diff --git a/.gitignore b/.gitignore
new file mode 100644
index 000000000..f925abfd9
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,45 @@
+.gradle
+build/
+!gradle/wrapper/gradle-wrapper.jar
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+### IntelliJ IDEA ###
+.idea/modules.xml
+.idea/jarRepositories.xml
+.idea/compiler.xml
+.idea/libraries/
+*.iws
+*.iml
+*.ipr
+out/
+!**/src/main/**/out/
+!**/src/test/**/out/
+
+### Eclipse ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+bin/
+!**/src/main/**/bin/
+!**/src/test/**/bin/
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+
+### VS Code ###
+.vscode/
+
+### Mac OS ###
+.DS_Store
+
+### .gitignore에 IntelliJ와 관련된 파일이 형상관리 되지 않도록 .idea디렉토리를 추가 ###
+.idea
\ No newline at end of file
diff --git a/build.gradle b/build.gradle
new file mode 100644
index 000000000..668101a29
--- /dev/null
+++ b/build.gradle
@@ -0,0 +1,19 @@
+plugins {
+    id 'java'
+}
+
+group = 'com.sprint.mission'
+version = '1.0-SNAPSHOT'
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    testImplementation platform('org.junit:junit-bom:5.10.0')
+    testImplementation 'org.junit.jupiter:junit-jupiter'
+}
+
+test {
+    useJUnitPlatform()
+}
\ No newline at end of file
diff --git a/gradle/wrapper/gradle-wrapper.jar b/gradle/wrapper/gradle-wrapper.jar
new file mode 100644
index 000000000..249e5832f
Binary files /dev/null and b/gradle/wrapper/gradle-wrapper.jar differ
diff --git a/gradle/wrapper/gradle-wrapper.properties b/gradle/wrapper/gradle-wrapper.properties
new file mode 100644
index 000000000..5772038e4
--- /dev/null
+++ b/gradle/wrapper/gradle-wrapper.properties
@@ -0,0 +1,6 @@
+#Tue Jun 03 09:07:44 KST 2025
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-8.8-bin.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
diff --git a/gradlew b/gradlew
new file mode 100644
index 000000000..1b6c78733
--- /dev/null
+++ b/gradlew
@@ -0,0 +1,234 @@
+#!/bin/sh
+
+#
+# Copyright © 2015-2021 the original authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+##############################################################################
+#
+#   Gradle start up script for POSIX generated by Gradle.
+#
+#   Important for running:
+#
+#   (1) You need a POSIX-compliant shell to run this script. If your /bin/sh is
+#       noncompliant, but you have some other compliant shell such as ksh or
+#       bash, then to run this script, type that shell name before the whole
+#       command line, like:
+#
+#           ksh Gradle
+#
+#       Busybox and similar reduced shells will NOT work, because this script
+#       requires all of these POSIX shell features:
+#         * functions;
+#         * expansions «$var», «${var}», «${var:-default}», «${var+SET}»,
+#           «${var#prefix}», «${var%suffix}», and «$( cmd )»;
+#         * compound commands having a testable exit status, especially «case»;
+#         * various built-in commands including «command», «set», and «ulimit».
+#
+#   Important for patching:
+#
+#   (2) This script targets any POSIX shell, so it avoids extensions provided
+#       by Bash, Ksh, etc; in particular arrays are avoided.
+#
+#       The "traditional" practice of packing multiple parameters into a
+#       space-separated string is a well documented source of bugs and security
+#       problems, so this is (mostly) avoided, by progressively accumulating
+#       options in "$@", and eventually passing that to Java.
+#
+#       Where the inherited environment variables (DEFAULT_JVM_OPTS, JAVA_OPTS,
+#       and GRADLE_OPTS) rely on word-splitting, this is performed explicitly;
+#       see the in-line comments for details.
+#
+#       There are tweaks for specific operating systems such as AIX, CygWin,
+#       Darwin, MinGW, and NonStop.
+#
+#   (3) This script is generated from the Groovy template
+#       https://github.com/gradle/gradle/blob/master/subprojects/plugins/src/main/resources/org/gradle/api/internal/plugins/unixStartScript.txt
+#       within the Gradle project.
+#
+#       You can find Gradle at https://github.com/gradle/gradle/.
+#
+##############################################################################
+
+# Attempt to set APP_HOME
+
+# Resolve links: $0 may be a link
+app_path=$0
+
+# Need this for daisy-chained symlinks.
+while
+    APP_HOME=${app_path%"${app_path##*/}"}  # leaves a trailing /; empty if no leading path
+    [ -h "$app_path" ]
+do
+    ls=$( ls -ld "$app_path" )
+    link=${ls#*' -> '}
+    case $link in             #(
+      /*)   app_path=$link ;; #(
+      *)    app_path=$APP_HOME$link ;;
+    esac
+done
+
+APP_HOME=$( cd "${APP_HOME:-./}" && pwd -P ) || exit
+
+APP_NAME="Gradle"
+APP_BASE_NAME=${0##*/}
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m" "-Xms64m"'
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD=maximum
+
+warn () {
+    echo "$*"
+} >&2
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+} >&2
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "$( uname )" in                #(
+  CYGWIN* )         cygwin=true  ;; #(
+  Darwin* )         darwin=true  ;; #(
+  MSYS* | MINGW* )  msys=true    ;; #(
+  NONSTOP* )        nonstop=true ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD=$JAVA_HOME/jre/sh/java
+    else
+        JAVACMD=$JAVA_HOME/bin/java
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD=java
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if ! "$cygwin" && ! "$darwin" && ! "$nonstop" ; then
+    case $MAX_FD in #(
+      max*)
+        MAX_FD=$( ulimit -H -n ) ||
+            warn "Could not query maximum file descriptor limit"
+    esac
+    case $MAX_FD in  #(
+      '' | soft) :;; #(
+      *)
+        ulimit -n "$MAX_FD" ||
+            warn "Could not set maximum file descriptor limit to $MAX_FD"
+    esac
+fi
+
+# Collect all arguments for the java command, stacking in reverse order:
+#   * args from the command line
+#   * the main class name
+#   * -classpath
+#   * -D...appname settings
+#   * --module-path (only if needed)
+#   * DEFAULT_JVM_OPTS, JAVA_OPTS, and GRADLE_OPTS environment variables.
+
+# For Cygwin or MSYS, switch paths to Windows format before running java
+if "$cygwin" || "$msys" ; then
+    APP_HOME=$( cygpath --path --mixed "$APP_HOME" )
+    CLASSPATH=$( cygpath --path --mixed "$CLASSPATH" )
+
+    JAVACMD=$( cygpath --unix "$JAVACMD" )
+
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    for arg do
+        if
+            case $arg in                                #(
+              -*)   false ;;                            # don't mess with options #(
+              /?*)  t=${arg#/} t=/${t%%/*}              # looks like a POSIX filepath
+                    [ -e "$t" ] ;;                      #(
+              *)    false ;;
+            esac
+        then
+            arg=$( cygpath --path --ignore --mixed "$arg" )
+        fi
+        # Roll the args list around exactly as many times as the number of
+        # args, so each arg winds up back in the position where it started, but
+        # possibly modified.
+        #
+        # NB: a `for` loop captures its iteration list before it begins, so
+        # changing the positional parameters here affects neither the number of
+        # iterations, nor the values presented in `arg`.
+        shift                   # remove old arg
+        set -- "$@" "$arg"      # push replacement arg
+    done
+fi
+
+# Collect all arguments for the java command;
+#   * $DEFAULT_JVM_OPTS, $JAVA_OPTS, and $GRADLE_OPTS can contain fragments of
+#     shell script including quotes and variable substitutions, so put them in
+#     double quotes to make sure that they get re-expanded; and
+#   * put everything else in single quotes, so that it's not re-expanded.
+
+set -- \
+        "-Dorg.gradle.appname=$APP_BASE_NAME" \
+        -classpath "$CLASSPATH" \
+        org.gradle.wrapper.GradleWrapperMain \
+        "$@"
+
+# Use "xargs" to parse quoted args.
+#
+# With -n1 it outputs one arg per line, with the quotes and backslashes removed.
+#
+# In Bash we could simply go:
+#
+#   readarray ARGS < <( xargs -n1 <<<"$var" ) &&
+#   set -- "${ARGS[@]}" "$@"
+#
+# but POSIX shell has neither arrays nor command substitution, so instead we
+# post-process each arg (as a line of input to sed) to backslash-escape any
+# character that might be a shell metacharacter, then use eval to reverse
+# that process (while maintaining the separation between arguments), and wrap
+# the whole thing up as a single "set" statement.
+#
+# This will of course break if any of these variables contains a newline or
+# an unmatched quote.
+#
+
+eval "set -- $(
+        printf '%s\n' "$DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS" |
+        xargs -n1 |
+        sed ' s~[^-[:alnum:]+,./:=@_]~\\&~g; ' |
+        tr '\n' ' '
+    )" '"$@"'
+
+exec "$JAVACMD" "$@"
diff --git a/gradlew.bat b/gradlew.bat
new file mode 100644
index 000000000..107acd32c
--- /dev/null
+++ b/gradlew.bat
@@ -0,0 +1,89 @@
+@rem
+@rem Copyright 2015 the original author or authors.
+@rem
+@rem Licensed under the Apache License, Version 2.0 (the "License");
+@rem you may not use this file except in compliance with the License.
+@rem You may obtain a copy of the License at
+@rem
+@rem      https://www.apache.org/licenses/LICENSE-2.0
+@rem
+@rem Unless required by applicable law or agreed to in writing, software
+@rem distributed under the License is distributed on an "AS IS" BASIS,
+@rem WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+@rem See the License for the specific language governing permissions and
+@rem limitations under the License.
+@rem
+
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Resolve any "." and ".." in APP_HOME to make it shorter.
+for %%i in ("%APP_HOME%") do set APP_HOME=%%~fi
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m" "-Xms64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto execute
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto execute
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %*
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega
diff --git a/settings.gradle b/settings.gradle
new file mode 100644
index 000000000..b71004546
--- /dev/null
+++ b/settings.gradle
@@ -0,0 +1,2 @@
+rootProject.name = '1-sprint-mission'
+
diff --git a/src/main/java/com/sprint/mission/Main.java b/src/main/java/com/sprint/mission/Main.java
new file mode 100644
index 000000000..8bc78a6ab
--- /dev/null
+++ b/src/main/java/com/sprint/mission/Main.java
@@ -0,0 +1,141 @@
+package com.sprint.mission;
+
+import com.sprint.mission.discodeit.entity.Channel;
+import com.sprint.mission.discodeit.entity.Message;
+import com.sprint.mission.discodeit.entity.User;
+import com.sprint.mission.discodeit.service.ChannelService;
+import com.sprint.mission.discodeit.service.MessageService;
+import com.sprint.mission.discodeit.service.UserService;
+import com.sprint.mission.discodeit.service.jcf.JCFChannelService;
+import com.sprint.mission.discodeit.service.jcf.JCFMessageService;
+import com.sprint.mission.discodeit.service.jcf.JCFUserService;
+
+import java.util.List;
+
+//TIP To <b>Run</b> code, press <shortcut actionId="Run"/> or
+// click the <icon src="AllIcons.Actions.Execute"/> icon in the gutter.
+public class Main {
+    public static void main(String[] args) {
+        try{
+            // User 관련
+            System.out.println("---------- USER ----------");
+            UserService userService = new JCFUserService();
+
+            // 등록
+            User user1 = userService.createUser("user1");
+            User user2 = userService.createUser("user2");
+            System.out.println("create user");
+            System.out.println("id: " + user1.getId() + ", name: " + user1.getUsername());
+            System.out.println("id: " + user2.getId() + ", name: " + user2.getUsername());
+
+            // 조회- 단건
+            User searchUser = userService.findUserById(user1.getId());
+            System.out.println("<search user> " + (searchUser != null ? searchUser.getUsername() : "!! null !!"));
+
+            // 조회 - 다건
+            List<User> searchUsers = userService.findAllUsers();
+            System.out.println("<search all users>");
+            for (User user : searchUsers) {
+                System.out.println(user.getUsername());
+            }
+
+            // 수정
+            userService.updateUserById(user1.getId(), "newName");
+            System.out.println("<update user name>");
+            // 수정 확인
+            List<User> afterUpdateUser = userService.findAllUsers();
+            for (User user : afterUpdateUser) {
+
+                System.out.println(user.getUsername());
+            }
+
+            // 삭제
+            userService.deleteUserById(user2.getId());
+            System.out.println("<delete user name : user2>");
+            // 삭제 확인
+            List<User> afterDeleteUser = userService.findAllUsers();
+            for (User user : afterDeleteUser) {
+                System.out.println(user.getUsername());
+            }
+
+
+            // 채널 관련
+            System.out.println("---------- CHANNEL ----------");
+            ChannelService channelService = new JCFChannelService();
+
+            // 등록
+            Channel channel1 = channelService.createChannel("channel1");
+            Channel channel2 = channelService.createChannel("channel2");
+            System.out.println("<create channel>");
+            System.out.println(channel1.getChannelName());
+            System.out.println(channel2.getChannelName());
+
+            // 단건 조회
+            Channel findChannel = channelService.findChannelById(channel1.getId());
+            System.out.println("<find one channel1 by id>");
+            System.out.println(findChannel.getChannelName());
+            // 전체 조회
+            List<Channel> findAllChannels = channelService.findAllChannels();
+            System.out.println("<find all channels>");
+            for (Channel channel : findAllChannels) {
+                System.out.println(channel.getChannelName());
+            }
+
+            // 수정
+            channelService.updateChannelById(channel1.getId(), "newName");
+            System.out.println("<update channel1 name by id>");
+            for (Channel channel : findAllChannels) {
+                System.out.println(channel.getChannelName());
+            }
+
+            // 삭제
+            channelService.deleteChannelById(channel1.getId());
+            System.out.println("<delete channel1 by id>");
+            List<Channel> afterDeleteChannel = channelService.findAllChannels();
+            for (Channel channel : afterDeleteChannel) {
+                System.out.println(channel.getChannelName());
+            }
+
+
+            // 메세지
+            System.out.println("---------- MESSAGE ----------");
+            MessageService messageService = new JCFMessageService();
+
+            // 등록
+            User sender = userService.createUser("sender");
+            Channel sendChannel = channelService.createChannel("sendChannel");
+            Message message1 = messageService.sendMessage(sender, sendChannel, "message1");
+            Message message2 = messageService.sendMessage(sender, channel2, "message2");
+
+            System.out.println("<send message>");
+            System.out.println(message1.getSender().getUsername() + " -> " + message1.getChannel().getChannelName() + ", content: " + message1.getContent());
+            System.out.println(message2.getSender().getUsername() + " -> " + message2.getChannel().getChannelName() + ", content: " + message2.getContent());
+
+            // 단건 조회
+            Message findMessage = messageService.findMessage(message1.getId());
+            System.out.println("<find one message1>");
+            System.out.println(findMessage.getSender().getUsername() + ", content: " + findMessage.getContent());
+            // 전체 조회
+            List<Message> findAllMessages = messageService.findAllMessages();
+            System.out.println("<find all messages>");
+            for (Message message : findAllMessages) {
+                System.out.println(message.getSender().getUsername() + " -> " + message.getChannel().getChannelName()+", content: " + message.getContent());
+            }
+            // 수정
+            messageService.updateMessage(message2.getId(), "new message2");
+            System.out.println("<after update message content>");
+            System.out.println(message2.getContent());
+
+            // 삭제
+            messageService.deleteMessage(message1.getId());
+            System.out.println("<after delete message>");
+            List<Message> afterDeleteMessage = messageService.findAllMessages();
+            for (Message message : afterDeleteMessage) {
+                System.out.println(message.getSender().getUsername() + " -> " + message.getChannel().getChannelName() + ", content: " + message.getContent());
+            }
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+
+    }
+}
\ No newline at end of file
diff --git a/src/main/java/com/sprint/mission/discodeit/entity/BaseEntity.java b/src/main/java/com/sprint/mission/discodeit/entity/BaseEntity.java
new file mode 100644
index 000000000..5ad51af4c
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/entity/BaseEntity.java
@@ -0,0 +1,36 @@
+package com.sprint.mission.discodeit.entity;
+
+import java.util.UUID;
+
+abstract class BaseEntity {
+    // ? 지금과 같은 상황에 BaseEntitiy를 만드나요 > yes ?
+    private UUID id;
+    private long createdAt;
+    private long updatedAt;
+
+    // 생성자
+    // final 처럼 사용하기 위해 사용
+    public BaseEntity(){
+        this.id = UUID.randomUUID();
+        this.createdAt = System.currentTimeMillis();
+        this.updatedAt = System.currentTimeMillis();
+    }
+
+    // setter && getter
+    // updatedAt 제외하고 나머지는 final이라 setter X
+    public void setUpdatedAt() {
+        this.updatedAt = System.currentTimeMillis();;
+    }
+
+    public UUID getId() {
+        return id;
+    }
+
+    public long getCreatedAt() {
+        return createdAt;
+    }
+
+    public long getUpdatedAt() {
+        return updatedAt;
+    }
+}
diff --git a/src/main/java/com/sprint/mission/discodeit/entity/Channel.java b/src/main/java/com/sprint/mission/discodeit/entity/Channel.java
new file mode 100644
index 000000000..807599efa
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/entity/Channel.java
@@ -0,0 +1,41 @@
+package com.sprint.mission.discodeit.entity;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Channel extends BaseEntity {
+    private String channelName;
+    private List<User> members = new ArrayList<>();
+    private List<Message> messages = new ArrayList<>();
+
+    // 생성자
+    public Channel(String channelName) {
+        super();
+        this.channelName = channelName;
+    }
+
+    // setter && getter
+    public String getChannelName() {
+        return channelName;
+    }
+
+    public void setChannelName(String channelName) {
+        this.channelName = channelName;
+    }
+
+    public List<User> getMembers() {
+        return members;
+    }
+
+    public void setMembers(List<User> members) {
+        this.members = members;
+    }
+
+    public List<Message> getMessages() {
+        return messages;
+    }
+
+    public void setMessages(List<Message> messages) {
+        this.messages = messages;
+    }
+}
diff --git a/src/main/java/com/sprint/mission/discodeit/entity/Message.java b/src/main/java/com/sprint/mission/discodeit/entity/Message.java
new file mode 100644
index 000000000..168b2045a
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/entity/Message.java
@@ -0,0 +1,42 @@
+package com.sprint.mission.discodeit.entity;
+
+
+
+public class Message extends BaseEntity {
+    private User sender;
+    private Channel channel;
+    private String content;
+
+    // 생성자
+    public Message(User sender, Channel channel, String content) {
+        super();
+        this.sender = sender;
+        this.channel = channel;
+        this.content = content;
+    }
+
+    // setter && getter
+    public void setContent(String content) {
+        this.content = content;
+    }
+
+    public void setSender(User sender) {
+        this.sender = sender;
+    }
+
+    public void setChannel(Channel channel) {
+        this.channel = channel;
+    }
+
+    public User getSender() {
+        return sender;
+    }
+
+    public Channel getChannel() {
+        return channel;
+    }
+
+    public String getContent() {
+        return content;
+    }
+}
diff --git a/src/main/java/com/sprint/mission/discodeit/entity/User.java b/src/main/java/com/sprint/mission/discodeit/entity/User.java
new file mode 100644
index 000000000..8de951cd3
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/entity/User.java
@@ -0,0 +1,41 @@
+package com.sprint.mission.discodeit.entity;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class User extends BaseEntity {
+    private String username;
+    private List<Channel> channels = new ArrayList<>();
+    private List<Message> messages = new ArrayList<>();
+
+    public List<Channel> getChannels() {
+        return channels;
+    }
+
+    public List<Message> getMessages() {
+        return messages;
+    }
+
+    // 생성자
+    public User(String name) {
+        super();
+        this.username = name;
+    }
+
+    // getter && setter
+    public String getUsername() {
+        return username;
+    }
+
+    public void setUsername(String username) {
+        this.username = username;
+    }
+
+    public void setChannels(List<Channel> channels) {
+        this.channels = channels;
+    }
+
+    public void setMessages(List<Message> messages) {
+        this.messages = messages;
+    }
+}
diff --git a/src/main/java/com/sprint/mission/discodeit/service/ChannelService.java b/src/main/java/com/sprint/mission/discodeit/service/ChannelService.java
new file mode 100644
index 000000000..0e1da4e67
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/service/ChannelService.java
@@ -0,0 +1,21 @@
+package com.sprint.mission.discodeit.service;
+
+import com.sprint.mission.discodeit.entity.Channel;
+
+import java.util.List;
+import java.util.UUID;
+
+public interface ChannelService {
+    // 등록
+    Channel createChannel(String name);
+
+    // 조회
+    Channel findChannelById(UUID id);
+    List<Channel> findAllChannels();
+
+    // 수정
+    Channel updateChannelById(UUID id, String newName);
+
+    // 삭제
+    Channel deleteChannelById(UUID id);
+}
diff --git a/src/main/java/com/sprint/mission/discodeit/service/MessageService.java b/src/main/java/com/sprint/mission/discodeit/service/MessageService.java
new file mode 100644
index 000000000..fb68af657
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/service/MessageService.java
@@ -0,0 +1,25 @@
+package com.sprint.mission.discodeit.service;
+
+import com.sprint.mission.discodeit.entity.Channel;
+import com.sprint.mission.discodeit.entity.Message;
+import com.sprint.mission.discodeit.entity.User;
+
+import java.util.List;
+import java.util.UUID;
+
+public interface MessageService {
+    // 등록
+    Message sendMessage(User sender, Channel channel, String content);
+
+    // 단건 조회
+    Message findMessage(UUID id);
+
+    // 다건 조회
+    List<Message> findAllMessages();
+
+    // 수정
+    Message updateMessage(UUID id, String newContent);
+
+    // 삭제
+    Message deleteMessage(UUID id);
+}
diff --git a/src/main/java/com/sprint/mission/discodeit/service/UserService.java b/src/main/java/com/sprint/mission/discodeit/service/UserService.java
new file mode 100644
index 000000000..627ef2b24
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/service/UserService.java
@@ -0,0 +1,22 @@
+package com.sprint.mission.discodeit.service;
+
+import com.sprint.mission.discodeit.entity.User;
+
+import java.util.List;
+import java.util.UUID;
+
+public interface UserService {
+    // 등록
+    User createUser(String name);
+
+    // 단건 조회
+    User findUserById(UUID id);
+    // 다건 조회
+    List<User> findAllUsers();
+
+    // 수정
+    User updateUserById(UUID id, String newName);
+
+    // 삭제
+    User deleteUserById(UUID id);
+}
diff --git a/src/main/java/com/sprint/mission/discodeit/service/jcf/JCFChannelService.java b/src/main/java/com/sprint/mission/discodeit/service/jcf/JCFChannelService.java
new file mode 100644
index 000000000..4f7eab6f1
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/service/jcf/JCFChannelService.java
@@ -0,0 +1,75 @@
+package com.sprint.mission.discodeit.service.jcf;
+
+import com.sprint.mission.discodeit.entity.Channel;
+import com.sprint.mission.discodeit.entity.Message;
+import com.sprint.mission.discodeit.entity.User;
+import com.sprint.mission.discodeit.service.ChannelService;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.UUID;
+
+public class JCFChannelService implements ChannelService {
+    private final List<Channel> data = new ArrayList<>();
+
+    // 등록
+    @Override
+    public Channel createChannel(String name) {
+        Channel channel = new Channel(name);
+        data.add(channel);
+        return channel;
+    }
+
+    // 단건 조회
+    /*@Override
+    public Channel findChannelById(UUID id) {
+        for (Channel channel : data) {
+            if (channel.getId().equals(id)) {
+                return channel;
+            }
+        }
+        return null;
+    }*/
+    // Stream 변경
+    @Override
+    public Channel findChannelById(UUID id) {
+        return data.stream()
+                .filter(channel -> channel.getId().equals(id))
+                .findFirst()
+                .orElse(null);
+    }
+
+    // 다건 조회
+    @Override
+    public List<Channel> findAllChannels() {
+        return new ArrayList<>(data);
+    }
+
+    // 수정
+    @Override
+    public Channel updateChannelById(UUID id, String newName) {
+        for (Channel channel : data) {
+            if (channel.getId().equals(id)) {
+                channel.setChannelName(newName);
+                channel.setUpdatedAt();
+                return channel;
+            }
+        }
+        return null;
+    }
+
+    // 삭제
+    @Override
+    public Channel deleteChannelById(UUID id) {
+        for (Channel channel : data) {
+            if (channel.getId().equals(id)) {
+                for (User member : channel.getMembers()) {
+                    member.getChannels().remove(channel);
+                }
+                data.remove(channel);
+                return channel;
+            }
+        }
+        return null;
+    }
+}
diff --git a/src/main/java/com/sprint/mission/discodeit/service/jcf/JCFMessageService.java b/src/main/java/com/sprint/mission/discodeit/service/jcf/JCFMessageService.java
new file mode 100644
index 000000000..4c0794e03
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/service/jcf/JCFMessageService.java
@@ -0,0 +1,83 @@
+package com.sprint.mission.discodeit.service.jcf;
+
+import com.sprint.mission.discodeit.entity.Channel;
+import com.sprint.mission.discodeit.entity.Message;
+import com.sprint.mission.discodeit.entity.User;
+import com.sprint.mission.discodeit.service.MessageService;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.UUID;
+
+public class JCFMessageService implements MessageService {
+    private final List<Message> data = new ArrayList<>();
+
+    // 등록
+    @Override
+    public Message sendMessage(User sender, Channel channel, String content) {
+        Message message = new Message(sender, channel, content);
+        data.add(message);
+        // 관계 설정
+        message.setSender(sender);
+        message.setChannel(channel);
+        // 양방향 관계
+        sender.getMessages().add(message);
+        channel.getMessages().add(message);
+        return message;
+    }
+
+    // 단건 조회
+    /*@Override
+    public Message findMessage(UUID id) {
+        for (Message message : data) {
+            if (message.getId().equals(id)) {
+                return message;
+            }
+        }
+        return null;
+    }*/
+    // Stream 변경
+    @Override
+    public Message findMessage(UUID id) {
+        return data.stream()
+                .filter(message -> message.getId().equals(id))
+                .findFirst()
+                .orElse(null);
+    }
+    // 다건 조회
+    @Override
+    public List<Message> findAllMessages() {
+        return new ArrayList<>(data);
+    }
+
+    // 수정
+    @Override
+    public Message updateMessage(UUID id, String newContent) {
+        for (Message message : data) {
+            if (message.getId().equals(id)) {
+                message.setContent(newContent);
+                message.setUpdatedAt();
+                return message;
+            }
+        }
+        return null;
+    }
+
+    // 삭제
+    @Override
+    public Message deleteMessage(UUID id) {
+        for (Message message : data) {
+            if (message.getId().equals(id)) {
+                data.remove(message);
+
+                // 양방향 해제
+                User sender = message.getSender();
+                Channel channel = message.getChannel();
+                sender.getMessages().remove(message);
+                channel.getMessages().remove(message);
+                return message;
+            }
+        }
+        return null;
+    }
+}
diff --git a/src/main/java/com/sprint/mission/discodeit/service/jcf/JCFUserService.java b/src/main/java/com/sprint/mission/discodeit/service/jcf/JCFUserService.java
new file mode 100644
index 000000000..897ca1388
--- /dev/null
+++ b/src/main/java/com/sprint/mission/discodeit/service/jcf/JCFUserService.java
@@ -0,0 +1,102 @@
+package com.sprint.mission.discodeit.service.jcf;
+
+import com.sprint.mission.discodeit.entity.Channel;
+import com.sprint.mission.discodeit.entity.User;
+import com.sprint.mission.discodeit.service.UserService;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.UUID;
+import java.util.stream.Collectors;
+
+public class JCFUserService implements UserService {
+    private final List<User> data;
+
+    public JCFUserService() {
+        data = new ArrayList<>();
+    }
+
+    // 등록
+    @Override
+    public User createUser(String name) {
+        User createUser = new User(name);
+        data.add(createUser);
+        return createUser;
+    }
+
+    // 단건 조회
+//    @Override
+//    public User findUserById(UUID id) {
+//        for (User user : data) {
+//            if (user.getId().equals(id)) {
+//                return user;
+//            }
+//        }
+//        return null;
+//    }
+    // Stream 변환
+    @Override
+    public User findUserById(UUID id) {
+        return data.stream()
+                .filter(user -> user.getId().equals(id))
+                .findFirst()
+                .orElse(null);
+    }
+
+    // 다건 조회
+    @Override
+    public List<User> findAllUsers() {
+        return new ArrayList<>(data);
+    }
+
+    // 수정
+/*    @Override
+    public User updateUserById(UUID id, String newName) {
+        for (User user : data) {
+            if (user.getId().equals(id)) {
+                user.setUsername(newName);
+                user.setUpdatedAt();
+                return user;
+            }
+        }
+        return null;
+    }*/
+    // Stream 변환
+    /*
+     * update 로직 : 찾음 > 수정 > 반환
+     * filter > findFirst로 찾고, map으로 수정
+     * 여기서 map은 중간 연산자 아니고, Optional!!
+     *
+     * +) Stream은 내부 반복자라 전체를 내부 순회하므로 update 할 요소가 많아지면 Stream 사용 권장 X
+     */
+    @Override
+    public User updateUserById(UUID id, String newName) {
+        return data.stream()
+                .filter(user -> user.getId().equals(id))
+                .findFirst()
+                .map(user -> {
+                    user.setUsername(newName);
+                    user.setUpdatedAt();
+                    return user;
+                })
+                .orElse(null);
+    }
+
+    // 삭제
+    /*
+     * delete는 Stream 사용 시 side effect 발생하므로 변경 X
+     */
+    @Override
+    public User deleteUserById(UUID id) {
+        for (User user : data) {
+            if (user.getId().equals(id)) {
+                for (Channel channel : user.getChannels()) {
+                    channel.getMembers().remove(user);
+                }
+                data.remove(user);
+                return user;
+            }
+        }
+        return null;
+    }
+}