Kamon-Servlet

Getting Started

The kamon-servlet module brings traces and metrics to your servlet based applications.

Kamon Servlet is currently available for Scala 2.10, 2.11 and 2.12.

Supported releases and dependencies are shown below.

kamon-servlet-2.5	status	jdk	scala
1.0.0	stable	1.8+	2.10, 2.11, 2.12
2.0.0	stable	1.8+	2.11, 2.12, 2.13

kamon-servlet-3.x.x	status	jdk	scala
1.0.0	stable	1.8+	2.10, 2.11, 2.12
2.0.0	stable	1.8+	2.11, 2.12, 2.13

To get kamon-servlet in your project:

Maven:

<dependencies>
  <dependency>
    <groupId>io.kamon</groupId>
    <artifactId>kamon-servlet-3_2.12</artifactId>
    <version>2.0.0</version>
  </dependency>
</dependencies>

Gradle:

dependencies {
  compile 'io.kamon:kamon-servlet-3_2.12:2.0.0'
}

SBT:

libraryDependencies += "io.kamon" %% "kamon-servlet-3" % "2.0.0"

Setting up

All you need to do is to add the Kamon Filter on your Web App:

For Servlet 2.5: kamon.servlet.v25.KamonFilterV25
For Servlet 3.x.x: kamon.servlet.v3.KamonFilterV3

You should register it in the specific way your framework required. Otherwise, you need to configure it manually. Below there are some example.

Servlet v3+

You could programmatically register it using a ServletContextListener:

package kamon.servlet.v3.example;

import java.util.EnumSet;
import javax.servlet.DispatcherType;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import kamon.Kamon;
import kamon.servlet.v3.KamonFilterV3;

public class KamonContextListener implements ServletContextListener {

  @Override
  public void contextInitialized(ServletContextEvent servletContextEvent) {
    // here you might subscribe all reporters you want. e.g. `Kamon.addReporter(new PrometheusReporter())`
    servletContextEvent
        .getServletContext()
        .addFilter("KamonFilter", new KamonFilterV3())
        .addMappingForUrlPatterns(EnumSet.allOf(DispatcherType.class), true, "/*");
  }

  @Override
  public void contextDestroyed(ServletContextEvent arg0) {
    // in case you have subscribed some reporters: `Kamon.stopAllReporters();`
    System.out.println("KamonContextListener destroyed");
  }
}

Servlet v2.5

For Servlet 2.5 there isn't a programmatic way to achieve it, so you have to define it in web.xml:

<filter>
   <filter-name>kamonFilter</filter-name>
   <filter-class>kamon.servlet.v25.KamonFilterV25</filter-class>
 </filter>
 <filter-mapping>
   <filter-name>kamonFilter</filter-name>
   <url-pattern>/*</url-pattern>
 </filter-mapping>

Config

kamon-servlet uses TypeSafe Config. Default configuration is in resources/reference.conf for each subproject:

You can customize/override any property adding an application.conf in the /resources/ of your app or by providing System properties (e.g. -Dpath.of.your.key=value). This is the standard behavior of TypeSafe Config, for more info see its doc.

Micro Benchmarks

Execute from your terminal:

sbt
project benchmarks-3 # or benchmarks-25
jmh:run -i 50 -wi 20 -f1 -t1 .*Benchmark.*