feature/ts-in-metric: add ts in metric (#6)

Author: dsun0720

README.md

@@ -45,7 +45,7 @@ install the sdk in using maven
     <dependency>
         <groupId>co.featbit</groupId>
         <artifactId>Featbit-Java-SDK</artifactId>
-        <version>1.0.2</version>
+        <version>1.0.3</version>
     </dependency>
 </dependencies>
 ```

pom.xml

@@ -6,7 +6,7 @@
 
     <groupId>co.featbit</groupId>
     <artifactId>featbit-java-sdk</artifactId>
-    <version>1.0.2</version>
+    <version>1.0.3</version>
 
     <name>featbit/featbit-java-sdk</name>
 

src/main/java/co/featbit/server/InsightTypes.java

@@ -13,7 +13,6 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
-import java.util.concurrent.Semaphore;
 
 public abstract class InsightTypes {
 
@@ -160,14 +159,18 @@ static final class Metric {
         private final String eventName;
         private final Double numericValue;
         private final String appType = "javaserverside";
+        private final long timestamp;
 
-        Metric(String eventName, Double numericValue) {
+        Metric(String eventName, Double numericValue, long timestamp) {
             this.eventName = eventName;
             this.numericValue = numericValue;
+            this.timestamp = timestamp;
         }
 
         static Metric of(String eventName, Double numericValue) {
-            return new Metric(eventName, numericValue == null ? 1.0D : numericValue);
+            return new Metric(eventName,
+                    numericValue == null ? 1.0D : numericValue,
+                    Instant.now().toEpochMilli());
         }
 
         public String getEventName() {
@@ -189,6 +192,10 @@ public String getType() {
         public String getAppType() {
             return appType;
         }
+
+        public long getTimestamp() {
+            return timestamp;
+        }
     }
 
     final static class UserEventSerializer implements JsonSerializer<UserEvent> {
@@ -235,6 +242,7 @@ public JsonElement serialize(MetricEvent metricEvent, Type type, JsonSerializati
                 var.addProperty("eventName", metric.getEventName());
                 var.addProperty("numericValue", metric.getNumericValue());
                 var.addProperty("appType", metric.getAppType());
+                var.addProperty("timestamp", metric.getTimestamp());
                 array1.add(var);
             }
             json.add("metrics", array1);