Global Variables State Management

Question

Background: I am working in a Java environment using Spring Boot, where I often encounter scenarios where global variable state management is critical, especially within singleton services. I have been exploring the idea of using annotations to automate cleanup global variable after used.

Goal: My objective is to streamline global variable management using annotations, enhancing code clarity and maintaining thread safety across singleton services.

Proposed Solution: I propose creating a custom annotation, let's call it @CleanAfterUse, that leverages ThreadLocal under-the-hood. This annotation would handle initialization, management, and cleanup of thread-local state automatically, reducing boilerplate code and potential errors.

Questions:

What are the best practices for implementing annotations in Java to manage ThreadLocal variables effectively? Are there alternative approaches within the Java ecosystem that could achieve similar thread-local state management goals?

Answer 1

According to Spring framework documentation section "Spring Framework / Core Technologies / The IoC Container / Bean Scopes" the IOC container supports following bean scopes.

Scope	Description
singleton	(Default) Scopes a single bean definition to a single object instance for each Spring IoC container.
prototype	Scopes a single bean definition to any number of object instances.
request	Scopes a single bean definition to the lifecycle of a single HTTP request. That is, each HTTP request has its own instance of a bean created off the back of a single bean definition. Only valid in the context of a web-aware Spring ApplicationContext.
session	Scopes a single bean definition to the lifecycle of an HTTP Session. Only valid in the context of a web-aware Spring ApplicationContext.
application	Scopes a single bean definition to the lifecycle of a ServletContext. Only valid in the context of a web-aware Spring ApplicationContext.
websocket	Scopes a single bean definition to the lifecycle of a WebSocket. Only valid in the context of a web-aware Spring ApplicationContext.

Alternatively to developing a new aspect to clean up an existing instance would it be suitable to use a new instance every time and make use of prototype scope?

The answer it is a question since Spring framework uses scopes related to beans and uses aspects on cross cutting concerns (e.g. for transactions, for exception handling so on and so forth)