public static Serializer getSerializer(String alias) {
        // 工厂模式  托管给ExtensionLoader
        return EXTENSION_LOADER.getExtension(alias);
    }
@Test
    public void getSerializer1() {
        Serializer serializer = SerializerFactory.getSerializer("test");
        Assert.assertNotNull(serializer);
        Assert.assertEquals(TestSerializer.class, serializer.getClass());
    }