.. _instrumenting-software-java-spring:

Instrumentation of Spring Applications
======================================

Depending on the circumstances, spring applications can be monitored with different configurations:
- Spring interceptors can be used if solely spring endpoints should be monitored. This is described in :ref:`tutorial-servlet-example`
- Spring applications **without** Sprinng Boot can be instrumented as any other Java application. This is described in :ref:`gt-aspectj-instrumentation-example`
- Spring applications **with** Spring Boot use a different classloader. Therefore, their instrumentation is described here.

Instrumenting Spring Boot Applications
======================================

The instrumentation of Spring Boot requires 3 steps:

- Specification of the instrumentation aspects in the ``aop.xml`` (equivalent to :ref:`gt-aspectj-instrumentation-example`)
- Adaption of the configuration: To adapt the configuration, the annotation ``@EnableLoadTimeWeaving`` needs to be added to the spring config. Furthermore, it needs to be specified that the ``InstrumentationLoadTimeWeaver`` is used. Therefore, an example configuration can look like this:

  .. code-block:: java
     :linenos:

     @Configuration
     @EnableLoadTimeWeaving
     public class AppConfig implements LoadTimeWeavingConfigurer {
     
         @Override
         public LoadTimeWeaver getLoadTimeWeaver() {
          return new InstrumentationLoadTimeWeaver();
         }
     }

- Configuring the CLI call: While regular applications are called using ``java -javaagent:kieker-$KIEKERVERSION-aspectj.jar``, Spring Boot applications should not be instrumented directly, but instead, the things loaded by the Spring Boot classloader should be instrumented. Therefore, ``spring-instrument-$SPRINGVERSION.jar`` needs to be added as an agent **before** the Kieker agent. Furthermore, the default aop configuration should be disabled for multi-classloader environments, using ``-Dkieker.monitoring.skipDefaultAOPConfiguration=true``. Overall, the call will look like

  .. code-block:: shell

     java -Dkieker.monitoring.skipDefaultAOPConfiguration=true \
     -javaagent:spring-instrument-$SPRINGVERSION.jar \
     -javaagent:lib/kieker-$KIEKERVERSION-aspectj.jar -jar MyJar.jar

A full example can be found in https://github.com/kieker-monitoring/kieker/tree/main/examples/monitoring/probe-spring-boot