Add a PrefixMetricWriter interface to cleanly separate write/read

The PrefixMetricGroupExporter only really makes sesne if the writer
is aware of the groups, so it seemed better to use a new interface
than mix read/write.

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

@@ -81,7 +81,9 @@ public abstract class AbstractMetricExporter implements Exporter {
 					}
 					values.add(value);
 				}
-				write(group, values);
+				if (!values.isEmpty()) {
+					write(group, values);
+				}
 			}
 		}
 		finally {

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

@@ -23,7 +23,7 @@ import java.util.Set;
 import org.springframework.boot.actuate.metrics.Metric;
 import org.springframework.boot.actuate.metrics.reader.PrefixMetricReader;
 import org.springframework.boot.actuate.metrics.repository.MultiMetricRepository;
-import org.springframework.boot.actuate.metrics.writer.MetricWriter;
+import org.springframework.boot.actuate.metrics.writer.PrefixMetricWriter;
 
 /**
  * A convenient exporter for a group of metrics from a {@link PrefixMetricReader}. Exports
@@ -35,7 +35,7 @@ public class PrefixMetricGroupExporter extends AbstractMetricExporter {
 
 	private final PrefixMetricReader reader;
 
-	private final MetricWriter writer;
+	private final PrefixMetricWriter writer;
 
 	private Set<String> groups = new HashSet<String>();
 
@@ -45,7 +45,7 @@ public class PrefixMetricGroupExporter extends AbstractMetricExporter {
 	 * @param reader a reader as the source of metrics
 	 * @param writer the writer to send the metrics to
 	 */
-	public PrefixMetricGroupExporter(PrefixMetricReader reader, MetricWriter writer) {
+	public PrefixMetricGroupExporter(PrefixMetricReader reader, PrefixMetricWriter writer) {
 		this(reader, writer, "");
 	}
 
@@ -56,8 +56,8 @@ public class PrefixMetricGroupExporter extends AbstractMetricExporter {
 	 * @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) {
+	public PrefixMetricGroupExporter(PrefixMetricReader reader,
+			PrefixMetricWriter writer, String prefix) {
 		super(prefix);
 		this.reader = reader;
 		this.writer = writer;
@@ -72,6 +72,9 @@ public class PrefixMetricGroupExporter extends AbstractMetricExporter {
 
 	@Override
 	protected Iterable<String> groups() {
+		if ((this.reader instanceof MultiMetricRepository) && this.groups.isEmpty()) {
+			return ((MultiMetricRepository) this.reader).groups();
+		}
 		return this.groups;
 	}
 
@@ -82,14 +85,7 @@ public class PrefixMetricGroupExporter extends AbstractMetricExporter {
 
 	@Override
 	protected void write(String group, Collection<Metric<?>> values) {
-		if (this.writer instanceof MultiMetricRepository && !values.isEmpty()) {
-			((MultiMetricRepository) this.writer).save(group, values);
-		}
-		else {
-			for (Metric<?> value : values) {
-				this.writer.set(value);
-			}
-		}
+		this.writer.save(group, values);
 	}
 
 }

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

@@ -72,7 +72,15 @@ public class InMemoryMetricRepository implements MetricRepository, MultiMetricRe
 
 	@Override
 	public void save(String group, Collection<Metric<?>> values) {
+		String prefix = group;
+		if (!prefix.endsWith(".")) {
+			prefix = prefix + ".";
+		}
 		for (Metric<?> metric : values) {
+			if (!metric.getName().startsWith(prefix)) {
+				metric = new Metric<Number>(prefix + metric.getName(), metric.getValue(),
+						metric.getTimestamp());
+			}
 			set(metric);
 		}
 		this.groups.add(group);

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

@@ -16,10 +16,8 @@
 
 package org.springframework.boot.actuate.metrics.repository;
 
-import java.util.Collection;
-
-import org.springframework.boot.actuate.metrics.Metric;
 import org.springframework.boot.actuate.metrics.reader.PrefixMetricReader;
+import org.springframework.boot.actuate.metrics.writer.PrefixMetricWriter;
 
 /**
  * A repository for metrics that allows efficient storage and retrieval of groups of
@@ -27,21 +25,7 @@ import org.springframework.boot.actuate.metrics.reader.PrefixMetricReader;
  * 
  * @author Dave Syer
  */
-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);
+public interface MultiMetricRepository extends PrefixMetricReader, PrefixMetricWriter {
 
 	/**
 	 * The names of all the groups known to this repository

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

@@ -44,7 +44,7 @@ public class RedisMultiMetricRepository implements MultiMetricRepository {
 
 	private String prefix = DEFAULT_METRICS_PREFIX;
 
-	private String keys = this.prefix + "keys";
+	private String keys = "keys." + this.prefix;
 
 	private final BoundZSetOperations<String, String> zSetOperations;
 
@@ -61,8 +61,11 @@ public class RedisMultiMetricRepository implements MultiMetricRepository {
 	 * @param prefix the prefix to set for all metrics keys
 	 */
 	public void setPrefix(String prefix) {
+		if (!prefix.endsWith(".")) {
+			prefix = prefix + ".";
+		}
 		this.prefix = prefix;
-		this.keys = this.prefix + "keys";
+		this.keys = "keys." + this.prefix;
 	}
 
 	@Override

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

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2012-2013 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.actuate.metrics.writer;
+
+import java.util.Collection;
+
+import org.springframework.boot.actuate.metrics.Metric;
+
+/**
+ * A writer for metrics that allows efficient storage of groups of metrics with a common
+ * name prefix (their group name).
+ * 
+ * @author Dave Syer
+ */
+public interface PrefixMetricWriter {
+
+	/**
+	 * 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);
+
+}

spring-boot-actuator/src/test/java/org/springframework/boot/actuate/metrics/export/PrefixMetricGroupExporterTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.actuate.metrics.export;
 
+import java.util.Arrays;
 import java.util.Collections;
 
 import org.junit.Test;
@@ -57,6 +58,15 @@ public class PrefixMetricGroupExporterTests {
 		assertEquals(0, Iterables.collection(this.writer.groups()).size());
 	}
 
+	@Test
+	public void multiMetricGroupsCopiedAsDefault() {
+		this.reader.save("foo", Arrays.<Metric<?>> asList(new Metric<Number>("bar", 2.3),
+				new Metric<Number>("spam", 1.3)));
+		this.exporter.export();
+		assertEquals(1, this.writer.countGroups());
+		assertEquals(2, Iterables.collection(this.writer.findAll("foo")).size());
+	}
+
 	@Test
 	public void onlyPrefixedMetricsCopied() {
 		this.reader.set(new Metric<Number>("foo.bar", 2.3));