This is an issue when a caching annotation designed to store method return values is applied to a method that returns no value (void). Since there is no value to cache, the annotation serves no purpose and indicates a misunderstanding of the caching mechanism.

Why is this an issue?

Return value caching annotations are designed to cache the output of a method. When a method annotated for result caching is invoked, the framework computes a cache key and checks if the result has been previously cached. If found, the cached value is returned without executing the method body. If not found, the method executes and its return value is stored in the cache.

This caching mechanism fundamentally requires a return value to function. A void method, by definition, does not return a value - it only produces side effects. Since there is no value to cache or retrieve, applying result caching annotations to a void method is meaningless and will not provide any caching benefits.

This misuse typically indicates one of the following:

• A misunderstanding of how result caching works
• An attempt to cache side effects, which is not supported by these annotations
• A method that should be refactored to return a value if caching is truly needed

Framework documentation explicitly states that result caching annotations cannot be used on methods returning void.

What is the potential impact?

While this issue does not cause runtime errors or security vulnerabilities, it can lead to:

• Confusion about the intended behavior of the code
• Wasted developer time investigating why caching is not working as expected
• Maintenance overhead from unnecessary annotations that serve no purpose
• Potential performance misconceptions if developers believe expensive operations are being cached when they are not

How to fix it

Remove the @CacheResult annotation from the void method if caching is not needed, or refactor the method to return a value that can be meaningfully cached.

Code examples

Noncompliant code example

@CacheResult(cacheName = "my-cache")
public void processData(String key) { // Noncompliant
    // Process expensive data
    expensiveService.process(key);
}

Compliant solution

@CacheResult(cacheName = "my-cache")
public String processData(String key) {
    // Process expensive data and return result
    String result = expensiveService.process(key);
    return result;
}

Resources

Documentation

• Quarkus Cache Guide - Application Data Caching
• Quarkus @CacheResult Annotation Reference - @CacheResult