Jonas' Blog

 <plugin>
     <groupId>org.apache.maven.plugins</groupId>
     <artifactId>maven-shade-plugin</artifactId>
     <executions>
         <execution>
             <phase>package</phase>
             <goals>
                 <goal>shade</goal>
             </goals>
         </execution>
     </executions>
     <configuration>
         <finalName>agent-shaded</finalName>
         <shadedArtifactAttached>true</shadedArtifactAttached>
         <shadedClassifierName>shaded</shadedClassifierName>
         <createDependencyReducedPom>true</createDependencyReducedPom>
         <relocations>
             <relocation>
                 <pattern>org.slf4j</pattern>
                 <shadedPattern>my.package.org.slf4j</shadedPattern>
             </relocation>
             <relocation>
                 <pattern>ch.qos.logback</pattern>
                 <shadedPattern>my.package.ch.qos.logback</shadedPattern>
             </relocation>
         </relocations>
         <transformers>
             <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                 <manifestEntries>
                     <Premain-Class>my.package.instrumentation.InstrumentationAgent</Premain-Class>
                     <Can-Redefine-Classes>true</Can-Redefine-Classes>
                     <Can-Retransform-Classes>true</Can-Retransform-Classes>
                 </manifestEntries>
             </transformer>
         </transformers>
     </configuration>
 </plugin>

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <appender name="OPS_FILE" class="my.package.ch.qos.logback.core.rolling.RollingFileAppender">
        <file>agent.log</file>
        <rollingPolicy class="my.package.ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">
            <fileNamePattern>agent.%d{yyyy-MM-dd}.%i.gz</fileNamePattern>
            <maxFileSize>20MB</maxFileSize>
            <maxHistory>30</maxHistory>
            <totalSizeCap>1GB</totalSizeCap>
        </rollingPolicy>
        <append>true</append>
        <immediateFlush>true</immediateFlush>
        <encoder>
            <pattern>%d{yyyy-MM-dd HH:mm:ss,SSS} %-5level %thread [%c{15}] %msg%ex%n</pattern>
        </encoder>
    </appender>
    <root level="DEBUG">
        <appender-ref ref="OPS_FILE"/>
    </root>
</configuration>

import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.security.ProtectionDomain;

import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;

public class LoggingTransformer implements ClassFileTransformer {

    @Override
     public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined,
            ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
        byte[] byteCode = classfileBuffer;

        if (className.equals("my/package/ch/qos/logback/classic/util/ContextInitializer")) {
            try {
                ClassPool cp = ClassPool.getDefault();
                CtClass cc = cp.get("my.package.ch.qos.logback.classic.util.ContextInitializer");
                CtMethod m = cc.getDeclaredMethod("autoConfig");
                // If we return null here we skip the default configuration file resolution.
                // Thus we have the BasicConfigurator.
                m.setBody("{return null;}");
                byteCode = cc.toBytecode();
                cc.detach();
            } catch (Exception ex) {
                ex.printStackTrace();
            }
        }
        return byteCode;
    }
}

        JoranConfigurator configurator = new JoranConfigurator();

        LoggerContext context = (LoggerContext) LoggerFactory.getILoggerFactory();
        configurator.setContext(context);

        String pathToLogbackConfig = System.getProperty("agent.logback.configurationFile");
        if (pathToLogbackConfig == null) {
            System.out.println("There was no configuration for logging of the agent provided.");
            return;
        }

        try {
            File file = new File(pathToLogbackConfig);
            if (file.exists()) {
                context.reset();
                configurator.doConfigure(file);
            } else {
                System.err.println(
                        "There was no 'agent-logback.xml' logging-configuration provided. This means all logging of the agent is lost!");
            }
        } catch (JoranException e) {
            System.err.println("There was an error during building the agent logging configuration.");
            System.out.println(e);
        }