log4j2 integration doesn't work, "logging.pattern.level" syntax incorrect in TraceEnvironmentPostProcessor

Description

traceId and spanId don’t appear in log when using log4j2, e.g.:

2021-08-12 12:54:14.737 INFO [hello-app,,] 106004 --- [nio-8080-exec-1] c.e.d.FooController : hello

Reproduce

1. exclude org.springframework.boot:spring-boot-starter-logging
2. include org.springframework.boot:spring-boot-starter-log4j2, org.springframework.cloud:spring-cloud-starter-sleuth and io.zipkin.brave:brave-context-log4j2
3. define bean of type ScopeDecorator with ThreadContextScopeDecorator.get()

Cause

The value for logging.pattern.level in TraceEnvironmentPostProcessor uses e.g. %X{traceId:-} but the syntax for an empty default value isn’t supported by log4j2. See Pattern Layout

Workaround

Override the property with e.g.:

logging.pattern.level=%5p [${spring.zipkin.service.name:${spring.application.name:}},%X{traceId},%X{spanId}]

i.e. no :-

[marcingrzejszczak]

Since manual work is required to add such support with Brave maybe it’s enough to document that the pattern must be changed? WDYT?

[farnetto]

spring-boot-starter-parent 2.5.3 and spring-cloud.version 2020.0.3