3.6 Windows Registry Access

mConfig provides two alternative modules for accessing the Windows Registry. Both support reading configuration data from HKEY_CURRENT_USER (USER scope), HKEY_LOCAL_MACHINE (MACHINE scope), and Group Policy Objects (GPO) in both hives (POLICY scope).

3.6.1 Choosing the Right Module

Feature	mConfigWinRegistry	mConfigWinRegistryJNI
Technology	JNR-FFI (Dynamic Native)	JNI (Java Native Interface)
Artifact Size	~13 KB	~47 KB (includes DLL)
Runtime Size	~1.5 MB (includes dependencies)	~47 KB
Dependencies	JNR-FFI, ASM, JFFI	None
Complexity	Zero (no DLL to manage)	Medium (DLL handling)
Build Req.	Standard Java/Maven	Linux + MinGW-w64 (for DLL)
Performance	High	Very High

mConfigWinRegistry (JNR-FFI based)

This module is the easiest to use as it requires no native toolchain and handles native access dynamically. - Pros: No native binaries to manage; works out-of-the-box. - Cons: Significantly larger footprint (~1.5 MB) due to the JNR-FFI ecosystem. - Requirement: Java 11+.

mConfigWinRegistryJNI (JNI based)

This module provides the smallest footprint and highest performance by using a custom-built DLL. - Pros: Extremely lightweight; no external dependencies. - Cons: Requires building a DLL on Linux (cross-compiled for Windows); the DLL must be provided to the end-user (usually bundled in the JAR). - Requirement: Windows DLL (mConfigWinRegistryJNI.dll). - Signing: The bundled DLL is provided unsigned. For production deployments, application developers are responsible for signing the DLL as part of their distribution to establish a "Chain of Trust".

3.6.2 Priority and Discovery

If both modules are present on the classpath, mConfig defaults to using mConfigWinRegistryJNI (registryjni) over mConfigWinRegistry (registry) for better performance.

To use a specific one, you can configure STORAGE_TYPE_PRIORITIES:

try (ConfigFactory factory = ConfigFactoryBuilder.create("company", "app")
    .setFeature(ConfigFeature.STORAGE_TYPE_PRIORITIES, List.of("registryjni")) // Force JNI
    .build())
    {
    // ...
    }

3.6.3 Base Path Configuration

By default, the registry source looks under Software\\[<CompanyName>\\\\]<ApplicationName> (company segment omitted if COMPANY_NAME blank/null/whitespace). You can override this using the REGISTRY_BASE_PATH feature:

try (ConfigFactory factory = ConfigFactoryBuilder.create("company", "app")
    .setFeature(ConfigFeature.REGISTRY_BASE_PATH, "Software\\LegacyPath\\App")
    .build())
    {
    // ...
    }