diff --git a/.gitignore b/.gitignore
index 0296a22..7e0ef2f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -12,7 +12,6 @@
 .mtj.tmp/
 
 # Package Files #
-*.jar
 *.war
 *.nar
 *.ear
@@ -26,3 +25,5 @@ replay_pid*
 
 # Kotlin Gradle plugin data, see https://kotlinlang.org/docs/whatsnew20.html#new-directory-for-kotlin-data-in-gradle-projects
 .kotlin/
+.gradle
+.idea
diff --git a/build.gradle.kts b/build.gradle.kts
new file mode 100644
index 0000000..4d824e7
--- /dev/null
+++ b/build.gradle.kts
@@ -0,0 +1,22 @@
+plugins {
+    kotlin("jvm") version "1.9.10"
+    application
+}
+
+kotlin {
+    jvmToolchain {
+        languageVersion.set(
+            JavaLanguageVersion.of(17)
+        )
+    }
+}
+
+application {
+    mainClass.set("ProgramKt")
+
+    val isDevelopment: Boolean = project.ext.has("development")
+    applicationDefaultJvmArgs = listOf("-Dio.ktor.development=$isDevelopment")
+}
+
+dependencies {
+}
diff --git a/gradle.properties b/gradle.properties
new file mode 100644
index 0000000..5b69144
--- /dev/null
+++ b/gradle.properties
@@ -0,0 +1,12 @@
+kotlin.code.style = official
+org.gradle.caching = true
+org.gradle.parallel=true
+org.gradle.vfs.watch = true
+version = 0.0.1
+
+
+#systemProp.http.proxyHost = 10.255.255.254
+#systemProp.http.proxyPort = 10808
+#
+#systemProp.https.proxyHost = 10.255.255.254
+#systemProp.https.proxyPort = 10808
diff --git a/gradle/wrapper/gradle-wrapper.jar b/gradle/wrapper/gradle-wrapper.jar
new file mode 100644
index 0000000..955e786
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 0000000..77017c1
--- /dev/null
+++ b/gradle/wrapper/gradle-wrapper.properties
@@ -0,0 +1,5 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://mirrors.cloud.tencent.com/gradle/gradle-8.4-all.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists
diff --git a/gradlew b/gradlew
new file mode 100755
index 0000000..17a9170
--- /dev/null
+++ b/gradlew
@@ -0,0 +1,176 @@
+#!/usr/bin/env sh
+
+##############################################################################
+##
+##  Gradle start up script for UN*X
+##
+##############################################################################
+
+# Attempt to set APP_HOME
+# Resolve links: $0 may be a link
+PRG="$0"
+# Need this for relative symlinks.
+while [ -h "$PRG" ] ; do
+    ls=`ls -ld "$PRG"`
+    link=`expr "$ls" : '.*-> \(.*\)$'`
+    if expr "$link" : '/.*' > /dev/null; then
+        PRG="$link"
+    else
+        PRG=`dirname "$PRG"`"/$link"
+    fi
+done
+SAVED="`pwd`"
+cd "`dirname \"$PRG\"`/" >/dev/null
+APP_HOME="`pwd -P`"
+cd "$SAVED" >/dev/null
+
+APP_NAME="Gradle"
+APP_BASE_NAME=`basename "$0"`
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS=""
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD="maximum"
+
+warn () {
+    echo "$*"
+}
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+}
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "`uname`" in
+  CYGWIN* )
+    cygwin=true
+    ;;
+  Darwin* )
+    darwin=true
+    ;;
+  MINGW* )
+    msys=true
+    ;;
+  NONSTOP* )
+    nonstop=true
+    ;;
+esac
+
+CLASSPATH=$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" = "false" -a "$darwin" = "false" -a "$nonstop" = "false" ] ; then
+    MAX_FD_LIMIT=`ulimit -H -n`
+    if [ $? -eq 0 ] ; then
+        if [ "$MAX_FD" = "maximum" -o "$MAX_FD" = "max" ] ; then
+            MAX_FD="$MAX_FD_LIMIT"
+        fi
+        ulimit -n $MAX_FD
+        if [ $? -ne 0 ] ; then
+            warn "Could not set maximum file descriptor limit: $MAX_FD"
+        fi
+    else
+        warn "Could not query maximum file descriptor limit: $MAX_FD_LIMIT"
+    fi
+fi
+
+# For Darwin, add options to specify how the application appears in the dock
+if $darwin; then
+    GRADLE_OPTS="$GRADLE_OPTS \"-Xdock:name=$APP_NAME\" \"-Xdock:icon=$APP_HOME/media/gradle.icns\""
+fi
+
+# For Cygwin, switch paths to Windows format before running java
+if $cygwin ; then
+    APP_HOME=`cygpath --path --mixed "$APP_HOME"`
+    CLASSPATH=`cygpath --path --mixed "$CLASSPATH"`
+    JAVACMD=`cygpath --unix "$JAVACMD"`
+
+    # We build the pattern for arguments to be converted via cygpath
+    ROOTDIRSRAW=`find -L / -maxdepth 1 -mindepth 1 -type d 2>/dev/null`
+    SEP=""
+    for dir in $ROOTDIRSRAW ; do
+        ROOTDIRS="$ROOTDIRS$SEP$dir"
+        SEP="|"
+    done
+    OURCYGPATTERN="(^($ROOTDIRS))"
+    # Add a user-defined pattern to the cygpath arguments
+    if [ "$GRADLE_CYGPATTERN" != "" ] ; then
+        OURCYGPATTERN="$OURCYGPATTERN|($GRADLE_CYGPATTERN)"
+    fi
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    i=0
+    for arg in "$@" ; do
+        CHECK=`echo "$arg"|egrep -c "$OURCYGPATTERN" -`
+        CHECK2=`echo "$arg"|egrep -c "^-"`                                 ### Determine if an option
+
+        if [ $CHECK -ne 0 ] && [ $CHECK2 -eq 0 ] ; then                    ### Added a condition
+            eval `echo args$i`=`cygpath --path --ignore --mixed "$arg"`
+        else
+            eval `echo args$i`="\"$arg\""
+        fi
+        i=$((i+1))
+    done
+    case $i in
+        (0) set -- ;;
+        (1) set -- "$args0" ;;
+        (2) set -- "$args0" "$args1" ;;
+        (3) set -- "$args0" "$args1" "$args2" ;;
+        (4) set -- "$args0" "$args1" "$args2" "$args3" ;;
+        (5) set -- "$args0" "$args1" "$args2" "$args3" "$args4" ;;
+        (6) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" ;;
+        (7) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" ;;
+        (8) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" ;;
+        (9) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" "$args8" ;;
+    esac
+fi
+
+# Escape application args
+save () {
+    for i do printf %s\\n "$i" | sed "s/'/'\\\\''/g;1s/^/'/;\$s/\$/' \\\\/" ; done
+    echo " "
+}
+APP_ARGS=$(save "$@")
+
+# Collect all arguments for the java command, following the shell quoting and substitution rules
+if $JAVACMD --add-opens java.base/java.lang=ALL-UNNAMED -version ; then
+    DEFAULT_JVM_OPTS="--add-opens java.base/java.lang=ALL-UNNAMED $DEFAULT_JVM_OPTS"
+fi
+
+eval set -- $DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS "\"-Dorg.gradle.appname=$APP_BASE_NAME\"" -classpath "\"$CLASSPATH\"" org.gradle.wrapper.GradleWrapperMain "$APP_ARGS"
+
+# by default we should be in the correct project dir, but when run from Finder on Mac, the cwd is wrong
+if [ "$(uname)" = "Darwin" ] && [ "$HOME" = "$PWD" ]; then
+  cd "$(dirname "$0")"
+fi
+
+exec "$JAVACMD" "$@"
diff --git a/gradlew.bat b/gradlew.bat
new file mode 100644
index 0000000..e95643d
--- /dev/null
+++ b/gradlew.bat
@@ -0,0 +1,84 @@
+@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 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=
+
+@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 init
+
+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 init
+
+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
+
+:init
+@rem Get command-line arguments, handling Windows variants
+
+if not "%OS%" == "Windows_NT" goto win9xME_args
+
+:win9xME_args
+@rem Slurp the command line arguments.
+set CMD_LINE_ARGS=
+set _SKIP=2
+
+:win9xME_args_slurp
+if "x%~1" == "x" goto execute
+
+set CMD_LINE_ARGS=%*
+
+: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 %CMD_LINE_ARGS%
+
+: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.kts b/settings.gradle.kts
new file mode 100644
index 0000000..d7b5f67
--- /dev/null
+++ b/settings.gradle.kts
@@ -0,0 +1,16 @@
+pluginManagement {
+    repositories {
+        gradlePluginPortal()
+        google()
+        mavenCentral()
+    }
+}
+dependencyResolutionManagement {
+    repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
+    repositories {
+        gradlePluginPortal()
+        google()
+        mavenCentral()
+    }
+}
+rootProject.name = "ddd-demo"
diff --git a/src/main/kotlin/Program.kt b/src/main/kotlin/Program.kt
new file mode 100644
index 0000000..7c0bcf2
--- /dev/null
+++ b/src/main/kotlin/Program.kt
@@ -0,0 +1,29 @@
+import ddd.application.DefaultUserService
+import ddd.application.dto.ChangeUsername
+import ddd.domain.service.ExistsUserDomainService
+import ddd.infrastructure.repository.MemoryUserRepository
+import ddd.infrastructure.verification.EmailVerificationService
+import mvc.controllers.UserController
+import mvc.dao.UserRepository
+import mvc.entities.User
+import mvc.services.UserSimpleService
+
+//fun main() {
+//    val controller = UserController(UserSimpleService(UserRepository()))
+//    val changeUsername = controller.changeUsername(User(1L, "nian", "3"))
+//    println(changeUsername)
+//}
+
+fun main() {
+    val memoryUserRepository = MemoryUserRepository()
+
+    val userController = ddd.controller.UserController(
+        DefaultUserService(
+            memoryUserRepository,
+            EmailVerificationService(),
+            ExistsUserDomainService(memoryUserRepository)
+        )
+    )
+    val changeUsername = userController.changeUsername(ChangeUsername(1L, "nian", "po",""))
+    println(changeUsername)
+}
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/application/DefaultUserService.kt b/src/main/kotlin/ddd/application/DefaultUserService.kt
new file mode 100644
index 0000000..7655c4a
--- /dev/null
+++ b/src/main/kotlin/ddd/application/DefaultUserService.kt
@@ -0,0 +1,27 @@
+package ddd.application
+
+import ddd.application.dto.ChangeUsername
+import ddd.domain.User
+import ddd.domain.port.VerificationService
+import ddd.domain.repository.UserRepository
+import ddd.domain.service.ExistsUserDomainService
+import ddd.domain.valueobject.Username
+import shared.exceptions.NotFoundException
+
+class DefaultUserService(
+    val userRepository: UserRepository,
+    val verificationService: VerificationService,
+    val existsUserDomainService: ExistsUserDomainService,
+) : UserService {
+    override fun changeUsername(userDto: ChangeUsername): User {
+        val user = userRepository.findById(userDto.id) ?: throw NotFoundException("User with id ${userDto.id} not found")
+        user.changeUsername(
+            Username(userDto.firstName, userDto.lastName),
+            userDto.verificationCode,
+            verificationService,
+            existsUserDomainService
+        )
+        userRepository.save(user)
+        return user
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/application/UserService.kt b/src/main/kotlin/ddd/application/UserService.kt
new file mode 100644
index 0000000..cee7c1a
--- /dev/null
+++ b/src/main/kotlin/ddd/application/UserService.kt
@@ -0,0 +1,8 @@
+package ddd.application
+
+import ddd.application.dto.ChangeUsername
+import ddd.domain.User
+
+interface UserService {
+    fun changeUsername(userDto: ChangeUsername): User
+}
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/application/dto/ChangeUsername.kt b/src/main/kotlin/ddd/application/dto/ChangeUsername.kt
new file mode 100644
index 0000000..9bf215d
--- /dev/null
+++ b/src/main/kotlin/ddd/application/dto/ChangeUsername.kt
@@ -0,0 +1,3 @@
+package ddd.application.dto
+
+data class ChangeUsername(val id: Long ,val firstName: String, val lastName: String, val verificationCode: String)
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/controller/UserController.kt b/src/main/kotlin/ddd/controller/UserController.kt
new file mode 100644
index 0000000..9d851ba
--- /dev/null
+++ b/src/main/kotlin/ddd/controller/UserController.kt
@@ -0,0 +1,9 @@
+package ddd.controller
+
+import ddd.application.UserService
+import ddd.application.dto.ChangeUsername
+
+
+class UserController(val service: UserService) {
+    fun changeUsername(changeUsername: ChangeUsername) = service.changeUsername(changeUsername)
+}
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/domain/User.kt b/src/main/kotlin/ddd/domain/User.kt
new file mode 100644
index 0000000..d9c6bf5
--- /dev/null
+++ b/src/main/kotlin/ddd/domain/User.kt
@@ -0,0 +1,74 @@
+package ddd.domain
+
+import ddd.domain.entity.UserRank
+import ddd.domain.valueobject.UserId
+import ddd.domain.valueobject.UserStatusEnum
+import ddd.domain.valueobject.Username
+import ddd.domain.port.VerificationService
+import ddd.domain.service.ExistsUserDomainService
+import ddd.domain.validation.changeUsername.EmailVerificationValidation
+import ddd.domain.validation.changeUsername.ExistsUsernameValidation
+import ddd.domain.validation.changeUsername.RankPolicyValidation
+import ddd.domain.validation.changeUsername.TimeIntervalValidation
+import ddd.domain.validation.changeUsername.UsernameChangeContext
+import shared.exceptions.ChangeUsernameException
+import shared.validation.ValidationChain
+import java.time.Clock
+import java.time.LocalDateTime
+
+class User(
+    val id: UserId,
+    var username: Username,
+    var status: UserStatusEnum,
+    var lastUsernameChange: LocalDateTime?,
+    var rank: UserRank,
+) {
+    // 领域方法：修改用户名（入口点）
+    fun changeUsername(
+        newUsername: Username,
+        verificationCode: String,
+        verificationService: VerificationService,
+        existsUserService: ExistsUserDomainService,
+        clock: Clock = Clock.systemDefaultZone()
+    ) {
+        validateState()
+        validateChangeUsername(newUsername, verificationCode, verificationService, existsUserService, clock)
+        executeUsernameChange(newUsername, clock)
+    }
+
+    private fun validateState() {
+        if (status != UserStatusEnum.ACTIVE) {
+            throw ChangeUsernameException("用户未激活")
+        }
+    }
+
+    private fun validateChangeUsername(
+        newUsername: Username,
+        verificationCode: String,
+        verificationService: VerificationService,
+        existsUserService: ExistsUserDomainService,
+        clock: Clock
+    ) {
+        val context = UsernameChangeContext(
+            user = this,
+            newUsername = newUsername,
+            verificationCode = verificationCode,
+            clock = clock,
+            verificationService = verificationService,
+            existsUserService = existsUserService
+        )
+
+        // 组合验证规则（责任链模式）
+        ValidationChain<UsernameChangeContext>()
+            .add(EmailVerificationValidation())
+            .add(RankPolicyValidation())
+            .add(TimeIntervalValidation())
+            .add(ExistsUsernameValidation())
+            .validate(context)
+    }
+
+    private fun executeUsernameChange(newUsername: Username, clock: Clock) {
+        username = newUsername
+        lastUsernameChange = LocalDateTime.now(clock)
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/domain/entity/InternalUserRankPolicy.kt b/src/main/kotlin/ddd/domain/entity/InternalUserRankPolicy.kt
new file mode 100644
index 0000000..9c68fc3
--- /dev/null
+++ b/src/main/kotlin/ddd/domain/entity/InternalUserRankPolicy.kt
@@ -0,0 +1,11 @@
+package ddd.domain.entity
+
+import ddd.domain.User
+
+class InternalUserRankPolicy : UserRankPolicy {
+    override fun canChangeUsername(user: User) = true
+
+    override fun requiresEmailVerification() = false
+
+    override fun getMaxChangeIntervalDays() = 0
+}
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/domain/entity/RegularUserRankPolicy.kt b/src/main/kotlin/ddd/domain/entity/RegularUserRankPolicy.kt
new file mode 100644
index 0000000..88ab010
--- /dev/null
+++ b/src/main/kotlin/ddd/domain/entity/RegularUserRankPolicy.kt
@@ -0,0 +1,10 @@
+package ddd.domain.entity
+
+import ddd.domain.User
+
+class RegularUserRankPolicy : UserRankPolicy {
+    override fun canChangeUsername(user: User) = false
+    override fun requiresEmailVerification() = false
+    override fun getMaxChangeIntervalDays() = Int.MAX_VALUE
+}
+
diff --git a/src/main/kotlin/ddd/domain/entity/UserRank.kt b/src/main/kotlin/ddd/domain/entity/UserRank.kt
new file mode 100644
index 0000000..6af1a98
--- /dev/null
+++ b/src/main/kotlin/ddd/domain/entity/UserRank.kt
@@ -0,0 +1,32 @@
+package ddd.domain.entity
+
+import ddd.domain.valueobject.UserRankEnum
+
+sealed interface UserRank {
+    val value: UserRankEnum
+    val policy: UserRankPolicy
+
+    class RegularUserRank() : UserRank {
+        override val value: UserRankEnum = UserRankEnum.REGULAR
+        override val policy = RegularUserRankPolicy()
+        override fun toString(): String {
+            return value.toString()
+        }
+    }
+
+    class VipUserRank() : UserRank {
+        override val value: UserRankEnum = UserRankEnum.VIP
+        override val policy = VipUserRankPolicy()
+        override fun toString(): String {
+            return value.toString()
+        }
+    }
+
+    class InternalUserRank() : UserRank {
+        override val value: UserRankEnum = UserRankEnum.INTERNAL
+        override val policy = InternalUserRankPolicy()
+        override fun toString(): String {
+            return value.toString()
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/domain/entity/UserRankPolicy.kt b/src/main/kotlin/ddd/domain/entity/UserRankPolicy.kt
new file mode 100644
index 0000000..0d41059
--- /dev/null
+++ b/src/main/kotlin/ddd/domain/entity/UserRankPolicy.kt
@@ -0,0 +1,9 @@
+package ddd.domain.entity
+
+import ddd.domain.User
+
+interface UserRankPolicy {
+    fun canChangeUsername(user: User): Boolean
+    fun requiresEmailVerification(): Boolean
+    fun getMaxChangeIntervalDays(): Int
+}
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/domain/entity/VipUserRankPolicy.kt b/src/main/kotlin/ddd/domain/entity/VipUserRankPolicy.kt
new file mode 100644
index 0000000..1207a34
--- /dev/null
+++ b/src/main/kotlin/ddd/domain/entity/VipUserRankPolicy.kt
@@ -0,0 +1,9 @@
+package ddd.domain.entity
+
+import ddd.domain.User
+
+class VipUserRankPolicy : UserRankPolicy {
+    override fun canChangeUsername(user: User) = true
+    override fun requiresEmailVerification() = true
+    override fun getMaxChangeIntervalDays() = 30
+}
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/domain/port/VerificationService.kt b/src/main/kotlin/ddd/domain/port/VerificationService.kt
new file mode 100644
index 0000000..918525b
--- /dev/null
+++ b/src/main/kotlin/ddd/domain/port/VerificationService.kt
@@ -0,0 +1,8 @@
+package ddd.domain.port
+
+import ddd.domain.valueobject.UserId
+
+interface VerificationService {
+    fun isVerified(userId: UserId, code: String): Boolean
+    fun sendVerificationCode(userId: UserId)
+}
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/domain/repository/UserRepository.kt b/src/main/kotlin/ddd/domain/repository/UserRepository.kt
new file mode 100644
index 0000000..b47e186
--- /dev/null
+++ b/src/main/kotlin/ddd/domain/repository/UserRepository.kt
@@ -0,0 +1,14 @@
+package ddd.domain.repository
+
+import ddd.domain.User
+import ddd.domain.valueobject.Username
+
+interface UserRepository {
+    fun save(user: User)
+
+    fun findById(id: Long): User?
+
+    fun findByUsername(username: Username): User?
+
+    fun update(user: User)
+}
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/domain/service/ExistsUserDomainService.kt b/src/main/kotlin/ddd/domain/service/ExistsUserDomainService.kt
new file mode 100644
index 0000000..ce29198
--- /dev/null
+++ b/src/main/kotlin/ddd/domain/service/ExistsUserDomainService.kt
@@ -0,0 +1,10 @@
+package ddd.domain.service
+
+import ddd.domain.repository.UserRepository
+import ddd.domain.valueobject.Username
+
+class ExistsUserDomainService(val userRepository: UserRepository) {
+    fun existsByUsername(username: Username): Boolean{
+        return userRepository.findByUsername(username) != null
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/domain/validation/changeUsername/EmailVerificationValidation.kt b/src/main/kotlin/ddd/domain/validation/changeUsername/EmailVerificationValidation.kt
new file mode 100644
index 0000000..016e46d
--- /dev/null
+++ b/src/main/kotlin/ddd/domain/validation/changeUsername/EmailVerificationValidation.kt
@@ -0,0 +1,17 @@
+package ddd.domain.validation.changeUsername
+
+import shared.exceptions.ChangeUsernameException
+import shared.validation.AbstractValidationHandler
+
+class EmailVerificationValidation : AbstractValidationHandler<UsernameChangeContext>() {
+    override fun validate(context: UsernameChangeContext) {
+        if(context.user.rank.policy.requiresEmailVerification()){
+            val emailVerified = context.verificationService.isVerified(context.user.id, context.verificationCode)
+            if (emailVerified) {
+                throw ChangeUsernameException("验证码错误")
+            }
+        }
+
+        next(context)
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/domain/validation/changeUsername/ExistsUsernameValidation.kt b/src/main/kotlin/ddd/domain/validation/changeUsername/ExistsUsernameValidation.kt
new file mode 100644
index 0000000..c4c1857
--- /dev/null
+++ b/src/main/kotlin/ddd/domain/validation/changeUsername/ExistsUsernameValidation.kt
@@ -0,0 +1,13 @@
+package ddd.domain.validation.changeUsername
+
+import shared.exceptions.ChangeUsernameException
+import shared.validation.AbstractValidationHandler
+
+class ExistsUsernameValidation : AbstractValidationHandler<UsernameChangeContext>() {
+    override fun validate(context: UsernameChangeContext) {
+        require(!context.existsUserService.existsByUsername(context.newUsername)) {
+            throw ChangeUsernameException("用户名已存在")
+        }
+        next(context)
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/domain/validation/changeUsername/RankPolicyValidation.kt b/src/main/kotlin/ddd/domain/validation/changeUsername/RankPolicyValidation.kt
new file mode 100644
index 0000000..790f290
--- /dev/null
+++ b/src/main/kotlin/ddd/domain/validation/changeUsername/RankPolicyValidation.kt
@@ -0,0 +1,13 @@
+package ddd.domain.validation.changeUsername
+
+import shared.exceptions.ChangeUsernameException
+import shared.validation.AbstractValidationHandler
+
+class RankPolicyValidation : AbstractValidationHandler<UsernameChangeContext>()  {
+    override fun validate(context: UsernameChangeContext) {
+        require (context.user.rank.policy.canChangeUsername(context.user)) {
+            throw ChangeUsernameException("用户${context.user.id}没有权限修改用户名")
+        }
+        next(context)
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/domain/validation/changeUsername/TimeIntervalValidation.kt b/src/main/kotlin/ddd/domain/validation/changeUsername/TimeIntervalValidation.kt
new file mode 100644
index 0000000..b156ccb
--- /dev/null
+++ b/src/main/kotlin/ddd/domain/validation/changeUsername/TimeIntervalValidation.kt
@@ -0,0 +1,21 @@
+package ddd.domain.validation.changeUsername
+
+import shared.exceptions.ChangeUsernameException
+import shared.validation.AbstractValidationHandler
+import java.time.Duration
+import java.time.LocalDateTime
+
+class TimeIntervalValidation : AbstractValidationHandler<UsernameChangeContext>() {
+    override fun validate(context: UsernameChangeContext) {
+        val lastChange = context.user.lastUsernameChange
+        val policy = context.user.rank.policy
+        
+        lastChange?.let { 
+            val daysBetween = Duration.between(it, LocalDateTime.now(context.clock)).toDays()
+            if (daysBetween < policy.getMaxChangeIntervalDays()) {
+                throw ChangeUsernameException("30天内禁止重复修改")
+            }
+        }
+        next(context) // 传递至下一个验证器
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/domain/validation/changeUsername/UsernameChangeContext.kt b/src/main/kotlin/ddd/domain/validation/changeUsername/UsernameChangeContext.kt
new file mode 100644
index 0000000..c06a3ba
--- /dev/null
+++ b/src/main/kotlin/ddd/domain/validation/changeUsername/UsernameChangeContext.kt
@@ -0,0 +1,16 @@
+package ddd.domain.validation.changeUsername
+
+import ddd.domain.User
+import ddd.domain.port.VerificationService
+import ddd.domain.service.ExistsUserDomainService
+import ddd.domain.valueobject.Username
+import java.time.Clock
+
+data class UsernameChangeContext(
+    val user: User,
+    val newUsername: Username,
+    val verificationCode: String,
+    val clock: Clock,
+    val verificationService: VerificationService,
+    val existsUserService: ExistsUserDomainService
+)
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/domain/valueobject/UserId.kt b/src/main/kotlin/ddd/domain/valueobject/UserId.kt
new file mode 100644
index 0000000..de9ce1d
--- /dev/null
+++ b/src/main/kotlin/ddd/domain/valueobject/UserId.kt
@@ -0,0 +1,3 @@
+package ddd.domain.valueobject
+
+data class UserId(val value: Long)
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/domain/valueobject/UserRankEnum.kt b/src/main/kotlin/ddd/domain/valueobject/UserRankEnum.kt
new file mode 100644
index 0000000..d050522
--- /dev/null
+++ b/src/main/kotlin/ddd/domain/valueobject/UserRankEnum.kt
@@ -0,0 +1,5 @@
+package ddd.domain.valueobject
+
+enum class UserRankEnum {
+    REGULAR, VIP, INTERNAL
+}
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/domain/valueobject/UserStatusEnum.java b/src/main/kotlin/ddd/domain/valueobject/UserStatusEnum.java
new file mode 100644
index 0000000..396235c
--- /dev/null
+++ b/src/main/kotlin/ddd/domain/valueobject/UserStatusEnum.java
@@ -0,0 +1,5 @@
+package ddd.domain.valueobject;
+
+public enum UserStatusEnum {
+    ACTIVE,DEACTIVATED,BANNED
+}
diff --git a/src/main/kotlin/ddd/domain/valueobject/Username.kt b/src/main/kotlin/ddd/domain/valueobject/Username.kt
new file mode 100644
index 0000000..1aea7cc
--- /dev/null
+++ b/src/main/kotlin/ddd/domain/valueobject/Username.kt
@@ -0,0 +1,14 @@
+package ddd.domain.valueobject
+
+data class Username(val firstName: String, val lastName: String) {
+    override fun toString(): String {
+        return "$firstName $lastName"
+    }
+
+    val regex = Regex("^[a-zA-Z0-9_]+$")
+
+    init {
+        require(toString().length in 4..20) { "用户名长度需在4-20之间" }
+        require(regex.matches(firstName) && regex.matches(lastName)) { "包含非法字符" }
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/infrastructure/repository/MemoryUserRepository.kt b/src/main/kotlin/ddd/infrastructure/repository/MemoryUserRepository.kt
new file mode 100644
index 0000000..5a9dc6d
--- /dev/null
+++ b/src/main/kotlin/ddd/infrastructure/repository/MemoryUserRepository.kt
@@ -0,0 +1,40 @@
+package ddd.infrastructure.repository
+
+import ddd.domain.User
+import ddd.domain.entity.UserRank
+import ddd.domain.repository.UserRepository
+import ddd.domain.valueobject.UserId
+import ddd.domain.valueobject.UserStatusEnum
+import ddd.domain.valueobject.Username
+
+class MemoryUserRepository : UserRepository {
+    val users = mutableMapOf<Long, User>()
+
+    init {
+        save(
+            User(
+                UserId(1L),
+                Username("nian", "chen"),
+                UserStatusEnum.ACTIVE,
+                null,
+                UserRank.RegularUserRank()
+            )
+        )
+    }
+
+    override fun save(user: User) {
+        users += user.id.value to user
+    }
+
+    override fun findById(id: Long): User? {
+        return users[id]
+    }
+
+    override fun findByUsername(username: Username): User? {
+        return users.entries.find { it.value.username == username }?.value
+    }
+
+    override fun update(user: User) {
+        users[user.id.value] = user
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/ddd/infrastructure/verification/EmailVerificationService.kt b/src/main/kotlin/ddd/infrastructure/verification/EmailVerificationService.kt
new file mode 100644
index 0000000..49fcc3e
--- /dev/null
+++ b/src/main/kotlin/ddd/infrastructure/verification/EmailVerificationService.kt
@@ -0,0 +1,9 @@
+package ddd.infrastructure.verification
+
+import ddd.domain.port.VerificationService
+import ddd.domain.valueobject.UserId
+
+class EmailVerificationService : VerificationService {
+    override fun isVerified(userId: UserId, code: String) = true
+    override fun sendVerificationCode(userId: UserId) = println("sending verification email")
+}
\ No newline at end of file
diff --git a/src/main/kotlin/mvc/controllers/UserController.kt b/src/main/kotlin/mvc/controllers/UserController.kt
new file mode 100644
index 0000000..ac5f288
--- /dev/null
+++ b/src/main/kotlin/mvc/controllers/UserController.kt
@@ -0,0 +1,8 @@
+package mvc.controllers
+
+import mvc.entities.User
+import mvc.services.UserService
+
+class UserController(val service: UserService) {
+    fun changeUsername(user: User) = service.changeUsername(user)
+}
\ No newline at end of file
diff --git a/src/main/kotlin/mvc/dao/UserRepository.kt b/src/main/kotlin/mvc/dao/UserRepository.kt
new file mode 100644
index 0000000..5ec0424
--- /dev/null
+++ b/src/main/kotlin/mvc/dao/UserRepository.kt
@@ -0,0 +1,23 @@
+package mvc.dao
+
+import mvc.entities.User
+
+class UserRepository {
+    val users = mutableMapOf<Long, User>()
+
+    init {
+        add(User(1L, "nian", "chen"))
+    }
+
+    fun add(user: User) {
+        users += user.id to user
+    }
+
+    fun findById(id: Long): User? {
+        return users[id]
+    }
+
+    fun update(user: User) {
+        users[user.id] = user
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/mvc/entities/User.kt b/src/main/kotlin/mvc/entities/User.kt
new file mode 100644
index 0000000..498c326
--- /dev/null
+++ b/src/main/kotlin/mvc/entities/User.kt
@@ -0,0 +1,7 @@
+package mvc.entities
+
+data class User (
+    val id: Long,
+    val firstName: String,
+    val lastName: String
+)
\ No newline at end of file
diff --git a/src/main/kotlin/mvc/services/UserComplexService.kt b/src/main/kotlin/mvc/services/UserComplexService.kt
new file mode 100644
index 0000000..5b96561
--- /dev/null
+++ b/src/main/kotlin/mvc/services/UserComplexService.kt
@@ -0,0 +1,18 @@
+package mvc.services
+
+import shared.exceptions.NotFoundException
+import mvc.dao.UserRepository
+import mvc.entities.User
+
+
+class UserComplexService(
+    val repository: UserRepository
+) : UserService {
+    // 用户
+    override fun changeUsername(user: User): User {
+        val findUser = repository.findById(user.id) ?: throw NotFoundException("User ${user.id} not found")
+        val copy = findUser.copy(firstName = user.firstName, lastName = user.lastName)
+        repository.update(copy)
+        return copy
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/mvc/services/UserService.kt b/src/main/kotlin/mvc/services/UserService.kt
new file mode 100644
index 0000000..68b06a4
--- /dev/null
+++ b/src/main/kotlin/mvc/services/UserService.kt
@@ -0,0 +1,7 @@
+package mvc.services
+
+import mvc.entities.User
+
+interface UserService {
+    fun changeUsername(user: User): User
+}
\ No newline at end of file
diff --git a/src/main/kotlin/mvc/services/UserSimpleService.kt b/src/main/kotlin/mvc/services/UserSimpleService.kt
new file mode 100644
index 0000000..bcf60a5
--- /dev/null
+++ b/src/main/kotlin/mvc/services/UserSimpleService.kt
@@ -0,0 +1,14 @@
+package mvc.services
+
+import shared.exceptions.NotFoundException
+import mvc.dao.UserRepository
+import mvc.entities.User
+
+class UserSimpleService(val repository: UserRepository) : UserService {
+    override fun changeUsername(user: User): User {
+        val findUser = repository.findById(user.id) ?: throw NotFoundException("User ${user.id} not found")
+        val copy = findUser.copy(firstName = user.firstName, lastName = user.lastName)
+        repository.update(copy)
+        return copy
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/shared/exceptions/ChangeUsernameException.kt b/src/main/kotlin/shared/exceptions/ChangeUsernameException.kt
new file mode 100644
index 0000000..131dacc
--- /dev/null
+++ b/src/main/kotlin/shared/exceptions/ChangeUsernameException.kt
@@ -0,0 +1,4 @@
+package shared.exceptions
+
+class ChangeUsernameException(msg: String) : RuntimeException(msg) {
+}
\ No newline at end of file
diff --git a/src/main/kotlin/shared/exceptions/NotFoundException.kt b/src/main/kotlin/shared/exceptions/NotFoundException.kt
new file mode 100644
index 0000000..9d14989
--- /dev/null
+++ b/src/main/kotlin/shared/exceptions/NotFoundException.kt
@@ -0,0 +1,4 @@
+package shared.exceptions
+
+class NotFoundException(msg: String) : RuntimeException(msg) {
+}
\ No newline at end of file
diff --git a/src/main/kotlin/shared/validation/AbstractValidationHandler.kt b/src/main/kotlin/shared/validation/AbstractValidationHandler.kt
new file mode 100644
index 0000000..9e06d99
--- /dev/null
+++ b/src/main/kotlin/shared/validation/AbstractValidationHandler.kt
@@ -0,0 +1,15 @@
+package shared.validation
+
+abstract class AbstractValidationHandler<T> : ValidationHandler<T> {
+    private lateinit var nextHandler: ValidationHandler<T>
+
+    override fun setNext(handler: ValidationHandler<T>) {
+        nextHandler = handler
+    }
+
+    protected fun next(context: T) {
+        if (::nextHandler.isInitialized) {
+            nextHandler.validate(context)
+        }
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/shared/validation/ValidationChain.kt b/src/main/kotlin/shared/validation/ValidationChain.kt
new file mode 100644
index 0000000..beff787
--- /dev/null
+++ b/src/main/kotlin/shared/validation/ValidationChain.kt
@@ -0,0 +1,22 @@
+package shared.validation
+
+class ValidationChain<T> {
+    private var firstHandler: ValidationHandler<T>? = null
+    private var lastHandler: ValidationHandler<T>? = null
+
+    fun add(handler: ValidationHandler<T>): ValidationChain<T> {
+        if (firstHandler == null) {
+            firstHandler = handler
+            lastHandler = handler
+        } else {
+            lastHandler?.setNext(handler)
+            lastHandler = handler
+        }
+        return this
+    }
+
+    fun validate(context: T) {
+        firstHandler?.validate(context)
+            ?: throw IllegalStateException("验证链未初始化")
+    }
+}
\ No newline at end of file
diff --git a/src/main/kotlin/shared/validation/ValidationHandler.kt b/src/main/kotlin/shared/validation/ValidationHandler.kt
new file mode 100644
index 0000000..86fbabc
--- /dev/null
+++ b/src/main/kotlin/shared/validation/ValidationHandler.kt
@@ -0,0 +1,6 @@
+package shared.validation
+
+interface ValidationHandler<T> {
+    fun validate(context: T)
+    fun setNext(handler: ValidationHandler<T>)
+}
\ No newline at end of file