New message servlet

src/main/java/shef/data/MessagePromise.java

@@ -32,7 +32,6 @@ public MessagePromise(MessageUpdate messageUpdate) {
     this.message = null;
     this.updated = false;
     this.messageUpdate = messageUpdate;
-    this.messageUpdate.addObserver(this);
   }
 
   /**
@@ -41,6 +40,8 @@ public MessagePromise(MessageUpdate messageUpdate) {
    * It then unblocks, and returns the message to the servlet.
    */
   public synchronized String getNextMessage() {
+    messageUpdate.addObserver(this);
+
     // Ensure that the thread waits until an update is detected.
     while (!updated) {
       try {
@@ -51,6 +52,7 @@ public synchronized String getNextMessage() {
     }
 
     messageUpdate.deleteObserver(this);
+    this.updated = false;
     return message;
   }
 

src/main/java/shef/data/MessageUpdate.java

@@ -31,14 +31,13 @@ public MessageUpdate() {
   }
 
   /** Sends the message to waiting observers via notifyObservers(). */
-  public synchronized void sendMessage() {
+  public void sendMessage() {
     notifyObservers(message);
   }
 
   /** Set the message and mark the MessageUpdate as changed. */
-  public synchronized void setMessage(String message) {
-    this.message = message;
+  public void setMessage(String message) {
+    this.message = message; 
     setChanged();
   }
-
-}
+}

src/main/java/shef/servlets/GroupchatServlet.java

@@ -27,6 +27,8 @@
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import java.util.ArrayList;
+import shef.data.Groupchat;
+
 
 @WebServlet("/load-groupchat")
 public class GroupchatServlet extends HttpServlet {
@@ -41,19 +43,11 @@ public void init() {
   @Override
   public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
     String keyString = request.getParameter("key");
-    Entity groupchatEntity = null;
-    try {
-      groupchatEntity = datastore.get(KeyFactory.stringToKey(keyString));
-    } catch (EntityNotFoundException e) {
-      e.printStackTrace();
-      return;
-    }
+    Groupchat group = new Groupchat(keyString);
 
-    Object messageObject = groupchatEntity.getProperty("messages");
-    ArrayList<String> messages = messageObject != null ? (ArrayList<String>) messageObject : new ArrayList<>();
     response.setContentType("application/json;");
     Gson gson = new Gson();
-    response.getWriter().println(gson.toJson(messages));
+    response.getWriter().println(gson.toJson(group.getMessages()));
   }
 
   @Override

src/main/java/shef/servlets/NewMessageServlet.java

@@ -12,6 +12,11 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+/*
+ * The following source informed the architecture of this servlet and its functional components:
+ * https://docstore.mik.ua/orelly/java-ent/servlet/ch10_03.htm
+ */
+
 package shef.servlets;
 
 import com.google.appengine.api.datastore.DatastoreService;
@@ -23,7 +28,13 @@
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import shef.data.MessageUpdate;
+import shef.data.MessagePromise;
+import shef.data.Groupchat;
 
+/**
+ * This servlet handles new messages, allowing for clients to see them as they're sent in real time.
+ * A client sends in new messages with doPost(), and doGet() distributes them to all other active clients.
+ */
 @WebServlet("/new-message")
 public class NewMessageServlet extends HttpServlet {
 
@@ -36,14 +47,44 @@ public void init() {
     datastore = DatastoreServiceFactory.getDatastoreService();
   }
 
+  /**
+   * Waits for incoming messages using MessagePromises.
+   * Each GET request instantiates a MessagePromise, which blocks until a new message is received.
+   * The MessagePromise then unblocks and allows the GET request to respond with the new message.
+   */
   @Override
   public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
+    MessagePromise newMessagePromise = new MessagePromise(messageUpdate);
+
+    // Blocks until the next message is received.
+    String newMessage = newMessagePromise.getNextMessage();
 
+    response.setContentType("text/html");
+    response.getWriter().println(newMessage);
   }
 
+  /**
+   * Posts new messages to Datastore and distributes them to active clients using MessageUpdates.
+   * The message is first added to the groupchat in Datastore, and then distributed to the waiting MessagePromises.
+   * Empty messages are ignored.
+   */
   @Override
   public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {
-
-  }
+    String message = request.getParameter("message");
+    if (message.equals("")) {
+      return;
+    }
 
+    // Upload new message to Datastore.
+    String keyString = request.getParameter("groupchat-key");
+    Groupchat group = new Groupchat(keyString);
+    group.addMessage(message);
+    group.update();
+
+    // Send new message to waiting MessagePromises.
+    messageUpdate.setMessage(message);
+    messageUpdate.sendMessage();
+
+    response.setStatus(response.SC_NO_CONTENT);
+  }
 }

src/main/webapp/groupchat.html

@@ -5,10 +5,18 @@
     <meta charset="utf-8">
     <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
     <title>shef</title>
-    <script type="text/javascript" src="script.js"></script>
+    <script type="text/javascript" src="script.js" onload="loadGroupchat()"></script>
   </head>
 
   <body>
     <h1>Groupchat</h1>
+    <div id="messages"></div>
+
+    <form onsubmit="postNextMessage();return false" style="position: absolute; bottom: 10px; width: 100%">
+      <label for="message-input">Type a message:</label></br>
+      <textarea id="message-input" name="message" rows="5" style="width: 99%"></textarea>
+      <input type="hidden" name="groupchat-key" id="groupchat-key"/>
+      <input type="submit"/>
+    </form>
   </body>
 </html>

src/main/webapp/index.html

@@ -0,0 +1,23 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <!-- Required meta tags -->
+    <meta charset="utf-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
+    <title>shef</title>
+    <script type="text/javascript" src="script.js"></script>
+  </head>
+
+  <body>
+    <h1>Groupchat Options</h1>
+    <h3>Create new groupchat</h3>
+    <button onclick="newGroupchat()">New Groupchat</button></br></br>
+
+    <h3>Load groupchat</h3>
+    <label for="groupchat-key">Groupchat Key:</label>
+    <input type="text" id="groupchat-key"></input></br></br>
+    <button onclick="redirectToGroupchat()">Go!</button>
+
+    <div id="messages"></div>
+  </body>
+</html>

src/main/webapp/script.js

@@ -1,6 +1,6 @@
 // Copyright 2019 Google LLC
 //
-// Licensed under the Apache License, Version 2.0 (the "License");
+// Licensed under the Apache License, Version 2.0 (the 'License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
@@ -38,3 +38,77 @@ function createCommentElement(comment) {
 function addParagraph(content) {
   return "<p>" + content + "</p>";
 }
+
+/** Creates a new groupchat and redirects the client to the chatting page. */
+function newGroupchat() {
+  var request = new Request("/load-groupchat", {method: 'POST'});
+  fetch(request).then(response => response.text()).then((key) => {
+    redirectToGroupchat(key);
+  });
+}
+
+/** Loads an existing groupchat. */
+function loadGroupchat() {
+  const urlParams = new URLSearchParams(window.location.search);
+  const key = urlParams.get('key');
+  fetch('/load-groupchat?key=' + key)
+    .then(response => response.json(), error => {
+      alert('Error: Groupchat does not exist ' + error);
+      window.location.href = 'index.html';
+    }).then((messages) => {
+      document.getElementById('messages').innerHTML = '';
+      document.getElementById('groupchat-key').value = key;
+      for (var i = 0; i < messages.length; i++) {
+        addMessage(messages[i]);
+      }
+      getNextMessage();
+  });
+}
+
+/** Posts a message to a groupchat. */
+function postNextMessage() {
+  const message = document.getElementById('message-input').value;
+  const groupKey = document.getElementById('groupchat-key').value;
+  var request = new Request('/new-message?message=' + message + '&groupchat-key=' + groupKey, {method: 'POST'});
+  fetch(request).then(
+    document.getElementById('message-input').value = ''
+  );
+}
+
+/**
+ * Sends a request to the server to get the next message.
+ * This method is recursive (upon success) so that each client is always waiting for the next message.
+ * Requests use asynchronous Promises, so the client can perform other functions while waiting for a message.
+ */
+function getNextMessage() {
+  var request = new Request("/new-message", {method: 'GET'})
+  fetch(request)
+    .then(response => {
+      if (response.ok) {
+        return response.text();
+      } else {
+        throw new Error('Servlet closed');
+      }
+    }).then(message => {
+      addMessage(message);
+      getNextMessage();
+    })
+    .catch(err => {
+      alert(err);
+      window.location.href = 'index.html';
+    });
+}
+
+/** Given a groupchat key, redirects the client to that groupchat. */
+function redirectToGroupchat(keyParameter) {
+  const key = keyParameter ? keyParameter : document.getElementById('groupchat-key').value;
+  window.location.href = "/groupchat.html?key=" + key;
+}
+
+/** Adds a <p> element containing a message to a groupchat. */
+function addMessage(message) {
+  var messagesContainer = document.getElementById('messages');
+  const messageElement = document.createElement('p');
+  messageElement.innerText = message;
+  messagesContainer.appendChild(messageElement);
+}