Merge branch 'develop' into f/themes

.github/ISSUE_TEMPLATE/bug_report.md

@@ -0,0 +1,38 @@
+---
+name: Bug report
+about: Create a report to help us improve
+title: ''
+labels: bug
+assignees: CyB3RC0nN0R, delvh, DieGurke, derharry333
+
+---
+
+**Describe the bug**
+A clear and concise description of what the bug is.
+
+**To Reproduce**
+Steps to reproduce the behavior:
+1. Go to '...'
+2. Click on '....'
+3. Scroll down to '....'
+4. See error
+
+**Expected behavior**
+A clear and concise description of what you expected to happen.
+
+**Screenshots**
+If applicable, add screenshots to help explain your problem.
+
+**Desktop (please complete the following information):**
+ - OS: [e.g. iOS]
+ - Browser [e.g. chrome, safari]
+ - Version [e.g. 22]
+
+**Smartphone (please complete the following information):**
+ - Device: [e.g. iPhone6]
+ - OS: [e.g. iOS8.1]
+ - Browser [e.g. stock browser, safari]
+ - Version [e.g. 22]
+
+**Additional context**
+Add any other context about the problem here.

.github/ISSUE_TEMPLATE/feature_request.md

@@ -0,0 +1,20 @@
+---
+name: Feature request
+about: Suggest an idea for this project
+title: ''
+labels: enhancement
+assignees: CyB3RC0nN0R, delvh, DieGurke
+
+---
+
+**Is your feature request related to a problem? Please describe.**
+A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
+
+**Describe the solution you'd like**
+A clear and concise description of what you want to happen.
+
+**Describe alternatives you've considered**
+A clear and concise description of any alternative solutions or features you've considered.
+
+**Additional context**
+Add any other context or screenshots about the feature request here.

.project

@@ -34,7 +34,5 @@
 	<natures>
 		<nature>org.eclipse.jdt.core.javanature</nature>
 		<nature>org.eclipse.m2e.core.maven2Nature</nature>
-		<nature>org.jboss.tools.jst.web.kb.kbnature</nature>
-		<nature>org.jboss.tools.cdi.core.cdinature</nature>
 	</natures>
 </projectDescription>

.settings/org.eclipse.jdt.core.prefs

@@ -1,8 +1,107 @@
 eclipse.preferences.version=1
+org.eclipse.jdt.core.compiler.annotation.inheritNullAnnotations=disabled
+org.eclipse.jdt.core.compiler.annotation.missingNonNullByDefaultAnnotation=ignore
+org.eclipse.jdt.core.compiler.annotation.nonnull=org.eclipse.jdt.annotation.NonNull
+org.eclipse.jdt.core.compiler.annotation.nonnull.secondary=
+org.eclipse.jdt.core.compiler.annotation.nonnullbydefault=org.eclipse.jdt.annotation.NonNullByDefault
+org.eclipse.jdt.core.compiler.annotation.nonnullbydefault.secondary=
+org.eclipse.jdt.core.compiler.annotation.nullable=org.eclipse.jdt.annotation.Nullable
+org.eclipse.jdt.core.compiler.annotation.nullable.secondary=
+org.eclipse.jdt.core.compiler.annotation.nullanalysis=disabled
 org.eclipse.jdt.core.compiler.codegen.targetPlatform=1.8
 org.eclipse.jdt.core.compiler.compliance=1.8
+org.eclipse.jdt.core.compiler.problem.APILeak=warning
+org.eclipse.jdt.core.compiler.problem.annotationSuperInterface=warning
+org.eclipse.jdt.core.compiler.problem.autoboxing=ignore
+org.eclipse.jdt.core.compiler.problem.comparingIdentical=warning
+org.eclipse.jdt.core.compiler.problem.deadCode=warning
+org.eclipse.jdt.core.compiler.problem.deprecation=warning
+org.eclipse.jdt.core.compiler.problem.deprecationInDeprecatedCode=disabled
+org.eclipse.jdt.core.compiler.problem.deprecationWhenOverridingDeprecatedMethod=disabled
+org.eclipse.jdt.core.compiler.problem.discouragedReference=warning
+org.eclipse.jdt.core.compiler.problem.emptyStatement=ignore
 org.eclipse.jdt.core.compiler.problem.enablePreviewFeatures=disabled
+org.eclipse.jdt.core.compiler.problem.explicitlyClosedAutoCloseable=ignore
+org.eclipse.jdt.core.compiler.problem.fallthroughCase=ignore
+org.eclipse.jdt.core.compiler.problem.fatalOptionalError=disabled
+org.eclipse.jdt.core.compiler.problem.fieldHiding=ignore
+org.eclipse.jdt.core.compiler.problem.finalParameterBound=warning
+org.eclipse.jdt.core.compiler.problem.finallyBlockNotCompletingNormally=warning
 org.eclipse.jdt.core.compiler.problem.forbiddenReference=warning
+org.eclipse.jdt.core.compiler.problem.hiddenCatchBlock=warning
+org.eclipse.jdt.core.compiler.problem.includeNullInfoFromAsserts=disabled
+org.eclipse.jdt.core.compiler.problem.incompatibleNonInheritedInterfaceMethod=warning
+org.eclipse.jdt.core.compiler.problem.incompleteEnumSwitch=ignore
+org.eclipse.jdt.core.compiler.problem.indirectStaticAccess=ignore
+org.eclipse.jdt.core.compiler.problem.localVariableHiding=ignore
+org.eclipse.jdt.core.compiler.problem.methodWithConstructorName=warning
+org.eclipse.jdt.core.compiler.problem.missingDefaultCase=ignore
+org.eclipse.jdt.core.compiler.problem.missingDeprecatedAnnotation=ignore
+org.eclipse.jdt.core.compiler.problem.missingEnumCaseDespiteDefault=disabled
+org.eclipse.jdt.core.compiler.problem.missingHashCodeMethod=ignore
+org.eclipse.jdt.core.compiler.problem.missingOverrideAnnotation=ignore
+org.eclipse.jdt.core.compiler.problem.missingOverrideAnnotationForInterfaceMethodImplementation=enabled
+org.eclipse.jdt.core.compiler.problem.missingSerialVersion=warning
+org.eclipse.jdt.core.compiler.problem.missingSynchronizedOnInheritedMethod=ignore
+org.eclipse.jdt.core.compiler.problem.noEffectAssignment=warning
+org.eclipse.jdt.core.compiler.problem.noImplicitStringConversion=warning
+org.eclipse.jdt.core.compiler.problem.nonExternalizedStringLiteral=ignore
+org.eclipse.jdt.core.compiler.problem.nonnullParameterAnnotationDropped=warning
+org.eclipse.jdt.core.compiler.problem.nonnullTypeVariableFromLegacyInvocation=warning
+org.eclipse.jdt.core.compiler.problem.nullAnnotationInferenceConflict=error
+org.eclipse.jdt.core.compiler.problem.nullReference=warning
+org.eclipse.jdt.core.compiler.problem.nullSpecViolation=error
+org.eclipse.jdt.core.compiler.problem.nullUncheckedConversion=warning
+org.eclipse.jdt.core.compiler.problem.overridingPackageDefaultMethod=warning
+org.eclipse.jdt.core.compiler.problem.parameterAssignment=ignore
+org.eclipse.jdt.core.compiler.problem.pessimisticNullAnalysisForFreeTypeVariables=warning
+org.eclipse.jdt.core.compiler.problem.possibleAccidentalBooleanAssignment=ignore
+org.eclipse.jdt.core.compiler.problem.potentialNullReference=ignore
+org.eclipse.jdt.core.compiler.problem.potentiallyUnclosedCloseable=ignore
+org.eclipse.jdt.core.compiler.problem.rawTypeReference=warning
+org.eclipse.jdt.core.compiler.problem.redundantNullAnnotation=warning
+org.eclipse.jdt.core.compiler.problem.redundantNullCheck=ignore
+org.eclipse.jdt.core.compiler.problem.redundantSpecificationOfTypeArguments=ignore
+org.eclipse.jdt.core.compiler.problem.redundantSuperinterface=ignore
+org.eclipse.jdt.core.compiler.problem.reportMethodCanBePotentiallyStatic=ignore
+org.eclipse.jdt.core.compiler.problem.reportMethodCanBeStatic=ignore
 org.eclipse.jdt.core.compiler.problem.reportPreviewFeatures=ignore
+org.eclipse.jdt.core.compiler.problem.specialParameterHidingField=disabled
+org.eclipse.jdt.core.compiler.problem.staticAccessReceiver=warning
+org.eclipse.jdt.core.compiler.problem.suppressOptionalErrors=disabled
+org.eclipse.jdt.core.compiler.problem.suppressWarnings=enabled
+org.eclipse.jdt.core.compiler.problem.syntacticNullAnalysisForFields=disabled
+org.eclipse.jdt.core.compiler.problem.syntheticAccessEmulation=ignore
+org.eclipse.jdt.core.compiler.problem.terminalDeprecation=warning
+org.eclipse.jdt.core.compiler.problem.typeParameterHiding=warning
+org.eclipse.jdt.core.compiler.problem.unavoidableGenericTypeProblems=enabled
+org.eclipse.jdt.core.compiler.problem.uncheckedTypeOperation=warning
+org.eclipse.jdt.core.compiler.problem.unclosedCloseable=warning
+org.eclipse.jdt.core.compiler.problem.undocumentedEmptyBlock=ignore
+org.eclipse.jdt.core.compiler.problem.unhandledWarningToken=warning
+org.eclipse.jdt.core.compiler.problem.unlikelyCollectionMethodArgumentType=warning
+org.eclipse.jdt.core.compiler.problem.unlikelyCollectionMethodArgumentTypeStrict=disabled
+org.eclipse.jdt.core.compiler.problem.unlikelyEqualsArgumentType=info
+org.eclipse.jdt.core.compiler.problem.unnecessaryElse=ignore
+org.eclipse.jdt.core.compiler.problem.unnecessaryTypeCheck=ignore
+org.eclipse.jdt.core.compiler.problem.unqualifiedFieldAccess=ignore
+org.eclipse.jdt.core.compiler.problem.unstableAutoModuleName=warning
+org.eclipse.jdt.core.compiler.problem.unusedDeclaredThrownException=ignore
+org.eclipse.jdt.core.compiler.problem.unusedDeclaredThrownExceptionExemptExceptionAndThrowable=enabled
+org.eclipse.jdt.core.compiler.problem.unusedDeclaredThrownExceptionIncludeDocCommentReference=enabled
+org.eclipse.jdt.core.compiler.problem.unusedDeclaredThrownExceptionWhenOverriding=disabled
+org.eclipse.jdt.core.compiler.problem.unusedExceptionParameter=ignore
+org.eclipse.jdt.core.compiler.problem.unusedImport=warning
+org.eclipse.jdt.core.compiler.problem.unusedLabel=warning
+org.eclipse.jdt.core.compiler.problem.unusedLocal=warning
+org.eclipse.jdt.core.compiler.problem.unusedObjectAllocation=ignore
+org.eclipse.jdt.core.compiler.problem.unusedParameter=ignore
+org.eclipse.jdt.core.compiler.problem.unusedParameterIncludeDocCommentReference=enabled
+org.eclipse.jdt.core.compiler.problem.unusedParameterWhenImplementingAbstract=disabled
+org.eclipse.jdt.core.compiler.problem.unusedParameterWhenOverridingConcrete=disabled
+org.eclipse.jdt.core.compiler.problem.unusedPrivateMember=warning
+org.eclipse.jdt.core.compiler.problem.unusedTypeParameter=ignore
+org.eclipse.jdt.core.compiler.problem.unusedWarningToken=warning
+org.eclipse.jdt.core.compiler.problem.varargsArgumentNeedCast=warning
 org.eclipse.jdt.core.compiler.release=disabled
 org.eclipse.jdt.core.compiler.source=1.8

CODE_OF_CONDUCT.md

@@ -0,0 +1,76 @@
+# Contributor Covenant Code of Conduct
+
+## Our Pledge
+
+In the interest of fostering an open and welcoming environment, we as
+contributors and maintainers pledge to making participation in our project and
+our community a harassment-free experience for everyone, regardless of age, body
+size, disability, ethnicity, sex characteristics, gender identity and expression,
+level of experience, education, socio-economic status, nationality, personal
+appearance, race, religion, or sexual identity and orientation.
+
+## Our Standards
+
+Examples of behavior that contributes to creating a positive environment
+include:
+
+* Using welcoming and inclusive language
+* Being respectful of differing viewpoints and experiences
+* Gracefully accepting constructive criticism
+* Focusing on what is best for the community
+* Showing empathy towards other community members
+
+Examples of unacceptable behavior by participants include:
+
+* The use of sexualized language or imagery and unwelcome sexual attention or
+ advances
+* Trolling, insulting/derogatory comments, and personal or political attacks
+* Public or private harassment
+* Publishing others' private information, such as a physical or electronic
+ address, without explicit permission
+* Other conduct which could reasonably be considered inappropriate in a
+ professional setting
+
+## Our Responsibilities
+
+Project maintainers are responsible for clarifying the standards of acceptable
+behavior and are expected to take appropriate and fair corrective action in
+response to any instances of unacceptable behavior.
+
+Project maintainers have the right and responsibility to remove, edit, or
+reject comments, commits, code, wiki edits, issues, and other contributions
+that are not aligned to this Code of Conduct, or to ban temporarily or
+permanently any contributor for other behaviors that they deem inappropriate,
+threatening, offensive, or harmful.
+
+## Scope
+
+This Code of Conduct applies both within project spaces and in public spaces
+when an individual is representing the project or its community. Examples of
+representing a project or community include using an official project e-mail
+address, posting via an official social media account, or acting as an appointed
+representative at an online or offline event. Representation of a project may be
+further defined and clarified by project maintainers.
+
+## Enforcement
+
+Instances of abusive, harassing, or otherwise unacceptable behavior may be
+reported by contacting the project team at kske@outlook.de. All
+complaints will be reviewed and investigated and will result in a response that
+is deemed necessary and appropriate to the circumstances. The project team is
+obligated to maintain confidentiality with regard to the reporter of an incident.
+Further details of specific enforcement policies may be posted separately.
+
+Project maintainers who do not follow or enforce the Code of Conduct in good
+faith may face temporary or permanent repercussions as determined by other
+members of the project's leadership.
+
+## Attribution
+
+This Code of Conduct is adapted from the [Contributor Covenant][homepage], version 1.4,
+available at https://www.contributor-covenant.org/version/1/4/code-of-conduct.html
+
+[homepage]: https://www.contributor-covenant.org
+
+For answers to common questions about this code of conduct, see
+https://www.contributor-covenant.org/faq

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

@@ -1,5 +1,7 @@
 package envoy.client;
 
+import java.util.logging.Logger;
+
 import javax.ws.rs.client.ClientBuilder;
 import javax.ws.rs.client.Entity;
 import javax.ws.rs.client.WebTarget;
@@ -28,18 +30,20 @@ public class Client {
 	private Config			config;
 	private User			sender, recipient;
 
+	private static final Logger logger = Logger.getLogger(Client.class.getSimpleName());
+
 	public Client(Config config, String username) {
 		this.config	= config;
 		sender		= getUser(username);
-		System.out.println("ID: " + sender.getID());
+
+		logger.info("ID: " + sender.getID());
 	}
 
 	private <T, R> R post(String uri, T body, Class<R> responseBodyClass) {
-		javax.ws.rs.client.Client	client	= ClientBuilder.newClient();
-		WebTarget					target	= client.target(uri);
-
-		Response	response		= target.request().post(Entity.entity(body, "application/xml"));
-		R			responseBody	= response.readEntity(responseBodyClass);
+		javax.ws.rs.client.Client	client			= ClientBuilder.newClient();
+		WebTarget					target			= client.target(uri);
+		Response					response		= target.request().post(Entity.entity(body, "application/xml"));
+		R							responseBody	= response.readEntity(responseBodyClass);
 		response.close();
 		client.close();
 
@@ -92,7 +96,7 @@ public class Client {
 		if (returnSenderSync.getUsers().size() == 1) {
 			returnSender = returnSenderSync.getUsers().get(0);
 		} else {
-			System.out.println("ERROR exiting...");
+			logger.warning("ERROR exiting...");
 		}
 
 		return returnSender;
@@ -129,7 +133,7 @@ public class Client {
 	 * Updating UserStatus of all users in LocalDB. (Server sends all users with
 	 * their updated UserStatus to the client.) <br>
 	 * 
-	 * @param userId the client who sends the sync
+	 * @param userId the id of the {@link Client} who sends the {@link Sync}
 	 * @param sync the sync object (yet to be converted from java class to sync.xml)
 	 * @return a returnSync.xml file
 	 * @since Envoy v0.1-alpha
@@ -166,16 +170,16 @@ public class Client {
 	public User getRecipient() { return recipient; }
 
 	/**
-     * Sets the 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; }
 }
-

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

@@ -32,7 +32,7 @@ public class Config {
 	 * 
 	 * @param properties a {@link Properties} object containing information about
 	 *                   the server and port, as well as the path to the local
-	 *                   database
+	 *                   database and the synchronization timeout
 	 * @since Envoy v0.1-alpha
 	 */
 	public void load(Properties properties) {
@@ -65,8 +65,6 @@ public class Config {
 					localDB = new File(args[++i]);
 					break;
 			}
-		if (localDB == null) localDB = new File(".\\localDB");
-		if (syncTimeout == 0) syncTimeout = 1000;
 	}
 
 	/**
@@ -116,7 +114,7 @@ public class Config {
 	/**
 	 * Changes the default local database.
 	 * Exclusively intended for development purposes.
-	 * 
+   *
 	 * @param localDB the file containing the local database
 	 * @since Envoy v0.1-alpha
 	 **/

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

@@ -9,10 +9,13 @@ import java.io.ObjectOutputStream;
 import java.time.Instant;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.logging.Logger;
 
 import javax.xml.datatype.DatatypeConfigurationException;
 import javax.xml.datatype.DatatypeFactory;
 
+import envoy.client.event.EventBus;
+import envoy.client.event.MessageCreationEvent;
 import envoy.exception.EnvoyException;
 import envoy.schema.Message;
 import envoy.schema.Message.Metadata.MessageState;
@@ -41,15 +44,16 @@ public class LocalDB {
 	private Sync	sync				= objectFactory.createSync();
 	private Sync	readMessages		= objectFactory.createSync();
 
+    private static final Logger logger = Logger.getLogger(LocalDB.class.getSimpleName());
+
 	/**
 	 * Constructs an empty local database.
 	 *
 	 * @param sender the user that is logged in with this client
 	 * @since Envoy v0.1-alpha
 	 */
-
 	public LocalDB(User sender) {
-		this.sender	= sender;
+		this.sender = sender;
 		try {
 			datatypeFactory = DatatypeFactory.newInstance();
 		} catch (DatatypeConfigurationException e) {
@@ -66,34 +70,25 @@ public class LocalDB {
 	 * @since Envoy v0.1-alpha
 	 */
 	public void initializeDBFile(File localDBDir) throws EnvoyException {
-		if (localDBDir.exists() && !localDBDir.isDirectory()) throw new EnvoyException(
-				String.format("LocalDBDir '%s' is not a directory!", localDBDir.getAbsolutePath()));
+		if (localDBDir.exists() && !localDBDir.isDirectory())
+			throw new EnvoyException(String.format("LocalDBDir '%s' is not a directory!", localDBDir.getAbsolutePath()));
 		localDB = new File(localDBDir, sender.getID() + ".db");
 		if (localDB.exists()) loadFromLocalDB();
 	}
 
 	/**
-	 * Saves the database into a file for future use.<br>
-	 * It is theoretically possible to fail due to unknown causes.<br>
-	 * In such a case, every message sent/ received during that session will be
-	 * lost.
+	 * Saves the database into a file for future use.
 	 *
-	 * @throws IOException gets thrown, if saving failed for some reason
+	 * @throws IOException if something went wrong during saving
 	 * @since Envoy v0.1-alpha
 	 */
-	public void saveToLocalDB() throws IOException{
-		try {
-			localDB.getParentFile().mkdirs();
-			localDB.createNewFile();
-		} catch (IOException e) {
-			e.printStackTrace();
-			System.err.println("unable to save the messages");
-		}
+	public void saveToLocalDB() throws IOException {
+		localDB.getParentFile().mkdirs();
+		localDB.createNewFile();
 		try (ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(localDB))) {
 			out.writeObject(chats);
 		} catch (IOException ex) {
-			ex.printStackTrace();
-			System.err.println("unable to save the messages");
+			throw ex;
 		}
 	}
 
@@ -117,8 +112,9 @@ public class LocalDB {
 	 * Creates a {@link Message} object serializable to XML.
 	 *
 	 * @param textContent The content (text) of the message
-	 * @param recipientID self explanatory
+	 * @param recipientID The recipient of the message
 	 * @return prepared {@link Message} object
+	 * @since Envoy v0.1-alpha
 	 */
 	public Message createMessage(String textContent, long recipientID) {
 		Message.Metadata metaData = objectFactory.createMessageMetadata();
@@ -138,102 +134,97 @@ public class LocalDB {
 		return message;
 	}
 
+    /**
+	 * Creates a {@link Sync} object filled with the changes that occurred to the
+	 * local database since the last synchronization.
+	 * 
+	 * @param userId the ID of the user that is synchronized by this client
+	 * @return {@link Sync} object filled with the current changes
+     * @since Envoy v0.1-alpha
+	 */
 	public Sync fillSync(long userId) {
 		addWaitingMessagesToSync();
 
 		sync.getMessages().addAll(readMessages.getMessages());
 		readMessages.getMessages().clear();
 
-		System.out.println(sync.getMessages().size());
+		logger.finest(String.format("Filled sync with %d messages.", sync.getMessages().size()));
 		return sync;
 	}
 
+	/**
+	 * Applies the changes carried by a {@link Sync} object to the local database
+	 * 
+	 * @param returnSync the {@link Sync} object to apply
+     * @since Envoy v0.1-alpha
+	 */
 	public void applySync(Sync returnSync) {
 		for (int i = 0; i < returnSync.getMessages().size(); i++) {
-			if (returnSync.getMessages().get(i).getMetadata().getMessageId() != 0
-					&& returnSync.getMessages().get(i).getMetadata().getState() == MessageState.SENT) {
-				// Update Local Messages with State WAITING (add Message ID and change State to
-				// SENT)
-				for (int j = 0; j < sync.getMessages().size(); j++) {
-					if (j == i) {
-						sync.getMessages().get(j).getMetadata().setMessageId(returnSync.getMessages().get(j).getMetadata().getMessageId());
-						sync.getMessages().get(j).getMetadata().setState(returnSync.getMessages().get(j).getMetadata().getState());
-					}
-				}
-			}
-			if (returnSync.getMessages().get(i).getMetadata().getMessageId() != 0 && returnSync.getMessages().get(i).getMetadata().getSender() != 0
-					&& returnSync.getMessages().get(i).getMetadata().getState() == MessageState.RECEIVED) {
-				// these are the unread Messages from the server
-				unreadMessagesSync.getMessages().add(returnSync.getMessages().get(i));
-			}
 
-			if (returnSync.getMessages().get(i).getMetadata().getMessageId() != 0 && returnSync.getMessages().get(i).getMetadata().getSender() == 0
-					&& returnSync.getMessages().get(i).getMetadata().getState() == MessageState.RECEIVED) {
-				// Update Messages in localDB to state RECEIVED
-				for (int j = 0; j < getChats().size(); j++) {
-					if (getChats().get(j).getRecipient().getID() == returnSync.getMessages().get(i).getMetadata().getRecipient()) {
-						for (int k = 0; k < getChats().get(j).getModel().getSize(); k++) {
-							if (getChats().get(j).getModel().get(k).getMetadata().getMessageId() == returnSync.getMessages()
-								.get(i)
-								.getMetadata()
-								.getMessageId()) {
-								// Update Message in LocalDB
-								getChats().get(j).getModel().get(k).getMetadata().setState(returnSync.getMessages().get(j).getMetadata().getState());
-							}
+			// The message has an ID
+			if (returnSync.getMessages().get(i).getMetadata().getMessageId() != 0) {
+
+				// Messages are processes differently corresponding to their state
+				switch (returnSync.getMessages().get(i).getMetadata().getState()) {
+					case SENT:
+						// Update previously waiting and now sent messages that were assigned an ID by
+						// the server
+						sync.getMessages().get(i).getMetadata().setMessageId(returnSync.getMessages().get(i).getMetadata().getMessageId());
+						sync.getMessages().get(i).getMetadata().setState(returnSync.getMessages().get(i).getMetadata().getState());
+						break;
+					case RECEIVED:
+						if (returnSync.getMessages().get(i).getMetadata().getSender() != 0) {
+							// these are the unread Messages from the server
+							unreadMessagesSync.getMessages().add(returnSync.getMessages().get(i));
+
+							// Create and dispatch message creation event
+							EventBus.getInstance().dispatch(new MessageCreationEvent(returnSync.getMessages().get(i)));
+						} else {
+							// Update Messages in localDB to state RECEIVED
+							for (Chat chat : getChats())
+								if (chat.getRecipient().getID() == returnSync.getMessages().get(i).getMetadata().getRecipient())
+									for (int j = 0; j < chat.getModel().getSize(); j++)
+									if (chat.getModel().get(j).getMetadata().getMessageId() == returnSync.getMessages()
+										.get(i)
+										.getMetadata()
+										.getMessageId())
+										chat.getModel().get(j).getMetadata().setState(returnSync.getMessages().get(i).getMetadata().getState());
 						}
-					}
-				}
-
-			}
-
-			if (returnSync.getMessages().get(i).getMetadata().getMessageId() != 0
-					&& returnSync.getMessages().get(i).getMetadata().getState() == MessageState.READ) {
-				// Update local Messages to state READ
-				System.out.println("Message with ID: " + returnSync.getMessages().get(i).getMetadata().getMessageId()
-						+ "was initialized to be set to READ in localDB.");
-				for (int j = 0; j < getChats().size(); j++) {
-					if (getChats().get(j).getRecipient().getID() == returnSync.getMessages().get(i).getMetadata().getRecipient()) {
-						System.out.println("Chat with: " + getChats().get(j).getRecipient().getID() + "was selected.");
-						for (int k = 0; k < getChats().get(j).getModel().getSize(); k++) {
-							if (getChats().get(j).getModel().get(k).getMetadata().getMessageId() == returnSync.getMessages()
-								.get(i)
-								.getMetadata()
-								.getMessageId()) {
-								System.out.println(
-										"Message with ID: " + getChats().get(j).getModel().get(k).getMetadata().getMessageId() + "was selected.");
-								getChats().get(j).getModel().get(k).getMetadata().setState(returnSync.getMessages().get(i).getMetadata().getState());
-								System.out
-									.println("Message State is now: " + getChats().get(j).getModel().get(k).getMetadata().getState().toString());
+						break;
+					case READ:
+						// Update local Messages to state READ
+						logger.info("Message with ID: " + returnSync.getMessages().get(i).getMetadata().getMessageId()
+								+ "was initialized to be set to READ in localDB.");
+						for (Chat chat : getChats())
+							if (chat.getRecipient().getID() == returnSync.getMessages().get(i).getMetadata().getRecipient()) {
+								logger.info("Chat with: " + chat.getRecipient().getID() + "was selected.");
+								for (int k = 0; k < chat.getModel().getSize(); k++)
+									if (chat.getModel().get(k).getMetadata().getMessageId() == returnSync.getMessages()
+										.get(i)
+										.getMetadata()
+										.getMessageId()) {
+										logger.info("Message with ID: " + chat.getModel().get(k).getMetadata().getMessageId() + "was selected.");
+										chat.getModel().get(k).getMetadata().setState(returnSync.getMessages().get(i).getMetadata().getState());
+										logger.info("Message State is now: " + chat.getModel().get(k).getMetadata().getState());
+									}
 							}
-						}
-					}
+						break;
 				}
 			}
 		}
 
 		// Updating UserStatus of all users in LocalDB
-		for (int j = 0; j < returnSync.getUsers().size(); j++) {
-			for (int k = 0; k < getChats().size(); k++) {
-				if (getChats().get(k).getRecipient().getID() == returnSync.getUsers().get(j).getID()) {
-
-					getChats().get(k).getRecipient().setStatus(returnSync.getUsers().get(j).getStatus());
-					System.out.println(getChats().get(k).getRecipient().getStatus().toString());
+		for (User user : returnSync.getUsers())
+			for (Chat chat : getChats())
+				if (user.getID() == chat.getRecipient().getID()) {
+					chat.getRecipient().setStatus(user.getStatus());
+					logger.info(chat.getRecipient().getStatus().toString());
 				}
-			}
-		}
 
 		sync.getMessages().clear();
 		sync.getUsers().clear();
 	}
 
-	/**
-	 * Adds a message to the "sync" Sync object.
-	 * 
-	 * @param message the message to send
-	 * @since Envoy v0.1-alpha
-	 */
-	public void addMessageToSync(Message message) { sync.getMessages().add(message); }
-
 	/**
 	 * Adds the unread messages returned from the server in the latest sync to the
 	 * right chats in the LocalDB.
@@ -241,11 +232,11 @@ public class LocalDB {
 	 * @since Envoy v0.1-alpha
 	 */
 	public void addUnreadMessagesToLocalDB() {
-		Sync unreadMessages = unreadMessagesSync;
-		for (int i = 0; i < unreadMessages.getMessages().size(); i++)
-			for (int j = 0; j < getChats().size(); j++)
-				if (getChats().get(j).getRecipient().getID() == unreadMessages.getMessages().get(i).getMetadata().getSender()) {
-					getChats().get(j).appendMessage(unreadMessages.getMessages().get(i));
+		for (Message message : unreadMessagesSync.getMessages())
+			for (Chat chat : getChats())
+				if (message.getMetadata().getSender() == chat.getRecipient().getID()) {
+					chat.appendMessage(message);
+					break;
 				}
 	}
 
@@ -255,7 +246,7 @@ public class LocalDB {
 	 * <br>
 	 * Adds these messages to the {@code readMessages} {@link Sync} object.
 	 *
-	 * @param currentChat the chat that was just opened
+	 * @param currentChat the {@link Chat} that was just opened
 	 * @since Envoy v0.1-alpha
 	 */
 	public void setMessagesToRead(Chat currentChat) {
@@ -271,22 +262,13 @@ public class LocalDB {
 	 * Adds all messages with state {@code WAITING} from the {@link LocalDB} to the
 	 * {@link Sync} object.
 	 *
-	 * @param message     the message that is not yet received by the other user
-	 * @param currentChat the chat that is currently open
-	 * @since Envoy v0.1-alpha
-	 */
-	public void addWaitingMessageToLocalDB(Message message, Chat currentChat) { currentChat.appendMessage(message); }
-
-	/**
-	 * Adds all messages with State WAITING from the {@link LocalDB} to the Sync.
-	 * 
 	 * @since Envoy v0.1-alpha
 	 */
 	private void addWaitingMessagesToSync() {
 		for (Chat chat : getChats())
 			for (int i = 0; i < chat.getModel().size(); i++)
 				if (chat.getModel().get(i).getMetadata().getState() == MessageState.WAITING) {
-					System.out.println("Got Waiting Message");
+					logger.info("Got Waiting Message");
 					sync.getMessages().add(chat.getModel().get(i));
 				}
 	}
@@ -299,8 +281,8 @@ public class LocalDB {
 	public void clearUnreadMessagesSync() { unreadMessagesSync.getMessages().clear(); }
 
 	/**
-	 * @return all saves {@link Chat} objects that list the client user as the
-	 *         client
+	 * @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; }

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

@@ -0,0 +1,17 @@
+package envoy.client.event;
+
+/**
+ * Project: <strong>envoy-clientChess</strong><br>
+ * File: <strong>Event.javaEvent.java</strong><br>
+ * Created: <strong>04.12.2019</strong><br>
+ * 
+ * @author Kai S. K. Engelbart
+ * @since Envoy v0.2-alpha
+ */
+public interface Event<T> {
+
+	/**
+	 * @return the data associated with this event
+	 */
+	T get();
+}

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

@@ -0,0 +1,71 @@
+package envoy.client.event;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * This class handles events by allowing {@link EventHandler} object to register
+ * themselves and then be notified about certain events dispatched by the event
+ * bus.<br>
+ * <br>
+ * The event bus is a singleton and can be used across the entire application to
+ * guarantee the propagation of events.
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>EventBus.java</strong><br>
+ * Created: <strong>04.12.2019</strong><br>
+ * 
+ * @author Kai S. K. Engelbart
+ * @since Envoy v0.2-alpha
+ */
+public class EventBus {
+
+	/**
+	 * Contains all {@link EventHandler} instances registered at this
+	 * {@link EventBus}.
+	 */
+	private List<EventHandler> handlers = new ArrayList<>();
+
+	/**
+	 * The singleton instance of this {@link EventBus} that is used across the
+	 * entire application.
+	 */
+	private static EventBus eventBus = new EventBus();
+
+	/**
+	 * This constructor is not accessible from outside this class because a
+	 * singleton instance of it is provided by the {@link EventBus#getInstance()}
+	 * method.
+	 */
+	private EventBus() {}
+
+	/**
+	 * @return the singleton instance of the {@link EventBus}
+	 * @since Envoy v0.2-alpha
+	 */
+	public static EventBus getInstance() { return eventBus; }
+
+	/**
+	 * Registers a list of {@link EventHandler} objects to be notified when a
+	 * {@link Event} is dispatched that they are subscribed to.
+	 * 
+	 * @param handlers the {@link EventHandler} objects to register
+	 * @since Envoy v0.2-alpha
+	 */
+	public void register(EventHandler... handlers) { this.handlers.addAll(Arrays.asList(handlers)); }
+
+	/**
+	 * Dispatches a {@link Event} to every {@link EventHandler} subscribed to it.
+	 * 
+	 * @param event the {@link Event} to dispatch
+	 * @since Envoy v0.2-alpha
+	 */
+	public void dispatch(Event<?> event) { handlers.stream().filter(h -> h.supports().contains(event.getClass())).forEach(h -> h.handle(event)); }
+
+	/**
+	 * @return a list of all {@link EventHandler} instances currently registered at
+	 *         this {@link EventBus}
+	 * @since Envoy v0.2-alpha
+	 */
+	public List<EventHandler> getHandlers() { return handlers; }
+}

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

@@ -0,0 +1,25 @@
+package envoy.client.event;
+
+import java.util.Set;
+
+/**
+ * Project: <strong>envoy-clientChess</strong><br>
+ * File: <strong>EventHandler.javaEvent.java</strong><br>
+ * Created: <strong>04.12.2019</strong><br>
+ * 
+ * @author Kai S. K. Engelbart
+ */
+public interface EventHandler {
+
+	/**
+	 * Consumes an event dispatched by the event bus.
+	 * 
+	 * @param event The event dispatched by the event bus, only of supported type
+	 */
+	void handle(Event<?> event);
+
+	/**
+	 * @return A set of classes this class is supposed to handle in events
+	 */
+	Set<Class<? extends Event<?>>> supports();
+}

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

@@ -0,0 +1,18 @@
+package envoy.client.event;
+
+import envoy.schema.Message;
+
+/**
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>MessageCreationEvent.java</strong><br>
+ * Created: <strong>4 Dec 2019</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ */
+public class MessageCreationEvent extends MessageEvent {
+
+	/**
+	 * @param message the {@link Message} that has been created
+	 */
+	public MessageCreationEvent(Message message) { super(message); }
+}

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

@@ -0,0 +1,20 @@
+package envoy.client.event;
+
+import envoy.schema.Message;
+
+/**
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>MessageCreationEvent.java</strong><br>
+ * Created: <strong>4 Dec 2019</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ */
+public class MessageEvent implements Event<Message> {
+
+	protected final Message message;
+
+	public MessageEvent(Message message) { this.message = message; }
+
+	@Override
+	public Message get() { return message; }
+}

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

@@ -0,0 +1,18 @@
+package envoy.client.event;
+
+import envoy.schema.Message;
+
+/**
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>MessageModificationEvent.java</strong><br>
+ * Created: <strong>4 Dec 2019</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ */
+public class MessageModificationEvent extends MessageEvent {
+
+	/**
+	 * @param message the {@link Message} that has been modified
+	 */
+	public MessageModificationEvent(Message message) { super(message); }
+}

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

@@ -1,15 +1,19 @@
 package envoy.client.ui;
 
+import java.awt.Color;
 import java.awt.ComponentOrientation;
 import java.awt.Font;
 import java.awt.GridBagConstraints;
 import java.awt.GridBagLayout;
 import java.awt.Insets;
+import java.awt.Toolkit;
 import java.awt.event.KeyAdapter;
 import java.awt.event.KeyEvent;
 import java.awt.event.WindowAdapter;
 import java.awt.event.WindowEvent;
 import java.io.IOException;
+import java.util.logging.Level;
+import java.util.logging.Logger;
 
 import javax.swing.DefaultListModel;
 import javax.swing.JButton;
@@ -65,6 +69,8 @@ public class ChatWindow extends JFrame {
 
 	private static int space = 4;
 
+	private static final Logger logger = Logger.getLogger(ChatWindow.class.getSimpleName());
+
 	public ChatWindow(Client client, LocalDB localDB) {
 		this.client		= client;
 		this.localDB	= localDB;
@@ -73,18 +79,19 @@ public class ChatWindow extends JFrame {
 		setBounds(100, 100, 600, 800);
 		setTitle("Envoy");
 		setLocationRelativeTo(null);
+		setIconImage(Toolkit.getDefaultToolkit().createImage(getClass().getClassLoader().getResource("envoy_logo.png")));
 
 		// Save chats when window closes
 		addWindowListener(new WindowAdapter() {
 
 			@Override
-			public void windowClosing(WindowEvent e) {
+			public void windowClosing(WindowEvent evt) {
 				try {
 					localDB.saveToLocalDB();
 					Settings.getInstance().save();
 				} catch (IOException e1) {
 					e1.printStackTrace();
-					System.err.println("Could not save localDB");
+					logger.log(Level.WARNING, "Unable to save the messages", e1);
 				}
 			}
 		});
@@ -125,14 +132,10 @@ public class ChatWindow extends JFrame {
 
 			@Override
 			public void keyReleased(KeyEvent e) {
-
 				if (e.getKeyCode() == KeyEvent.VK_ENTER
 						&& ((Settings.getInstance().isEnterToSend() && e.getModifiersEx() == 0)
 								|| (e.getModifiersEx() == KeyEvent.CTRL_DOWN_MASK))) {
-
 					postMessage(messageList);
-				}
-
 			}
 		});
 		// Checks for changed Message
@@ -178,11 +181,10 @@ public class ChatWindow extends JFrame {
 		settingsButton.addActionListener((evt) -> {
 			try {
 				SettingsScreen.open();
-				
 				changeChatWindowColors(Settings.getInstance().getCurrentTheme());			
-				
-			} catch (Exception e) {
-				System.err.println("An error occured while opening the settings screen: " + e);
+                } catch (Exception e) {
+				SettingsScreen.open();
+				logger.log(Level.WARNING, "An error occured while opening the settings screen", e);
 				e.printStackTrace();
 			}
 		});
@@ -209,11 +211,7 @@ public class ChatWindow extends JFrame {
 				final User			user				= selectedUserList.getSelectedValue();
 				client.setRecipient(user);
 
-				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();
 
 				// Set all unread messages in the chat to read
 				readCurrentChat();
@@ -247,7 +245,6 @@ public class ChatWindow extends JFrame {
 		contentPane.revalidate();
 	}
 
-
 	/**
 	 * Used to immediately reload the ChatWindow when settings were changed.
 	 * 
@@ -290,18 +287,15 @@ public class ChatWindow extends JFrame {
     
 	private void postMessage(JList<Message> messageList) {
 		if (!client.hasRecipient()) {
-			JOptionPane.showMessageDialog(this,
-					"Please select a recipient!",
-					"Cannot send message",
-					JOptionPane.INFORMATION_MESSAGE);
+			JOptionPane.showMessageDialog(this, "Please select a recipient!", "Cannot send message", JOptionPane.INFORMATION_MESSAGE);
+			return;
 		}
 
 		if (!messageEnterTextArea.getText().isEmpty()) try {
 
 			// Create and send message object
-			final Message message = localDB.createMessage(messageEnterTextArea.getText(),
-					currentChat.getRecipient().getID());
-			localDB.addWaitingMessageToLocalDB(message, currentChat);
+			final Message message = localDB.createMessage(messageEnterTextArea.getText(), currentChat.getRecipient());
+			currentChat.appendMessage(message);
 			messageList.setModel(currentChat.getModel());
 
 			// Clear text field
@@ -350,8 +344,7 @@ public class ChatWindow extends JFrame {
 			new Thread(() -> {
 
 				// Synchronize
-				localDB.applySync(
-						client.sendSync(client.getSender().getID(), localDB.fillSync(client.getSender().getID())));
+				localDB.applySync(client.sendSync(client.getSender().getID(), localDB.fillSync(client.getSender().getID())));
 
 				// Process unread messages
 				localDB.addUnreadMessagesToLocalDB();
@@ -361,8 +354,7 @@ public class ChatWindow extends JFrame {
 				readCurrentChat();
 
 				// Update UI
-				SwingUtilities
-					.invokeLater(() -> { updateUserStates(); contentPane.revalidate(); contentPane.repaint(); });
+				SwingUtilities.invokeLater(() -> { updateUserStates(); contentPane.revalidate(); contentPane.repaint(); });
 			}).start();
 		}).start();
 	}

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

@@ -28,8 +28,7 @@ public class MessageListRenderer extends JLabel implements ListCellRenderer<Mess
 	private static final long serialVersionUID = 5164417379767181198L;
 
 	@Override
-	public Component getListCellRendererComponent(JList<? extends Message> list, Message value, int index,
-			boolean isSelected, boolean cellHasFocus) {
+	public Component getListCellRendererComponent(JList<? extends Message> list, Message value, int index, boolean isSelected, boolean cellHasFocus) {
 		if (isSelected) {
 			setBackground(list.getSelectionBackground());
 			setForeground(list.getSelectionForeground());
@@ -64,7 +63,6 @@ public class MessageListRenderer extends JLabel implements ListCellRenderer<Mess
 				textColor,
 				text,
 				state));
-
 		return this;
 	}
 

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

@@ -509,4 +509,5 @@ public class SettingsScreen extends JDialog {
 
 		colorsPanel.add(panel);
 	}
+
 }

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

@@ -3,6 +3,8 @@ package envoy.client.ui;
 import java.awt.EventQueue;
 import java.io.IOException;
 import java.util.Properties;
+import java.util.logging.Level;
+import java.util.logging.Logger;
 
 import javax.swing.JOptionPane;
 
@@ -26,29 +28,35 @@ import envoy.exception.EnvoyException;
  */
 public class Startup {
 
+	private static final Logger logger = Logger.getLogger(Startup.class.getSimpleName());
+
 	public static void main(String[] args) {
+		logger.setLevel(Level.ALL);
+
 		Config config = Config.getInstance();
-		if (args.length > 0) {
-			config.load(args);
-		} else {
-			ClassLoader loader = Thread.currentThread().getContextClassLoader();
-			try {
-				Properties configProperties = new Properties();
-				configProperties.load(loader.getResourceAsStream("client.properties"));
-				config.load(configProperties);
-			} catch (IOException e) {
-				e.printStackTrace();
-			}
+
+		// Load the configuration from client.properties first
+		ClassLoader loader = Thread.currentThread().getContextClassLoader();
+		try {
+			Properties configProperties = new Properties();
+			configProperties.load(loader.getResourceAsStream("client.properties"));
+			config.load(configProperties);
+		} catch (IOException e) {
+			e.printStackTrace();
 		}
 
+		// Override configuration values with command line arguments
+		if (args.length > 0) config.load(args);
+
 		if (!config.isInitialized()) {
-			System.err.println("Server or port are not defined. Exiting...");
+			logger.severe("Server or port are not defined. Exiting...");
+			JOptionPane.showMessageDialog(null, "Error loading configuration values.", "Configuration error", JOptionPane.ERROR_MESSAGE);
 			System.exit(1);
 		}
 
 		String userName = JOptionPane.showInputDialog("Please enter your username");
 		if (userName == null || userName.isEmpty()) {
-			System.err.println("User name is not set or empty. Exiting...");
+			logger.severe("User name is not set or empty. Exiting...");
 			System.exit(1);
 		}
 		Client	client	= new Client(config, userName);
@@ -66,8 +74,9 @@ public class Startup {
 		
 		EventQueue.invokeLater(() -> {
 			try {
-				ChatWindow frame = new ChatWindow(client, localDB);
-				frame.setVisible(true);
+				ChatWindow chatWindow = new ChatWindow(client, localDB);
+				new StatusTrayIcon(chatWindow).show();
+				chatWindow.setVisible(true);
 			} catch (Exception e) {
 				e.printStackTrace();
 			}

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

@@ -0,0 +1,133 @@
+package envoy.client.ui;
+
+import java.awt.AWTException;
+import java.awt.Image;
+import java.awt.MenuItem;
+import java.awt.PopupMenu;
+import java.awt.SystemTray;
+import java.awt.Toolkit;
+import java.awt.TrayIcon;
+import java.awt.TrayIcon.MessageType;
+import java.awt.Window;
+import java.awt.event.WindowAdapter;
+import java.awt.event.WindowEvent;
+import java.util.HashSet;
+import java.util.Set;
+
+import envoy.client.event.Event;
+import envoy.client.event.EventBus;
+import envoy.client.event.EventHandler;
+import envoy.client.event.MessageCreationEvent;
+import envoy.exception.EnvoyException;
+import envoy.schema.Message;
+
+/**
+ * Project: <strong>envoy-client</strong><br>
+ * File: <strong>StatusTrayIcon.java</strong><br>
+ * Created: <strong>3 Dec 2019</strong><br>
+ *
+ * @author Kai S. K. Engelbart
+ * @since Envoy v0.2-alpha
+ */
+public class StatusTrayIcon implements EventHandler {
+
+	/**
+	 * The {@link TrayIcon} provided by the System Tray API for controlling the
+	 * system tray. This includes displaying the icon, but also creating
+	 * notifications when new messages are received.
+	 */
+	private TrayIcon trayIcon;
+
+	/**
+	 * A received {@link Message} is only displayed as a system tray notification if
+	 * this variable is set to {@code true}.
+	 */
+	private boolean displayMessages = false;
+
+	/**
+	 * Creates a {@link StatusTrayIcon} with the Envoy logo, a tool tip and a pop-up
+	 * menu.
+	 *
+	 * @param focusTarget the {@link Window} which focus determines if message
+	 *                    notifications are displayed
+	 * @throws EnvoyException if the currently used OS does not support the System
+	 *                        Tray API
+	 * @since Envoy v0.2-alpha
+	 */
+	public StatusTrayIcon(Window focusTarget) throws EnvoyException {
+		if (!SystemTray.isSupported()) throw new EnvoyException("The Envoy tray icon is not supported.");
+
+		ClassLoader	loader	= Thread.currentThread().getContextClassLoader();
+		Image		img		= Toolkit.getDefaultToolkit().createImage(loader.getResource("envoy_logo.png"));
+		trayIcon = new TrayIcon(img, "Envoy Client");
+		trayIcon.setImageAutoSize(true);
+		trayIcon.setToolTip("You are notified if you have unread messages.");
+
+		PopupMenu popup = new PopupMenu();
+
+		MenuItem exitMenuItem = new MenuItem("Exit");
+		exitMenuItem.addActionListener((evt) -> System.exit(0));
+		popup.add(exitMenuItem);
+
+		trayIcon.setPopupMenu(popup);
+
+		// Only display messages if the chat window is not focused
+		focusTarget.addWindowFocusListener(new WindowAdapter() {
+
+			@Override
+			public void windowGainedFocus(WindowEvent e) {
+				displayMessages = false;
+			}
+
+			@Override
+			public void windowLostFocus(WindowEvent e) {
+				displayMessages = true;
+			}
+		});
+
+		// Start processing message events
+		EventBus.getInstance().register(this);
+	}
+
+	/**
+	 * Makes this {@link StatusTrayIcon} appear in the system tray.
+	 *
+	 * @throws EnvoyException if the status icon could not be attaches to the system
+	 *                        tray for system-internal reasons
+	 * @since Envoy v0.2-alpha
+	 */
+	public void show() throws EnvoyException {
+		try {
+			SystemTray.getSystemTray().add(trayIcon);
+		} catch (AWTException e) {
+			throw new EnvoyException("Could not attach Envoy tray icon to system tray.", e);
+		}
+	}
+
+	/**
+	 * Notifies the user of a message by displaying a pop-up every time a new
+	 * message is received.
+	 *
+	 * @since Envoy v0.2-alpha
+	 */
+	@Override
+	public void handle(Event<?> event) {
+		System.out.println("Message received. Displaying message: " + displayMessages);
+		if (displayMessages)
+			trayIcon.displayMessage("New message received", ((MessageCreationEvent) event).get().getContent().get(0).getText(), MessageType.INFO);
+	}
+
+	/**
+	 * The {@link StatusTrayIcon} only reacts to {@link MessageCreationEvent}
+	 * instances which signify newly received messages.
+	 *
+	 * @return A set with the single element {@code MessageCreationEvent.class}
+	 * @since Envoy v0.2-alpha
+	 */
+	@Override
+	public Set<Class<? extends Event<?>>> supports() {
+		Set<Class<? extends Event<?>>> supportedEvents = new HashSet<>();
+		supportedEvents.add(MessageCreationEvent.class);
+		return supportedEvents;
+	}
+}

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

@@ -28,8 +28,7 @@ public class UserListRenderer extends JLabel implements ListCellRenderer<User> {
 
 	@SuppressWarnings("incomplete-switch")
 	@Override
-	public Component getListCellRendererComponent(JList<? extends User> list, User value, int index, boolean isSelected,
-			boolean cellHasFocus) {
+	public Component getListCellRendererComponent(JList<? extends User> list, User value, int index, boolean isSelected, boolean cellHasFocus) {
 		if (isSelected) {
 			setBackground(list.getSelectionBackground());
 			setForeground(list.getSelectionForeground());
@@ -41,7 +40,6 @@ public class UserListRenderer extends JLabel implements ListCellRenderer<User> {
 		// Enable background rendering
 		setOpaque(true);
 
-
 		final String		name	= value.getName();
 		final UserStatus	status	= value.getStatus();
 
@@ -50,7 +48,6 @@ public class UserListRenderer extends JLabel implements ListCellRenderer<User> {
 
 		textColor = toHex(
 				Settings.getInstance().getThemes().get(Settings.getInstance().getCurrentTheme()).getUserNameColor());
-		
 		switch (status) {
 			case ONLINE:
 				setText(String.format(
@@ -59,7 +56,6 @@ public class UserListRenderer extends JLabel implements ListCellRenderer<User> {
 						textColor,
 						name));
 				break;
-
 			case OFFLINE:
 				setText(String.format(
 						"<html><p style=\"color:#fc0303\"><b><small>%s</b></small><br><p style=\"color:%s\">%s</html>",
@@ -68,9 +64,6 @@ public class UserListRenderer extends JLabel implements ListCellRenderer<User> {
 						name));
 				break;
 		}
-
-		
-
 		return this;
 	}