public MemoryCache() {
        this.mainCache = new ConcurrentHashMap<>();
    }
@Test
    public void testMemoryCache() {
        final MemoryCache memoryCache = new MemoryCache();
        final String key = "data";
        memoryCache.isExist(key).subscribe(v -> assertEquals(Boolean.FALSE, v));
        memoryCache.cacheData(key, "data".getBytes(StandardCharsets.UTF_8), 10)
                .subscribe(v -> assertEquals(Boolean.TRUE, v));
        memoryCache.isExist(key).subscribe(v -> assertEquals(Boolean.TRUE, v));
        memoryCache.getData(key).subscribe(v -> assertEquals("data", new String(v, StandardCharsets.UTF_8)));
    }