How to elegantly turn asynchronous operations into synchronous operations in Java?

Best practices for asynchronous Java to synchronous

In Java applications, it is often necessary to convert asynchronous operations into synchronous operations. For example, the controller method sends a message to a message queue (MQ), and after MQ processing, the result is written to Redis, and the controller needs to return the processing result immediately. Direct polling for Redis is not the best solution, and this article explores a more elegant implementation method.

Although polling is not completely undesirable, it should be avoided when pursuing efficient and elegant code. We can use the asynchronous process callback mechanism to allow consumers to actively notify producers.

Several feasible solutions:

1. Redis Publish/Subscribe (Pub/Sub): After the controller sends a message to MQ, it also subscribes to a specific channel in Redis. After the MQ consumer processing is completed, the result message will be posted to the channel. The controller thread blocks on the subscription operation until a result message is received or timed out.

2. MQ completion message: After the MQ consumer completes processing, he sends a completion message to MQ, including the processing result. The controller starts a listening thread, receives this completion message specifically, and wakes up the main thread.

3. Local HTTP callback: After the controller starts the asynchronous task, it also starts a local HTTP server to listen to a specific port. After the asynchronous task is completed, the controller is notified via HTTP request. The controller thread blocks and waits for the HTTP request, and can get the result after receiving the request.

Compared with inefficient polling, these methods significantly improve code efficiency and readability, avoiding unnecessary resource consumption and waiting. Which method to choose depends on the specific application scenario and technology stack. For example, if the system has integrated Redis, the Pub/Sub solution is more convenient; if MQ has a complete callback mechanism, the second solution is more suitable. Local HTTP callbacks provide a general solution for a variety of environments. The key is to avoid blocking the main thread and implement an elegant transition from asynchronous to synchronous through efficient mechanisms.

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