🧩 Solving Request Context Mysteries in Spring Boot with Async Services 🚀

Ah, Spring Boot. It's like a magic wand for Java developers – until it suddenly isn’t. Recently, I found myself in a bit of a pickle while working with Spring Boot (3.x) and Tomcat 10+. What started as a simple asynchronous service turned into a wild goose chase to get my hands on the request context. 🤯

Let me take you on the journey of what went wrong, my troubleshooting adventures, and how I finally cracked the case. 🕵️‍♂️🔍

🛑 The Problem: “Help! My Request Context is Gone!” 🛑

Picture this: You have a Spring Boot controller that receives a request, calls an async service, and returns a response – all while your async service works its magic in the background. 🎩✨

Sounds great, right? Until I tried accessing the request context inside the async service. Every time, I hit a NullPointerException faster than I could say “RequestContextHolder” 😬.

Error message:
Cannot invoke web.context.request.ServletRequestAttributes.getRequest() because "attributes" is null

Apparently, in an async method, the original request context doesn’t carry over to the new thread by default. In short, the request was out partying elsewhere, leaving me with nothing but null. 🎉🙄

🚧 My Initial Attempts and “Solutions” 🚧

1. Passing the HttpServletRequest directly to the async method:
   Seemed like a solid plan at first. But nope! As the async method was executed after the controller returned, the original request was long gone. 🚶‍♂️💨

2. Using a TaskDecorator to manually copy the context:
   This was like using duct tape to fix a leaky pipe – it kind of worked but wasn’t reliable enough for certain request attributes. 🩹😅

✨ Adding the TaskDecorator Magic ✨

To keep the request context alive in async threads, I added a custom TaskDecorator. Here’s what it looked like:

@Component
public class ContextCopyingTaskDecorator implements TaskDecorator {
    @Override
    public Runnable decorate(Runnable runnable) {
        // Capture the current request attributes
        RequestAttributes context = RequestContextHolder.currentRequestAttributes();
        return () -> {
            try {
                // Set the request attributes for this thread
                RequestContextHolder.setRequestAttributes(context);
                runnable.run();
            } finally {
                // Reset the request attributes after execution
                RequestContextHolder.resetRequestAttributes();
            }
        };
    }
}

This decorator captures the current request attributes and sets them for the new thread that runs the async task. It’s like copying the keys to a new door so the request context can still get in. 🏠🔑

🔧 Setting Up the Async Configuration

Then, I configured the TaskDecorator in my async setup:

@Configuration
public class AsyncConfig implements AsyncConfigurer {
    @Autowired
    private ContextCopyingTaskDecorator taskDecorator;

    @Override
    public Executor getAsyncExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(5);
        executor.setMaxPoolSize(10);
        executor.setQueueCapacity(25);
        executor.setTaskDecorator(taskDecorator);
        executor.initialize();
        return executor;
    }
}

The custom TaskDecorator worked well in most scenarios, but for some strange reason, I still occasionally found that the request context wasn’t available. 🤔

🔍 The Breakthrough: “Just Don’t Discard the Facade!” 🎉

After some deep digging and desperate Googling 🏊‍♂️💻, I stumbled upon the culprit: Tomcat’s discardFacade setting.

By default, Tomcat throws away the request facades for security reasons, which is a problem when you want to access request info in an async context.

💡 The Solution: One Line of Code to Save the Day! 💪✨

The fix turned out to be surprisingly simple – just a one-liner configuration to tell Tomcat to stop discarding facades:

@Bean
TomcatConnectorCustomizer disableFacadeDiscard() {
    return (connector) -> connector.setDiscardFacades(false);
}

Yep, that's it! I created this bean in the configuration class to disable facade discard, and boom 💥! The request attributes were available even after the original request had completed. 🎊🎈

📝 Key Lessons Learned (a.k.a., How I Stopped Worrying and Learned to Love Async)

1. Context Doesn’t Follow You (Unless You Tell It To):
   In async processing, the request context is like a pet cat 🐱 – it does its own thing. If you need it to follow you around, you’ll have to configure it correctly.

2. Tomcat's Facade Management Matters:
   Disabling the discardFacade property can be a game-changer when you need access to the request context in async scenarios.

3. Avoid Overcomplicated Workarounds:
   Custom decorators and directly passing the HttpServletRequest might seem like clever ideas at first, but they can be unreliable. Sometimes, the simplest solutions really are the best. 🧑‍🔧🔧

🤔 Why Did This Work?

By setting discardFacades to false, Tomcat doesn’t throw away the request data prematurely. This allows the async service to access the original request information even after the controller has returned the response. It’s like giving the request a backstage pass to the async show. 🎫🎤

🚀 Wrapping Up: My Async Troubles Are Over... For Now 👻

So, if you’re ever struggling with Spring Boot, async services, and request context woes, give this solution a try. You might just save yourself hours of frustration – and several cups of coffee. ☕️😅