【设计一个缓存--针对各种类型的缓存】

1. 设计顶层接口

// 定义为一个泛型接口,提供给抽象类使用
public interface CacheManager<T> {// 获取所有的缓存itemList<T> getAll();// 根据条件获取某些缓存itemList<T> get(Predicate<T> predicate);// 设置缓存boolean set(T t);// 设置缓存listboolean set(List<T> tList);
}

有接口必定有实现类或者抽象类，实现接口。
那为了更好地控制子类的行为，可以做一个抽象类，控制子类行为。

• 分析：
  • 抽象类作为缓存管理的话，那么就需要提供安全访问数据
  • 需要考虑线程安全问题。
  • 花絮： 不仅要满足上述需求，而且让代码尽量简洁。

2. 设计抽象类 – AbstractCacheManager

• 属性设计：
  • 需要一个缓存
  • 需要一个线程安全机制方案
• 行为设计：
  • 自己的行为：
    • 利用线程安全机制控制缓存的读写。
    • 权限：仅自己可访问
  • 后代的行为：
    • 访问一些简单api方法即可实现安全访问缓存
    • 权限：公共访问
• 设计模式：
  • 包裹思想，将后代行为方法中，包裹一层安全访问的行为。

Java Code：

 // properties design:
protected ConcurrentMap<String, T> cache;private ReentrantReadWriteLock lock = new ReentrantReadWriteLock();// subclass to implements these abstract methods.protected abstract List<T> getAllByCache();protected abstract void setByCache(T t);protected abstract void setByCache(List<T> tList);protected abstract List<T> getByCache(Predicate<T> predicate);// next content needs to consider safety of multithreads. following methods do implements.
// entry to use
@Override
public final List<T> getAll() {return this.readLockThenGet(() -> this.getAllByCache());
}@Override
public final List<T> get(Predicate<T> predicate) {return this.readLockThenGet(pre -> getByCache(pre), predicate);
}@Override
public final boolean set(T t) {return this.writeLockThenSet((Consumer<T>) obj -> set(obj), t);
}@Override
public final boolean set(List<T> tList) {return this.writeLockThenSet((Consumer<List<T>>) list -> set(list), tList);
}// current abstract class access cache object.
private boolean writeLockThenSet(Consumer consumer, Object object){boolean wLock = false;try {if (!(wLock = lock.writeLock().tryLock(100, TimeUnit.MICROSECONDS))) {return false;}consumer.accept(object);return true;} catch (Exception e) {return false;} finally {if(wLock) {lock.writeLock().unlock();}}
}private List<T> readLockThenGet(Supplier<List<T>> supplier){boolean rLock = false;try{if(!(rLock = lock.readLock().tryLock(100, TimeUnit.MICROSECONDS))){return null;}return supplier.get();}catch (Exception e){return null;}finally {if(rLock) {lock.readLock().unlock();}}
}private List<T> readLockThenGet(Function<Predicate<T>, List<T>> function, Predicate<T> predicate){boolean rLock = false;try{if(!(rLock = lock.readLock().tryLock(100, TimeUnit.MICROSECONDS))){return null;}return function.apply(predicate);}catch (Exception e){return null;}finally {if(rLock) {lock.readLock().unlock();}}
}

3. 具体子类

3.1 – AlertRuleItemExpCacheManager

@Component("alertRuleItemExpCacheManager")
public class AlertRuleItemExpCacheManager<T extends AlertRuleItemExpCache> extends AbstractCacheManager<AlertRuleItemExpCache> {@Resourceprivate AlertRuleItemExpDao alertRuleItemExpDao;@Overrideprotected List<AlertRuleItemExpCache> getAllByCache() {if (null == cache) {List<AlertRuleItemExp> alertRuleItemSrcList =alertRuleItemExpDao.selectList(Wrappers.<AlertRuleItemExp>lambdaQuery().eq(AlertRuleItemExp::getDeleted, 0));cache = alertRuleItemSrcList.stream().map(entity -> entity.toCache()).collect(Collectors.toConcurrentMap(cache -> cache.getId().toString(), cache -> cache));}return cache.values().stream().sorted(Comparator.comparing(AlertRuleItemExpCache::getId)).collect(Collectors.toList());}@Overrideprotected void setByCache(AlertRuleItemExpCache alertRuleItemExpCache) {cache.put(alertRuleItemExpCache.getId().toString(), alertRuleItemExpCache);}@Overrideprotected void setByCache(List<AlertRuleItemExpCache> alertRuleItemExpCacheList) {alertRuleItemExpCacheList.parallelStream().forEach(alertRuleItemExpCache ->cache.put(alertRuleItemExpCache.getId().toString(), alertRuleItemExpCache));}@Overrideprotected List<AlertRuleItemExpCache> getByCache(Predicate<AlertRuleItemExpCache> predicate) {return getAllByCache().stream().filter(cache -> predicate.test(cache)).collect(Collectors.toList());}
}

3.2 – AlertRuleItemSrcCacheManager

@Component("alertRuleItemSrcCacheManager")
public class AlertRuleItemSrcCacheManager<T extends AlertRuleItemSrcCache> extends AbstractCacheManager<AlertRuleItemSrcCache> {@Resourceprivate AlertRuleItemSrcDao alertRuleItemSrcDao;@Overrideprotected List<AlertRuleItemSrcCache> getAllByCache() {if (null == cache) {List<AlertRuleItemSrc> alertRuleItemSrcList =alertRuleItemSrcDao.selectList(Wrappers.<AlertRuleItemSrc>lambdaQuery().eq(AlertRuleItemSrc::getDeleted, 0));cache = alertRuleItemSrcList.stream().map(entity -> entity.toCache()).collect(Collectors.toConcurrentMap(cache -> cache.getId().toString(), cache -> cache));}return cache.values().stream().sorted(Comparator.comparing(AlertRuleItemSrcCache::getId)).collect(Collectors.toList());}@Overrideprotected void setByCache(AlertRuleItemSrcCache alertRuleItemSrcCache) {cache.put(alertRuleItemSrcCache.getId().toString(), alertRuleItemSrcCache);}@Overrideprotected void setByCache(List<AlertRuleItemSrcCache> alertRuleItemSrcCacheList) {alertRuleItemSrcCacheList.parallelStream().forEach(alertRuleItemSrcCache ->cache.put(alertRuleItemSrcCache.getId().toString(), alertRuleItemSrcCache));}@Overrideprotected List<AlertRuleItemSrcCache> getByCache(Predicate<AlertRuleItemSrcCache> predicate) {return getAllByCache().stream().filter(cache -> predicate.test(cache)).collect(Collectors.toList());}
}

4. 类图关系