##About

The metrics-spring module integrates Yammer Metrics with Spring AOP, and provides XML and Java configuration.

This module does the following things:

• Proxies beans which contain methods annotated with @Timed, @Metered, and @ExceptionMetered
• Registers a Gauge for beans which have members annotated with @Gauge
• Autowires Timers, Meters, Counters and Histograms into fields annotated with @InjectMetric
• Registers with the HealthCheckRegistry any beans which extend the class HealthCheck

###Maven

Current release version is 2.1.4, which works with Metrics 2.x.

<dependency>
	<groupId>com.ryantenney.metrics</groupId>
	<artifactId>metrics-spring</artifactId>
	<version>2.1.4</version>
</dependency>

Currently working on 3.0.0-SNAPSHOT for Metrics 3 compatibility.

<repository>
	<id>sonatype-nexus-snapshots</id>
	<name>Sonatype Nexus Snapshots</name>
	<url>http://oss.sonatype.org/content/repositories/snapshots</url>
</repository>

<dependency>
	<groupId>com.ryantenney.metrics</groupId>
	<artifactId>metrics-spring</artifactId>
	<version>3.0.0-SNAPSHOT</version>
</dependency>

This module was formerly contained in the Yammer Metrics repository.

###Basic Usage

Pull requests to improve or expand this documentation would be most welcome.

Spring Context XML:

<beans xmlns="http://www.springframework.org/schema/beans"
	   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	   xmlns:metrics="http://www.ryantenney.com/schema/metrics"
	   xsi:schemaLocation="
			http://www.springframework.org/schema/beans
			http://www.springframework.org/schema/beans/spring-beans-3.2.xsd
			http://www.ryantenney.com/schema/metrics
			http://www.ryantenney.com/schema/metrics/metrics-3.0.xsd">

	<metrics:annotation-driven />

	<!-- beans -->

</beans>

Java Config (available in 3.0.0-SNAPSHOT):

import org.springframework.context.annotation.Configuration;
import com.ryantenney.metrics.spring.config.annotation.EnableMetrics;

@Configuration
@EnableMetrics
public class SpringConfiguringClass {
	// ...
}

###XML Config

The <metrics:annotation-driven /> element is required, and has 4 optional arguments:

• metric-registry - the id of the MetricRegsitry bean with which the generated metrics should be registered. If omitted a new MetricRegistry bean is created.
• health-check-registry - the id of the HealthCheckRegsitry bean with which to register any beans which extend the class HealthCheck. If omitted a new HealthCheckRegistry bean is created.
• proxy-target-class - if set to true, always creates CGLIB proxies instead of defaulting to JDK proxies. This may be necessary if you use class-based autowiring.
• expose-proxy - if set to true, the target can access the proxy which wraps it by calling AopContext.currentProxy().

The element <metrics:reporter /> currently doesn't do a damn thing, but it will soon!

###A Note on the Limitations of Spring AOP

Due to limitations of Spring AOP only public methods can be proxied, so @Timed, @Metered, and @ExceptionMetered have no effect on non-public methods. Additionally, calling an annotated method from within the same class will not go through the proxy.

public class Foo {
	
	@Timed
	public void bar() { /* … */ }
	
	public void baz() {
		this.bar(); // doesn't pass through the proxy
		
		// fix: reengineer
		// workaround: enable `expose-proxy` and change to:
		((Foo) AopContext.currentProxy()).bar(); // hideous, but it works
	}
}

As @Gauge doesn’t involve a proxy, it may be used on non-public fields and methods. Additionally, @InjectMetric may be used on non-public, non-final fields.

Copyright (c) 2012 Ryan Tenney, Martello Technologies

Published under Apache Software License 2.0, see LICENSE