Support setting timestamp

README.md

@@ -158,6 +158,16 @@ Examples:
 setNamespace("MyApplication")
 ```
 
+- MetricsLogger **setTimestamp**(Instant timestamp)
+
+Sets the timestamp of the metrics. If not set, current time of the client will be used.
+
+Examples:
+
+```java
+setTimestamp(Instant.now())
+```
+
 - **flush**()
 
 Flushes the current MetricsContext to the configured sink and resets all properties, dimensions and metric values. The namespace and default dimensions will be preserved across flushes.

src/main/java/software/amazon/cloudwatchlogs/emf/logger/MetricsLogger.java

@@ -16,6 +16,7 @@
 
 package software.amazon.cloudwatchlogs.emf.logger;
 
+import java.time.Instant;
 import java.util.concurrent.CompletableFuture;
 import lombok.extern.slf4j.Slf4j;
 import software.amazon.cloudwatchlogs.emf.environment.Environment;
@@ -165,6 +166,17 @@ public MetricsLogger setNamespace(String namespace) {
         return this;
     }
 
+    /**
+     * Set the timestamp to be used for metrics.
+     *
+     * @param timestamp value of timestamp to be set
+     * @return the current logger
+     */
+    public MetricsLogger setTimestamp(Instant timestamp) {
+        this.context.setTimestamp(timestamp);
+        return this;
+    }
+
     private void configureContextForEnvironment(MetricsContext context, Environment environment) {
         if (context.hasDefaultDimensions()) {
             return;

src/main/java/software/amazon/cloudwatchlogs/emf/model/MetricsContext.java

@@ -17,6 +17,7 @@
 package software.amazon.cloudwatchlogs.emf.model;
 
 import com.fasterxml.jackson.core.JsonProcessingException;
+import java.time.Instant;
 import java.util.*;
 import lombok.Getter;
 import software.amazon.cloudwatchlogs.emf.Constants;
@@ -195,6 +196,20 @@ public void putMetadata(String key, Object value) {
         rootNode.getAws().putCustomMetadata(key, value);
     }
 
+    /** @return timestamp field from the metadata. */
+    public Instant getTimestamp() {
+        return rootNode.getAws().getTimestamp();
+    }
+
+    /**
+     * Update timestamp field in the metadata
+     *
+     * @param timestamp value of timestamp to be set
+     */
+    public void setTimestamp(Instant timestamp) {
+        rootNode.getAws().setTimestamp(timestamp);
+    }
+
     /** @return Creates an independently flushable context. */
     public MetricsContext createCopyWithContext() {
         return new MetricsContext(metricDirective.copyWithoutMetrics());

src/test/java/software/amazon/cloudwatchlogs/emf/logger/MetricsLoggerTest.java

@@ -21,6 +21,7 @@
 import static org.junit.Assert.assertTrue;
 import static org.mockito.Mockito.*;
 
+import java.time.Instant;
 import java.util.List;
 import java.util.concurrent.CompletableFuture;
 import org.junit.Assert;
@@ -118,6 +119,21 @@ public void testSetNamespace() {
         Assert.assertEquals(sink.getContext().getNamespace(), namespace);
     }
 
+    @Test
+    public void testFlushWithDefaultTimestamp() {
+        logger.flush();
+        Assert.assertNotNull(sink.getContext().getTimestamp());
+    }
+
+    @Test
+    public void testSetTimestamp() {
+        Instant now = Instant.now();
+        logger.setTimestamp(now);
+        logger.flush();
+
+        Assert.assertEquals(sink.getContext().getTimestamp(), now);
+    }
+
     @Test
     public void testFlushWithConfiguredServiceName() {
         String serviceName = "TestServiceName";

src/test/java/software/amazon/cloudwatchlogs/emf/model/MetricsContextTest.java

@@ -23,6 +23,7 @@
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.core.type.TypeReference;
 import com.fasterxml.jackson.databind.json.JsonMapper;
+import java.time.Instant;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
@@ -140,19 +141,37 @@ public void testSerializeZeroMetric() throws JsonProcessingException {
         int expectedEventCount = 1;
         assertEquals(expectedEventCount, events.size());
 
-        JsonMapper objectMapper = new JsonMapper();
-        Map<String, Object> metadata_map =
-                objectMapper.readValue(events.get(0), new TypeReference<Map<String, Object>>() {});
+        Map<String, Object> rootNode = parseRootNode(events.get(0));
         // If there's no metric added, the _aws would be filtered out from the log event
-        assertFalse(metadata_map.containsKey("_aws"));
+        assertFalse(rootNode.containsKey("_aws"));
+    }
+
+    @Test
+    @SuppressWarnings("unchecked")
+    public void testSetTimestamp() throws JsonProcessingException {
+        MetricsContext mc = new MetricsContext();
+        mc.putMetric("Metric", 0);
+
+        Instant now = Instant.now();
+        mc.setTimestamp(now);
+
+        List<String> events = mc.serialize();
+
+        int expectedEventCount = 1;
+        assertEquals(expectedEventCount, events.size());
+        Map<String, Object> rootNode = parseRootNode(events.get(0));
+
+        assertTrue(rootNode.containsKey("_aws"));
+        Map<String, Object> metadata = (Map<String, Object>) rootNode.get("_aws");
+
+        assertTrue(metadata.containsKey("Timestamp"));
+        assertEquals(metadata.get("Timestamp"), now.toEpochMilli());
     }
 
     @SuppressWarnings("unchecked")
     private ArrayList<MetricDefinition> parseMetrics(String event) throws JsonProcessingException {
-        JsonMapper objectMapper = new JsonMapper();
-        Map<String, Object> metadata_map =
-                objectMapper.readValue(event, new TypeReference<Map<String, Object>>() {});
-        Map<String, Object> metadata = (Map<String, Object>) metadata_map.get("_aws");
+        Map<String, Object> rootNode = parseRootNode(event);
+        Map<String, Object> metadata = (Map<String, Object>) rootNode.get("_aws");
         ArrayList<Map<String, Object>> metricDirectives =
                 (ArrayList<Map<String, Object>>) metadata.get("CloudWatchMetrics");
         ArrayList<Map<String, String>> metrics =
@@ -162,7 +181,7 @@ private ArrayList<MetricDefinition> parseMetrics(String event) throws JsonProces
         for (Map<String, String> metric : metrics) {
             String name = metric.get("Name");
             Unit unit = Unit.fromValue(metric.get("Unit"));
-            Object value = metadata_map.get(name);
+            Object value = rootNode.get(name);
             if (value instanceof ArrayList) {
                 metricDefinitions.add(new MetricDefinition(name, unit, (ArrayList) value));
             } else {
@@ -171,4 +190,8 @@ private ArrayList<MetricDefinition> parseMetrics(String event) throws JsonProces
         }
         return metricDefinitions;
     }
+
+    private Map<String, Object> parseRootNode(String event) throws JsonProcessingException {
+        return new JsonMapper().readValue(event, new TypeReference<Map<String, Object>>() {});
+    }
 }