Add javadocs to some Metrics interfaces

Fixes gh-250

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/export/PrefixMetricGroupExporter.java

@@ -26,6 +26,9 @@ import org.springframework.boot.actuate.metrics.repository.MultiMetricRepository
 import org.springframework.boot.actuate.metrics.writer.MetricWriter;
 
 /**
+ * A convenient exporter for a group of metrics from a {@link PrefixMetricReader}. Exports
+ * all metrics whose name starts with a prefix (or all metrics if the prefix is empty).
+ * 
  * @author Dave Syer
  */
 public class PrefixMetricGroupExporter extends AbstractMetricExporter {
@@ -36,10 +39,25 @@ public class PrefixMetricGroupExporter extends AbstractMetricExporter {
 
 	private Set<String> groups = new HashSet<String>();
 
+	/**
+	 * Create a new exporter for metrics to a writer based on an empty prefix for the
+	 * metric names.
+	 * 
+	 * @param reader a reader as the source of metrics
+	 * @param writer the writer to send the metrics to
+	 */
 	public PrefixMetricGroupExporter(PrefixMetricReader reader, MetricWriter writer) {
 		this(reader, writer, "");
 	}
 
+	/**
+	 * Create a new exporter for metrics to a writer based on a prefix for the metric
+	 * names.
+	 * 
+	 * @param reader a reader as the source of metrics
+	 * @param writer the writer to send the metrics to
+	 * @param prefix the prefix for metrics to export
+	 */
 	public PrefixMetricGroupExporter(PrefixMetricReader reader, MetricWriter writer,
 			String prefix) {
 		super(prefix);

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/reader/MetricReader.java

@@ -25,10 +25,27 @@ import org.springframework.boot.actuate.metrics.Metric;
  */
 public interface MetricReader {
 
+	/**
+	 * Find an instance of the metric with the given name (usually the latest recorded
+	 * value).
+	 * 
+	 * @param metricName the name of the metric to find
+	 * @return a metric value or null if there are none with that name
+	 */
 	Metric<?> findOne(String metricName);
 
+	/**
+	 * Find all the metrics known to this reader.
+	 * 
+	 * @return all instances of metrics known to this reader
+	 */
 	Iterable<Metric<?>> findAll();
 
+	/**
+	 * The number of metrics known to this reader.
+	 * 
+	 * @return the number of metrics
+	 */
 	long count();
 
 }

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/reader/PrefixMetricReader.java

@@ -25,6 +25,12 @@ import org.springframework.boot.actuate.metrics.Metric;
  */
 public interface PrefixMetricReader {
 
+	/**
+	 * Find all metrics whose name starts with the given prefix.
+	 * 
+	 * @param prefix the prefix for metric names
+	 * @return all metrics with names starting with the prefix
+	 */
 	Iterable<Metric<?>> findAll(String prefix);
 
 }

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/repository/MultiMetricRepository.java

@@ -29,12 +29,32 @@ import org.springframework.boot.actuate.metrics.reader.PrefixMetricReader;
  */
 public interface MultiMetricRepository extends PrefixMetricReader {
 
+	/**
+	 * Save some metric values and associate them with a group name.
+	 * 
+	 * @param group the name of the group
+	 * @param values the metric values to save
+	 */
 	void save(String group, Collection<Metric<?>> values);
 
+	/**
+	 * Rest the values of all metrics in the group. Implementations may choose to discard
+	 * the old values.
+	 * 
+	 * @param group reset the whole group
+	 */
 	void reset(String group);
 
+	/**
+	 * The names of all the groups known to this repository
+	 * 
+	 * @return all available group names
+	 */
 	Iterable<String> groups();
 
+	/**
+	 * @return the number of groups available
+	 */
 	long count();
 
 }

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/rich/RichGaugeReader.java

@@ -23,10 +23,24 @@ package org.springframework.boot.actuate.metrics.rich;
  */
 public interface RichGaugeReader {
 
+	/**
+	 * Find a single instance of a rich gauge by name.
+	 * 
+	 * @param name the name of the gauge
+	 * @return a rich gauge value
+	 */
 	RichGauge findOne(String name);
 
+	/**
+	 * Find all instances of rich gauge known to this reader.
+	 * 
+	 * @return all instances known to this reader
+	 */
 	Iterable<RichGauge> findAll();
 
+	/**
+	 * @return the number of gauge values available
+	 */
 	long count();
 
 }

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/writer/MetricWriter.java

@@ -25,10 +25,27 @@ import org.springframework.boot.actuate.metrics.Metric;
  */
 public interface MetricWriter {
 
+	/**
+	 * Increment the value of a metric (or decrement if the delta is negative). The name
+	 * of the delta is the name of the metric to increment.
+	 * 
+	 * @param delta the amount to increment by
+	 */
 	void increment(Delta<?> delta);
 
+	/**
+	 * Set the value of a metric.
+	 * 
+	 * @param value
+	 */
 	void set(Metric<?> value);
 
+	/**
+	 * Reset the value of a metric, usually to zero value. Implementations can discard the
+	 * old values if desired, but may choose not to.
+	 * 
+	 * @param metricName the name to reset
+	 */
 	void reset(String metricName);
 
 }