Log4j2问题：无法在日志文件中查看Spring日志

Hey there, let’s figure out why your Spring framework logs aren’t showing up in your log file—especially since your application’s own class logs are working fine. Based on your description, here are the key areas to check and fix:

1. Ensure Spring-Specific Loggers Are Configured in log4j2.xml #

First off, make sure you’ve explicitly set up loggers for Spring’s package hierarchy in your log4j2.xml file. If you only have the root logger configured, Spring logs might not be routed to your file appender.

Add a logger entry like this (adjust the appender name to match your setup):

<Logger name="org.springframework" level="INFO" additivity="false">
    <AppenderRef ref="YourFileAppenderName"/>
</Logger>

• level="INFO" captures standard Spring startup and runtime logs; use DEBUG if you need more detailed output.
• additivity="false" prevents Spring logs from being duplicated in the root logger (if your root logger uses a different appender).

If you need logs from specific Spring modules (like spring-web or spring-data), you can add more granular loggers:

<Logger name="org.springframework.web" level="DEBUG" additivity="false">
    <AppenderRef ref="YourFileAppenderName"/>
</Logger>

2. Fix Dependency Conflicts in pom.xml #

J2EE containers (like Tomcat) often ship with their own logging libraries (e.g., commons-logging) which can clash with Log4j2. Here’s how to resolve this:

• Exclude commons-logging from Spring dependencies: Spring uses commons-logging by default, but we want it to use Log4j2 instead. Add exclusions to your Spring core/web dependencies:

  <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-core</artifactId>
      <version>your-spring-version</version>
      <exclusions>
          <exclusion>
              <groupId>commons-logging</groupId>
              <artifactId>commons-logging</artifactId>
          </exclusion>
      </exclusions>
  </dependency>
  

• Add the Log4j2 commons-logging bridge: This lets Spring use Log4j2 for logging instead of commons-logging:

  <dependency>
      <groupId>org.apache.logging.log4j</groupId>
      <artifactId>log4j-jcl</artifactId>
      <version>your-log4j2-version</version>
  </dependency>
  

• Verify Log4j2 version consistency: Make sure log4j-api, log4j-core, and any bridge dependencies are using the same version to avoid compatibility issues.

3. Check Appender Filter Rules #

Your file appender might have a threshold filter that’s blocking Spring logs. For example, if the filter is set to ERROR, all INFO and DEBUG logs (including Spring’s) will be ignored.

Check your appender configuration for something like this:

<Appender name="YourFileAppenderName" type="File">
    <FileName>logs/your-app.log</FileName>
    <Layout type="PatternLayout" pattern="%d{yyyy-MM-dd HH:mm:ss} %-5p %c{1}:%L - %m%n"/>
    <!-- Ensure this level isn't higher than your desired Spring log level -->
    <ThresholdFilter level="INFO" onMatch="ACCEPT" onMismatch="DENY"/>
</Appender>

Adjust the level value to match or be lower than the level you set for Spring’s logger.

4. Verify Log4j2 Configuration Loading #

Sometimes Log4j2 might not be picking up your configuration file correctly. To debug this:

• Add the JVM argument -Dlog4j.debug when starting your application server. This will print Log4j2’s initialization logs to the console, showing:
  • Whether your log4j2.xml was found and loaded.
  • How each logger (including Spring’s) is configured.
• Ensure your log4j2.xml is placed in src/main/resources (so it gets packaged into WEB-INF/classes in your WAR file).

5. Test with a Lower Log Level #

Temporarily set Spring’s logger level to TRACE to see if any logs show up. This helps rule out the possibility that Spring is generating logs, but they’re at a level higher than your current configuration allows.

内容的提问来源于stack exchange，提问作者JavaSheriff