Add flag to TraceRepository to reverse order of listing

Default to true (so existing apps change their behaviour, but that
seems to be the majority vote).

Fixes spring-projectsgh-2794

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/trace/InMemoryTraceRepository.java

@@ -16,9 +16,9 @@
 
 package org.springframework.boot.actuate.trace;
 
-import java.util.ArrayList;
 import java.util.Collections;
 import java.util.Date;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 
@@ -31,7 +31,18 @@ public class InMemoryTraceRepository implements TraceRepository {
 
 	private int capacity = 100;
 
-	private final List<Trace> traces = new ArrayList<Trace>();
+	private boolean reverse = true;
+
+	private final List<Trace> traces = new LinkedList<Trace>();
+
+	/**
+	 * Flag to say that the repository lists traces in reverse order.
+	 *
+	 * @param reverse flag value (default true)
+	 */
+	public void setReverse(boolean reverse) {
+		this.reverse = reverse;
+	}
 
 	/**
 	 * @param capacity the capacity to set
@@ -52,9 +63,14 @@ public void add(Map<String, Object> map) {
 		Trace trace = new Trace(new Date(), map);
 		synchronized (this.traces) {
 			while (this.traces.size() >= this.capacity) {
-				this.traces.remove(0);
+				this.traces.remove(this.capacity - 1);
+			}
+			if (this.reverse) {
+				this.traces.add(0, trace);
+			}
+			else {
+				this.traces.add(trace);
 			}
-			this.traces.add(trace);
 		}
 	}
 

spring-boot-actuator/src/test/java/org/springframework/boot/actuate/trace/InMemoryTraceRepositoryTests.java

@@ -40,7 +40,7 @@ public void capacityLimited() {
 		this.repository.add(Collections.<String, Object> singletonMap("bar", "bar"));
 		List<Trace> traces = this.repository.findAll();
 		assertEquals(2, traces.size());
-		assertEquals("bar", traces.get(1).getInfo().get("bar"));
+		assertEquals("bar", traces.get(0).getInfo().get("bar"));
 	}
 
 }