Slf4j binding issues

[hazendaz]

Review slf4j/logback binding issues when running waffle at container layer. See https://github.com/grgrzybek/tomcat-slf4j-logback on how to approach this unless better solution is found

[ljluestc]

To resolve SLF4J binding issues, follow these steps:

Step 1: Ensure Only One SLF4J Binding is Present
Remove all unnecessary SLF4J bindings from your application and container.

For example, if you are using Logback, ensure that only slf4j-logback is in the classpath, and remove slf4j-log4j or other bindings.

Step 2: Use the Correct SLF4J Version
Ensure that the SLF4J API (slf4j-api) and the binding (e.g., slf4j-logback) are compatible versions.

For example:

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>2.0.9</version>
</dependency>
<dependency>
    <groupId>ch.qos.logback</groupId>
    <artifactId>logback-classic</artifactId>
    <version>1.4.11</version>
</dependency>

Step 3: Configure Logging at the Container Level
Use the approach described in tomcat-slf4j-logback to configure SLF4J and Logback at the Tomcat container level.

This involves:

Adding the necessary SLF4J and Logback JARs to Tomcat's lib directory.

Configuring Logback via a logback.xml file placed in Tomcat's conf directory.

Step 4: Exclude Conflicting Dependencies
If you are using a build tool like Maven or Gradle, exclude conflicting logging dependencies from your dependencies.

For example, in Maven:

<dependency>
    <groupId>com.github.waffle</groupId>
    <artifactId>waffle-jna</artifactId>
    <version>3.0.0</version>
    <exclusions>
        <exclusion>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
        </exclusion>
    </exclusions>
</dependency>

Step 5: Use a Parent-First ClassLoader
In Tomcat, configure the classloader to use a parent-first strategy for loading SLF4J classes. This ensures that the container-level SLF4J binding is used instead of the application-level binding.

Add the following to your context.xml:

<Context>
    <Loader delegate="true"/>
</Context>

3. Example Configuration
   Here’s an example of how to configure SLF4J and Logback in a Tomcat environment:

Step 1: Add SLF4J and Logback JARs to Tomcat
Place the following JARs in Tomcat's lib directory:

slf4j-api-2.0.9.jar

logback-classic-1.4.11.jar

logback-core-1.4.11.jar

Step 2: Configure Logback
Create a logback.xml file in Tomcat's conf directory:

<configuration>
    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
        <encoder>
            <pattern>%d{yyyy-MM-dd HH:mm:ss} %-5level %logger{36} - %msg%n</pattern>
        </encoder>
    </appender>

    <root level="INFO">
        <appender-ref ref="STDOUT" />
    </root>
</configuration>

Step 3: Exclude Conflicting Dependencies in Your Application
In your pom.xml, exclude conflicting logging dependencies:

<dependency>
    <groupId>com.github.waffle</groupId>
    <artifactId>waffle-jna</artifactId>
    <version>3.0.0</version>
    <exclusions>
        <exclusion>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
        </exclusion>
    </exclusions>
</dependency>

Step 4: Configure Tomcat ClassLoader
Add the following to your context.xml:

<Context>
    <Loader delegate="true"/>
</Context>