Guava 常用功能，防止阁下重复造轮子

淩亂°似流年 2024-02-22 08:53 48阅读 0赞

#### 1. 本地缓存 ####

/**
         * 功能：缓存
         * 文档：<a href="https://github.com/google/guava/wiki/CachesExplained">CachesExplained</a>
         */
        @Test
        public void test_cache() {
            Cache<String, String> cache = CacheBuilder.newBuilder()
                    // 最大存储条数，缓存将尝试逐出最近或不经常使用的条目
                    .maximumSize(10000)
                    // 可以设定删除时候的权重判断
                    //.weigher((Weigher<String, String>) (x, y) -> x.length() - y.length())
                    // 有效时间
                    .expireAfterWrite(3, TimeUnit.SECONDS)
                    // 记录次数
                    .recordStats()
                    .build();
    
            cache.put("Lasse", "You are handsome.");
            log.info("测试结果：{}", cache.getIfPresent("Lasse"));
    
            cache.invalidate("Lasse"); // cache.invalidateAll(); 也可以全部删除
            log.info("测试结果：{}", cache.getIfPresent("Lasse"));
    
            log.info("测试结果：{}", cache.stats());
        }

#### 2. MQ ####

@Test
        public void test_eventbus() {
            EventBus eventBus = new EventBus();
            eventBus.register(new Listener());
            // 可以由其他服务推送消息，之后就可以在监听中收到了
            eventBus.post("消息总线，订单号：100001");
        }
    
        static class Listener {
            @Subscribe
            public void handleEvent(String orderId) {
                log.info("测试结果：{}", orderId);
            }
        }

#### 3. 并发回调 ####

/**
         * 功能：并发回调
         * 文档：https://github.com/google/guava/wiki/ListenableFutureExplained
         */
        @Test
        public void test_ListenableFuture() throws InterruptedException {
            CountDownLatch countDownLatch = new CountDownLatch(1);
    
            ListeningExecutorService executorService = MoreExecutors.listeningDecorator(Executors.newFixedThreadPool(10));
            ListenableFuture<String> explosion = executorService.submit(() -> "finished");
    
            ExecutorService callBackService = Executors.newFixedThreadPool(1);
            Futures.addCallback(explosion, new FutureCallback<String>() {
                public void onSuccess(String explosion) {
                    System.out.println("onSuccess");
                    countDownLatch.countDown();
                }
    
                public void onFailure(Throwable thrown) {
                    System.out.println("onFailure");
                    countDownLatch.countDown();
                }
            }, callBackService);
    
            countDownLatch.await();
        }

#### 4. 布隆过滤器 ####

/**
         * 功能：布隆过滤器
         * 文档：https://github.com/google/guava/wiki/HashingExplained#bloomfilter
         */
        @Test
        public void test_BloomFilter() {
            BloomFilter<String> bloomFilter = BloomFilter.create(Funnels.stringFunnel(Charset.defaultCharset()),
                    1000,
                    0.01);
    
            // 向布隆过滤器中添加元素
            bloomFilter.put("apple");
            bloomFilter.put("banana");
            bloomFilter.put("orange");
    
            // 检查元素是否存在于布隆过滤器中
            System.out.println(bloomFilter.mightContain("apple"));   // true
            System.out.println(bloomFilter.mightContain("banana"));  // true
            System.out.println(bloomFilter.mightContain("orange"));  // true
            System.out.println(bloomFilter.mightContain("grape"));   // false
    
            // 输出布隆过滤器的统计信息
            System.out.println("Expected FPP: " + bloomFilter.expectedFpp());
            System.out.println("Number of Inserted Elements: " + bloomFilter.approximateElementCount());
        }

#### 5. 反射工具包 ####

/**
         * 功能：反射
         * 文档：https://github.com/google/guava/wiki/ReflectionExplained
         */
        @Test
        public void test_Invokable() throws NoSuchMethodException {
            Method method = UserEntity.class.getMethod("getCreateTime");
            Invokable<?, ?> invokable = Invokable.from(method);
            log.info("测试结果 - 方法名称：{}", invokable.getName());
            log.info("测试结果 - 参数类型：{}", JSON.toJSONString(invokable.getTypeParameters()));
            log.info("测试结果 - 静态判断：{}", invokable.isStatic());
            // !(Modifier.isFinal(method.getModifiers()) || Modifiers.isPrivate(method.getModifiers()) || Modifiers.isStatic(method.getModifiers()) || Modifiers.isFinal(method.getDeclaringClass().getModifiers()))
            log.info("测试结果 - isOverridable：{}", invokable.isOverridable());
        }