Servlets can be instrumented utilizing javax.servlet.ServletContextListerner,
javax.servlet.http.HttpSessionListener and javax.servlet.Filter.
The first is triggered when a Servlet context is created (instantiation of the Servlet) and destroyed. The second is triggered every time a new session is created. And the last is invoked every time a request is sent to the Servlet. In the following we will address all three types.
Please note that Servlets can also use other listeners which could in principle also used to trigger monitoring. However, such probes do not exist within Kieker, but can be build easily with Kieker framework functionality..
Todo
Add how to add context listeners here (iObserve)
Todo
Add how to add session listeners here (Kieker, iObserve)
The Java Servlet API includes the javax.servlet.Filter and interface.
It can be used to implement interceptors for incoming HTTP requests.
Kieker uses this interface to implement different probes. To add
such interceptor to a Servlet, you have to edit the web.xml file in
your Servlet project. For example:
<filter>
<filter−name>sessionAndTraceRegistrationFilter</filter−name>
<filter−class>kieker.monitoring.probe.servlet.SessionAndTraceRegistrationFilter</filter−class>
<init−param>
<param−name>logFilterExecution</param−name>
<param−value>true</param−value>
</init−param>
</filter>
<filter−mapping>
<filter−name>sessionAndTraceRegistrationFilter</filter−name>
<url−pattern>/∗</url−pattern>
</filter−mapping>
This configuration adds the
kieker.monitoring.probe.servlet.SessionAndTraceRegistrationFilter
interceptor to the Servlet configuration and identifies it with
sessionAndTraceRegistrationFilter. It sets one parameter
logFilterExecution to true. In the filter mapping, the
sessionAndTraceRegistrationFilter is mapped to all URLs, i.e., to
all Servlet in the project.