Google Guava-基于泛型的使用方式

private static Cache<String, String> cacheFormCallable = null;

public static <K, V> Cache<K, V> callableCached() throws Exception {
		Cache<K, V> cache = CacheBuilder.newBuilder().maximumSize(10000).expireAfterWrite(10, TimeUnit.MINUTES).build();
		return cache;
	}

private String getCallableCache(final String userName) {
		try {
			// Callable只有在缓存值不存在时，才会调用
			return cacheFormCallable.get(userName, new Callable<String>() {
				@Override
				public String call() throws Exception {
					System.out.println(userName + " from db");
					return "hello " + userName + "!";
				}
			});
		} catch (ExecutionException e) {
			e.printStackTrace();
			return null;
		}
	}