Async health check

metrics-healthchecks/src/main/java/io/dropwizard/metrics/health/AsyncHealthCheck.java

@@ -0,0 +1,43 @@
+package io.dropwizard.metrics.health;
+
+import java.util.Date;
+import java.util.concurrent.TimeUnit;
+
+public class AsyncHealthCheck extends HealthCheck implements Runnable {
+    private final HealthCheck synchronousHealthCheck;
+    private final int maxStaleAge;
+    private final TimeUnit maxStaleAgeUnit;
+
+    private volatile CachedResult lastResult;
+
+    public AsyncHealthCheck(HealthCheck synchronousHealthCheck, int maxStaleAge, TimeUnit maxStaleAgeUnit) {
+        this.synchronousHealthCheck = synchronousHealthCheck;
+        this.maxStaleAge = maxStaleAge;
+        this.maxStaleAgeUnit = maxStaleAgeUnit;
+    }
+
+    @Override
+    protected Result check() throws Exception {
+        if (new Date(lastResult.whenCheckFinished.getTime() + maxStaleAgeUnit.toSeconds(maxStaleAge)).before(new Date())) {
+            return Result.unhealthy("Stale");
+        } else {
+            return lastResult.result;
+        }
+    }
+
+    @Override
+    public void run() {
+        Result check = synchronousHealthCheck.execute();
+        lastResult = new CachedResult(check, new Date());
+    }
+
+    private static class CachedResult {
+        public final Result result;
+        public final Date whenCheckFinished;
+
+        private CachedResult(Result result, Date whenCheckFinished) {
+            this.result = result;
+            this.whenCheckFinished = whenCheckFinished;
+        }
+    }
+}