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4.2 Logging in mConfig

mConfig uses a custom logging abstraction defined by the ConfigLoggingInterface. This allows the library to remain independent of specific logging frameworks while still providing necessary diagnostic information.

Available Implementations

Implementation Module Priority Service Name Use Case
NullLogging mConfigCore 0 null Default; silent operation.
ConsoleLogging mConfigCore 1 console Dev/tests; prints to stdout/stderr. Not for production.
Slf4j2Logger mConfigLoggingSlf4j 5 slf4j Production use; forwards to SLF4J.

Internal and Hidden Implementations

InternalLogger (mConfigCore, impl.core): Activated if ConfigFeature.LOGGING_REDIRECT_TARGET is set. Redirects to specified target.

Using SLF4J2Logger in Production

Slf4j2Logger (priority 5) bridges mConfig logging to SLF4J.

4.2.1 Add Dependencies

Maven:

<dependency>
    <groupId>org.metabit.platform.support.config</groupId>
    <artifactId>mConfigLoggingSlf4j</artifactId>
    <version>${mconfig.version}</version>
</dependency>

Gradle:

implementation 'org.metabit.platform.support.config:mConfigLoggingSlf4j:${mconfig.version}'

Note: Also need SLF4J API + impl (e.g., logback-classic).

4.2.2 Auto-Discovery

With mConfigLoggingSlf4j on classpath, auto-selected (highest prio).

Override with ConfigFactoryBuilder.setFeature(ConfigFeature.LOGGING_TO_USE_IN_CONFIGLIB, "slf4j").

4.2.3 Configuration

Configure SLF4J via logback.xml, etc.

Slf4j2Logger uses logger name from ConfigFactoryBuilder company/app or default "mConfig".

ConsoleLogging for Development and Tests

ConsoleLogging is a lightweight console logger (stdout for lower levels, stderr for WARN/ERROR) for debugging mConfig internals. No external dependencies required.

4.2.4 Build Configuration (Maven & Gradle)

To use ConsoleLogging in modules other than mConfigCore, you must include the mConfigCore test-jar dependency in your build:

Maven:

<dependency>
    <groupId>org.metabit.platform.support.config</groupId>
    <artifactId>mConfigCore</artifactId>
    <version>${mconfig.version}</version>
    <type>test-jar</type>
    <scope>test</scope>
</dependency>

Gradle:

testImplementation 'org.metabit.platform.support.config:mConfigCore:${mconfig.version}:tests'

4.2.5 Manual Activation

You can instantiate ConsoleLogging directly and pass it to components.

import org.metabit.platform.support.config.impl.logging.ConsoleLogging;
import org.metabit.platform.support.config.ConfigFeature;

// ... in your test ...
ConsoleLogging logger = new ConsoleLogging("MyModuleTest");
logger.setLevel("DEBUG");

// Use with a component that takes a logger
component.testComponent(settings, logger);

4.2.6 Usage with ConfigFactoryBuilder

ConfigFactoryBuilder uses ServiceLoader to discover ConfigLoggingInterface implementations.

Note for Modular Projects: ConsoleLogging is fully supported via provides in the mConfigCore module-info.java.

To force the use of ConsoleLogging when using ConfigFactoryBuilder in tests, you can set the feature:

ConfigFactoryBuilder builder = ConfigFactoryBuilder.create("company", "app");
builder.setFeature(ConfigFeature.LOGGING_TO_USE_IN_CONFIGLIB, "console");

This will only work if the ConsoleLogging class is discoverable by ServiceLoader. If discovery fails, it will fall back to NullLogging.

Configuration

Log Levels

Available levels: TRACE, DEBUG, INFO, WARN, ERROR. Default level for ConsoleLogging is INFO.

You can set the level via setLevel(String): 

logger.setLevel("TRACE");

Output Redirection

  • INFO, DEBUG, TRACE are printed to System.out.
  • WARN, ERROR are printed to System.err.

How Logging is Discovered and Selected

In DefaultConfigFactoryBuilder.findLoggerForConfigUse():

  1. If ConfigFeature.LOGGING_REDIRECT_TARGET is set, instantiate InternalLogger with target and init.

  2. Load ServiceLoader<ConfigLoggingInterface>:

  3. Prefer exact match to ConfigFeature.LOGGING_TO_USE_IN_CONFIGLIB by service name (case-insensitive).
  4. Otherwise, select highest priority (getServiceModulePriority()) among those that init() successfully.
  5. Fallback to NullLogging.

All loggers must implement init(ConfigFactorySettings) (usually returns true) and exit().