Class MetricsFilter

java.lang.Object
io.prometheus.client.filter.MetricsFilter
All Implemented Interfaces:
javax.servlet.Filter
public class MetricsFilter extends Object implements javax.servlet.Filter
The MetricsFilter class provides a high-level filter that enables tunable collection of metrics for Servlet performance. This is the Javax version of the MetricsFilter. If you are using Jakarta Servlet, there is a Jakarta version available in simpleclient-servlet-jakarta.

The metric name itself is required, and configured with a metric-name init parameter.

The help parameter, configured with the help init parameter, is not required but strongly recommended.

The Histogram buckets can be configured with a buckets init parameter whose value is a comma-separated list * of valid double values. If omitted, the default buckets from Histogram are used.

By default, this filter will provide metrics that distinguish only 1 level deep for the request path (including servlet context path), but can be configured with the path-components init parameter. Any number provided that is less than 1 will provide the full path granularity (warning, this may affect performance).

The strip-context-path init parameter can be used to avoid including the leading path components which are part of the context (i.e. the folder where the servlet is deployed) so that the same project deployed under different paths can produce the same metrics.

HTTP statuses will be aggregated via Counter. The name for this counter will be derived from the metric-name init parameter. 

<filter>
  <filter-name>prometheusFilter</filter-name>
  <!-- This example shows the javax version. For Jakarta you would use -->
  <!-- <filter-class>io.prometheus.client.filter.servlet.jakarta.MetricsFilter</filter-class> -->
  <filter-class>io.prometheus.client.filter.MetricsFilter</filter-class>
  <init-param>
    <param-name>metric-name</param-name>
    <param-value>webapp_metrics_filter</param-value>
  </init-param>
  <!-- help is optional, defaults to the message below -->
  <init-param>
    <param-name>help</param-name>
    <param-value>This is the help for your metrics filter</param-value>
  </init-param>
  <!-- buckets is optional, unless specified the default buckets from io.prometheus.client.Histogram are used -->
  <init-param>
    <param-name>buckets</param-name>
    <param-value>0.005,0.01,0.025,0.05,0.075,0.1,0.25,0.5,0.75,1,2.5,5,7.5,10</param-value>
  </init-param>
  <!-- path-components is optional, anything less than 1 (1 is the default) means full granularity -->
  <init-param>
    <param-name>path-components</param-name>
    <param-value>1</param-value>
  </init-param>
  <!-- strip-context-path is optional, defaults to false -->
  <init-param>
    <param-name>strip-context-path</param-name>
    <param-value>false</param-value>
  </init-param>
</filter>

<!-- You will most likely want this to be the first filter in the chain
(therefore the first <filter-mapping> in the web.xml file), so that you can get
the most accurate measurement of latency. -->
<filter-mapping>
  <filter-name>prometheusFilter</filter-name>
  <url-pattern>/*</url-pattern>
</filter-mapping>

  • Field Details

    • delegate

      private final Filter delegate

  • Constructor Details

  • Method Details

    • init

      public void init(javax.servlet.FilterConfig filterConfig) throws javax.servlet.ServletException
      Specified by:
      init in interface javax.servlet.Filter
      Throws:
      javax.servlet.ServletException

    • doFilter

      public void doFilter(javax.servlet.ServletRequest servletRequest, javax.servlet.ServletResponse servletResponse, javax.servlet.FilterChain filterChain) throws IOException, javax.servlet.ServletException
      Specified by:
      doFilter in interface javax.servlet.Filter
      Throws:
      IOException
      javax.servlet.ServletException

    • destroy

      public void destroy()
      Specified by:
      destroy in interface javax.servlet.Filter