Add support for configurable initial snapshot.

Author: dario-weswit

README.md

@@ -14,7 +14,8 @@ This project includes the implementation of the [SmartDataProvider](https://ligh
 ### Data Adapter
 The `ChatDataAdapter.java` class contains the source code for the Chat Data Adapter. The Data Adapter accepts message submission for the unique chat room. The sender is identified by an IP address and a nickname.
 
-It's possible to flush chat history based on optional parameters provided in the `adapters.xml` file.
+It's possible to configure a custom initial chat history (i.e. snapshot) based on optional parameters provided in the `adapters.xml` file.
+It's also possible to flush chat history (and restore any configured custom initial history) based on optional parameters provided in the `adapters.xml` file.
 
 ### Metadata Adapter
 The `ChatMetadataAdapter.java` class contains the source code for a Metadata Adapter to be associated with the Chat Demo Data Adapter.
@@ -61,6 +62,13 @@ The `adapters.xml` file for the Basic Chat Demo, should look like:
 
         <adapter_class>com.lightstreamer.examples.chat_demo.adapters.ChatDataAdapter</adapter_class>
 
+        <!-- Optional for ChatDataAdapter.
+             Configuration of a custom initial snapshot at subscription time.
+             Use progressive numbers after "custom_snapshot_", starting from 1.
+             Default: empty snapshot. -->
+        <param name="custom_snapshot_1">Hello</param>
+        <param name="custom_snapshot_2">How're you doing?</param>
+
         <!-- Optional for ChatDataAdapter.
              Configuration flag for periodic flush of the snapshot.
              Default: false. -->

pom.xml

@@ -4,7 +4,7 @@
 
   <groupId>com.lightstreamer.examples</groupId>
   <artifactId>chat-adapter-java</artifactId>
-  <version>1.1.0</version>
+  <version>1.1.1</version>
   <packaging>jar</packaging>
 
   <name>Lightstreamer Chat Demo Java Adapter</name>

src/main/java/com/lightstreamer/examples/chat_demo/adapters/ChatDataAdapter.java

@@ -20,6 +20,7 @@
 import java.text.SimpleDateFormat;
 import java.util.Date;
 import java.util.HashMap;
+import java.util.LinkedList;
 import java.util.Map;
 import java.util.Timer;
 import java.util.TimerTask;
@@ -74,6 +75,11 @@ public class ChatDataAdapter implements SmartDataProvider {
      */
     private volatile Object subscribed;
 
+    /**
+     * A configurable list of messages for a custom initial snapshot.
+     */
+    private final LinkedList<String> customSnapshot = new LinkedList<>();
+
     /**
      * Boolean flag for periodic flush of snapshot (call clearSnaphot).
      */
@@ -115,6 +121,15 @@ public void init(Map params, File configDir) throws DataProviderException {
         // Read the Adapter Set name, which is supplied by the Server as a parameter
         String adapterSetId = (String) params.get("adapters_conf.id");
 
+        boolean stop = false;
+        for (int i = 1; ! stop; i++) {
+            if (params.containsKey("custom_snapshot_" + i)) {
+                String msg = (String) params.get("custom_snapshot_" + i);
+                this.customSnapshot.add(msg);
+            } else {
+                stop = true;
+            }
+        }
 
         if (params.containsKey("flush_snapshot")) {
             String tmp = (String) params.get("flush_snapshot");
@@ -153,6 +168,8 @@ public void subscribe(String item, Object handle, boolean arg2)
 
         subscribed = handle;
 
+        sendCustomSnapshot();
+
         if(this.flushSnapshot) {
         	// Start Thread for periodic flush of the snapshot.
             myTimer = new Timer(true);
@@ -161,6 +178,7 @@ public void subscribe(String item, Object handle, boolean arg2)
                @Override
                 public void run() {
                     clearHistory();
+                    sendCustomSnapshot();
                 }
             }, new Date(System.currentTimeMillis() + this.flushInterval), this.flushInterval);
         } 
@@ -253,6 +271,14 @@ public void run() {
         return true;
     }
 
+    private void sendCustomSnapshot() {
+        int i = 1;
+        for (String snapshotMsg : customSnapshot) {
+            sendMessage("0.0.0.0", "user" + i, snapshotMsg);
+            i++;
+        }
+    }
+
     // used in case of flush_snapshot set to true.
     public void clearHistory() {
         final Object currSubscribed = subscribed;