# spring-boot-sfj4j2

**Repository Path**: qdbp/spring-boot-sfj4j2

## Basic Information

- **Project Name**: spring-boot-sfj4j2
- **Description**: 解决在spring-boot-2.x中升级slf4j至2.x时出现的报错问题
- **Primary Language**: Unknown
- **License**: Apache-2.0
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 0
- **Forks**: 1
- **Created**: 2025-08-15
- **Last Updated**: 2026-06-26

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

# spring-boot-sfj4j2

#### Introduction
Solve the error problem that occurs when upgrading slf4j to 2.x in the spring-boot-2.x

#### Problem Cause
We have a legacy project using spring-boot-2.7.18.<br>
Recently, a vulnerability scan revealed issues with logback.<br>
The project was using logback 1.2.x,<br>
and even after upgrading to the latest version (as of August 2025) 1.2.13,<br>
there are still 3 medium-risk vulnerabilities reported.<br>
To upgrade further, we need to simultaneously upgrade slf4j to 2.x.<br>
After making these changes and starting the project,<br>
we encountered this error: ClassNotFoundException: org.slf4j.impl.StaticLoggerBinder<br>
The reason is that slf4j changed its logger instance discovery mechanism from<br>
the previous static binding mechanism to the SPI mechanism.<br>
However, the LogbackLoggingSystem in spring-boot-2.7.x uses the old class,<br>
resulting in the error:

``` log
Exception in thread "main" java.lang.NoClassDefFoundError: org/slf4j/impl/StaticLoggerBinder
	at org.springframework.boot.logging.logback.LogbackLoggingSystem.getLoggerContext(LogbackLoggingSystem.java:304)
	at org.springframework.boot.logging.logback.LogbackLoggingSystem.beforeInitialize(LogbackLoggingSystem.java:118)
	at org.springframework.boot.context.logging.LoggingApplicationListener.onApplicationStartingEvent(LoggingApplicationListener.java:238)
	at org.springframework.boot.context.logging.LoggingApplicationListener.onApplicationEvent(LoggingApplicationListener.java:220)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:178)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:171)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:145)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:133)
	at org.springframework.boot.context.event.EventPublishingRunListener.starting(EventPublishingRunListener.java:79)
	at org.springframework.boot.SpringApplicationRunListeners.lambda$starting$0(SpringApplicationRunListeners.java:56)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
	at org.springframework.boot.SpringApplicationRunListeners.doWithListeners(SpringApplicationRunListeners.java:120)
	at org.springframework.boot.SpringApplicationRunListeners.starting(SpringApplicationRunListeners.java:56)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:299)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1300)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1289)
	at com.gitee.qdbp.slf4j2.test.Application.main(Application.java:26)
Caused by: java.lang.ClassNotFoundException: org.slf4j.impl.StaticLoggerBinder
	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641)
	at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521)
	... 17 more
```

#### Problem Analysis
The main role of LoggingSystem in Spring Boot is to support variable reading in logback.xml:
``` xml
<springProperty scope="context" name="appName" source="spring.application.name"/>
......
<appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
    <file>${LOG_HOME}/${appName}.log</file>
    ......
</appender>
```
Online solutions suggest disabling LoggingSystem, which allows the project to start.<br>
but then the above variables cannot be read,<br>
and logback-spring.xml needs to be renamed to logback.xml
``` java
System.setProperty("org.springframework.boot.logging.LoggingSystem", "none");
SpringApplication.run(Application.class, args);
```

After reviewing the source code of spring-boot's LoggingSystem,<br>
we found that we can implement a custom LogbackLoggingSystem.<br>
By adding a LoggingSystem Factory through META-INF/spring.factories,<br>
we can modify the underlying implementation.<br>
By comparing the different implementations of<br>
LogbackLoggingSystem in versions 2.7.18 and 3.5.4,<br>
we can basically migrate the logic from 3.5.4.

#### Code Implementation
Call Relationship Diagram
![调用关系图](https://foruda.gitee.com/images/1755183992405025114/c4048460_610326.png "调用关系图")

When running, we can see that an additional LoggingSystem Factory implementation has been added,<br>
with Slf4j2LogbackLoggingSystem ranked first:
![工厂类实例](https://foruda.gitee.com/images/1755181430686892162/7cca967a_610326.png "工厂类实例")

The key entry point is here:
``` java
@Order(Ordered.LOWEST_PRECEDENCE - 10000) // 提高优先级
public static class Factory implements LoggingSystemFactory {

        // 有LoggerContext且没有StaticLoggerBinder才生效
	private static final boolean PRESENT = ClassUtils.isPresent("ch.qos.logback.classic.LoggerContext",
			Factory.class.getClassLoader())
			&& !ClassUtils.isPresent("org.slf4j.impl.StaticLoggerBinder", Factory.class.getClassLoader());

	@Override
	public LoggingSystem getLoggingSystem(ClassLoader classLoader) {
		if (PRESENT) {
			return new Slf4j2LogbackLoggingSystem(classLoader);
		}
		return null;
	}
}
```

#### Log Testing
The main test is to verify that the project starts normally after adding the spring-boot-sfj4j2 dependency,<br>
without the error: `NoClassDefFoundError: org/slf4j/impl/StaticLoggerBinder.`<br>
Additionally, test that the appName variable in logback-spring.xml is successfully retrieved:<br>
`<file>${LOG_HOME}/${appName}.log</file>`<br>
In the test project: spring-boot-sfj4j2-test-logback<br>
after successful startup, there should be a <b>slf4j2-test-logback.log</b>file in the logs directory.

#### Maven Dependency
[https://repo1.maven.org/maven2/com/gitee/qdbp/spring-boot-sfj4j2/2.7.18/](https://repo1.maven.org/maven2/com/gitee/qdbp/spring-boot-sfj4j2/2.7.18/)
``` xml
<dependency>
	<groupId>com.gitee.qdbp</groupId>
	<artifactId>spring-boot-sfj4j2</artifactId>
	<version>2.7.18</version>
</dependency>
```