Merge pull request #19 from informatik-ag-ngl/f/groups

Added support for groups

.classpath

@@ -8,9 +8,9 @@
 	</classpathentry>
 	<classpathentry kind="src" output="target/test-classes" path="src/test/java">
 		<attributes>
+			<attribute name="test" value="true"/>
 			<attribute name="optional" value="true"/>
 			<attribute name="maven.pomderived" value="true"/>
-			<attribute name="test" value="true"/>
 		</attributes>
 	</classpathentry>
 	<classpathentry kind="con" path="org.eclipse.m2e.MAVEN2_CLASSPATH_CONTAINER">

.settings/org.eclipse.core.resources.prefs

@@ -1,6 +1,5 @@
 eclipse.preferences.version=1
 encoding//src/main/java=UTF-8
-encoding//src/main/resources=UTF-8
 encoding//src/test/java=UTF-8
 encoding//src/test/resources=UTF-8
 encoding/<project>=UTF-8

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

@@ -109,3 +109,364 @@ 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=11
+org.eclipse.jdt.core.formatter.align_assignment_statements_on_columns=true
+org.eclipse.jdt.core.formatter.align_fields_grouping_blank_lines=1
+org.eclipse.jdt.core.formatter.align_type_members_on_columns=true
+org.eclipse.jdt.core.formatter.align_variable_declarations_on_columns=true
+org.eclipse.jdt.core.formatter.align_with_spaces=false
+org.eclipse.jdt.core.formatter.alignment_for_additive_operator=16
+org.eclipse.jdt.core.formatter.alignment_for_arguments_in_allocation_expression=16
+org.eclipse.jdt.core.formatter.alignment_for_arguments_in_annotation=84
+org.eclipse.jdt.core.formatter.alignment_for_arguments_in_enum_constant=16
+org.eclipse.jdt.core.formatter.alignment_for_arguments_in_explicit_constructor_call=16
+org.eclipse.jdt.core.formatter.alignment_for_arguments_in_method_invocation=80
+org.eclipse.jdt.core.formatter.alignment_for_arguments_in_qualified_allocation_expression=20
+org.eclipse.jdt.core.formatter.alignment_for_assignment=0
+org.eclipse.jdt.core.formatter.alignment_for_bitwise_operator=16
+org.eclipse.jdt.core.formatter.alignment_for_compact_if=16
+org.eclipse.jdt.core.formatter.alignment_for_compact_loops=16
+org.eclipse.jdt.core.formatter.alignment_for_conditional_expression=80
+org.eclipse.jdt.core.formatter.alignment_for_conditional_expression_chain=0
+org.eclipse.jdt.core.formatter.alignment_for_enum_constants=16
+org.eclipse.jdt.core.formatter.alignment_for_expressions_in_array_initializer=16
+org.eclipse.jdt.core.formatter.alignment_for_expressions_in_for_loop_header=0
+org.eclipse.jdt.core.formatter.alignment_for_logical_operator=16
+org.eclipse.jdt.core.formatter.alignment_for_method_declaration=0
+org.eclipse.jdt.core.formatter.alignment_for_module_statements=16
+org.eclipse.jdt.core.formatter.alignment_for_multiple_fields=16
+org.eclipse.jdt.core.formatter.alignment_for_multiplicative_operator=16
+org.eclipse.jdt.core.formatter.alignment_for_parameterized_type_references=0
+org.eclipse.jdt.core.formatter.alignment_for_parameters_in_constructor_declaration=16
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+org.eclipse.jdt.core.formatter.alignment_for_resources_in_try=80
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+org.eclipse.jdt.core.formatter.insert_space_before_opening_brace_in_method_declaration=insert
+org.eclipse.jdt.core.formatter.insert_space_before_opening_brace_in_switch=insert
+org.eclipse.jdt.core.formatter.insert_space_before_opening_brace_in_type_declaration=insert
+org.eclipse.jdt.core.formatter.insert_space_before_opening_bracket_in_array_allocation_expression=do not insert
+org.eclipse.jdt.core.formatter.insert_space_before_opening_bracket_in_array_reference=do not insert
+org.eclipse.jdt.core.formatter.insert_space_before_opening_bracket_in_array_type_reference=do not insert
+org.eclipse.jdt.core.formatter.insert_space_before_opening_paren_in_annotation=do not insert
+org.eclipse.jdt.core.formatter.insert_space_before_opening_paren_in_annotation_type_member_declaration=do not insert
+org.eclipse.jdt.core.formatter.insert_space_before_opening_paren_in_catch=insert
+org.eclipse.jdt.core.formatter.insert_space_before_opening_paren_in_constructor_declaration=do not insert
+org.eclipse.jdt.core.formatter.insert_space_before_opening_paren_in_enum_constant=do not insert
+org.eclipse.jdt.core.formatter.insert_space_before_opening_paren_in_for=insert
+org.eclipse.jdt.core.formatter.insert_space_before_opening_paren_in_if=insert
+org.eclipse.jdt.core.formatter.insert_space_before_opening_paren_in_method_declaration=do not insert
+org.eclipse.jdt.core.formatter.insert_space_before_opening_paren_in_method_invocation=do not insert
+org.eclipse.jdt.core.formatter.insert_space_before_opening_paren_in_parenthesized_expression=do not insert
+org.eclipse.jdt.core.formatter.insert_space_before_opening_paren_in_switch=insert
+org.eclipse.jdt.core.formatter.insert_space_before_opening_paren_in_synchronized=insert
+org.eclipse.jdt.core.formatter.insert_space_before_opening_paren_in_try=insert
+org.eclipse.jdt.core.formatter.insert_space_before_opening_paren_in_while=insert
+org.eclipse.jdt.core.formatter.insert_space_before_parenthesized_expression_in_return=insert
+org.eclipse.jdt.core.formatter.insert_space_before_parenthesized_expression_in_throw=insert
+org.eclipse.jdt.core.formatter.insert_space_before_postfix_operator=do not insert
+org.eclipse.jdt.core.formatter.insert_space_before_prefix_operator=do not insert
+org.eclipse.jdt.core.formatter.insert_space_before_question_in_conditional=insert
+org.eclipse.jdt.core.formatter.insert_space_before_question_in_wildcard=do not insert
+org.eclipse.jdt.core.formatter.insert_space_before_relational_operator=insert
+org.eclipse.jdt.core.formatter.insert_space_before_semicolon=do not insert
+org.eclipse.jdt.core.formatter.insert_space_before_semicolon_in_for=do not insert
+org.eclipse.jdt.core.formatter.insert_space_before_semicolon_in_try_resources=do not insert
+org.eclipse.jdt.core.formatter.insert_space_before_shift_operator=insert
+org.eclipse.jdt.core.formatter.insert_space_before_string_concatenation=insert
+org.eclipse.jdt.core.formatter.insert_space_before_unary_operator=do not insert
+org.eclipse.jdt.core.formatter.insert_space_between_brackets_in_array_type_reference=do not insert
+org.eclipse.jdt.core.formatter.insert_space_between_empty_braces_in_array_initializer=do not insert
+org.eclipse.jdt.core.formatter.insert_space_between_empty_brackets_in_array_allocation_expression=do not insert
+org.eclipse.jdt.core.formatter.insert_space_between_empty_parens_in_annotation_type_member_declaration=do not insert
+org.eclipse.jdt.core.formatter.insert_space_between_empty_parens_in_constructor_declaration=do not insert
+org.eclipse.jdt.core.formatter.insert_space_between_empty_parens_in_enum_constant=do not insert
+org.eclipse.jdt.core.formatter.insert_space_between_empty_parens_in_method_declaration=do not insert
+org.eclipse.jdt.core.formatter.insert_space_between_empty_parens_in_method_invocation=do not insert
+org.eclipse.jdt.core.formatter.join_lines_in_comments=false
+org.eclipse.jdt.core.formatter.join_wrapped_lines=true
+org.eclipse.jdt.core.formatter.keep_annotation_declaration_on_one_line=one_line_if_single_item
+org.eclipse.jdt.core.formatter.keep_anonymous_type_declaration_on_one_line=one_line_never
+org.eclipse.jdt.core.formatter.keep_code_block_on_one_line=one_line_if_empty
+org.eclipse.jdt.core.formatter.keep_else_statement_on_same_line=true
+org.eclipse.jdt.core.formatter.keep_empty_array_initializer_on_one_line=false
+org.eclipse.jdt.core.formatter.keep_enum_constant_declaration_on_one_line=one_line_never
+org.eclipse.jdt.core.formatter.keep_enum_declaration_on_one_line=one_line_never
+org.eclipse.jdt.core.formatter.keep_if_then_body_block_on_one_line=one_line_if_single_item
+org.eclipse.jdt.core.formatter.keep_imple_if_on_one_line=false
+org.eclipse.jdt.core.formatter.keep_lambda_body_block_on_one_line=one_line_always
+org.eclipse.jdt.core.formatter.keep_loop_body_block_on_one_line=one_line_if_empty
+org.eclipse.jdt.core.formatter.keep_method_body_on_one_line=one_line_if_single_item
+org.eclipse.jdt.core.formatter.keep_simple_do_while_body_on_same_line=false
+org.eclipse.jdt.core.formatter.keep_simple_for_body_on_same_line=false
+org.eclipse.jdt.core.formatter.keep_simple_getter_setter_on_one_line=true
+org.eclipse.jdt.core.formatter.keep_simple_while_body_on_same_line=false
+org.eclipse.jdt.core.formatter.keep_then_statement_on_same_line=true
+org.eclipse.jdt.core.formatter.keep_type_declaration_on_one_line=one_line_never
+org.eclipse.jdt.core.formatter.lineSplit=150
+org.eclipse.jdt.core.formatter.never_indent_block_comments_on_first_column=false
+org.eclipse.jdt.core.formatter.never_indent_line_comments_on_first_column=false
+org.eclipse.jdt.core.formatter.number_of_blank_lines_after_code_block=0
+org.eclipse.jdt.core.formatter.number_of_blank_lines_at_beginning_of_code_block=0
+org.eclipse.jdt.core.formatter.number_of_blank_lines_at_beginning_of_method_body=0
+org.eclipse.jdt.core.formatter.number_of_blank_lines_at_end_of_code_block=0
+org.eclipse.jdt.core.formatter.number_of_blank_lines_at_end_of_method_body=0
+org.eclipse.jdt.core.formatter.number_of_blank_lines_before_code_block=0
+org.eclipse.jdt.core.formatter.number_of_empty_lines_to_preserve=1
+org.eclipse.jdt.core.formatter.parentheses_positions_in_annotation=separate_lines_if_wrapped
+org.eclipse.jdt.core.formatter.parentheses_positions_in_catch_clause=common_lines
+org.eclipse.jdt.core.formatter.parentheses_positions_in_enum_constant_declaration=common_lines
+org.eclipse.jdt.core.formatter.parentheses_positions_in_for_statment=common_lines
+org.eclipse.jdt.core.formatter.parentheses_positions_in_if_while_statement=common_lines
+org.eclipse.jdt.core.formatter.parentheses_positions_in_lambda_declaration=common_lines
+org.eclipse.jdt.core.formatter.parentheses_positions_in_method_delcaration=common_lines
+org.eclipse.jdt.core.formatter.parentheses_positions_in_method_invocation=common_lines
+org.eclipse.jdt.core.formatter.parentheses_positions_in_switch_statement=common_lines
+org.eclipse.jdt.core.formatter.parentheses_positions_in_try_clause=common_lines
+org.eclipse.jdt.core.formatter.put_empty_statement_on_new_line=true
+org.eclipse.jdt.core.formatter.tabulation.char=tab
+org.eclipse.jdt.core.formatter.tabulation.size=4
+org.eclipse.jdt.core.formatter.text_block_indentation=0
+org.eclipse.jdt.core.formatter.use_on_off_tags=false
+org.eclipse.jdt.core.formatter.use_tabs_only_for_leading_indentations=false
+org.eclipse.jdt.core.formatter.wrap_before_additive_operator=true
+org.eclipse.jdt.core.formatter.wrap_before_assignment_operator=false
+org.eclipse.jdt.core.formatter.wrap_before_bitwise_operator=true
+org.eclipse.jdt.core.formatter.wrap_before_conditional_operator=true
+org.eclipse.jdt.core.formatter.wrap_before_logical_operator=true
+org.eclipse.jdt.core.formatter.wrap_before_multiplicative_operator=true
+org.eclipse.jdt.core.formatter.wrap_before_or_operator_multicatch=true
+org.eclipse.jdt.core.formatter.wrap_before_relational_operator=true
+org.eclipse.jdt.core.formatter.wrap_before_shift_operator=true
+org.eclipse.jdt.core.formatter.wrap_before_string_concatenation=true
+org.eclipse.jdt.core.formatter.wrap_outer_expressions_when_nested=true
+org.eclipse.jdt.core.javaFormatter=org.eclipse.jdt.core.defaultJavaFormatter

.settings/org.eclipse.wst.common.component

@@ -3,13 +3,21 @@
     
     
     
+    
+    
+    
     <wb-module deploy-name="envoy-common">
                                                                 
         
         
         
+        
+        
+        
         <wb-resource deploy-path="/" source-path="/src/main/java"/>
-        <wb-resource deploy-path="/" source-path="/src/main/resources"/>
+                                                            
+    
+    
     
     
     
@@ -19,4 +27,7 @@
 
 
 
+
+
+
 </project-modules>

pom.xml

@@ -16,13 +16,19 @@
 		<maven.compiler.target>11</maven.compiler.target>
 	</properties>
 
+	<dependencies>
+		<dependency>
+			<groupId>org.junit.jupiter</groupId>
+			<artifactId>junit-jupiter-engine</artifactId>
+			<version>5.5.2</version>
+		</dependency>
+	</dependencies>
 	<build>
 		<finalName>envoy-common</finalName>
-		<resources>
+		
-			<resource>
+		<!-- Disable resource folder -->
-				<directory>src/main/resources</directory>
+		<resources />
-			</resource>
+		
-		</resources>
 		<pluginManagement>
 			<plugins>
 				<plugin>

src/main/java/envoy/data/Config.java

@@ -61,6 +61,14 @@ public class Config {
 				} else throw new EnvoyException("Malformed command line argument at position " + i);
 	}
 
+	/**
+	 * Initializes config items from a map.
+	 * 
+	 * @param items the items to include in this config
+	 * @since Envoy Common v0.1-beta
+	 */
+	public void load(Map<String, ConfigItem<?>> items) { this.items.putAll(items); }
+
 	/**
 	 * @return {@code true} if all mandatory config items are initialized
 	 * @since Envoy Common v0.1-beta

src/main/java/envoy/data/Contact.java

@@ -0,0 +1,91 @@
+package envoy.data;
+
+import java.io.Serializable;
+import java.util.Objects;
+import java.util.Set;
+
+/**
+ * This class is the superclass for both {@link User} and {@link Group}.<br>
+ * It provides an id and a name for each user and group.<br>
+ * <br>
+ * Project: <strong>envoy-common</strong><br>
+ * File: <strong>Contact.java</strong><br>
+ * Created: <strong>24 Mar 2020</strong><br>
+ *
+ * @author Leon Hofmeister
+ * @since Envoy v0.1-beta
+ */
+public abstract class Contact implements Serializable {
+
+	private final long								id;
+	private final transient Set<? extends Contact>	contacts;
+	private String									name;
+
+	private static final long serialVersionUID = 0L;
+
+	/**
+	 * Creates a new instance of a {@link Contact}.
+	 *
+	 * @param id       the ID of this contact
+	 * @param name     the name of this contact
+	 * @param contacts the contacts of this {@link Contact}
+	 * @since Envoy Common v0.1-beta
+	 */
+	public Contact(long id, String name, Set<? extends Contact> contacts) {
+		this.id			= id;
+		this.name		= name;
+		this.contacts	= contacts;
+	}
+
+	/**
+	 * @return the ID of this {@link Contact}
+	 * @since Envoy Common v0.2-alpha
+	 */
+	public long getID() { return id; }
+
+	/**
+	 * @return the name of this {@link Contact}
+	 * @since Envoy Common v0.2-alpha
+	 */
+	public String getName() { return name; }
+
+	/**
+	 * @param name the new name of this {@link Contact}
+	 * @since Envoy Common v0.1-beta
+	 */
+	public void setName(String name) { this.name = name; }
+
+	/**
+	 * {@inheritDoc}
+	 */
+	@Override
+	public String toString() { return String.format("Contact[id=%d,name=%s, contacts=%s]", id, name, contacts); }
+
+	/**
+	 * Provides a hash code based on the ID of this contact.
+	 * 
+	 * @since Envoy Common v0.1-beta
+	 */
+	@Override
+	public int hashCode() { return Objects.hash(id); }
+
+	/**
+	 * Tests equality to another object. If that object is a contact as well,
+	 * equality is determined by the ID.
+	 * 
+	 * @param obj the object to test for equality to this contact
+	 * @return {code true} if both objects are contacts and have identical IDs
+	 */
+	@Override
+	public boolean equals(Object obj) {
+		if (this == obj) return true;
+		if (!(obj instanceof Contact)) return false;
+		return id == ((Contact) obj).id;
+	}
+
+	/**
+	 * @return the contacts of this {@link Contact}
+	 * @since Envoy Common v0.1-beta
+	 */
+	public Set<? extends Contact> getContacts() { return contacts; }
+}

src/main/java/envoy/data/Contacts.java

@@ -1,36 +0,0 @@
-package envoy.data;
-
-import java.io.Serializable;
-import java.util.List;
-
-/**
- * Project: <strong>envoy-common</strong><br>
- * File: <strong>Contacts.java</strong><br>
- * Created: <strong>02.01.2020</strong><br>
- *
- * @author Kai S. K. Engelbart
- * @since Envoy Common v0.2-alpha
- */
-public class Contacts implements Serializable {
-
-	private final List<User> contacts;
-
-	private static final long serialVersionUID = 136970804968152871L;
-
-	/**
-	 * Creates an instance of {@link Contacts}.
-	 *
-	 * @param contacts the contact list
-	 * @since Envoy Common v0.2-alpha
-	 */
-	public Contacts(List<User> contacts) { this.contacts = contacts; }
-
-	@Override
-	public String toString() { return String.format("Contacts[%s]", contacts); }
-
-	/**
-	 * @return a list of users messages can be sent to
-	 * @since Envoy Common v0.2-alpha
-	 */
-	public List<User> getContacts() { return contacts; }
-}

src/main/java/envoy/data/Group.java

@@ -0,0 +1,55 @@
+package envoy.data;
+
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * Project: <strong>envoy-common</strong><br>
+ * File: <strong>Group.java</strong><br>
+ * Created: <strong>24 Mar 2020</strong><br>
+ *
+ * @author Leon Hofmeister
+ * @since Envoy Common v0.1-beta
+ */
+public final class Group extends Contact {
+
+	private static final long serialVersionUID = 0L;
+
+	/**
+	 * Creates a new instance of a {@link Group} without any members.
+	 *
+	 * @param id   the ID of this group
+	 * @param name the name of this group
+	 * @since Envoy Common v0.1-beta
+	 */
+	public Group(long id, String name) { this(id, name, new HashSet<User>()); }
+
+	/**
+	 * Creates an instance of a {@link Group}.
+	 *
+	 * @param id      the ID of this group
+	 * @param name    the name of this group
+	 * @param members all members that should be preinitialized
+	 * @since Envoy Common v0.1-beta
+	 */
+	public Group(long id, String name, Set<User> members) { super(id, name, members); }
+
+	private void readObject(ObjectInputStream inputStream) throws Exception {
+		inputStream.defaultReadObject();
+		var contacts = Contact.class.getDeclaredField("contacts");
+		contacts.setAccessible(true);
+		contacts.set(this, inputStream.readObject());
+	}
+
+	private void writeObject(ObjectOutputStream outputStream) throws Exception {
+		outputStream.defaultWriteObject();
+		getContacts().forEach(user -> user.serializeContacts(false));
+		outputStream.writeObject(getContacts());
+	}
+
+	@SuppressWarnings("unchecked")
+	@Override
+	public Set<User> getContacts() { return (Set<User>) super.getContacts(); }
+}

src/main/java/envoy/data/GroupMessage.java

@@ -0,0 +1,69 @@
+package envoy.data;
+
+import java.util.Collections;
+import java.util.Date;
+import java.util.Map;
+
+/**
+ * Project: <strong>envoy-common</strong><br>
+ * File: <strong>GroupMessage.java</strong><br>
+ * Created: <strong>26.03.2020</strong><br>
+ *
+ * @author Maximilian K&auml;fer
+ * @since Envoy Common v0.1-beta
+ */
+public final class GroupMessage extends Message {
+
+	private final Map<Long, MessageStatus> memberStatuses;
+
+	private static final long serialVersionUID = 0L;
+
+	/**
+	 * Initializes a {@link GroupMessage} with values for all of its properties. The
+	 * use
+	 * of this constructor is only intended for the {@link MessageBuilder} class, as
+	 * this class provides {@code null} checks and default values for all
+	 * properties.
+	 *
+	 * @param id             unique ID
+	 * @param senderID       the ID of the user who sends the message
+	 * @param groupID        the ID of the group which receives the message
+	 * @param creationDate   the creation date of the message
+	 * @param text           the text content of the message
+	 * @param attachment     the attachment of the message, if present
+	 * @param status         the current {@link Message.MessageStatus} of the
+	 *                       message
+	 * @param forwarded      whether this message was forwarded
+	 * @param memberStatuses a map of all members and their status according to this
+	 *                       {@link GroupMessage}
+	 * @since Envoy Common v0.1-beta
+	 */
+	GroupMessage(long id, long senderID, long groupID, Date creationDate, String text, MessageAttachment<?> attachment, MessageStatus status,
+			boolean forwarded, Map<Long, MessageStatus> memberStatuses) {
+		super(id, senderID, groupID, creationDate, text, attachment, status, forwarded);
+		this.memberStatuses = memberStatuses;
+	}
+
+	/**
+	 * Sets the status to be the minimum of all members.
+	 *
+	 * @since Envoy Common v0.1-beta
+	 */
+	public void updateStatus() {
+		setStatus(Collections.min(memberStatuses.values()));
+		switch (getStatus()) {
+			case RECEIVED:
+				setReceivedDate(new Date());
+				break;
+			case READ:
+				setReadDate(new Date());
+				break;
+		}
+	}
+
+	/**
+	 * @return the map of all statuses in this {@link GroupMessage}
+	 * @since Envoy Common v0.1-beta
+	 */
+	public Map<Long, MessageStatus> getMemberStatuses() { return memberStatuses; }
+}

src/main/java/envoy/data/IDGenerator.java

@@ -6,33 +6,33 @@ import java.io.Serializable;
  * Generates increasing IDs between two numbers.<br>
  * <br>
  * Project: <strong>envoy-common</strong><br>
- * File: <strong>IdGenerator.java</strong><br>
+ * File: <strong>IDGenerator.java</strong><br>
  * Created: <strong>31.12.2019</strong><br>
  *
  * @author Kai S. K. Engelbart
  * @since Envoy Common v0.2-alpha
  */
-public class IdGenerator implements Serializable {
+public class IDGenerator implements Serializable {
 
 	private final long	end;
 	private long		current;
 
-	private static final long serialVersionUID = -1517378307055845147L;
+	private static final long serialVersionUID = 0L;
 
 	/**
-	 * Creates an instance of {@link IdGenerator}.
+	 * Creates an instance of {@link IDGenerator}.
 	 *
 	 * @param begin the first ID
 	 * @param size  the amount of IDs to provide
 	 * @since Envoy Common v0.2-alpha
 	 */
-	public IdGenerator(long begin, long size) {
+	public IDGenerator(long begin, long size) {
 		current	= begin;
 		end		= begin + size;
 	}
 
 	@Override
-	public String toString() { return String.format("IdGenerator[current=%d,end=%d]", current, end); }
+	public String toString() { return String.format("IDGenerator[current=%d,end=%d]", current, end); }
 
 	/**
 	 * @return {@code true} if there are unused IDs remaining

src/main/java/envoy/data/LoginCredentials.java

@@ -30,16 +30,22 @@ public class LoginCredentials implements Serializable {
 	 * @param password     the password of the user (will be converted to a hash)
 	 * @param registration signifies that these credentials are used for user
 	 *                     registration instead of user login
-	 * @throws NoSuchAlgorithmException if the algorithm used is unknown
 	 * @since Envoy Common v0.2-alpha
 	 */
-	public LoginCredentials(String identifier, char[] password, boolean registration) throws NoSuchAlgorithmException {
+	public LoginCredentials(String identifier, char[] password, boolean registration) {
 		this.identifier		= identifier;
 		passwordHash		= getSha256(toByteArray(password));
 		this.registration	= registration;
 	}
 
-	private byte[] getSha256(byte[] input) throws NoSuchAlgorithmException { return MessageDigest.getInstance("SHA-256").digest(input); }
+	private byte[] getSha256(byte[] input) {
+		try {
+			return MessageDigest.getInstance("SHA-256").digest(input);
+		} catch (NoSuchAlgorithmException e) {
+			// This will never happen
+			throw new RuntimeException(e);
+		}
+	}
 
 	private byte[] toByteArray(char[] chars) {
 		byte[] bytes = new byte[chars.length * 2];
@@ -54,8 +60,8 @@ public class LoginCredentials implements Serializable {
 	public String toString() {
 		try (Formatter form = new Formatter()) {
 			form.format("LoginCredentials[identifier=%s,passwordHash=", identifier);
-			for (byte element : passwordHash)
+			for (int i = 0; i < 3; i++)
-				form.format("%02x", element);
+				form.format("%02x", passwordHash[i]);
 			return form.format(",registration=%b]", registration).toString();
 		}
 	}

src/main/java/envoy/data/Message.java

@@ -48,7 +48,7 @@ public class Message implements Serializable {
 		READ
 	}
 
-	private final long					id, senderId, recipientId;
+	private final long					id, senderID, recipientID;
 	private final boolean				forwarded;
 	private final Date					creationDate;
 	private final String				text;
@@ -57,7 +57,7 @@ public class Message implements Serializable {
 	private Date			receivedDate, readDate;
 	private MessageStatus	status;
 
-	private static final long serialVersionUID = -4393477412979594435L;
+	private static final long serialVersionUID = 0L;
 
 	/**
 	 * Initializes a {@link Message} with values for all of its properties. The use
@@ -66,8 +66,8 @@ public class Message implements Serializable {
 	 * properties.
 	 *
 	 * @param id           unique ID
-	 * @param senderId     the ID of the user who sends the message
+	 * @param senderID     the ID of the user who sends the message
-	 * @param recipientId  the ID of the user who receives the message
+	 * @param recipientID  the ID of the user who receives the message
 	 * @param creationDate the creation date of the message
 	 * @param text         the text content of the message
 	 * @param attachment   the attachment of the message, if present
@@ -75,11 +75,11 @@ public class Message implements Serializable {
 	 * @param forwarded    whether this message was forwarded
 	 * @since Envoy Common v0.2-alpha
 	 */
-	Message(long id, long senderId, long recipientId, Date creationDate, String text, MessageAttachment<?> attachment, MessageStatus status,
+	Message(long id, long senderID, long recipientID, Date creationDate, String text, MessageAttachment<?> attachment, MessageStatus status,
 			boolean forwarded) {
 		this.id				= id;
-		this.senderId		= senderId;
+		this.senderID		= senderID;
-		this.recipientId	= recipientId;
+		this.recipientID	= recipientID;
 		this.creationDate	= creationDate;
 		this.text			= text;
 		this.attachment		= attachment;
@@ -107,13 +107,14 @@ public class Message implements Serializable {
 
 	@Override
 	public String toString() {
-		return String.format("TextMessage[id=%d,sender=%s,recipient=%s,date=%s,status=%s,text=%s,hasAttachment=%b]",
+		return String.format("Message[id=%d,sender=%s,recipient=%s,date=%s,status=%s,text=%s,forwarded=%b,hasAttachment=%b]",
 				id,
-				senderId,
+				senderID,
-				recipientId,
+				recipientID,
 				new SimpleDateFormat("dd.MM.yyyy HH:mm:ss").format(creationDate),
 				status,
 				text,
+				forwarded,
 				attachment != null);
 	}
 
@@ -121,19 +122,19 @@ public class Message implements Serializable {
 	 * @return the ID of this message
 	 * @since Envoy Common v0.2-alpha
 	 */
-	public long getId() { return id; }
+	public long getID() { return id; }
 
 	/**
 	 * @return the sender ID of this message
 	 * @since Envoy Common v0.2-alpha
 	 */
-	public long getSenderId() { return senderId; }
+	public long getSenderID() { return senderID; }
 
 	/**
 	 * @return the recipient ID of this message
 	 * @since Envoy Common v0.2-alpha
 	 */
-	public long getRecipientId() { return recipientId; }
+	public long getRecipientID() { return recipientID; }
 
 	/**
 	 * @return the date at which this message was created

src/main/java/envoy/data/MessageAttachment.java

@@ -19,7 +19,7 @@ import envoy.util.SerializationUtils;
  */
 public class MessageAttachment<T> implements Serializable {
 
-	private static final long	serialVersionUID	= 262683855157198013L;
+	private static final long	serialVersionUID	= 0L;
 	private T					value;
 
 	/**

src/main/java/envoy/data/MessageBuilder.java

@@ -1,6 +1,8 @@
 package envoy.data;
 
 import java.util.Date;
+import java.util.HashMap;
+import java.util.Map;
 
 import envoy.data.Message.MessageStatus;
 
@@ -17,7 +19,7 @@ import envoy.data.Message.MessageStatus;
 public class MessageBuilder {
 
 	// Mandatory properties without default values
-	private final long senderId, recipientId;
+	private final long senderID, recipientID;
 
 	// Properties with default values
 	private long					id;
@@ -31,26 +33,26 @@ public class MessageBuilder {
 	 * Creates an instance of {@link MessageBuilder} with all mandatory values
 	 * without defaults for the {@link Message} class.
 	 *
-	 * @param senderId    the ID of the user who sends the {@link Message}
+	 * @param senderID    the ID of the user who sends the {@link Message}
-	 * @param recipientId the ID of the user who receives the {@link Message}
+	 * @param recipientID the ID of the user who receives the {@link Message}
 	 * @param idGenerator the ID generator used to generate a unique {@link Message}
 	 *                    id
 	 * @since Envoy Common v0.2-alpha
 	 */
-	public MessageBuilder(long senderId, long recipientId, IdGenerator idGenerator) { this(senderId, recipientId, idGenerator.next()); }
+	public MessageBuilder(long senderID, long recipientID, IDGenerator idGenerator) { this(senderID, recipientID, idGenerator.next()); }
 
 	/**
 	 * Creates an instance of {@link MessageBuilder} with all mandatory values
 	 * without defaults for the {@link Message} class.
 	 *
-	 * @param senderId    the ID of the user who sends the {@link Message}
+	 * @param senderID    the ID of the user who sends the {@link Message}
-	 * @param recipientId the ID of the user who receives the {@link Message}
+	 * @param recipientID the ID of the user who receives the {@link Message}
 	 * @param messageId   the ID of the {@link Message}
 	 * @since Envoy Common v0.2-alpha
 	 */
-	public MessageBuilder(long senderId, long recipientId, long messageId) {
+	public MessageBuilder(long senderID, long recipientID, long messageId) {
-		this.senderId		= senderId;
+		this.senderID		= senderID;
-		this.recipientId	= recipientId;
+		this.recipientID	= recipientID;
 		id					= messageId;
 	}
 
@@ -60,13 +62,13 @@ public class MessageBuilder {
 	 * This makes it especially useful in the case of forwarding messages.
 	 *
 	 * @param msg         the message to copy
-	 * @param recipientId the ID of the user who receives the {@link Message}
+	 * @param recipientID the ID of the user who receives the {@link Message}
-	 * @param idGenerator the ID generator used to generate a unique {@link Message}
+	 * @param iDGenerator the ID generator used to generate a unique {@link Message}
 	 *                    id
 	 * @since Envoy v0.1-beta
 	 */
-	public MessageBuilder(Message msg, long recipientId, IdGenerator idGenerator) {
+	public MessageBuilder(Message msg, long recipientID, IDGenerator iDGenerator) {
-		this(msg.getRecipientId(), recipientId, idGenerator.next());
+		this(msg.getRecipientID(), recipientID, iDGenerator.next());
 		this.attachment		= msg.getAttachment();
 		this.creationDate	= new Date();
 		this.forwarded		= true;
@@ -97,12 +99,71 @@ public class MessageBuilder {
 	 * @since Envoy Common v0.2-alpha
 	 */
 	public Message build() {
-		// Supplement default values
+		supplyDefaults();
+		return new Message(id, senderID, recipientID, creationDate, text, attachment, status, forwarded);
+	}
+
+	/**
+	 * Creates an instance of {@link GroupMessage} with the previously supplied
+	 * values. <br>
+	 * <b> Sets all member statuses to {@link MessageStatus#WAITING}.</b><br>
+	 * If a mandatory value is not set, a default value will be used
+	 * instead:<br>
+	 * <br>
+	 * <table border="1">
+	 * <tr>
+	 * <td>{@code date}</td>
+	 * <td>{@code new Date()}</td>
+	 * <tr>
+	 * <tr>
+	 * <td>{@code text}</td>
+	 * <td>{@code ""}</td>
+	 * <tr>
+	 * </table>
+	 *
+	 * @param group the {@link Group} that is used to fill the map of member
+	 *              statuses
+	 * @return a new instance of {@link GroupMessage}
+	 * @since Envoy Common v0.2-alpha
+	 */
+	public GroupMessage buildGroupMessage(Group group) {
+		var memberStatuses = new HashMap<Long, Message.MessageStatus>();
+		group.getContacts().forEach(user -> memberStatuses.put(user.getID(), MessageStatus.WAITING));
+		return buildGroupMessage(group, memberStatuses);
+	}
+
+	/**
+	 * Creates an instance of {@link GroupMessage} with the previously supplied
+	 * values. If a mandatory value is not set, a default value will be used
+	 * instead:<br>
+	 * <br>
+	 * <table border="1">
+	 * <tr>
+	 * <td>{@code date}</td>
+	 * <td>{@code new Date()}</td>
+	 * <tr>
+	 * <tr>
+	 * <td>{@code text}</td>
+	 * <td>{@code ""}</td>
+	 * <tr>
+	 * </table>
+	 *
+	 * @param group          the {@link Group} that is used to fill the map of
+	 *                       member statuses
+	 * @param memberStatuses the map of all current statuses
+	 * @return a new instance of {@link GroupMessage}
+	 * @since Envoy Common v0.1-beta
+	 */
+	public GroupMessage buildGroupMessage(Group group, Map<Long, MessageStatus> memberStatuses) {
+		if (group == null || memberStatuses == null) throw new NullPointerException();
+		supplyDefaults();
+		return new GroupMessage(id, senderID, recipientID, creationDate, text, attachment, status, forwarded, memberStatuses);
+	}
+
+	private void supplyDefaults() {
 		if (creationDate == null) creationDate = new Date();
 		if (text == null) text = "";
 		if (status == null) status = MessageStatus.WAITING;
-
-		return new Message(id, senderId, recipientId, creationDate, text, attachment, status, forwarded);
 	}
 
 	/**

src/main/java/envoy/data/User.java

@@ -1,6 +1,9 @@
 package envoy.data;
 
-import java.io.Serializable;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.util.HashSet;
+import java.util.Set;
 
 /**
  * Represents a unique user with a unique, numeric ID, a name and a current
@@ -13,7 +16,16 @@ import java.io.Serializable;
  * @author Kai S. K. Engelbart
  * @since Envoy Common v0.2-alpha
  */
-public class User implements Serializable {
+public final class User extends Contact {
+
+	private UserStatus status;
+
+	/**
+	 * Used to serialize contact list to a maximum depth of one.
+	 */
+	private transient boolean serializeContacts = true;
+
+	private static final long serialVersionUID = 1L;
 
 	/**
 	 * This enumeration defines all possible statuses a user can have.
@@ -44,54 +56,50 @@ public class User implements Serializable {
 		OFFLINE;
 	}
 
-	private final long		id;
-	private final String	name;
-
-	private UserStatus status;
-
-	private static final long serialVersionUID = 3530947374856708236L;
-
 	/**
-	 * Initializes a {@link User}. The {@link UserStatus} is set to
+	 * Initializes a {@link User}. <br>
-	 * {@link UserStatus#ONLINE}.
+	 * The {@link UserStatus} is set to {@link UserStatus#ONLINE}.
+	 * No contacts are initialized.
 	 *
 	 * @param id   unique ID
 	 * @param name user name
 	 * @since Envoy Common v0.2-alpha
 	 */
 	public User(long id, String name) {
-		this.id		= id;
+		super(id, name, new HashSet<>());
-		this.name	= name;
+		status = UserStatus.ONLINE;
-		status		= UserStatus.ONLINE;
+	}
+
+	/**
+	 * Initializes a {@link User}. <br>
+	 * The {@link UserStatus} is set to {@link UserStatus#ONLINE}.
+	 *
+	 * @param id       unique ID
+	 * @param name     user name
+	 * @param contacts the contacts of this user
+	 * @since Envoy Common v0.2-alpha
+	 */
+	public User(long id, String name, Set<Contact> contacts) {
+		super(id, name, contacts);
+		status = UserStatus.ONLINE;
 	}
 
 	/**
 	 * Initializes a {@link User}.
 	 *
-	 * @param id     unique ID
+	 * @param id       unique ID
-	 * @param name   user name
+	 * @param name     user name
-	 * @param status the status of the user
+	 * @param status   the status of this user
+	 * @param contacts the contacts of this user
 	 * @since Envoy Common v0.2-alpha
 	 */
-	public User(long id, String name, UserStatus status) {
+	public User(long id, String name, UserStatus status, Set<Contact> contacts) {
-		this(id, name);
+		super(id, name, contacts);
 		this.status = status;
 	}
 
 	@Override
-	public String toString() { return String.format("User[id=%d,name=%s,status=%s]", id, name, status); }
+	public String toString() { return String.format("User[id=%d,name=%s,status=%s,contacts=%s]", getID(), getName(), status, getContacts()); }
-
-	/**
-	 * @return the ID of this {@link User}
-	 * @since Envoy Common v0.2-alpha
-	 */
-	public long getId() { return id; }
-
-	/**
-	 * @return the name of this {@link User}
-	 * @since Envoy Common v0.2-alpha
-	 */
-	public String getName() { return name; }
 
 	/**
 	 * @return the current status of this user
@@ -104,4 +112,26 @@ public class User implements Serializable {
 	 * @since Envoy Common v0.2-alpha
 	 */
 	public void setStatus(UserStatus status) { this.status = status; }
+
+	private void readObject(ObjectInputStream inputStream) throws Exception {
+		inputStream.defaultReadObject();
+		var contacts = Contact.class.getDeclaredField("contacts");
+		contacts.setAccessible(true);
+		contacts.set(this, inputStream.readObject());
+	}
+
+	private void writeObject(ObjectOutputStream outputStream) throws Exception {
+		outputStream.defaultWriteObject();
+		if (serializeContacts) {
+			getContacts().stream().filter(User.class::isInstance).map(User.class::cast).forEach(user -> user.serializeContacts = false);
+			outputStream.writeObject(getContacts());
+		} else outputStream.writeObject(new HashSet<>());
+	}
+
+	/**
+	 * @param serializeContacts whether the contacts of this {@link User} should be
+	 *                          serialized
+	 * @since Envoy Common v0.1-beta
+	 */
+	public void serializeContacts(boolean serializeContacts) { this.serializeContacts = serializeContacts; }
 }

src/main/java/envoy/event/ContactOperationEvent.java

@@ -1,61 +0,0 @@
-package envoy.event;
-
-import envoy.data.User;
-
-/**
- * Signifies the modification of a contact list.<br>
- * <br>
- * Project: <strong>envoy-common</strong><br>
- * File: <strong>ContactOperationEvent.java</strong><br>
- * Created: <strong>05.02.2020</strong><br>
- *
- * @author Maximilian K&auml;fer
- * @since Envoy Common v0.2-alpha
- */
-public class ContactOperationEvent extends Event<User> {
-
-	/**
-	 * Specifies the operation performed on a contact list.<br>
-	 * <br>
-	 * Project: <strong>envoy-common</strong><br>
-	 * File: <strong>ContactOperationEvent.java</strong><br>
-	 * Created: <strong>05.02.2020</strong><br>
-	 *
-	 * @author Maximilian K&auml;fer
-	 * @since Envoy Common v0.2-alpha
-	 */
-	public enum Operation {
-
-		/**
-		 * Adds a user to the contact list.
-		 */
-		ADD,
-
-		/**
-		 * Removes a user from the contact list.
-		 */
-		REMOVE;
-	}
-
-	private final Operation operationType;
-
-	private static final long serialVersionUID = -1166652868189511553L;
-
-	/**
-	 * Initializes a {@link ContactOperationEvent}.
-	 *
-	 * @param contact       the user on which the operation is performed
-	 * @param operationType the type of operation to perform
-	 * @since Envoy Common v0.2-alpha
-	 */
-	public ContactOperationEvent(User contact, Operation operationType) {
-		super(contact);
-		this.operationType = operationType;
-	}
-
-	/**
-	 * @return the type of operation to perform
-	 * @since Envoy Common v0.2-alpha
-	 */
-	public Operation getOperationType() { return operationType; }
-}

src/main/java/envoy/event/ElementOperation.java

@@ -0,0 +1,28 @@
+package envoy.event;
+
+/**
+ * This enum declares all modification possibilities for a given container.<br>
+ * These can be: {@link ElementOperation#ADD} or
+ * {@link ElementOperation#REMOVE}.<br>
+ * <br>
+ * Project: <strong>envoy-common</strong><br>
+ * File: <strong>ElementOperation.java</strong><br>
+ * Created: <strong>25 Mar 2020</strong><br>
+ *
+ * @author Leon Hofmeister
+ * @since Envoy Common v0.1-beta
+ */
+public enum ElementOperation {
+
+	/**
+	 * Select this element, if the given element should be added to the given
+	 * container.
+	 */
+	ADD,
+
+	/**
+	 * Select this element, if the given element should be removed from the given
+	 * container.
+	 */
+	REMOVE
+}

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

@@ -15,7 +15,7 @@ public abstract class Event<T> implements Serializable {
 
 	protected final T value;
 
-	private static final long serialVersionUID = 4673659457380399167L;
+	private static final long serialVersionUID = 0L;
 
 	protected Event(T value) { this.value = value; }
 
@@ -39,7 +39,7 @@ public abstract class Event<T> implements Serializable {
 	 */
 	public static abstract class Valueless extends Event<Void> {
 
-		private static final long serialVersionUID = -9019362144094097997L;
+		private static final long serialVersionUID = 0L;
 
 		protected Valueless() { super(null); }
 

src/main/java/envoy/event/GroupCreationEvent.java

@@ -0,0 +1,42 @@
+package envoy.event;
+
+import java.util.HashSet;
+import java.util.Set;
+
+import envoy.data.User;
+
+/**
+ * This event creates a group with the given name.<br>
+ * <br>
+ * Project: <strong>envoy-common</strong><br>
+ * File: <strong>GroupCreationEvent.java</strong><br>
+ * Created: <strong>25 Mar 2020</strong><br>
+ *
+ * @author Leon Hofmeister
+ * @since Envoy Common v0.1-beta
+ */
+public class GroupCreationEvent extends Event<String> {
+
+	private final Set<Long> initialMemberIDs;
+
+	private static final long serialVersionUID = 0L;
+
+	/**
+	 * @param value            the name of this group at creation time
+	 * @param initialMemberIDs the IDs of all {@link User}s that should be group
+	 *                         members from the beginning on (excluding the creator
+	 *                         of this group)
+	 * @since Envoy Common v0.1-beta
+	 */
+	public GroupCreationEvent(String value, Set<Long> initialMemberIDs) {
+		super(value);
+		this.initialMemberIDs = (initialMemberIDs != null) ? initialMemberIDs : new HashSet<>();
+	}
+
+	/**
+	 * @return the IDs of all {@link User}s that are members from the beginning
+	 *         (excluding the creator of this group)
+	 * @since Envoy Common v0.1-beta
+	 */
+	public Set<Long> getInitialMemberIDs() { return initialMemberIDs; }
+}

src/main/java/envoy/event/GroupMessageStatusChangeEvent.java

@@ -0,0 +1,46 @@
+package envoy.event;
+
+import java.util.Date;
+
+import envoy.data.GroupMessage;
+import envoy.data.Message.MessageStatus;
+
+/**
+ * Project: <strong>envoy-common</strong><br>
+ * File: <strong>GroupMessageStatusChangeEvent.java</strong><br>
+ * Created: <strong>18.04.2020</strong><br>
+ * 
+ * @author Maximilian K&auml;fer
+ * @since Envoy Common v0.1-beta
+ */
+public class GroupMessageStatusChangeEvent extends MessageStatusChangeEvent {
+
+	private final long memberID;
+
+	private static final long serialVersionUID = 0L;
+
+	/**
+	 * Initializes a {@link GroupMessageStatusChangeEvent}.
+	 * 
+	 * @param id       the ID of the {@link GroupMessage} this event is related to
+	 * @param status   the status of this specific members {@link GroupMessage}
+	 * @param date     the date at which the MessageStatus change occurred for
+	 *                 this specific member
+	 * @param memberID the ID of the group member that caused the status change
+	 * @since Envoy Common v0.1-beta
+	 */
+	public GroupMessageStatusChangeEvent(long id, MessageStatus status, Date date, long memberID) {
+		super(id, status, date);
+		this.memberID = memberID;
+	}
+
+	/**
+	 * @return the memberID which the user who sends this event has
+	 * @since Envoy Common v0.1-beta
+	 */
+	public long getMemberID() { return memberID; }
+
+	@Override
+	public String toString() { return String.format("GroupMessageStatusChangeEvent[meta=%s,memberID=%d]", super.toString(), memberID); }
+
+}

src/main/java/envoy/event/GroupResizeEvent.java

@@ -0,0 +1,65 @@
+package envoy.event;
+
+import envoy.data.Contact;
+import envoy.data.Group;
+import envoy.data.User;
+
+/**
+ * This event is used to communicate changes in the group size between client
+ * and server.<br>
+ * Possible actions are adding or removing certain {@link User}s to or from a
+ * certain {@link Group}.
+ * <br>
+ * Project: <strong>envoy-common</strong><br>
+ * File: <strong>GroupResizeEvent.java</strong><br>
+ * Created: <strong>25 Mar 2020</strong><br>
+ *
+ * @author Leon Hofmeister
+ * @since Envoy Common v0.1-beta
+ */
+public class GroupResizeEvent extends Event<User> {
+
+	private final long				groupID;
+	private final ElementOperation	operation;
+
+	private static final long serialVersionUID = 0L;
+
+	/**
+	 * Initializes a {@link GroupResizeEvent} through a Contact where the name has
+	 * already been set.
+	 *
+	 * @param user      the {@link User} who wants to join or leave a group
+	 * @param group     the {@link Group} he wants to join or leave
+	 * @param operation describes what to do with the given user:<br>
+	 *                  add him to this group or remove him from it
+	 * @since Envoy Common v0.2-alpha
+	 */
+	public GroupResizeEvent(User user, Group group, ElementOperation operation) {
+		super(user);
+		if (group.getContacts().contains(user)) {
+			if (operation.equals(ElementOperation.ADD)) throw new IllegalArgumentException(
+					"Cannot add " + user + " to group " + group.getID() + " because he is already a member of this group");
+		} else if (operation.equals(ElementOperation.REMOVE))
+			throw new IllegalArgumentException("Cannot remove " + user + " from group " + group.getID() + " because he is no part of this group");
+		groupID			= group.getID();
+		this.operation	= operation;
+	}
+
+	/**
+	 * @return the ID of the {@link Contact} this event is related to
+	 * @since Envoy Common v0.2-alpha
+	 */
+	public long getGroupID() { return groupID; }
+
+	/**
+	 * @return the operationType
+	 * @since Envoy Common v0.1-beta
+	 */
+	public ElementOperation getOperation() { return operation; }
+
+	/**
+	 * {@inheritDoc}
+	 */
+	@Override
+	public String toString() { return String.format("GroupResizeEvent[userid=%d,groupid=%d,operation=%s]", get(), groupID, operation); }
+}

src/main/java/envoy/event/HandshakeRejectionEvent.java

@@ -1,7 +1,5 @@
 package envoy.event;
 
-import envoy.data.LoginCredentials;
-
 /**
  * Signifies to the client that the handshake failed for the attached
  * reason.<br>
@@ -16,35 +14,16 @@ import envoy.data.LoginCredentials;
 public class HandshakeRejectionEvent extends Event<String> {
 
 	/**
-	 * Select this value if a given password hash was incorrect
+	 * Select this value if a given password hash or user was incorrect.
 	 */
-	public static final String WRONG_PASSWORD = "an incorrect password was entered";
+	public static final String WRONG_PASSWORD_OR_USER = "Incorrect user name or password.";
 
 	/**
-	 * Select this value if a given {@link LoginCredentials} pointed at a client who
+	 * Select this value if the handshake could not be completed for some reason.
-	 * is already online
 	 */
-	public static final String ALREADY_ONLINE = "user is already online";
+	public static final String INTERNAL_ERROR = "An internal error occured.";
 
-	/**
+	private static final long serialVersionUID = 0L;
-	 * Select this value if a given {@link LoginCredentials} pointed at a client who
-	 * does not exist
-	 */
-	public static final String USER_DOES_NOT_EXIST = "user does not exist";
-
-	/**
-	 * Select this value if a given {@link LoginCredentials} with
-	 * {@link LoginCredentials#isRegistration()}==true points at an already existing
-	 * user
-	 */
-	public static final String USER_EXISTS_ALREADY = "user can not be created as he already exists";
-
-	/**
-	 * Select this value if an unknown error occurred
-	 */
-	public static final String UNKNOWN_REASON = "cause of failure is unknown";
-
-	private static final long serialVersionUID = -8723270093452609197L;
 
 	/**
 	 * Creates an instance of {@link HandshakeRejectionEvent} with an empty reason.

src/main/java/envoy/event/IDGeneratorRequest.java

@@ -2,16 +2,16 @@ package envoy.event;
 
 /**
  * Signifies to the server that the client needs a new
- * {@link envoy.data.IdGenerator} instance.<br>
+ * {@link envoy.data.IDGenerator} instance.<br>
  * <br>
  * Project: <strong>envoy-common</strong><br>
- * File: <strong>IdGeneratorRequest.java</strong><br>
+ * File: <strong>IDGeneratorRequest.java</strong><br>
  * Created: <strong>28 Jan 2020</strong><br>
  *
  * @author Kai S. K. Engelbart
  * @since Envoy Common v0.3-alpha
  */
-public class IdGeneratorRequest extends Event.Valueless {
+public class IDGeneratorRequest extends Event.Valueless {
 
 	private static final long serialVersionUID = 1431107413883364583L;
 }

src/main/java/envoy/event/MessageStatusChangeEvent.java

@@ -14,10 +14,10 @@ import envoy.data.Message;
  */
 public class MessageStatusChangeEvent extends Event<Message.MessageStatus> {
 
-	private final long					id;
+	private final long	id;
-	private final Date					date;
+	private final Date	date;
 
-	private static final long serialVersionUID = 4566145392192761313L;
+	private static final long serialVersionUID = 0L;
 
 	/**
 	 * Initializes a {@link MessageStatusChangeEvent}.
@@ -40,13 +40,13 @@ public class MessageStatusChangeEvent extends Event<Message.MessageStatus> {
 	 * @param message the message from which to build the event
 	 * @since Envoy Common v0.2-alpha
 	 */
-	public MessageStatusChangeEvent(Message message) { this(message.getId(), message.getStatus(), new Date()); }
+	public MessageStatusChangeEvent(Message message) { this(message.getID(), message.getStatus(), new Date()); }
 
 	/**
 	 * @return the ID of the {@link Message} this event is related to
 	 * @since Envoy Common v0.2-alpha
 	 */
-	public long getId() { return id; }
+	public long getID() { return id; }
 
 	/**
 	 * @return the date at which the status change occurred

src/main/java/envoy/event/NameChangeEvent.java

@@ -0,0 +1,52 @@
+package envoy.event;
+
+import envoy.data.Contact;
+
+/**
+ * This event informs<br>
+ * a) the server of the name change of a user or a group.
+ * b) another user of this users name change.
+ *
+ * Project: <strong>envoy-common</strong><br>
+ * File: <strong>NameChangeEvent.java</strong><br>
+ * Created: <strong>25 Mar 2020</strong><br>
+ *
+ * @author Leon Hofmeister
+ * @since Envoy Common v0.1-beta
+ */
+public class NameChangeEvent extends Event<String> {
+
+	private final long id;
+
+	private static final long	serialVersionUID	= 0L;
+
+	/**
+	 * Creates a new {@link NameChangeEvent} for a user or a group.
+	 *
+	 * @param contactID the id of the {@link Contact} who wishes to change his name
+	 * @param newName   the new name of this contact
+	 * @since Envoy Common v0.1-beta
+	 */
+	public NameChangeEvent(long contactID, String newName) {
+		super(newName);
+		id = contactID;
+	}
+
+	/**
+	 * Initializes a {@link NameChangeEvent} through a Contact where the name has
+	 * already been set.
+	 *
+	 * @param contact the contact whose name was updated
+	 * @since Envoy Common v0.2-alpha
+	 */
+	public NameChangeEvent(Contact contact) { this(contact.getID(), contact.getName()); }
+
+	/**
+	 * @return the ID of the {@link Contact} this event is related to
+	 * @since Envoy Common v0.2-alpha
+	 */
+	public long getID() { return id; }
+
+	@Override
+	public String toString() { return String.format("NameChangeEvent[id=%d,name=%s]", id, value); }
+}

src/main/java/envoy/event/UserStatusChangeEvent.java

@@ -15,7 +15,7 @@ public class UserStatusChangeEvent extends Event<UserStatus> {
 
 	private final long id;
 
-	private static final long serialVersionUID = 4566145392192761313L;
+	private static final long serialVersionUID = 0L;
 
 	/**
 	 * Initializes a {@link UserStatusChangeEvent}.
@@ -36,13 +36,13 @@ public class UserStatusChangeEvent extends Event<UserStatus> {
 	 * @param user the User from which to build the event
 	 * @since Envoy Common v0.2-alpha
 	 */
-	public UserStatusChangeEvent(User user) { this(user.getId(), user.getStatus()); }
+	public UserStatusChangeEvent(User user) { this(user.getID(), user.getStatus()); }
 
 	/**
 	 * @return the ID of the {@link User} this event is related to
 	 * @since Envoy Common v0.2-alpha
 	 */
-	public long getId() { return id; }
+	public long getID() { return id; }
 
 	@Override
 	public String toString() { return String.format("UserStatusChangeEvent[id=%d,status=%s]", id, value); }

src/main/java/envoy/event/contact/ContactOperationEvent.java

@@ -0,0 +1,40 @@
+package envoy.event.contact;
+
+import envoy.data.Contact;
+import envoy.event.ElementOperation;
+import envoy.event.Event;
+
+/**
+ * Signifies the modification of a contact list.<br>
+ * <br>
+ * Project: <strong>envoy-common</strong><br>
+ * File: <strong>ContactOperationEvent.java</strong><br>
+ * Created: <strong>05.02.2020</strong><br>
+ *
+ * @author Maximilian K&auml;fer
+ * @since Envoy Common v0.2-alpha
+ */
+public class ContactOperationEvent extends Event<Contact> {
+
+	private final ElementOperation operationType;
+
+	private static final long serialVersionUID = 1L;
+
+	/**
+	 * Initializes a {@link ContactOperationEvent}.
+	 *
+	 * @param contact       the user on which the operation is performed
+	 * @param operationType the type of operation to perform
+	 * @since Envoy Common v0.2-alpha
+	 */
+	public ContactOperationEvent(Contact contact, ElementOperation operationType) {
+		super(contact);
+		this.operationType = operationType;
+	}
+
+	/**
+	 * @return the type of operation to perform
+	 * @since Envoy Common v0.2-alpha
+	 */
+	public ElementOperation getOperationType() { return operationType; }
+}

src/main/java/envoy/event/contact/ContactSearchRequest.java

@@ -1,4 +1,6 @@
-package envoy.event;
+package envoy.event.contact;
+
+import envoy.event.Event;
 
 /**
  * Requests a contact search from the server.<br>
@@ -12,7 +14,7 @@ package envoy.event;
  */
 public class ContactSearchRequest extends Event<String> {
 
-	private static final long serialVersionUID = -7969312055630533627L;
+	private static final long serialVersionUID = 0L;
 
 	/**
 	 * Initializes a {@link ContactSearchRequest}.

src/main/java/envoy/event/contact/ContactSearchResult.java

@@ -1,11 +1,12 @@
-package envoy.event;
+package envoy.event.contact;
 
 import java.util.List;
 
-import envoy.data.User;
+import envoy.data.Contact;
+import envoy.event.Event;
 
 /**
- * Contains a list of {@link User}s for which a search was performed.<br>
+ * Contains a list of {@link Contact}s for which a search was performed.<br>
  * <br>
  * Project: <strong>envoy-common</strong><br>
  * File: <strong>ContactSearchResult.java</strong><br>
@@ -14,9 +15,9 @@ import envoy.data.User;
  * @author Kai S. K. Engelbart
  * @since Envoy Common v0.2-alpha
  */
-public class ContactSearchResult extends Event<List<User>> {
+public class ContactSearchResult extends Event<List<Contact>> {
 
-	private static final long serialVersionUID = -8934154116102031561L;
+	private static final long serialVersionUID = 0L;
 
 	/**
 	 * Creates an instance of {@link ContactSearchResult}.
@@ -24,5 +25,5 @@ public class ContactSearchResult extends Event<List<User>> {
 	 * @param users the users found during the search
 	 * @since Envoy Common v0.2-alpha
 	 */
-	public ContactSearchResult(List<User> users) { super(users); }
+	public ContactSearchResult(List<Contact> users) { super(users); }
 }

src/main/java/envoy/event/contact/package-info.java

@@ -0,0 +1,13 @@
+/**
+ * This package contains all contact-related events.<br>
+ * <br>
+ * Project: <strong>envoy-common</strong><br>
+ * File: <strong>package-info.java</strong><br>
+ * Created: <strong>28 Mar 2020</strong><br>
+ *
+ * @author Leon Hofmeister
+ * @author Maximilian K&auml;fer
+ * @author Kai S.K. Engelbart
+ * @since Envoy Common v0.1-beta
+ */
+package envoy.event.contact;

src/main/java/envoy/util/EnvoyLog.java

@@ -60,7 +60,14 @@ public class EnvoyLog {
 		} catch (SecurityException | IOException e) {
 			e.printStackTrace();
 		}
-		consoleHandler = new StreamHandler(System.out, formatter);
+		consoleHandler = new StreamHandler(System.out, formatter) {
+
+			@Override
+			public synchronized void publish(LogRecord record) {
+				super.publish(record);
+				flush();
+			}
+		};
 		consoleHandler.setLevel((Level) config.get("consoleLevelBarrier").get());
 		consoleHandler.setFormatter(formatter);
 

src/main/java/module-info.java

@@ -5,7 +5,7 @@
  * @author Leon Hofmeister
  * @author Maximilian Käfer
  * @author Kai S.K. Engelbart
- * @since Envoy common v0.1-beta
+ * @since Envoy Common v0.1-beta
  */
 module envoy.common {
 
@@ -13,6 +13,7 @@ module envoy.common {
 	exports envoy.util;
 	exports envoy.exception;
 	exports envoy.event;
+	exports envoy.event.contact;
 
 	requires transitive java.logging;
 }

src/test/java/envoy/data/UserTest.java

@@ -0,0 +1,34 @@
+package envoy.data;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.io.IOException;
+import java.util.Set;
+
+import org.junit.jupiter.api.Test;
+
+import envoy.data.User.UserStatus;
+import envoy.util.SerializationUtils;
+
+/**
+ * Project: <strong>envoy-common</strong><br>
+ * File: <strong>UserTest.java</strong><br>
+ * Created: <strong>31 Mar 2020</strong><br>
+ *
+ * @author Leon Hofmeister
+ * @since Envoy Common v0.1-beta
+ */
+class UserTest {
+
+	@Test
+	void test() throws IOException, ClassNotFoundException {
+		User	user2				= new User(2, "kai");
+		User	user3				= new User(3, "ai");
+		User	user4				= new User(4, "ki", Set.of(user2, user3));
+		User	user5				= new User(5, "ka", Set.of(user2, user3, user4));
+		User	user				= new User(1, "maxi", UserStatus.AWAY, Set.of(user2, user3, user4, user5));
+		var		serializedUser		= SerializationUtils.writeToByteArray(user);
+		var		deserializedUser	= SerializationUtils.read(serializedUser, User.class);
+		assertEquals(user.getContacts(), deserializedUser.getContacts());
+	}
+}