Expose setter for Map store in InMemoryMetricRepository

User can then use a weak reference map (for instance), if worried
about memory usage.

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

@@ -20,6 +20,7 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.Date;
 import java.util.HashSet;
+import java.util.concurrent.ConcurrentNavigableMap;
 
 import org.springframework.boot.actuate.metrics.Metric;
 import org.springframework.boot.actuate.metrics.reader.PrefixMetricReader;
@@ -40,6 +41,10 @@ public class InMemoryMetricRepository implements MetricRepository, MultiMetricRe
 
 	private final Collection<String> groups = new HashSet<String>();
 
+	public void setValues(ConcurrentNavigableMap<String, Metric<?>> values) {
+		this.metrics.setValues(values);
+	}
+
 	@Override
 	public void increment(Delta<?> delta) {
 		final String metricName = delta.getName();

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/util/SimpleInMemoryRepository.java

@@ -18,11 +18,12 @@ package org.springframework.boot.actuate.metrics.util;
 
 import java.util.ArrayList;
 import java.util.NavigableMap;
-import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 import java.util.concurrent.ConcurrentNavigableMap;
 import java.util.concurrent.ConcurrentSkipListMap;
 
+import org.springframework.util.ConcurrentReferenceHashMap;
+
 /**
  * Repository utility that stores stuff in memory with period-separated String keys.
  * 
@@ -30,9 +31,9 @@ import java.util.concurrent.ConcurrentSkipListMap;
  */
 public class SimpleInMemoryRepository<T> {
 
-	private final ConcurrentNavigableMap<String, T> values = new ConcurrentSkipListMap<String, T>();
+	private ConcurrentNavigableMap<String, T> values = new ConcurrentSkipListMap<String, T>();
 
-	private final ConcurrentMap<String, Object> locks = new ConcurrentHashMap<String, Object>();
+	private final ConcurrentMap<String, Object> locks = new ConcurrentReferenceHashMap<String, Object>();
 
 	public static interface Callback<T> {
 		T modify(T current);
@@ -96,6 +97,10 @@ public class SimpleInMemoryRepository<T> {
 				.values());
 	}
 
+	public void setValues(ConcurrentNavigableMap<String, T> values) {
+		this.values = values;
+	}
+
 	protected NavigableMap<String, T> getValues() {
 		return this.values;
 	}