ScopedValue-based MDC for Logback Classic, designed for virtual threads and structured concurrency on Java 25+.

Logback's built-in MDC is ThreadLocal-based, so values placed in it are not inherited by virtual threads forked via java.util.concurrent.StructuredTaskScope. ScopedMDC is backed by java.lang.ScopedValue, which is inherited by forked tasks — making it a natural fit for virtual-thread and structured-concurrency code. A pattern converter (%scopedContext / %Y) lets existing logback pattern layouts read its values.

<dependency>
    <groupId>ch.qos.logback</groupId>
    <artifactId>logback-scoped-mdc</artifactId>
    <version>${project-version}</version>
</dependency>

ScopedMDC.put("requestId", "abc-123")
         .put("userId", "user-42")
         .run(() -> {
             logger.info("Processing request");
         });

Also available:

• ScopedMDC.putAll(Map<String, String>) for bulk entries.
• Binding.call(CallableOp) for value-returning operations that may throw.

Nested scopes inherit (and may override) parent entries; parent entries are restored automatically when the nested scope exits. Values bound via ScopedMDC are automatically visible inside virtual threads forked from a StructuredTaskScope.

Register the converter in logback.xml:

<conversionRule conversionWord="scopedContext"
    converterClass="ch.qos.logback.classic.scoped.ScopedMDCConverter" />
<conversionRule conversionWord="Y"
    converterClass="ch.qos.logback.classic.scoped.ScopedMDCConverter" />

Then use it in a pattern:

• %scopedContext — all entries, formatted as key1=value1, key2=value2.
• %scopedContext{requestId} — value for a specific key, or empty string if absent.
• %scopedContext{requestId:-unknown} — value for a specific key with default.

• JDK 25+
• Maven 3.9+

mvn clean verify

Tests run with --enable-preview (configured via the surefire argLine in pom.xml) because StructuredTaskScope is still not stable. Main sources compile as plain Java 25 — no preview flag needed at runtime since ScopedValue is stable.

Dual-licensed under EPL-2.0 or LGPL-2.1, matching Logback. See LICENSE.txt.