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 * Licensed under the Apache License, Version 2.0 (the "License");
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 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
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 * See the License for the specific language governing permissions
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[[library-metrics,Metrics Library]]
= Metrics Library=

The Metrics library is available to application code to get production metrics from their applications. It allows
applications to easily mark critical section for metrics gathering, without handling the details with the Metrics
Extension.

include::../../build/docs/buildinfo/artifact.txt[]

== Usage ==
There are currently the following possibilities available;

    * @TimingCapture - capture timing on a single method
    * TimingCaptureAll - capture timing on all methods of a composite

Before looking at the details of these, we need to point out that there are some pre-conditions for Metrics to be
working. First of all, you need to install a Metrics Extensions, most likely the
<<extension-metrics-yammer, Yammer Metrics Extension>>. See your chosen extension for details on how to do that.

Once the Metrics extension is installed, you will also need a suitable backend to gather all the data out of a
production plant and likewise a good front-end to view this. See your chosen Metrics Extension for this as well.

== TimingCaptureAll ==
There is a TimingCaptureAllConcern, which when added to a composite will install a _Timer_ for every method call
in the composite.

== @TimingCapture ==
The +@TimingCapture+ annotation can be placed on any method of the composite, to indicate that
a Timer is wanted on that method.

Example;

[snippet,java]
----
source=libraries/metrics/src/test/java/org/qi4j/library/metrics/DocumentationSupport.java
tag=capture
----

== Which method? ==
It is valid to annotate either the composite interface methods or the mixin implementation methods.
Any of the method declarations should work. From the testcases we have the following example;

[snippet,java]
----
source=libraries/metrics/src/test/java/org/qi4j/library/metrics/MetricsTest.java
tag=complex-capture
----