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1.Overview

Designed to run specific code with a timer, which is a self-organising server with loose coupling and high avaiability.

Features

• Your application registers a callback whith exact trigger time that the callback server will then invoke.
• Your application could cancel a callback before it's invocation arrival.
• The callback server confirms callback invocation if that callback has retry strategy being set.
• The callback server is born with HA, you only need to deploy multiple instances.
• Callback trigger time is accurate to second.
• Registration can be idempotent. (while idempotent of callback invocation should be consideration of your application.)
• Callbacks are grouped by your application name.
• Easy to use, just like writing local java callbacks.

2.Projects

delay-callback-server

The callback server persists registered callbacks (to redis), ensuring that callbacks will always be invoked. Besides, the callback server is stateless, so out-of-the-box, it can be scaled out easily.

Main components

• Facade: register && unRegister
• ScanJob: scheduled job scans available callback tasks. Master election will be made automatically if you have more than one instance deployed.
• Distributor: distributes callback tasks based on dubbo's loadbanlance that can be customed by configuration.
• Processor: processes callbacks under protection of distributed lock.

Dependencies

dubbo/spring cloud/zookeeper/redis

delay-callback-client

The callback client encapsulates communication detail between your application and the callback server, and provides a helper to easily write registration and callback code.

Main components

• Initializer: initializes local callback implementation
• Registry: registers callback client to zookeeper
• Refer: discovers callabck server from zookeeper
• Helper: DelayCallbackHelper, the main class you will interact with:

public class DelayCallbackHelper {
    /**
     * register callback
     *
     * @param callbackParam params
     * @param delayCallback implementation of callback logic
     * @return unique id
     */
    public static RegisterResult register(CallbackParam callbackParam, DelayCallback delayCallback) {...}

    /**
     * cancel registration
     *
     * @param uid unique id
     * @return result
     */
    public static UnRegisterResult unRegister(String uid) {...}
}

Dependencies

dubbo/spring

delay-callback-interface

common interfaces and objects used by client and server

client-demo

Shows how to use delay-callback-client to register callback and write callback logic.

3.Get started

i.Start server

cd delay-callback-server
# edit application.properties
mvn spring-boot:run

ii.Add dependency to your application

        <dependency>
            <groupId>com.johnli</groupId>
            <artifactId>delay-callback-client</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>

iii.Write java code in your application

        // params that will be delivered while callback
        List<String> params = new ArrayList<>();
        params.add("hello");
        params.add("world");

        // will callback in 3 seconds
        int delaySeconds = 3;
        
        // do register
        RegisterResult register = DelayCallbackHelper.register(new CallbackParam(params, delaySeconds), new DelayCallback() {
            @Override
            public String alias() {
                return "callback01";
            }

            @Override
            public boolean onCallback(CallbackRequest request) {
                // do whatever you want here

                return true;
            }
        });

        if (register.isSuccess()) {
            System.out.println("register successfully");

            // you can cancel before the callback being invoked.
            //DelayCallbackHelper.unRegister(register.getUid());
        }

You see, just like writing local java callback.

iv.run your application

4.Advanced usages

// todo

5.License

delay-callback is under the Apache 2.0 license. See the LICENSE file for details.