1. 背景

泛型调用适用于观察者模式，即有很多广泛的消费者，但生产者又不想依赖消费者的client包，比如常见的API开放平台的回调机制；

2. 泛型调用

要实现泛型调用，几个核心点：

• 泛型入参如何构建
• 泛型服务service 如何构建
• 泛型调用结果如何拿到

2.1 泛型入参

泛型入参须是HashMap, 并且第1个参数的key为class, value为实际RPC方法入参的class name，其余参数则为入参类里的字段。示例如下

    private Map<String, Object> buildParams() {
        Map<String, Object> params = new HashMap<>();
        params.put("class", "com.my.dubbo.client.generic.TestParams");
        params.put("name", "zhangsan");
        params.put("id", 1234556);
        params.put("phone", "12345");
        return params;
    }

2.2 泛型Service

泛型Service须借助dubbo本身提供的缓存机制org.apache.dubbo.config.utils.SimpleReferenceCache，减少每次重复创建Service的开销。

    @Test
    void testGenericCall() throws Exception {
        ApplicationConfig applicationConfig = new ApplicationConfig();
        applicationConfig.setName("generic-demo-consumer");

        RegistryConfig registryConfig = new RegistryConfig();
        registryConfig.setId("dubbo-registry-id");
        registryConfig.setAddress("zookeeper://myzk1:port");
        registryConfig.setTimeout(20000);
        applicationConfig.setRegistry(registryConfig);
        ReferenceConfig<GenericService> referenceConfig = new ReferenceConfig<>();
        referenceConfig.setApplication(applicationConfig);
        referenceConfig.setInterface("com.my.dubbo.client.generic.HelloService");
        referenceConfig.setGeneric("true");
        referenceConfig.setVersion("1.0.0");
        referenceConfig.setCheck(true);
        referenceConfig.setGroup("DEMO-GROUP");
        referenceConfig.setAsync(true);
        referenceConfig.setTimeout(10000);
        SimpleReferenceCache referenceCache = SimpleReferenceCache.getCache();
        GenericService genericService = referenceCache.get(referenceConfig);
        Map<String, Object> params = buildParams();
        String[] paramTypes = new String[] {"com.my.dubbo.client.generic.TestParams"};
        Object result = genericService.$invoke("sayHello", paramTypes, new Object[]{params});
        CountDownLatch latch = new CountDownLatch(1);
        CompletableFuture<Object> future = RpcContext.getContext().getCompletableFuture();
        future.whenComplete((value, t) -> {
             result = value;
             System.out.println("invokeAsyncHello(whenComplete): " + value);
             latch.countDown();
        });
        latch.await(5000, TimeUnit.MILLISECONDS);
}

3. 注意事项

SpringBoot应用，需添加EnableDubbo标签才能调用泛型，否则无法获取到genericSerivce实例。

以上。