Design and Implementation of a Simple Single‑Node Configuration Center in Spring Boot

Overview

The author presents a minimal configuration‑center implementation for Spring Boot micro‑service projects, focusing on the essential feature of real‑time configuration refresh after file changes.

Core Classes

The design revolves around eight classes in the core package. ScanRunner implements CommandLineRunner to run after the Spring context is ready, scanning all compiled .class files with FileScanner . Classes annotated with @Component , @Controller or @Service are collected into VariablePool , where fields marked with @Value are recorded.

File Scanning

FileScanner recursively walks a given root directory, filters files by suffix (e.g., .class or .yml ), and normalizes Windows paths to obtain fully‑qualified class names for reflection.

Variable Pool

VariablePool stores a map of configuration keys to the classes and field names that depend on them, using a regular expression to validate ${…} placeholders before stripping the delimiters.

Environment Initialization

EnvInitializer loads all .yml resources found by FileScanner , parses them with Spring’s YamlMapFactoryBean , and merges the resulting maps into a single‑layer envMap via YamlConverter.doConvert .

YAML Conversion

YamlConverter provides three utilities: doConvert flattens nested maps, monoToMultiLayer reconstructs a hierarchical map from dot‑separated keys, and convert parses a YAML string back into a flat map for change detection.

Controller and Property Trigger

ConfigController exposes /get and /save endpoints. /get returns the current configuration as a YAML string, while /save receives edited YAML, invokes PropertyTrigger.change , which compares old and new values, updates envMap , and uses reflection together with SpringContextUtil to set the new values on the affected beans.

Limitations

Does not support @ConfigurationProperties annotation.

Only processes YAML files, not .properties .

Works only with singleton‑scoped beans; prototype beans are not handled.

Reflection introduces performance overhead for heavily used properties.

Currently embedded in the application and lacks independent deployment or remote registration capabilities.

Conclusion

While the prototype demonstrates the core mechanics of a dynamic configuration center, many features such as broader annotation support, property‑file handling, prototype scope, performance optimisation, and distributed deployment remain to be implemented.