Merge pull request #99 from informatik-ag-ngl/f/message_synchronization

Fully implemented online message synchronization

src/main/java/envoy/client/Config.java

@@ -1,9 +1,7 @@
 package envoy.client;
 
 import java.io.File;
-import java.util.HashMap;
+import java.util.*;
-import java.util.Map;
-import java.util.Properties;
 import java.util.logging.Level;
 
 import envoy.exception.EnvoyException;
@@ -31,6 +29,7 @@ public class Config {
 		items.put("server", new ConfigItem<>("server", "s", (input) -> input, null));
 		items.put("port", new ConfigItem<>("port", "p", (input) -> Integer.parseInt(input), null));
 		items.put("localDB", new ConfigItem<>("localDB", "db", (input) -> new File(input), new File("localDB")));
+		items.put("ignoreLocalDB", new ConfigItem<>("ignoreLocalDB", "nodb", (input) -> Boolean.parseBoolean(input), false));
 		items.put("homeDirectory",
 				new ConfigItem<>("homeDirectory", "h", (input) -> new File(input), new File(System.getProperty("user.home"), ".envoy")));
 		items.put("fileLevelBarrier", new ConfigItem<>("fileLevelBarrier", "fb", (input) -> Level.parse(input), Level.CONFIG));
@@ -99,7 +98,7 @@ public class Config {
 	 * @return {@code true} if server, port and localDB directory are known.
 	 * @since Envoy v0.1-alpha
 	 */
-	public boolean isInitialized() { return items.values().stream().noneMatch(item -> item.get() == null); }
+	public boolean isInitialized() { return items.values().stream().map(ConfigItem::get).noneMatch(Objects::isNull); }
 
 	/**
 	 * @return the host name of the Envoy server
@@ -119,6 +118,12 @@ public class Config {
 	 */
 	public File getLocalDB() { return (File) items.get("localDB").get(); }
 
+	/**
+	 * @return {@code true} if the local database is to be ignored
+	 * @since Envoy v0.3-alpha
+	 */
+	public Boolean isIgnoreLocalDB() { return (Boolean) items.get("ignoreLocalDB").get(); }
+
 	/**
 	 * @return the directory in which all local files are saves
 	 * @since Envoy v0.2-alpha

src/main/java/envoy/client/LocalDB.java

@@ -1,163 +0,0 @@
-package envoy.client;
-
-import java.io.File;
-import java.io.IOException;
-import java.util.*;
-
-import envoy.data.IdGenerator;
-import envoy.data.User;
-import envoy.util.SerializationUtils;
-
-/**
- * Stored information about the current {@link User} and their {@link Chat}s.
- * For message ID generation a {@link IdGenerator} is stored as well.
- * These object are persisted inside a folder of the local file system.<br>
- * <br>
- * Project: <strong>envoy-client</strong><br>
- * File: <strong>LocalDB.java</strong><br>
- * Created: <strong>27.10.2019</strong><br>
- *
- * @author Kai S. K. Engelbart
- * @author Maximilian K&auml;fer
- * @since Envoy v0.1-alpha
- */
-public class LocalDB {
-
-	private File				localDBDir, localDBFile, usersFile, idGeneratorFile;
-	private User				user;
-	private Map<String, User>	users	= new HashMap<>();
-	private List<Chat>			chats	= new ArrayList<>();
-	private IdGenerator			idGenerator;
-
-	/**
-	 * Constructs an empty local database. To serialize any chats to the file
-	 * system, call {@link LocalDB#initializeDBFile()}.
-	 *
-	 * @param localDBDir the directory in which to store users and chats
-	 * @throws IOException if the LocalDB could not be initialized
-	 * @since Envoy v0.1-alpha
-	 */
-	public LocalDB(File localDBDir) throws IOException {
-		this.localDBDir = localDBDir;
-
-		// Initialize local database directory
-		if (localDBDir.exists() && !localDBDir.isDirectory())
-			throw new IOException(String.format("LocalDBDir '%s' is not a directory!", localDBDir.getAbsolutePath()));
-		usersFile		= new File(localDBDir, "users.db");
-		idGeneratorFile	= new File(localDBDir, "id_generator.db");
-	}
-
-	/**
-	 * Creates a database file for a user-specific list of chats.
-	 *
-	 * @throws NullPointerException if the client user is not yet specified
-	 * @since Envoy v0.1-alpha
-	 */
-	public void initializeDBFile() {
-		if (user == null) throw new NullPointerException("Client user is null");
-		localDBFile = new File(localDBDir, user.getId() + ".db");
-	}
-
-	/**
-	 * Stores all users to the local database. If the client user is specified, the
-	 * chats related to this user are stored as well. The message id generator will
-	 * also be saved if present.
-	 *
-	 * @throws IOException if something went wrong during saving
-	 * @since Envoy v0.1-alpha
-	 */
-	public void save() throws IOException {
-		// Save users
-		SerializationUtils.write(usersFile, users);
-
-		// Save chats
-		if (user != null) SerializationUtils.write(localDBFile, chats);
-
-		// Save id generator
-		if (hasIdGenerator()) SerializationUtils.write(idGeneratorFile, idGenerator);
-	}
-
-	/**
-	 * Loads all users that are stored in the local database.
-	 *
-	 * @throws IOException            if the loading process failed
-	 * @throws ClassNotFoundException if the loading process failed
-	 * @since Envoy v0.2-alpha
-	 */
-	public void loadUsers() throws ClassNotFoundException, IOException { users = SerializationUtils.read(usersFile, HashMap.class); }
-
-	/**
-	 * Loads all chats saved by Envoy for the client user.
-	 *
-	 * @throws IOException            if the loading process failed
-	 * @throws ClassNotFoundException if the loading process failed
-	 * @since Envoy v0.1-alpha
-	 */
-	public void loadChats() throws ClassNotFoundException, IOException { chats = SerializationUtils.read(localDBFile, ArrayList.class); }
-
-	/**
-	 * Loads the message ID generator that is stored in the local database. If the
-	 * file is not found, the exception is ignored.
-	 *
-	 * @since Envoy v0.3-alpha
-	 */
-	public void loadIdGenerator() {
-		try {
-			idGenerator = SerializationUtils.read(idGeneratorFile, IdGenerator.class);
-		} catch (ClassNotFoundException | IOException e) {}
-	}
-
-	/**
-	 * @return a {@code Map<String, User>} of all users stored locally with their
-	 *         user names as keys
-	 * @since Envoy v0.2-alpha
-	 */
-	public Map<String, User> getUsers() { return users; }
-
-	/**
-	 * @param users the users to set
-	 */
-	public void setUsers(Map<String, User> users) { this.users = users; }
-
-	/**
-	 * @return all saved {@link Chat} objects that list the client user as the
-	 *         sender
-	 * @since Envoy v0.1-alpha
-	 **/
-	public List<Chat> getChats() { return chats; }
-
-	/**
-	 * @param chats the chats to set
-	 */
-	public void setChats(List<Chat> chats) { this.chats = chats; }
-
-	/**
-	 * @return the {@link User} who initialized the local database
-	 * @since Envoy v0.2-alpha
-	 */
-	public User getUser() { return user; }
-
-	/**
-	 * @param user the user to set
-	 * @since Envoy v0.2-alpha
-	 */
-	public void setUser(User user) { this.user = user; }
-
-	/**
-	 * @return the message ID generator
-	 * @since Envoy v0.3-alpha
-	 */
-	public IdGenerator getIdGenerator() { return idGenerator; }
-
-	/**
-	 * @param idGenerator the message ID generator to set
-	 * @since Envoy v0.3-alpha
-	 */
-	public void setIdGenerator(IdGenerator idGenerator) { this.idGenerator = idGenerator; }
-
-	/**
-	 * @return {@code true} if an {@link IdGenerator} is present
-	 * @since Envoy v0.3-alpha
-	 */
-	public boolean hasIdGenerator() { return idGenerator != null; }
-}

src/main/java/envoy/client/data/Chat.java

@@ -1,11 +1,14 @@
-package envoy.client;
+package envoy.client.data;
 
+import java.io.IOException;
 import java.io.Serializable;
 
+import envoy.client.net.Client;
 import envoy.client.ui.list.ComponentListModel;
 import envoy.data.Message;
 import envoy.data.Message.MessageStatus;
 import envoy.data.User;
+import envoy.event.MessageStatusChangeEvent;
 
 /**
  * Represents a chat between two {@link User}s <br>
@@ -24,8 +27,8 @@ public class Chat implements Serializable {
 
 	private static final long serialVersionUID = -7751248474547242056L;
 
-	private User						recipient;
+	private final User							recipient;
-	private ComponentListModel<Message>	model	= new ComponentListModel<>();
+	private final ComponentListModel<Message>	model	= new ComponentListModel<>();
 
 	/**
 	 * Provides the list of messages that the recipient receives.<br>
@@ -45,16 +48,37 @@ public class Chat implements Serializable {
 	public void appendMessage(Message message) { model.add(message); }
 
 	/**
-	 * Sets the status of all chat messages to {@code READ} starting from the bottom
+	 * Sets the status of all chat messages received from the recipient to
-	 * and stopping once a read message is found.
+	 * {@code READ} starting from the bottom and stopping once a read message is
+	 * found.
 	 *
+	 * @param client the client instance used to notify the server about the message
+	 *               status changes
+	 * @throws IOException if a {@link MessageStatusChangeEvent} could not be
+	 *                     delivered to the server
 	 * @since Envoy v0.3-alpha
 	 */
-	public void read() {
+	public void read(Client client) throws IOException {
-		for (int i = model.size() - 1; i >= 0; --i)
+		for (int i = model.size() - 1; i >= 0; --i) {
-			if (model.get(i).getStatus() == MessageStatus.READ) break;
+			final Message m = model.get(i);
-			else model.get(i).setStatus(MessageStatus.READ);
+			if (m.getSenderId() == recipient.getId()) {
+				if (m.getStatus() == MessageStatus.READ) break;
+				else {
+					m.setStatus(MessageStatus.READ);
+
+					// TODO: Cache events in offline mode
+					client.sendEvent(new MessageStatusChangeEvent(m));
 				}
+			}
+		}
+	}
+
+	/**
+	 * @return {@code true} if the newest message received in the chat doesn't have
+	 *         the status {@code READ}
+	 * @since Envoy v0.3-alpha
+	 */
+	public boolean isUnread() { return !model.isEmpty() && model.get(model.size() - 1).getStatus() != MessageStatus.READ; }
 
 	/**
 	 * @return all messages in the current chat

src/main/java/envoy/client/data/LocalDb.java

@@ -0,0 +1,118 @@
+package envoy.client.data;
+
+import java.util.*;
+
+import envoy.data.IdGenerator;
+import envoy.data.User;
+
+/**
+ * Stores information about the current {@link User} and their {@link Chat}s.
+ * For message ID generation a {@link IdGenerator} is stored as well.<br>
+ * <br>
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>LocalDb.java</strong><br>
+ * Created: <strong>3 Feb 2020</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ * @since Envoy v0.3-alpha
+ */
+public abstract class LocalDb {
+
+	protected User				user;
+	protected Map<String, User>	users	= new HashMap<>();
+	protected List<Chat>		chats	= new ArrayList<>();
+	protected IdGenerator		idGenerator;
+
+	/**
+	 * Initializes a storage space for a user-specific list of chats.
+	 *
+	 * @since Envoy v0.3-alpha
+	 */
+	public void initializeUserStorage() {}
+
+	/**
+	 * Stores all users. If the client user is specified, their chats will be stored
+	 * as well. The message id generator will also be saved if present.
+	 *
+	 * @throws Exception if the saving process failed
+	 * @since Envoy v0.3-alpha
+	 */
+	public void save() throws Exception {}
+
+	/**
+	 * Loads all user data.
+	 *
+	 * @throws Exception if the loading process failed
+	 * @since Envoy v0.3-alpha
+	 */
+	public void loadUsers() throws Exception {}
+
+	/**
+	 * Loads all chat data of the client user.
+	 *
+	 * @throws Exception if the loading process failed
+	 * @since Envoy v0.3-alpha
+	 */
+	public void loadChats() throws Exception {}
+
+	/**
+	 * Loads the ID generator. Any exception thrown during this process is ignored.
+	 *
+	 * @since Envoy v0.3-alpha
+	 */
+	public void loadIdGenerator() {}
+
+	/**
+	 * @return a {@code Map<String, User>} of all users stored locally with their
+	 *         user names as keys
+	 * @since Envoy v0.2-alpha
+	 */
+	public Map<String, User> getUsers() { return users; }
+
+	/**
+	 * @param users the users to set
+	 */
+	public void setUsers(Map<String, User> users) { this.users = users; }
+
+	/**
+	 * @return all saved {@link Chat} objects that list the client user as the
+	 *         sender
+	 * @since Envoy v0.1-alpha
+	 **/
+	public List<Chat> getChats() { return chats; }
+
+	/**
+	 * @param chats the chats to set
+	 */
+	public void setChats(List<Chat> chats) { this.chats = chats; }
+
+	/**
+	 * @return the {@link User} who initialized the local database
+	 * @since Envoy v0.2-alpha
+	 */
+	public User getUser() { return user; }
+
+	/**
+	 * @param user the user to set
+	 * @since Envoy v0.2-alpha
+	 */
+	public void setUser(User user) { this.user = user; }
+
+	/**
+	 * @return the message ID generator
+	 * @since Envoy v0.3-alpha
+	 */
+	public IdGenerator getIdGenerator() { return idGenerator; }
+
+	/**
+	 * @param idGenerator the message ID generator to set
+	 * @since Envoy v0.3-alpha
+	 */
+	public void setIdGenerator(IdGenerator idGenerator) { this.idGenerator = idGenerator; }
+
+	/**
+	 * @return {@code true} if an {@link IdGenerator} is present
+	 * @since Envoy v0.3-alpha
+	 */
+	public boolean hasIdGenerator() { return idGenerator != null; }
+}

src/main/java/envoy/client/data/PersistentLocalDb.java

@@ -0,0 +1,93 @@
+package envoy.client.data;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.HashMap;
+
+import envoy.client.ConfigItem;
+import envoy.data.IdGenerator;
+import envoy.util.SerializationUtils;
+
+/**
+ * Implements a {@link LocalDb} in a way that stores all information inside a
+ * folder on the local file system.<br>
+ * <br>
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>PersistentLocalDb.java</strong><br>
+ * Created: <strong>27.10.2019</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ * @author Maximilian K&auml;fer
+ * @since Envoy v0.1-alpha
+ */
+public class PersistentLocalDb extends LocalDb {
+
+	private File localDBDir, localDBFile, usersFile, idGeneratorFile;
+
+	/**
+	 * Initializes an empty local database without a directory. All changes made to
+	 * this instance cannot be saved to the file system.<br>
+	 * <br>
+	 * This constructor shall be used in conjunction with the {@code ignoreLocalDB}
+	 * {@link ConfigItem}.
+	 *
+	 * @since Envoy v0.3-alpha
+	 */
+	public PersistentLocalDb() {}
+
+	/**
+	 * Constructs an empty local database. To serialize any chats to the file
+	 * system, call {@link PersistentLocalDb#initializeUserStorage()}.
+	 *
+	 * @param localDBDir the directory in which to store users and chats
+	 * @throws IOException if the PersistentLocalDb could not be initialized
+	 * @since Envoy v0.1-alpha
+	 */
+	public PersistentLocalDb(File localDBDir) throws IOException {
+		this.localDBDir = localDBDir;
+
+		// Initialize local database directory
+		if (localDBDir.exists() && !localDBDir.isDirectory())
+			throw new IOException(String.format("LocalDBDir '%s' is not a directory!", localDBDir.getAbsolutePath()));
+		usersFile		= new File(localDBDir, "users.db");
+		idGeneratorFile	= new File(localDBDir, "id_generator.db");
+	}
+
+	/**
+	 * Creates a database file for a user-specific list of chats.
+	 *
+	 * @throws NullPointerException if the client user is not yet specified
+	 * @since Envoy v0.1-alpha
+	 */
+	@Override
+	public void initializeUserStorage() {
+		if (user == null) throw new NullPointerException("Client user is null");
+		localDBFile = new File(localDBDir, user.getId() + ".db");
+	}
+
+	@Override
+	public void save() throws IOException {
+		// Save users
+		SerializationUtils.write(usersFile, users);
+
+		// Save chats
+		if (user != null) SerializationUtils.write(localDBFile, chats);
+
+		// Save id generator
+		if (hasIdGenerator()) SerializationUtils.write(idGeneratorFile, idGenerator);
+	}
+
+	@Override
+	public void loadUsers() throws ClassNotFoundException, IOException { users = SerializationUtils.read(usersFile, HashMap.class); }
+
+	@Override
+	public void loadChats() throws ClassNotFoundException, IOException { chats = SerializationUtils.read(localDBFile, ArrayList.class); }
+
+	@Override
+	public void loadIdGenerator() {
+		try {
+			idGenerator = SerializationUtils.read(idGeneratorFile, IdGenerator.class);
+		} catch (ClassNotFoundException | IOException e) {}
+	}
+}

src/main/java/envoy/client/data/TransientLocalDb.java

@@ -0,0 +1,15 @@
+package envoy.client.data;
+
+/**
+ * Implements a {@link LocalDb} in a way that does not persist any information
+ * after application shutdown.<br>
+ * <br>
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>TransientLocalDb.java</strong><br>
+ * Created: <strong>3 Feb 2020</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ * @since Envoy v0.3-alpha
+ */
+public class TransientLocalDb extends LocalDb {
+}

src/main/java/envoy/client/event/MessageCreationEvent.java

@@ -8,9 +8,12 @@ import envoy.data.Message;
  * Created: <strong>4 Dec 2019</strong><br>
  *
  * @author Kai S. K. Engelbart
+ * @since Envoy v0.2-alpha
  */
 public class MessageCreationEvent extends MessageEvent {
 
+	private static final long serialVersionUID = -6451021678064566774L;
+
 	/**
 	 * @param message the {@link Message} that has been created
 	 */

src/main/java/envoy/client/event/MessageEvent.java

@@ -9,9 +9,12 @@ import envoy.event.Event;
  * Created: <strong>4 Dec 2019</strong><br>
  *
  * @author Kai S. K. Engelbart
+ * @since Envoy v0.2-alpha
  */
 public class MessageEvent implements Event<Message> {
 
+	private static final long serialVersionUID = 7658989461923112804L;
+
 	/**
 	 * the {@link Message} attached to this {@link MessageEvent}.
 	 */

src/main/java/envoy/client/event/MessageModificationEvent.java

@@ -8,9 +8,12 @@ import envoy.data.Message;
  * Created: <strong>4 Dec 2019</strong><br>
  *
  * @author Kai S. K. Engelbart
+ * @since Envoy v0.2-alpha
  */
 public class MessageModificationEvent extends MessageEvent {
 
+	private static final long serialVersionUID = 4650039506439563116L;
+
 	/**
 	 * @param message the {@link Message} that has been modified
 	 */

src/main/java/envoy/client/event/ThemeChangeEvent.java

@@ -13,6 +13,7 @@ import envoy.event.Event;
  */
 public class ThemeChangeEvent implements Event<Theme> {
 
+	private static final long	serialVersionUID	= 6756772448803774547L;
 	private final Theme			theme;
 
 	/**

src/main/java/envoy/client/net/Client.java

@@ -1,4 +1,4 @@
-package envoy.client;
+package envoy.client.net;
 
 import java.io.Closeable;
 import java.io.IOException;
@@ -9,12 +9,19 @@ import java.util.logging.Logger;
 
 import javax.naming.TimeLimitExceededException;
 
+import envoy.client.Config;
+import envoy.client.data.LocalDb;
 import envoy.client.util.EnvoyLog;
 import envoy.data.*;
+import envoy.event.Event;
 import envoy.event.IdGeneratorRequest;
+import envoy.event.MessageStatusChangeEvent;
 import envoy.util.SerializationUtils;
 
 /**
+ * Establishes a connection to the server, performs a handshake and delivers
+ * certain objects to the server.<br>
+ * <br>
  * Project: <strong>envoy-client</strong><br>
  * File: <strong>Client.java</strong><br>
  * Created: <strong>28 Sep 2019</strong><br>
@@ -26,17 +33,17 @@ import envoy.util.SerializationUtils;
  */
 public class Client implements Closeable {
 
+	// Connection handling
 	private Socket		socket;
 	private Receiver	receiver;
 	private boolean		online;
 
+	// Asynchronously initialized during handshake
 	private volatile User		sender;
-	private User			recipient;
-
 	private volatile Contacts	contacts;
 
-	private Config config = Config.getInstance();
+	// Configuration and logging
-
+	private static final Config	config	= Config.getInstance();
 	private static final Logger	logger	= EnvoyLog.getLogger(Client.class.getSimpleName());
 
 	/**
@@ -46,13 +53,15 @@ public class Client implements Closeable {
 	 * an exception is thrown.
 	 *
 	 * @param credentials the login credentials of the user
-	 * @param localDB     the local database used to persist the current
+	 * @param localDb     the local database used to persist the current
 	 *                    {@link IdGenerator}
+	 * @return a message cache containing all unread messages from the server that
+	 *         can be relayed after initialization
 	 * @throws Exception if the online mode could not be entered or the request
 	 *                   failed for some other reason
 	 * @since Envoy v0.2-alpha
 	 */
-	public void onlineInit(LoginCredentials credentials, LocalDB localDB) throws Exception {
+	public MessageCache onlineInit(LoginCredentials credentials, LocalDb localDb) throws Exception {
 		// Establish TCP connection
 		logger.info(String.format("Attempting connection to server %s:%d...", config.getServer(), config.getPort()));
 		socket = new Socket(config.getServer(), config.getPort());
@@ -61,9 +70,13 @@ public class Client implements Closeable {
 		// Create message receiver
 		receiver = new Receiver(socket.getInputStream());
 
-		// Register user creation processor
+		// Create cache for unread messages
+		final MessageCache cache = new MessageCache();
+
+		// Register user creation processor, contact list processor and message cache
 		receiver.registerProcessor(User.class, sender -> { logger.info("Acquired user object " + sender); this.sender = sender; });
 		receiver.registerProcessor(Contacts.class, contacts -> { logger.info("Acquired contacts object " + contacts); this.contacts = contacts; });
+		receiver.registerProcessor(Message.class, cache);
 
 		// Start receiver
 		new Thread(receiver).start();
@@ -86,18 +99,27 @@ public class Client implements Closeable {
 		receiver.removeAllProcessors();
 
 		// Register processors for message and status handling
-		receiver.registerProcessor(Message.class, new ReceivedMessageProcessor());
+		final ReceivedMessageProcessor receivedMessageProcessor = new ReceivedMessageProcessor();
-		// TODO: Status handling
+		receiver.registerProcessor(Message.class, receivedMessageProcessor);
+
+		// Relay cached unread messages
+		cache.setProcessor(receivedMessageProcessor);
+
+		// Process message status changes
+		receiver.registerProcessor(MessageStatusChangeEvent.class, new MessageStatusChangeEventProcessor());
 
 		// Process message ID generation
-		receiver.registerProcessor(IdGenerator.class, localDB::setIdGenerator);
+		receiver.registerProcessor(IdGenerator.class, localDb::setIdGenerator);
 
-		// Request a generator if none is present
+		// Request a generator if none is present or the existing one is consumed
-		if (!localDB.hasIdGenerator() || !localDB.getIdGenerator().hasNext()) requestIdGenerator();
+		if (!localDb.hasIdGenerator() || !localDb.getIdGenerator().hasNext()) requestIdGenerator();
+
+		return cache;
 	}
 
 	/**
-	 * Sends a message to the server.
+	 * Sends a message to the server. The message's status will be incremented once
+	 * it was delivered successfully.
 	 *
 	 * @param message the message to send
 	 * @throws IOException if the message does not reach the server
@@ -108,6 +130,14 @@ public class Client implements Closeable {
 		message.nextStatus();
 	}
 
+	/**
+	 * Sends an event to the server.
+	 *
+	 * @param evt the event to send
+	 * @throws IOException if the event did not reach the server
+	 */
+	public void sendEvent(Event<?> evt) throws IOException { writeObject(evt); }
+
 	/**
 	 * Requests a new {@link IdGenerator} from the server.
 	 *
@@ -155,26 +185,6 @@ public class Client implements Closeable {
 	 */
 	public void setSender(User sender) { this.sender = sender; }
 
-	/**
-	 * @return the current recipient of the current chat.
-	 * @since Envoy v0.1-alpha
-	 */
-	public User getRecipient() { return recipient; }
-
-	/**
-	 * Sets the recipient.
-	 *
-	 * @param recipient the recipient to set
-	 * @since Envoy v0.1-alpha
-	 */
-	public void setRecipient(User recipient) { this.recipient = recipient; }
-
-	/**
-	 * @return true, if a recipient is selected
-	 * @since Envoy v0.1-alpha
-	 */
-	public boolean hasRecipient() { return recipient != null; }
-
 	/**
 	 * @return the {@link Receiver} used by this {@link Client}
 	 */

src/main/java/envoy/client/net/MessageCache.java

@@ -0,0 +1,54 @@
+package envoy.client.net;
+
+import java.util.LinkedList;
+import java.util.Queue;
+import java.util.function.Consumer;
+import java.util.logging.Logger;
+
+import envoy.client.util.EnvoyLog;
+import envoy.data.Message;
+
+/**
+ * Stores messages in a queue until the application initialization is complete.
+ * The messages can then be relayed to a processor.<br>
+ * <br>
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>MessageCache.java</strong><br>
+ * Created: <strong>4 Feb 2020</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ * @since Envoy v0.3-alpha
+ */
+public class MessageCache implements Consumer<Message> {
+
+	private final Queue<Message>	messages	= new LinkedList<>();
+	private Consumer<Message>		processor;
+
+	private static final Logger logger = EnvoyLog.getLogger(MessageCache.class.getSimpleName());
+
+	/**
+	 * Adds a message to the cache.
+	 *
+	 * @since Envoy v0.3-alpha
+	 */
+	@Override
+	public void accept(Message message) {
+		logger.info(String.format("Adding message %s to cache", message));
+		messages.add(message);
+	}
+
+	/**
+	 * Sets the processor to which messages are relayed.
+	 *
+	 * @param processor the processor to set
+	 * @since Envoy v0.3-alpha
+	 */
+	public void setProcessor(Consumer<Message> processor) { this.processor = processor; }
+
+	/**
+	 * Relays all cached messages to the processor.
+	 *
+	 * @since Envoy v0.3-alpha
+	 */
+	public void relayMessages() { messages.forEach(processor::accept); }
+}

src/main/java/envoy/client/net/MessageStatusChangeEventProcessor.java

@@ -0,0 +1,38 @@
+package envoy.client.net;
+
+import java.util.function.Consumer;
+import java.util.logging.Logger;
+
+import envoy.client.util.EnvoyLog;
+import envoy.data.Message.MessageStatus;
+import envoy.event.EventBus;
+import envoy.event.MessageStatusChangeEvent;
+
+/**
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>MessageStatusChangeEventProcessor.java</strong><br>
+ * Created: <strong>4 Feb 2020</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ * @since Envoy v0.3-alpha
+ */
+public class MessageStatusChangeEventProcessor implements Consumer<MessageStatusChangeEvent> {
+
+	private static final Logger logger = EnvoyLog.getLogger(MessageStatusChangeEventProcessor.class.getSimpleName());
+
+	/**
+	 * Dispatches a {@link MessageStatusChangeEvent} if the status is
+	 * {@code RECEIVED} or {@code READ}.
+	 *
+	 * @param evt the status change event
+	 * @since Envoy v0.3-alpha
+	 */
+	@Override
+	public void accept(MessageStatusChangeEvent evt) {
+		if (evt.get().ordinal() < MessageStatus.RECEIVED.ordinal()) logger.info("Received invalid message status change " + evt);
+		else {
+			logger.info("Received " + evt.toString());
+			EventBus.getInstance().dispatch(evt);
+		}
+	}
+}

src/main/java/envoy/client/net/ReceivedMessageProcessor.java

@@ -1,4 +1,4 @@
-package envoy.client;
+package envoy.client.net;
 
 import java.util.function.Consumer;
 import java.util.logging.Logger;
@@ -25,8 +25,12 @@ public class ReceivedMessageProcessor implements Consumer<Message> {
 	public void accept(Message message) {
 		logger.info("Received message object " + message);
 		if (message.getStatus() != MessageStatus.SENT) logger.warning("The message has the unexpected status " + message.getStatus());
-		else
+		else {
+			// Update status to RECEIVED
+			message.nextStatus();
+
 			// Dispatch event
 			EventBus.getInstance().dispatch(new MessageCreationEvent(message));
 		}
+	}
 }

src/main/java/envoy/client/net/Receiver.java

@@ -1,4 +1,4 @@
-package envoy.client;
+package envoy.client.net;
 
 import java.io.ByteArrayInputStream;
 import java.io.InputStream;

src/main/java/envoy/client/ui/ChatWindow.java

@@ -3,22 +3,28 @@ package envoy.client.ui;
 import java.awt.*;
 import java.awt.event.KeyAdapter;
 import java.awt.event.KeyEvent;
+import java.io.IOException;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 
 import javax.swing.*;
 import javax.swing.border.EmptyBorder;
 
-import envoy.client.*;
+import envoy.client.Settings;
+import envoy.client.data.Chat;
+import envoy.client.data.LocalDb;
 import envoy.client.event.MessageCreationEvent;
 import envoy.client.event.ThemeChangeEvent;
+import envoy.client.net.Client;
 import envoy.client.ui.list.ComponentList;
 import envoy.client.ui.settings.SettingsScreen;
 import envoy.client.util.EnvoyLog;
 import envoy.data.Message;
+import envoy.data.Message.MessageStatus;
 import envoy.data.MessageBuilder;
 import envoy.data.User;
 import envoy.event.EventBus;
+import envoy.event.MessageStatusChangeEvent;
 
 /**
  * Project: <strong>envoy-client</strong><br>
@@ -34,7 +40,7 @@ public class ChatWindow extends JFrame {
 
 	// User specific objects
 	private Client	client;
-	private LocalDB	localDB;
+	private LocalDb	localDb;
 
 	// GUI components
 	private JPanel					contentPane				= new JPanel();
@@ -161,25 +167,25 @@ public class ChatWindow extends JFrame {
 		userList.setCellRenderer(new UserListRenderer());
 		userList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
 		userList.addListSelectionListener((listSelectionEvent) -> {
-			if (client != null && localDB != null && !listSelectionEvent.getValueIsAdjusting()) {
+			if (client != null && localDb != null && !listSelectionEvent.getValueIsAdjusting()) {
 				@SuppressWarnings("unchecked")
 				final JList<User>	selectedUserList	= (JList<User>) listSelectionEvent.getSource();
 				final User			user				= selectedUserList.getSelectedValue();
 
 				// Select current chat
-				currentChat = localDB.getChats().stream().filter(chat -> chat.getRecipient().getId() == user.getId()).findFirst().get();
+				currentChat = localDb.getChats().stream().filter(chat -> chat.getRecipient().getId() == user.getId()).findFirst().get();
 
-				// Read current Chat
+				// Read current chat
-				currentChat.read();
+				readCurrentChat();
 
-				// Set recipient in client and chat title
+				// Set chat title
-				client.setRecipient(user);
 				textPane.setText(currentChat.getRecipient().getName());
 
 				// Update model and scroll down
 				messageList.setModel(currentChat.getModel());
 				scrollPane.setChatOpened(true);
 
+				messageList.synchronizeModel();
 				revalidate();
 				repaint();
 			}
@@ -206,7 +212,35 @@ public class ChatWindow extends JFrame {
 		// Listen to received messages
 		EventBus.getInstance().register(MessageCreationEvent.class, (evt) -> {
 			Message message = ((MessageCreationEvent) evt).get();
-			localDB.getChats().stream().filter(c -> c.getRecipient().getId() == message.getSenderId()).findFirst().get().appendMessage(message);
+			Chat	chat	= localDb.getChats().stream().filter(c -> c.getRecipient().getId() == message.getSenderId()).findFirst().get();
+			chat.appendMessage(message);
+
+			// Read message and update UI if in current chat
+			if (chat == currentChat) readCurrentChat();
+
+			revalidate();
+			repaint();
+		});
+
+		// Listen to message status changes
+		EventBus.getInstance().register(MessageStatusChangeEvent.class, (evt) -> {
+			final long			id		= ((MessageStatusChangeEvent) evt).getId();
+			final MessageStatus	status	= (MessageStatus) evt.get();
+
+			for (Chat c : localDb.getChats())
+				for (Message m : c.getModel())
+					if (m.getId() == id) {
+
+						// Update message status
+						m.setStatus(status);
+
+						// Update model and scroll down if current chat
+						if (c == currentChat) {
+							messageList.setModel(currentChat.getModel());
+							scrollPane.setChatOpened(true);
+						} else messageList.synchronizeModel();
+					}
+
 			revalidate();
 			repaint();
 		});
@@ -254,7 +288,7 @@ public class ChatWindow extends JFrame {
 	}
 
 	private void postMessage() {
-		if (!client.hasRecipient()) {
+		if (userList.isSelectionEmpty()) {
 			JOptionPane.showMessageDialog(this, "Please select a recipient!", "Cannot send message", JOptionPane.INFORMATION_MESSAGE);
 			return;
 		}
@@ -262,7 +296,7 @@ public class ChatWindow extends JFrame {
 		if (!messageEnterTextArea.getText().isEmpty()) try {
 
 			// Create message
-			final Message message = new MessageBuilder(localDB.getUser().getId(), currentChat.getRecipient().getId(), localDB.getIdGenerator())
+			final Message message = new MessageBuilder(localDb.getUser().getId(), currentChat.getRecipient().getId(), localDb.getIdGenerator())
 				.setText(messageEnterTextArea.getText())
 				.build();
 
@@ -270,9 +304,8 @@ public class ChatWindow extends JFrame {
 			// TODO: Store offline messages
 			client.sendMessage(message);
 
-			// Add message to LocalDB and update UI
+			// Add message to PersistentLocalDb and update UI
 			currentChat.appendMessage(message);
-			// messageList.setModel(currentChat.getModel());
 
 			// Clear text field
 			messageEnterTextArea.setText("");
@@ -281,14 +314,11 @@ public class ChatWindow extends JFrame {
 			revalidate();
 			repaint();
 
-			// Request a new id generator if all ids were used
+			// Request a new id generator if all IDs were used
-			if (!localDB.getIdGenerator().hasNext()) client.requestIdGenerator();
+			if (!localDb.getIdGenerator().hasNext()) client.requestIdGenerator();
 
 		} catch (Exception e) {
-			JOptionPane.showMessageDialog(this,
+			JOptionPane.showMessageDialog(this, "Error sending message:\n" + e.toString(), "Message sending error", JOptionPane.ERROR_MESSAGE);
-					"Error sending message:\n" + e.toString(),
-					"Message sending error",
-					JOptionPane.ERROR_MESSAGE);
 			e.printStackTrace();
 		}
 	}
@@ -302,36 +332,46 @@ public class ChatWindow extends JFrame {
 	private void loadUsersAndChats() {
 		new Thread(() -> {
 			DefaultListModel<User> userListModel = new DefaultListModel<>();
-			localDB.getUsers().values().forEach(user -> {
+			localDb.getUsers().values().forEach(user -> {
 				userListModel.addElement(user);
 
 				// Check if user exists in local DB
-				if (localDB.getChats().stream().filter(c -> c.getRecipient().getId() == user.getId()).count() == 0)
+				if (localDb.getChats().stream().filter(c -> c.getRecipient().getId() == user.getId()).count() == 0)
-					localDB.getChats().add(new Chat(user));
+					localDb.getChats().add(new Chat(user));
 			});
 			SwingUtilities.invokeLater(() -> userList.setModel(userListModel));
 		}).start();
 	}
 
+	private void readCurrentChat() {
+		try {
+			currentChat.read(client);
+			messageList.synchronizeModel();
+		} catch (IOException e) {
+			e.printStackTrace();
+			logger.log(Level.WARNING, "Couldn't notify server about message status change", e);
+		}
+	}
+
 	/**
 	 * Sets the {@link Client} used by this {@link ChatWindow}.
 	 *
 	 * @param client the {@link Client} used to send and receive messages
 	 * @since Envoy v0.2-alpha
 	 */
-	public void setClient(Client client) {
+	public void setClient(Client client) { this.client = client; }
-		this.client = client;
-	}
 
 	/**
-	 * Sets the {@link LocalDB} used by this {@link ChatWindow}. After invoking this
+	 * Sets the {@link LocalDb} used by this {@link ChatWindow}. After
+	 * invoking this
 	 * method, users and chats will be loaded from the database into the GUI.
 	 *
-	 * @param localDB the {@link LocalDB} used to manage stored messages and users
+	 * @param localDb the {@link LocalDb} used to manage stored messages
+	 *                and users
 	 * @since Envoy v0.2-alpha
 	 */
-	public void setLocalDB(LocalDB localDB) {
+	public void setLocalDB(LocalDb localDb) {
-		this.localDB = localDB;
+		this.localDb = localDb;
 		loadUsersAndChats();
 	}
 }

src/main/java/envoy/client/ui/Startup.java

@@ -11,7 +11,13 @@ import javax.swing.JFrame;
 import javax.swing.JOptionPane;
 import javax.swing.SwingUtilities;
 
-import envoy.client.*;
+import envoy.client.Config;
+import envoy.client.Settings;
+import envoy.client.data.LocalDb;
+import envoy.client.data.PersistentLocalDb;
+import envoy.client.data.TransientLocalDb;
+import envoy.client.net.Client;
+import envoy.client.net.MessageCache;
 import envoy.client.util.EnvoyLog;
 import envoy.data.LoginCredentials;
 import envoy.data.User;
@@ -63,8 +69,8 @@ public class Startup {
 		} catch (Exception e) {
 			JOptionPane
 				.showMessageDialog(null, "Error loading configuration values:\n" + e.toString(), "Configuration error", JOptionPane.ERROR_MESSAGE);
-			System.exit(1);
 			e.printStackTrace();
+			System.exit(1);
 		}
 
 		// Set new logger levels loaded from config
@@ -80,12 +86,19 @@ public class Startup {
 		}
 
 		// Initialize the local database
-		LocalDB localDB;
+		LocalDb localDb;
-		try {
+		if (config.isIgnoreLocalDB()) {
-			localDB = new LocalDB(new File(config.getHomeDirectory(), config.getLocalDB().getPath()));
+			localDb = new TransientLocalDb();
+			JOptionPane.showMessageDialog(null,
+					"Ignoring local database.\nMessages will not be saved!",
+					"Local database warning",
+					JOptionPane.WARNING_MESSAGE);
+		} else try {
+			localDb = new PersistentLocalDb(new File(config.getHomeDirectory(), config.getLocalDB().getPath()));
 		} catch (IOException e3) {
 			logger.log(Level.SEVERE, "Could not initialize local database", e3);
-			JOptionPane.showMessageDialog(null, "Could not initialize local database!\n" + e3.toString());
+			JOptionPane
+				.showMessageDialog(null, "Could not initialize local database!\n" + e3.toString(), "Local database error", JOptionPane.ERROR_MESSAGE);
 			System.exit(1);
 			return;
 		}
@@ -95,17 +108,18 @@ public class Startup {
 		// Acquire the client user (with ID) either from the server or from the local
 		// database, which triggers offline mode
 		Client			client	= new Client();
+		MessageCache	cache	= null;
 		try {
 			// Try entering online mode first
-			localDB.loadIdGenerator();
+			localDb.loadIdGenerator();
-			client.onlineInit(credentials, localDB);
+			cache = client.onlineInit(credentials, localDb);
 		} catch (Exception e1) {
 			logger.warning("Could not connect to server. Trying offline mode...");
 			e1.printStackTrace();
 			try {
 				// Try entering offline mode
-				localDB.loadUsers();
+				localDb.loadUsers();
-				User clientUser = localDB.getUsers().get(credentials.getName());
+				User clientUser = localDb.getUsers().get(credentials.getName());
 				if (clientUser == null) throw new EnvoyException("Could not enter offline mode: user name unknown");
 				client.setSender(clientUser);
 				JOptionPane.showMessageDialog(null,
@@ -120,12 +134,12 @@ public class Startup {
 		}
 
 		// Set client user in local database
-		localDB.setUser(client.getSender());
+		localDb.setUser(client.getSender());
 
 		// Initialize chats in local database
 		try {
-			localDB.initializeDBFile();
+			localDb.initializeUserStorage();
-			localDB.loadChats();
+			localDb.loadChats();
 		} catch (FileNotFoundException e) {
 			// The local database file has not yet been created, probably first login
 		} catch (Exception e) {
@@ -137,12 +151,13 @@ public class Startup {
 		}
 
 		// Save all users to the local database
-		if (client.isOnline()) localDB.setUsers(client.getUsers());
+		if (client.isOnline()) localDb.setUsers(client.getUsers());
 
+		// Display ChatWindow and StatusTrayIcon
 		EventQueue.invokeLater(() -> {
 			try {
 				chatWindow.setClient(client);
-				chatWindow.setLocalDB(localDB);
+				chatWindow.setLocalDB(localDb);
 
 				try {
 					new StatusTrayIcon(chatWindow).show();
@@ -162,16 +177,19 @@ public class Startup {
 			}
 		});
 
-		// Save Settings and LocalDB on shutdown
+		// Relay unread messages from cache
+		if (cache != null) cache.relayMessages();
+
+		// Save Settings and PersistentLocalDb on shutdown
 		Runtime.getRuntime().addShutdownHook(new Thread(() -> {
 			try {
 				logger.info("Closing connection...");
 				client.close();
 
 				logger.info("Saving local database and settings...");
-				localDB.save();
+				localDb.save();
 				Settings.getInstance().save();
-			} catch (IOException e) {
+			} catch (Exception e) {
 				logger.log(Level.SEVERE, "Unable to save local files", e);
 			}
 		}));

src/main/java/envoy/client/ui/list/ComponentList.java

@@ -66,6 +66,18 @@ public class ComponentList<E> extends JPanel {
 		synchronizeModel();
 	}
 
+	/**
+	 * Removes all child components and then adds all components representing the
+	 * elements of the {@link ComponentListModel}.
+	 *
+	 * @since Envoy v0.3-alpha
+	 */
+	public void synchronizeModel() {
+		removeAll();
+		if (model != null) for (E elem : model)
+			add(elem);
+	}
+
 	/**
 	 * Adds an object to the list by rendering it with the current
 	 * {@link ComponentListCellRenderer}.
@@ -76,16 +88,4 @@ public class ComponentList<E> extends JPanel {
 	void add(E elem) {
 		add(renderer.getListCellComponent(this, elem, false));
 	}
-
-	/**
-	 * Removes all child components and then adds all components representing the
-	 * elements of the {@link ComponentListModel}.
-	 *
-	 * @since Envoy v0.3-alpha
-	 */
-	void synchronizeModel() {
-		removeAll();
-		if (model != null) for (E elem : model)
-			add(elem);
-	}
 }

src/main/java/envoy/client/ui/list/ComponentListModel.java

@@ -78,6 +78,12 @@ public final class ComponentListModel<E> implements Iterable<E>, Serializable {
 	 */
 	public int size() { return elements.size(); }
 
+	/**
+	 * @return {@code true} if this model contains no elements
+	 * @see java.util.List#isEmpty()
+	 */
+	public boolean isEmpty() { return elements.isEmpty(); }
+
 	/**
 	 * @return an iterator over the elements of this list model
 	 * @see java.util.List#iterator()