Allow customizing start log message in PushMeterRegistry implementati…

…ons (#4848)

It will be helpful in troubleshooting to be able to log more specific information to the implementation than is available at the level of PushMeterRegistry. Allowing this to be overridden also avoids registry implementations from logging similar messages resulting in multiple logs on start for essentially the same thing.

micrometer-core/src/main/java/io/micrometer/core/instrument/push/PushMeterRegistry.java

@@ -107,8 +107,7 @@ public void start(ThreadFactory threadFactory) {
             stop();
 
         if (config.enabled()) {
-            logger.info("publishing metrics for " + getClass().getSimpleName() + " every "
-                    + TimeUtils.format(config.step()));
+            logger.info(startMessage());
 
             scheduledExecutorService = Executors.newSingleThreadScheduledExecutor(threadFactory);
             long stepMillis = config.step().toMillis();
@@ -118,6 +117,17 @@ public void start(ThreadFactory threadFactory) {
         }
     }
 
+    /**
+     * Message that will be logged when the registry is {@link #start(ThreadFactory)
+     * started}. This can be overridden to customize the message with info specific to the
+     * registry implementation that may be helpful in troubleshooting. By default, the
+     * registry class name and step interval are included.
+     * @return message to log on registry start
+     */
+    protected String startMessage() {
+        return "publishing metrics for " + getClass().getSimpleName() + " every " + TimeUtils.format(config.step());
+    }
+
     public void stop() {
         if (scheduledExecutorService != null) {
             scheduledExecutorService.shutdown();