NoSuchMethodException when forcing the use of Log4J2LoggingSystem using org.springframework.boot.logging.LoggingSystem system property by FBibonne · Pull Request #49343 · spring-projects/spring-boot

FBibonne · 2026-02-27T11:14:42Z

The Spring Boot documentation states that users can force a particular logging system by setting the system property org.springframework.boot.logging.LoggingSystem to the fully qualified class name of a LoggingSystem implementation.

When attempting to do so for Log4J2 (setting org.springframework.boot.logging.LoggingSystem = org.springframework.boot.logging.log4j2.Log4J2LoggingSystem), Spring Boot crashes with the following error (Spring Boot 4.0.3):

java.lang.NoSuchMethodException: org.springframework.boot.logging.log4j2.Log4J2LoggingSystem.<init>(java.lang.ClassLoader)
	at java.base/java.lang.Class.getConstructor0(Class.java:3187)
	at java.base/java.lang.Class.getDeclaredConstructor(Class.java:2491)
	at org.springframework.boot.logging.LoggingSystem.get(LoggingSystem.java:178)
	... 17 more

A different error occurs with Spring Boot 3.5.x, but this PR focuses on Spring Boot 4.

Reproduction

The issue can be reproduced by running the following main method with spring-boot-starter and spring-boot-starter-log4j2 on the classpath (with java 25):

@SpringBootApplication
public class Main {
    void main() {
        System.setProperty("org.springframework.boot.logging.LoggingSystem", "org.springframework.boot.logging.log4j2.Log4J2LoggingSystem");
        SpringApplication.run(Main.class);
    }
}

An example project is available at: https://framagit.org/FBibonne/poc-java/-/tree/spring-boot-force-log4j2 (make sure to stay on the spring-boot-force-log4j2 branch).

Root cause and fix

The error message above (java.lang.NoSuchMethodException: org.springframework.boot.logging.log4j2.Log4J2LoggingSystem.<init>) indicates that a specific constructor is missing in Log4J2LoggingSystem : the missing constructor was removed in PR #47424. This PR proposes reintroducing it as a private constructor (to prevent unintentional direct use) since it is invoked via reflection. The constructor body reuses the code introduced by PR #47424 in org.springframework.boot.logging.log4j2.Log4J2LoggingSystem.Factory to obtain a loggerContext.

The test org.springframework.boot.logging.LoggingSystemTests#log4J2CanBeForced reproduces the problem: it fails if Log4J2LoggingSystem is not fixed.

Note on tests

The build of the core/spring-boot module succeeds; however, the full project build fails due to some container-based tests:

DataLdapTestDockerTests, OpenLdapContainerConnectionDetailsFactoryIntegrationTests, OpenLdapDockerComposeConnectionDetailsFactoryIntegrationTests: disabled because they require exposing a privileged port (389), which is not permitted on my machine.
PulsarDockerComposeConnectionDetailsFactoryIntegrationTests: required adding the property services.pulsar.security_opt with the value seccomp:unconfined in pulsar-compose.yaml to bypass a security restriction.
ZipkinContainerConnectionDetailsFactoryIntegrationTests: disabled — root cause not yet identified.

Signed-off-by: Fabrice Bibonne <fabrice.bibonne@courriel.eco>

- fix the missing constructor in Log4J2LoggingSystem class (can be called by LoggingSystem.get(ClassLoader, String) Signed-off-by: Fabrice Bibonne <fabrice.bibonne@courriel.eco>

Signed-off-by: Fabrice Bibonne <fabrice.bibonne@courriel.eco>

wilkinsona · 2026-02-27T11:25:37Z

Thanks for the PR.

A different error occurs with Spring Boot 3.5.x, but this PR focuses on Spring Boot 4.

Can you please share some details about the error that occurs with 3.5.x? I can't reproduce a failure with that version. Furthermore, there's a public Log4J2LoggingSystem(ClassLoader classLoader) constructor so I cannot see why an error would occur either.

FBibonne · 2026-02-27T13:46:48Z

With Spring Boot 3.5.11 (in the project located at https://framagit.org/FBibonne/poc-java/-/tree/spring-boot-force-log4j2, I set the version of spring-boot-starter-parent at 3.5.11), I get this error if I run the poc.Main class :

Exception in thread "main" java.lang.ClassCastException: class org.apache.logging.slf4j.SLF4JLoggerContext cannot be cast to class org.apache.logging.log4j.core.LoggerContext (org.apache.logging.slf4j.SLF4JLoggerContext and org.apache.logging.log4j.core.LoggerContext are in unnamed module of loader 'app')
        at org.springframework.boot.logging.log4j2.Log4J2LoggingSystem.getLoggerContext(Log4J2LoggingSystem.java:497)
        at org.springframework.boot.logging.log4j2.Log4J2LoggingSystem.beforeInitialize(Log4J2LoggingSystem.java:155)
        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:185)
        at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:178)
        at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:156)
        at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:138)
        at org.springframework.boot.context.event.EventPublishingRunListener.multicastInitialEvent(EventPublishingRunListener.java:136)
        at org.springframework.boot.context.event.EventPublishingRunListener.starting(EventPublishingRunListener.java:75)
        at org.springframework.boot.SpringApplicationRunListeners.lambda$starting$0(SpringApplicationRunListeners.java:54)
        at java.base/java.util.ImmutableCollections$List12.forEach(ImmutableCollections.java:681)
        at org.springframework.boot.SpringApplicationRunListeners.doWithListeners(SpringApplicationRunListeners.java:118)
        at org.springframework.boot.SpringApplicationRunListeners.starting(SpringApplicationRunListeners.java:54)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:310)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1361)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1350)

It is true that the constructor of Log4J2LoggingSystem exists and is called successfully. But the exception above is raised just after (nex line in org.springframework.boot.context.logging.LoggingApplicationListener#onApplicationStartingEvent). I think that this class cast exception is what PR #47424 pointed out.

So if I exclude spring-boot-starter-logging from the dependencies, the exception above does not occur and the application does not crash. Sorry, I missed the exclusion.

core/spring-boot/src/test/java/org/springframework/boot/logging/LoggingSystemTests.java

core/spring-boot/src/main/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystem.java

- refactor the test for log4j - add test for JUL Signed-off-by: Fabrice Bibonne <fabrice.bibonne@courriel.eco>

- code sharing between factory and constructor - unique origin for the loggerContext generated inside the class Signed-off-by: Fabrice Bibonne <fabrice.bibonne@courriel.eco>

…ge private Signed-off-by: Fabrice Bibonne <fabrice.bibonne@courriel.eco>

core/spring-boot/src/main/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystem.java

…LoggerContext) - see comment spring-projects#49343 (comment) Signed-off-by: Fabrice Bibonne <fabrice.bibonne@courriel.eco>

…lassLoader, LoggerContext) removal - remove LoggerContext from LoggerContextFactory after each unit test to avoid that it is reused Signed-off-by: Fabrice Bibonne <fabrice.bibonne@courriel.eco>

wilkinsona · 2026-03-02T08:22:35Z

...ing-boot/src/test/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystemTests.java

 		this.loggingSystem.getConfiguration().stop();
 		this.loggingSystem.cleanUp();
 		PluginRegistry.getInstance().clear();
+		LogManager.getFactory().removeContext(this.loggingSystem.getLoggerContext());


Why is this necessary?

wilkinsona · 2026-03-02T08:22:45Z

...ing-boot/src/test/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystemTests.java

-		assertThat(configuration.getConfigurationSource().getFile()).isNotNull();
+		assertThat(configuration.getConfigurationSource().getLocation()).contains("log4j2-test.xml");


This change appears to be unrelated. Please revert

wilkinsona · 2026-03-02T08:25:40Z

core/spring-boot/src/main/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystem.java

-	 * Create a new {@link Log4J2LoggingSystem} instance.
+	 * Create a new {@link Log4J2LoggingSystem} instance. The loggerContext is
+	 * instantiated internally in the class from
+	 * {@link LogManager#getContext(ClassLoader, boolean)} <br/>
+	 * This constructor is also intended to be used by
+	 * <code>LoggingSystem.get(ClassLoader, String)</code> with reflection.
 	 * @param classLoader the class loader to use.
-	 * @param loggerContext the {@link LoggerContext} to use.
+	 * @throws IllegalArgumentException if the loggerContext instantiated internally is
+	 * not of type org.apache.logging.log4j.core.LoggerContext


I don't think these changes add much, particular not the part that's describing what the code does. We generally reserve comments for situations where we need to describe why something is the way it is. The code itself describes the what. Please revert. This will leave this constructor more closely aligned with the other logging system constructors.

Ok. I just wonder if you have an other way that the test to figure that the constructor is called using the reflection API (seems to be important to avoid accidental removing)

FBibonne added 3 commits February 26, 2026 06:05

test: failing test log4j2 can be forced

fe8fc8d

Signed-off-by: Fabrice Bibonne <fabrice.bibonne@courriel.eco>

log4j2 can be forced

4551f16

- fix the missing constructor in Log4J2LoggingSystem class (can be called by LoggingSystem.get(ClassLoader, String) Signed-off-by: Fabrice Bibonne <fabrice.bibonne@courriel.eco>

refactor: formatting issues

e2215b3

Signed-off-by: Fabrice Bibonne <fabrice.bibonne@courriel.eco>

spring-projects-issues added the status: waiting-for-triage An issue we've not yet triaged label Feb 27, 2026

wilkinsona added the status: waiting-for-feedback We need additional information before we can continue label Feb 27, 2026

spring-projects-issues added status: feedback-provided Feedback has been provided and removed status: waiting-for-feedback We need additional information before we can continue labels Feb 27, 2026

wilkinsona changed the title ~~Error when forcing the logging system with the org.springframework.boot.logging.LoggingSystem property~~ NoSuchMethodException when forcing the use of Log4J2LoggingSystem using org.springframework.boot.logging.LoggingSystem system property Feb 27, 2026

wilkinsona added type: regression A regression from a previous release and removed status: waiting-for-triage An issue we've not yet triaged status: feedback-provided Feedback has been provided labels Feb 27, 2026

wilkinsona added this to the 4.0.x milestone Feb 27, 2026

wilkinsona requested changes Feb 27, 2026

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core/spring-boot/src/test/java/org/springframework/boot/logging/LoggingSystemTests.java Show resolved Hide resolved

core/spring-boot/src/main/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystem.java Show resolved Hide resolved

quaff reviewed Feb 28, 2026

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core/spring-boot/src/main/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystem.java Outdated Show resolved Hide resolved

FBibonne added 3 commits February 28, 2026 08:52

test: check that LoggingSystem can be forced

da03b94

- refactor the test for log4j - add test for JUL Signed-off-by: Fabrice Bibonne <fabrice.bibonne@courriel.eco>

refactor: Log4J2LoggingSystem constructor and factory

d83f1bc

- code sharing between factory and constructor - unique origin for the loggerContext generated inside the class Signed-off-by: Fabrice Bibonne <fabrice.bibonne@courriel.eco>

refactor: make Log4J2LoggingSystem single parameter constructor packa…

325393b

…ge private Signed-off-by: Fabrice Bibonne <fabrice.bibonne@courriel.eco>

wilkinsona reviewed Feb 28, 2026

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core/spring-boot/src/main/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystem.java Outdated Show resolved Hide resolved

wilkinsona reviewed Feb 28, 2026

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core/spring-boot/src/main/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystem.java Outdated Show resolved Hide resolved

wilkinsona requested changes Feb 28, 2026

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FBibonne added 2 commits February 28, 2026 22:08

refactor: remove constructor Log4J2LoggingSystem.<init>(ClassLoader, …

f6360af

…LoggerContext) - see comment spring-projects#49343 (comment) Signed-off-by: Fabrice Bibonne <fabrice.bibonne@courriel.eco>

refactor: change tests after constructor Log4J2LoggingSystem.<init>(C…

7a7a758

…lassLoader, LoggerContext) removal - remove LoggerContext from LoggerContextFactory after each unit test to avoid that it is reused Signed-off-by: Fabrice Bibonne <fabrice.bibonne@courriel.eco>

wilkinsona requested changes Mar 2, 2026

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NoSuchMethodException when forcing the use of Log4J2LoggingSystem using org.springframework.boot.logging.LoggingSystem system property#49343

NoSuchMethodException when forcing the use of Log4J2LoggingSystem using org.springframework.boot.logging.LoggingSystem system property#49343
FBibonne wants to merge 8 commits intospring-projects:mainfrom
FBibonne:fix-Log4J2-forced

FBibonne commented Feb 27, 2026

Uh oh!

wilkinsona commented Feb 27, 2026

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		assertThat(configuration.getConfigurationSource().getFile()).isNotNull();
		assertThat(configuration.getConfigurationSource().getLocation()).contains("log4j2-test.xml");

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FBibonne commented Feb 27, 2026

Reproduction

Root cause and fix

Note on tests

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