
 
  /**
   * 清除对应缓存
   * @param key
   */
  public void clearByKey(String key) {
    if (this.isContains(key)) {
      caches.remove(key);
    }
  }
 
  /**
   * 缓存是否超时失效
   * @param key
   * @return
   */
  public boolean isTimeOut(String key) {
    if (!caches.containsKey(key)) {
      return true;
    }
    EntityCache cache = caches.get(key);
    long timeOut = cache.getTimeOut();
    long lastRefreshTime = cache.getLastRefeshTime();
    if (timeOut == 0 || System.currentTimeMillis() - lastRefreshTime >= timeOut) {
      return true;
    }
    return false;
  }
 
  /**
   * 获取所有key
   * @return
   */
  public Set<String> getAllKeys() {
    return caches.keySet();
  }
}
CacheListener.java,监听失效数据并移除。
public class CacheListener{
  Logger logger = Logger.getLogger("cacheLog");
  private CacheManagerImpl cacheManagerImpl;
  public CacheListener(CacheManagerImpl cacheManagerImpl) {
    this.cacheManagerImpl = cacheManagerImpl;
  }
 
  public void startListen() {
    new Thread(){
      public void run() {
        while (true) {
          for(String key : cacheManagerImpl.getAllKeys()) {
            if (cacheManagerImpl.isTimeOut(key)) {
             cacheManagerImpl.clearByKey(key);
             logger.info(key + "缓存被清除");
           }
          } 
        }
      } 
    }.start();
 
  }
}
测试类TestCache.java
public class TestCache {
  Logger logger = Logger.getLogger("cacheLog");
  /**
   * 测试缓存和缓存失效
   */
  @Test
  public void testCacheManager() {
    CacheManagerImpl cacheManagerImpl = new CacheManagerImpl();
    cacheManagerImpl.putCache("test", "test", 10 * 1000L);
    cacheManagerImpl.putCache("myTest", "myTest", 15 * 1000L);
    CacheListener cacheListener = new CacheListener(cacheManagerImpl);
    cacheListener.startListen();
    logger.info("test:" + cacheManagerImpl.getCacheByKey("test").getDatas());
    logger.info("myTest:" + cacheManagerImpl.getCacheByKey("myTest").getDatas());
    try {
      TimeUnit.SECONDS.sleep(20);
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
    logger.info("test:" + cacheManagerImpl.getCacheByKey("test"));
    logger.info("myTest:" + cacheManagerImpl.getCacheByKey("myTest"));
  }
 
  /**
   * 测试线程安全
   */
  @Test
  public void testThredSafe() {
    final String key = "thread";
    final CacheManagerImpl cacheManagerImpl = new CacheManagerImpl();
    ExecutorService exec = Executors.newCachedThreadPool();
    for (int i = 0; i < 100; i++) {
      exec.execute(new Runnable() {
        public void run() {
            if (!cacheManagerImpl.isContains(key)) {
              cacheManagerImpl.putCache(key, 1, 0);
            } else {
              //因为+1和赋值操作不是原子性的，所以把它用synchronize块包起来
              synchronized (cacheManagerImpl) {
                int value = (Integer) cacheManagerImpl.getCacheDataByKey(key) + 1; 
                cacheManagerImpl.putCache(key,value , 0);
              }
            }
        }
      });
    }
    exec.shutdown(); 
    try {
      exec.awaitTermination(1, TimeUnit.DAYS);
    } catch (InterruptedException e1) {
      e1.printStackTrace();
    } 
 
    logger.info(cacheManagerImpl.getCacheDataByKey(key).toString());
  }
}
 
 
来源：http://www.jb51.net/article/111518.htm

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