diff --git a/build.gradle b/build.gradle
index f467acb..ba76629 100644
--- a/build.gradle
+++ b/build.gradle
@@ -13,5 +13,7 @@ repositories {
 
 dependencies {
     implementation 'org.java-websocket:Java-WebSocket:1.4.0'
+    implementation group: 'org.json', name: 'json', version: '20180813'
+
     testCompile group: 'junit', name: 'junit', version: '4.12'
 }
diff --git a/src/main/java/io/github/chronosx88/GunJava/Dup.java b/src/main/java/io/github/chronosx88/GunJava/Dup.java
new file mode 100644
index 0000000..d033851
--- /dev/null
+++ b/src/main/java/io/github/chronosx88/GunJava/Dup.java
@@ -0,0 +1,50 @@
+package io.github.chronosx88.GunJava;
+
+import java.util.Map;
+import java.util.Random;
+import java.util.concurrent.ConcurrentHashMap;
+
+public class Dup {
+    private static char[] randomPack = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ".toCharArray();
+    private static Random random = new Random(System.currentTimeMillis());
+    private Map<String, Long> s = new ConcurrentHashMap<>();
+    private DupOpt opt = new DupOpt();
+    private Thread to = null;
+
+    public Dup() {
+        opt.max = 1000;
+        opt.age = 1000 * 9;
+    }
+
+    public String track(String id) {
+        s.put(id, System.currentTimeMillis());
+        if(to == null) {
+            Utils.setTimeout(() -> {
+                for(Map.Entry<String, Long> entry : s.entrySet()) {
+                    if(opt.age > (System.currentTimeMillis() - entry.getValue()))
+                        continue;
+                    s.remove(entry.getKey());
+                }
+                to = null;
+            }, opt.age);
+        }
+        return id;
+    }
+
+    public boolean check(String id) {
+        if(s.containsKey(id)) {
+            track(id);
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    public String random() {
+        StringBuilder sb = new StringBuilder();
+        for (int i = 0; i < randomPack.length; i++) {
+            sb.append(randomPack[random.nextInt(randomPack.length)]);
+        }
+        return sb.toString();
+    }
+}
diff --git a/src/main/java/io/github/chronosx88/GunJava/DupOpt.java b/src/main/java/io/github/chronosx88/GunJava/DupOpt.java
new file mode 100644
index 0000000..029a9b3
--- /dev/null
+++ b/src/main/java/io/github/chronosx88/GunJava/DupOpt.java
@@ -0,0 +1,6 @@
+package io.github.chronosx88.GunJava;
+
+public class DupOpt {
+    public int max;
+    public int age;
+}
diff --git a/src/main/java/io/github/chronosx88/GunJava/Main.java b/src/main/java/io/github/chronosx88/GunJava/Main.java
index c6cea04..3a647ad 100644
--- a/src/main/java/io/github/chronosx88/GunJava/Main.java
+++ b/src/main/java/io/github/chronosx88/GunJava/Main.java
@@ -2,6 +2,7 @@ package io.github.chronosx88.GunJava;
 
 import org.java_websocket.client.WebSocketClient;
 import org.java_websocket.handshake.ServerHandshake;
+import org.json.JSONObject;
 
 import java.net.URI;
 import java.net.URISyntaxException;
@@ -18,7 +19,9 @@ public class Main {
 
             @Override
             public void onMessage(String message) {
-                System.out.println(message);
+                JSONObject msg = new JSONObject(message);
+                System.out.println(msg);
+                this.send(message);
             }
 
             @Override
diff --git a/src/main/java/io/github/chronosx88/GunJava/Server.java b/src/main/java/io/github/chronosx88/GunJava/Server.java
index c9cac51..f1a584b 100644
--- a/src/main/java/io/github/chronosx88/GunJava/Server.java
+++ b/src/main/java/io/github/chronosx88/GunJava/Server.java
@@ -3,6 +3,7 @@ package io.github.chronosx88.GunJava;
 import org.java_websocket.WebSocket;
 import org.java_websocket.handshake.ClientHandshake;
 import org.java_websocket.server.WebSocketServer;
+import org.json.JSONObject;
 
 import java.net.InetSocketAddress;
 import java.util.Timer;
@@ -10,6 +11,7 @@ import java.util.TimerTask;
 
 public class Server extends WebSocketServer {
     private Timer timer = new Timer(true);
+    private Dup dup = new Dup();
 
     public Server(int port) {
         super(new InetSocketAddress(port));
@@ -22,7 +24,9 @@ public class Server extends WebSocketServer {
             @Override
             public void run() {
                 count[0] += 1;
-                conn.send("hello world " + count[0]);
+                JSONObject msg = new JSONObject();
+                msg.put("#", dup.track(String.valueOf(count[0])));
+                conn.send(msg.toString());
             }
         }, 0, 1000);
     }
@@ -34,7 +38,10 @@ public class Server extends WebSocketServer {
 
     @Override
     public void onMessage(WebSocket conn, String message) {
-        System.out.println("received: " + message);
+        JSONObject msg = new JSONObject(message);
+        //if(dup.check(msg.getString("#"))) { return; }
+        dup.track(msg.getString("#"));
+        System.out.println("received: " + msg.toString());
     }
 
     @Override
diff --git a/src/main/java/io/github/chronosx88/GunJava/Utils.java b/src/main/java/io/github/chronosx88/GunJava/Utils.java
new file mode 100644
index 0000000..14d87cc
--- /dev/null
+++ b/src/main/java/io/github/chronosx88/GunJava/Utils.java
@@ -0,0 +1,17 @@
+package io.github.chronosx88.GunJava;
+
+public class Utils {
+    public static Thread setTimeout(Runnable runnable, int delay){
+        Thread thread = new Thread(() -> {
+            try {
+                Thread.sleep(delay);
+                runnable.run();
+            }
+            catch (Exception e){
+                e.printStackTrace();
+            }
+        });
+        thread.start();
+        return thread;
+    }
+}