dubbo 3.2.0 @Method 及callback 和notify 简单分析

@Method 及callback

dubbo 对callback的说明在 https://cn.dubbo.apache.org/zh-cn/overview/mannual/java-sdk/advanced-features-and-usage/service/callback-parameter/

关键内容如下：
特性说明
参数回调方式与调用本地 callback 或 listener 相同，只需要在 Spring 的配置文件中声明哪个参数是 callback 类型即可。Dubbo 将基于长连接生成反向代理，这样就可以从服务器端调用客户端逻辑。可以参考 dubbo 项目中的示例代码。
使用场景
回调函数通知客户端执行结果，或发送通知，在方法执行时间比较长时，类似异步调用，审批工作流中回调客户端审批结果。

最核心的配置其实是下面这一段

<bean id="callbackService" class="com.callback.impl.CallbackServiceImpl" />
<dubbo:service interface="com.callback.CallbackService" ref="callbackService" connections="1" callbacks="1000">
    <dubbo:method name="addListener">
        <dubbo:argument index="1" callback="true" />
        
        
    dubbo:method>
dubbo:service>

实际example 代码是示意annotation 的，如下

@DubboService(token = "true", connections = 1, callbacks = 1000,
        methods = @Method(name = "addListener", arguments = @Argument(index = 1, callback = true)))
public class CallbackServiceImpl implements CallbackService {

    private final Map<String, CallbackListener> listeners = new ConcurrentHashMap<String, CallbackListener>();

注意上的@Method及@Argument ，通过Argument 的index=1 定义了第一个参数是callback 函数，目前Argument只支持callback一种类型，@Method 还有一个Parameter 用于定义其它自定义参数。

跟踪分析，可以看到consumer获取到的service信息如下

DefaultServiceInstance{serviceName=‘callback-provider’, host=‘192.168.1.14’, port=20880, enabled=true, healthy=true, metadata={dubbo.endpoints=[{“port”:20880,“protocol”:“dubbo”}], dubbo.metadata-service.url-params={“prefer.serialization”:“fastjson2,hessian2”,“token”:“491567bd-21d1-4465-a500-15c852ce9899”,“version”:“1.0.0”,“dubbo”:“2.0.2”,“release”:“3.2.0”,“side”:“provider”,“port”:“20880”,“protocol”:“dubbo”}, dubbo.metadata.revision=5289ac26fb59bd436247504d9762b074, dubbo.metadata.storage-type=local, timestamp=1686452741890}}, service{name=‘org.apache.dubbo.samples.callback.api.CallbackService’,group=‘null’,version=‘null’,protocol=‘dubbo’,port=‘20880’,params={executor-management-mode=isolation, side=provider, file-cache=true, addListener.return=true, release=3.2.0, methods=addListener, deprecated=false, dubbo=2.0.2, callbacks=1000, interface=org.apache.dubbo.samples.callback.api.CallbackService, service-name-mapping=true, generic=false, token=4eb91b86-6f19-4277-ada3-4a2e2618c3db, addListener.sent=true, application=callback-provider, prefer.serialization=fastjson2,hessian2, addListener.1.callback=true, background=false, dynamic=true, connections=1, anyhost=true},}

然后通过代码public class CallbackServiceCodec的

private static byte isCallBack(URL url, String protocolServiceKey, String methodName, int argIndex) {
        // parameter callback rule: method-name.parameter-index(starting from 0).callback
        byte isCallback = CALLBACK_NONE;
        if (url != null && url.hasServiceMethodParameter(protocolServiceKey, methodName)) {
            String callback = url.getServiceParameter(protocolServiceKey, methodName + "." + argIndex + ".callback");
            if (callback != null) {
                if ("true".equalsIgnoreCase(callback)) {
                    isCallback = CALLBACK_CREATE;
                } else if ("false".equalsIgnoreCase(callback)) {
                    isCallback = CALLBACK_DESTROY;
                }
            }
        }
        return isCallback;
    }

核心是String callback = url.getServiceParameter(protocolServiceKey, methodName + “.” + argIndex + “.callback”);

开放一个服务，在log可以看到如下信息

2023-06-11 11:08:53.112 INFO 15528 — [ main] o.a.d.r.p.dubbo.CallbackServiceCodec : [DUBBO] Export a callback service :dubbo://192.168.1.14:55315/org.apache.dubbo.samples.callback.api.CallbackListener.522631570?addListener.1.callback=true&addListener.return=true&addListener.sent=true&anyhost=true&application=callback-consumer&background=false&callbacks=1000&connections=1&deprecated=false&dubbo=2.0.2&dubbo.endpoints=[{“port”:20880,“protocol”:“dubbo”}]&dubbo.metadata-service.url-params={“prefer.serialization”:“fastjson2,hessian2”,“token”:“491567bd-21d1-4465-a500-15c852ce9899”,“version”:“1.0.0”,“dubbo”:“2.0.2”,“release”:“3.2.0”,“side”:“provider”,“port”:“20880”,“protocol”:“dubbo”}&dubbo.metadata.revision=5289ac26fb59bd436247504d9762b074&dubbo.metadata.storage-type=local&dynamic=true&executor-management-mode=isolation&file-cache=true&generic=false&interface=org.apache.dubbo.samples.callback.api.CallbackListener&is_callback_service=true&isserver=false&methods=changed&pid=15528&prefer.serialization=fastjson2,hessian2&qos.enable=false®ister.ip=192.168.1.14&release=3.2.0&service-name-mapping=true&side=consumer&sticky=false×tamp=1686452741890&token=4eb91b86-6f19-4277-ada3-4a2e2618c3db&unloadClusterRelated=false, on NettyChannel [channel=[id: 0xd3dc4a8a, L:/192.168.1.14:55315 - R:/192.168.1.14:20880]], url is: DefaultServiceInstance{serviceName=‘callback-provider’, host=‘192.168.1.14’, port=20880, enabled=true, healthy=true, metadata={dubbo.endpoints=[{“port”:20880,“protocol”:“dubbo”}], dubbo.metadata-service.url-params={“prefer.serialization”:“fastjson2,hessian2”,“token”:“491567bd-21d1-4465-a500-15c852ce9899”,“version”:“1.0.0”,“dubbo”:“2.0.2”,“release”:“3.2.0”,“side”:“provider”,“port”:“20880”,“protocol”:“dubbo”}, dubbo.metadata.revision=5289ac26fb59bd436247504d9762b074, dubbo.metadata.storage-type=local, timestamp=1686452741890}}, service{name=‘org.apache.dubbo.samples.callback.api.CallbackService’,group=‘null’,version=‘null’,protocol=‘dubbo’,port=‘20880’,params={executor-management-mode=isolation, side=provider, file-cache=true, addListener.return=true, release=3.2.0, methods=addListener, deprecated=false, dubbo=2.0.2, callbacks=1000, interface=org.apache.dubbo.samples.callback.api.CallbackService, service-name-mapping=true, generic=false, token=4eb91b86-6f19-4277-ada3-4a2e2618c3db, addListener.sent=true, application=callback-provider, prefer.serialization=fastjson2,hessian2, addListener.1.callback=true, background=false, dynamic=true, connections=1, anyhost=true},}, dubbo version: 3.2.0, current host: 192.168.1.14

notify

所谓notify就是利用Method 的onXXX实现调用跟踪

public @interface Method {
    String name();

    int timeout() default -1;

    int retries() default -1;

    String loadbalance() default "";

    boolean async() default false;

    boolean sent() default true;

    int actives() default -1;

    int executes() default -1;

    boolean deprecated() default false;

    boolean sticky() default false;

    boolean isReturn() default true;

    String oninvoke() default "";

    String onreturn() default "";

    String onthrow() default "";

    String cache() default "";

    String validation() default "";

    String merger() default "";

    Argument[] arguments() default {};

    /**
     * Customized parameter key-value pair, for example: {key1, value1, key2, value2} or {"key1=value1", "key2=value2"}
     */
    String[] parameters() default {};

}
 

官方example code如下

// @Component
public class Task implements CommandLineRunner {

    // @DubboReference
    @DubboReference(methods = @Method(name = "sayHello", onreturn = "notify.onReturn", onthrow = "notify.onThrow"))
    private DemoService demoService;