How is logging supposed to work in JDTLS?

[guw]

I'm writing an extension which gets added to JDTLS using vscode-java extension mechanism. I am using SLF4J log api within my plug-in code to generate log messages.

In the deployed JDTLS I noticed the following issue in the Eclipse client.log file:

{
  message: 'SLF4J: No SLF4J providers were found.\n' +
    'SLF4J: Defaulting to no-operation (NOP) logger implementation\n' +
    'SLF4J: See https://www.slf4j.org/codes.html#noProviders for further details.\n',
  level: 'info',
  timestamp: '2023-07-18 15:28:14.047'
}

Inspecting the layout on filesystem I can see some confusion:

l ~/.vscode/extensions/redhat.java-1.20.0-darwin-x64/server/plugins/

ch.qos.logback.classic_1.2.12.jar
ch.qos.logback.core_1.2.12.jar
...
org.slf4j.api_1.7.30.v20221112-0806.jar
slf4j.api_2.0.7.jar
slf4j.nop_2.0.7.jar

1. There are multiple version of SLF4J API (2.0 as well as 1.7.)
2. There is NOP implementation installed for 2.0
3. There is logback installed (I assume for 1.7?)

It's hard to judge where the SLF4J No SLF4J providers were found message is coming from. This is unexpected with logback being deployed. It could be from 2.0 which is using ServiceLoader mechanism. I don't see the ServiceLoader mechanism installed/active in JDTLS.

What is the strategy for JDTLS and what should I do with my extension?

[snjeza]

@guw You may want to take a look at

• https://github.com/eclipse/eclipse.jdt.ls/blob/6868b6b6383200a9ce1a2c392339527b7cf9afb7/org.eclipse.jdt.ls.logback.appender/src/META-INF/services/ch.qos.logback.classic.spi.Configurator#L1
• https://github.com/eclipse/eclipse.jdt.ls/blob/master/org.eclipse.jdt.ls.logback.appender/src/org/eclipse/jdt/ls/logback/appender/JavaLsConfigurator.java
• https://github.com/qos-ch/logback/blob/a388193052c298ca87cc64192319df723288c6ab/logback-classic/src/main/java/ch/qos/logback/classic/util/ContextInitializer.java#L136

[guw]

@snjeza I see this one adds an appender to Logback. However, I don't think JDTLS currently does the proper binding of Logback to SLF4J.

• https://github.com/qos-ch/slf4j/blob/e63f87f02cdc732d9efb0d806675f94e5b7a67fc/slf4j-api/src/main/java/org/slf4j/LoggerFactory.java#L107C39-L107C59
• https://github.com/qos-ch/logback/blob/be5afc288c9db97e17fdf0e6d68aebfab7f00a89/logback-classic/src/main/resources/META-INF/services/org.slf4j.spi.SLF4JServiceProvider

In order for this to work in OSGi one needs an extension such as SPI Fly. I did not find that in JDTLS. Thus, I think it's not working currently.

• core: Add support for ServiceLoader to the Core Framework osgi/osgi#372

[snjeza]

@guw You have to add -Djdt.ls.debug=true JVM argument.
After that, you can debug https://github.com/eclipse/eclipse.jdt.ls/blob/6868b6b6383200a9ce1a2c392339527b7cf9afb7/org.eclipse.jdt.ls.logback.appender/src/org/eclipse/jdt/ls/logback/appender/EclipseLogAppender.java#L34

It is similar to m2e logback. See osgi/osgi#372 (comment)

[guw]

@snjeza Thanks! How do I add/trigger that inside a running VS Code instance? In my case JDTLS works fine if I run it in debug mode and the extension in hosted mode. But deployed in VSCode it seems unresponsive.

[snjeza]

@guw You can use the standard Eclipse logging. See https://github.com/eclipse/eclipse.jdt.ls/blob/cf251804ed7abfd1c106d6681930c646717d6438/org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/JavaLanguageServerPlugin.java#L385