#Metrics for Spring

##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, @ExceptionMetered, and @Counted
• 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
• Creates reporters and binds them to the Spring lifecycle

###Maven

Current version is 3.0.0-RC2, which is compatible with Metrics 3.0

<dependency>
	<groupId>com.ryantenney.metrics</groupId>
	<artifactId>metrics-spring</artifactId>
	<version>3.0.0-RC2</version>
</dependency>

This module was formerly contained in the Yammer Metrics repository.

###Basic Usage

As of version 3, metrics-spring may be configured using XML or Java, depending on your personal preference.

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">

	<!-- registry and reporters should be defined in only one context xml file -->
	<metrics:metric-registry id="registry" name="springMetrics" />
	<metrics:reporter type="console" metric-registry="registry" period="1m" />
	
	<!-- annotation-driven must be included in all context files -->
	<metrics:annotation-driven metric-registry="registry" />

	<!-- beans -->

</beans>

Java Annotation Config:

import java.util.concurrent.TimeUnit;
import org.springframework.context.annotation.Configuration;
import com.codahale.metrics.ConsoleReporter;
import com.codahale.metrics.MetricRegistry;
import com.codahale.metrics.SharedMetricRegistries;
import com.ryantenney.metrics.spring.config.annotation.EnableMetrics;
import com.ryantenney.metrics.spring.config.annotation.MetricsConfigurerAdapter;

@Configuration
@EnableMetrics
public class SpringConfiguringClass extends MetricsConfigurerAdapter {

	@Override
	public MetricRegistry getMetricRegistry() {
		return SharedMetricRegistries.getOrCreate("springMetrics");
	}

	@Override
	public void configureReporters(MetricRegistry metricRegistry) {
		ConsoleReporter.forRegistry(registry)
			.outputTo(output)
			.build()
			.start(1, TimeUnit.MINUTES);
	}

}

###XML Config Documentation

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 <metrics:metric-registry /> element constructs a new MetricRegistry or retrieves a shared registry:

• id - the bean name with which to register the MetricRegistry bean
• name - the name of the MetricRegistry, if present, this calls SharedMetricRegistries.getOrCreate(name)

The <metrics:health-check-registry /> element constructs a new HealthCheckRegistry:

• id - the bean name with which to register the HealthCheckRegistry bean

The <metrics:reporter /> element creates and starts a reporter.

• id - the bean name
• metric-registry - the id of the MetricRegsitry bean for which the reporter should retrieve metrics
• type - the type of the reporter. Additional types may be registered through SPI (more on this later).
• console: ConsoleReporter
• jmx: JmxReporter
• slf4j: Slf4jReporter
• ganglia: GangliaReporter (requires metrics-ganglia)
• graphite: GraphiteReporter (requires metrics-graphite)

###Java Config Documentation

A @Configuration class annotated with @EnableMetrics is functionally equivalent to using the <metrics:annotation-driven /> element.

• proxyTargetClass - if set to true, always creates CGLIB proxies instead of defaulting to JDK proxies. This may be necessary if you use class-based autowiring.
• exposeProxy - if set to true, the target can access the proxy which wraps it by calling AopContext.currentProxy().

The class may also implement the interface MetricsConfigurer, or extend the abstract class MetricsConfigurerAdapter

• getMetricRegistry() - return the MetricRegsitry instance with which metrics should be registered. If omitted a new MetricRegistry instance is created.
• getHealthCheckRegistry() - return the HealthCheckRegsitry instance with which to register any beans which extend the class HealthCheck. If omitted a new HealthCheckRegistry instance is created.
• configureReporters(MetricRegistry) - configure reporters

###A Note on the Limitations of Spring AOP

Due to limitations of Spring AOP only public methods can be proxied, so @Timed, @Metered, @ExceptionMetered, and @Counted 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.

###Users of the Maven Shade plugin

Please see the Shade Readme

###Documentation

Javadocs are hosted at http://ryantenney.github.io/metrics-spring/docs/

License

Copyright (c) 2012-2013 Ryan Tenney, Martello Technologies

Published under Apache Software License 2.0, see LICENSE