diff --git a/BookCart/src/BookMain.java b/BookCart/src/BookMain.java
index 11d63ba..475a5e3 100644
--- a/BookCart/src/BookMain.java
+++ b/BookCart/src/BookMain.java
@@ -4,7 +4,7 @@
 import service.BookService;
 import service.UserService;
 import vo.CartElement;
-import vo.User;
+import entity.User;
 
 public class BookMain {
     static Scanner sc = new Scanner(System.in);
@@ -14,15 +14,7 @@ public static void main(String[] args) {
         BookService bookService = new BookService();
         AdminService adminService = new AdminService();
 
-        //고객 정보 입력
-        System.out.print("당신의 이름을 입력하세요 : ");
-        String name = sc.nextLine();
-        System.out.print("연락처를 입력하세요 : ");
-        String phoneNumber = sc.nextLine();
-
-        //customer1 고객 객체 생성 & 기입
-        User user1 = new User(name, phoneNumber);
-        userService.join(user1);
+        String user1 = userService.join();
 
         // 실행 문구
         printWelcome();
@@ -37,18 +29,12 @@ public static void main(String[] args) {
                 case 1 -> //고객 정보 확인하기
                         userService.menuGuestInfo(user1);
                 case 2 ->  //장바구니 상품 목록 보기
-                {
-                    List<CartElement> list1 = bookService.getUserCart(user1.getId());
-                    for (CartElement cartElement : list1) {
-                        System.out.println(cartElement);
-                    }
-
-                }
+                    bookService.getUserCart(user1);
                 case 3 -> // 장바구니 항목 비우기
-                        bookService.clearAll(user1.getId());
+                        bookService.clearAll(user1);
                 case 4 -> { //바구니에 항목 추가하기
                     bookService.getAllBooks();
-                    bookService.addBook(user1.getId());
+                    bookService.addBook(user1);
                 }
                 case 5 -> System.out.println("장바구니 수량 줄이기");
                 case 6 -> System.out.println("장바구니 항목 삭제하기");
diff --git a/BookCart/src/vo/Admin.java b/BookCart/src/entity/Admin.java
similarity index 55%
rename from BookCart/src/vo/Admin.java
rename to BookCart/src/entity/Admin.java
index c1887e5..584fc20 100644
--- a/BookCart/src/vo/Admin.java
+++ b/BookCart/src/entity/Admin.java
@@ -1,10 +1,11 @@
-package vo;
+package entity;
 
 public class Admin extends Person{
     private String id = "Admin";
     private String password = "Admin1234";
 
-    public Admin(String name, String phoneNumber) {
-        super(name, phoneNumber);
+
+    public Admin(Builder builder) {
+        super(builder);
     }
 }
diff --git a/BookCart/src/vo/Book.java b/BookCart/src/entity/Book.java
similarity index 98%
rename from BookCart/src/vo/Book.java
rename to BookCart/src/entity/Book.java
index 2200eca..98d76b9 100644
--- a/BookCart/src/vo/Book.java
+++ b/BookCart/src/entity/Book.java
@@ -1,4 +1,4 @@
-package vo;
+package entity;
 
 public class Book {
     private String bookId;
diff --git a/BookCart/src/entity/Person.java b/BookCart/src/entity/Person.java
new file mode 100644
index 0000000..84c5eb7
--- /dev/null
+++ b/BookCart/src/entity/Person.java
@@ -0,0 +1,54 @@
+package entity;
+
+public class Person {
+    private final String id;
+    private final String password;
+    private final String name;
+    private final String phoneNumber;
+    private final String address;
+
+    public Person(Builder builder) {
+        this.id = builder.id;
+        this.password = builder.password;
+        this.name = builder.name;
+        this.phoneNumber = builder.phoneNumber;
+        this.address = builder.address;
+    }
+
+    public static class Builder {
+        private String id;
+        private String password;
+        private final String name;
+        private final String phoneNumber;
+
+        private String address;
+
+        public Builder(String id, String password, String name, String phoneNumber) {
+            this.id = id;
+            this.password = password;
+            this.name = name;
+            this.phoneNumber = phoneNumber;
+        }
+
+        public Builder address(String val) {
+            address=val;
+            return this;
+        }
+
+        public Person build() {
+            return new Person(this);
+        }
+    }
+
+    public String getId() {
+        return id;
+    }
+    public String getName() {
+        return name;
+    }
+    public String getPhoneNumber() {
+        return phoneNumber;
+    }
+    public String getPassword() { return password; }
+    public String getAddress() { return address; }
+}
diff --git a/BookCart/src/entity/User.java b/BookCart/src/entity/User.java
new file mode 100644
index 0000000..656304b
--- /dev/null
+++ b/BookCart/src/entity/User.java
@@ -0,0 +1,8 @@
+package entity;
+
+public class User extends Person {
+
+    public User(Builder builder) {
+        super(builder);
+    }
+}
diff --git a/BookCart/src/mapper/BookMapper.java b/BookCart/src/mapper/BookMapper.java
index c00b492..85f5ee5 100644
--- a/BookCart/src/mapper/BookMapper.java
+++ b/BookCart/src/mapper/BookMapper.java
@@ -1,63 +1,24 @@
 package mapper;
 
-import java.util.ArrayList;
-import java.util.HashMap;
+import entity.Book;
+import vo.CartElement;
+
 import java.util.List;
 import java.util.Map;
-import vo.Book;
-import vo.CartElement;
 
-public class BookMapper {
-    private Map<String, Book> books = new HashMap<>();
-    private Map<String, List<CartElement>> cart = new HashMap<>();
-
-    public BookMapper() {
-        books.put("ISBN1234", new Book("ISBN1234", "쉽게 배우는 JSP 웹 프로그래밍", 27000, "송미영", "단계별로 쇼핑몰을 구현하며 배우는 JSP 웹 프로그래밍", "IT전문서", "2018/10/08"));
-        books.put("ISBN1235", new Book("ISBN1235", "안드로이드 프로그래밍", 33000, "우재남", "실습 단계별 명쾌한 멘토링!", "IT전문서", "2022/01/22"));
-        books.put("ISBN1236", new Book("ISBN1236", "스크래치", 22000, "고광일", "컴퓨팅 사고력을 키우는 블록 코딩", "컴퓨터 입문", "2019/06/10"));
-    }
-
-    // 장바구니에 도서 담기
-    public void save(String userId, String bookId) {
-        List<CartElement> userCart = cart.get(userId);
-        boolean flag = false;
-
-        if (userCart == null) {
-            userCart = new ArrayList<>();
-            cart.put(userId, userCart);
-        }
-        for (int i = 0; i < userCart.size(); i++) {
-            if(userCart.get(i).getBook().getBookId().equals(bookId))
-            {
-                flag = true;
-                cart.get(userId).get(i).plusAmount();
-                break;
-            }
-        }
-        if(flag == false)
-        {
-            cart.get(userId).add(new CartElement(books.get(bookId)));
-        }
-    }
-
-    // 모든 도서 조회
-    public List<Book> findAll() {
-        return new ArrayList<>(books.values());
-    }
-
-    // bookId로 Book 객체 찾아서 반환
-    public Book findByBookId(String bookId) {
-        return books.get(bookId);
-    }
-
-    // userId로 User 장바구니 조회
-    public List<CartElement> findCartByUserId(String userId) {
-        return cart.get(userId);
-    }
-
-    public void clear(String userId)
-    {
-        List<CartElement> userCart = cart.get(userId);
-        userCart.clear();
-    }
+public interface BookMapper {
+
+    // C
+    void save(String userId, CartElement element);
+
+    // R
+    List<Book> findAll();
+    Book findByBookId(String bookId);
+    Map<String, Integer> findCartByUserId(String userId);
+
+    // U
+
+    // D
+    void clear(String userId);
+
 }
diff --git a/BookCart/src/mapper/BookMapperImpl.java b/BookCart/src/mapper/BookMapperImpl.java
new file mode 100644
index 0000000..c32d955
--- /dev/null
+++ b/BookCart/src/mapper/BookMapperImpl.java
@@ -0,0 +1,50 @@
+package mapper;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import entity.Book;
+import vo.CartElement;
+
+public class BookMapperImpl implements BookMapper{
+    private Map<String, Book> books = new HashMap<>();
+    private static final Map<String, Map<String, Integer>> cart = new HashMap<>();
+
+    public BookMapperImpl() {
+        books.put("ISBN1234", new Book("ISBN1234", "쉽게 배우는 JSP 웹 프로그래밍", 27000, "송미영", "단계별로 쇼핑몰을 구현하며 배우는 JSP 웹 프로그래밍", "IT전문서", "2018/10/08"));
+        books.put("ISBN1235", new Book("ISBN1235", "안드로이드 프로그래밍", 33000, "우재남", "실습 단계별 명쾌한 멘토링!", "IT전문서", "2022/01/22"));
+        books.put("ISBN1236", new Book("ISBN1236", "스크래치", 22000, "고광일", "컴퓨팅 사고력을 키우는 블록 코딩", "컴퓨터 입문", "2019/06/10"));
+    }
+
+    // 장바구니에 도서 담기
+    public void save(String userId, CartElement element) {
+        Map<String, Integer> userCart = cart.get(userId);
+        userCart.put(element.getBookId(), element.getAmount());
+    }
+
+    // 모든 도서 조회
+    public List<Book> findAll() {
+        return new ArrayList<>(books.values());
+    }
+
+    // bookId로 Book 객체 찾아서 반환
+    public Book findByBookId(String bookId) {
+        return books.get(bookId);
+    }
+
+    // userId로 User 장바구니 조회
+    public Map<String, Integer> findCartByUserId(String userId) {
+        return cart.get(userId);
+    }
+
+    // 장바구니 비우기
+    public void clear(String userId) {
+        cart.get(userId).clear();
+    }
+
+    public void insertCart(String userId) {
+        Map<String, Integer> newCart = new HashMap<>();
+        cart.put(userId, newCart);
+    }
+}
diff --git a/BookCart/src/mapper/PersonMapper.java b/BookCart/src/mapper/PersonMapper.java
index ef716fb..7834b35 100644
--- a/BookCart/src/mapper/PersonMapper.java
+++ b/BookCart/src/mapper/PersonMapper.java
@@ -1,19 +1,8 @@
 package mapper;
 
-import java.util.HashMap;
-import java.util.Map;
-import vo.Person;
+import entity.Person;
 
-public class PersonMapper {
-    private Map<String, Person> store = new HashMap<>();
-
-    // 회원가입
-    public void save(Person person) {
-        store.put(person.getId(), person);
-    }
-
-    // 사용자 조회
-    public Person findById(String id) {
-        return store.get(id);
-    }
+public interface PersonMapper {
+    void save(Person person);
+    Person findById(String id);
 }
diff --git a/BookCart/src/mapper/PersonMapperImpl.java b/BookCart/src/mapper/PersonMapperImpl.java
new file mode 100644
index 0000000..1e80e40
--- /dev/null
+++ b/BookCart/src/mapper/PersonMapperImpl.java
@@ -0,0 +1,19 @@
+package mapper;
+
+import java.util.HashMap;
+import java.util.Map;
+import entity.Person;
+
+public class PersonMapperImpl implements PersonMapper{
+    private final Map<String, Person> store = new HashMap<>();
+
+    // 회원가입
+    public void save(Person person) {
+        store.put(person.getId(), person);
+    }
+
+    // 사용자 조회
+    public Person findById(String id) {
+        return store.get(id);
+    }
+}
diff --git a/BookCart/src/service/AdminService.java b/BookCart/src/service/AdminService.java
index 6246ff1..d7fd39e 100644
--- a/BookCart/src/service/AdminService.java
+++ b/BookCart/src/service/AdminService.java
@@ -1,7 +1,8 @@
 package service;
 
 import java.util.Scanner;
-import vo.Admin;
+import entity.Admin;
+import entity.Person;
 
 public class AdminService{
 
@@ -15,7 +16,7 @@ public void menuAdminLogin() {
         System.out.print("비밀번호 : ");
         String adminPw = sc.next();
 
-        Admin admin = new Admin("jang", "01012346578");
+        Person admin = new Admin.Builder("Admin", "Admin1234", "jang", "01012345678").build();
 
         if (adminId.equals(admin.getId()) && adminPw.equals(admin.getPassword())) {
             System.out.println("\n로그인 성공");
diff --git a/BookCart/src/service/BookService.java b/BookCart/src/service/BookService.java
index cd9bec2..8a013f1 100644
--- a/BookCart/src/service/BookService.java
+++ b/BookCart/src/service/BookService.java
@@ -1,15 +1,15 @@
 package service;
 
 
-import java.util.ArrayList;
-import java.util.List;
-import java.util.Scanner;
+import java.util.*;
+
 import mapper.BookMapper;
-import vo.Book;
+import entity.Book;
+import mapper.BookMapperImpl;
 import vo.CartElement;
 
 public class BookService {
-    private BookMapper bookMapper = new BookMapper();
+    private BookMapperImpl bookMapper = new BookMapperImpl();
 
     // 장바구니에 도서 추가
     public void addBook(String userId) {
@@ -18,8 +18,8 @@ public void addBook(String userId) {
         System.out.println("장바구니에 추가할 도서의 ID를 입력하세요 :");
         String bookId = sc.next();
 
-        if (!findBookById(bookId)) {
-            System.out.printf("%s는 도서 목록에 없습니다.\n", bookId);
+        if (findByBookId(bookId) == null) {
+            System.out.println(bookId + "는 도서 목록에 없습니다.");
             return;
         }
 
@@ -27,16 +27,37 @@ public void addBook(String userId) {
         String confirm = sc.next();
 
         if (confirm.equals("Y") || confirm.equals("y")) {
-            bookMapper.save(userId, bookId);
+            int amount = findBookInCart(userId, bookId);
+            CartElement element = new CartElement(bookId, amount+1);
+            bookMapper.save(userId, element);
             System.out.printf("%s 도서가 장바구니에 추가되었습니다.\n", bookId);
+
         } else {
             System.out.println("장바구니 추가를 취소하였습니다.");
         }
     }
 
-    // bookId가 도서 리스트에 존재하는지 확인
-    public boolean findBookById(String bookId) {
-        return bookMapper.findByBookId(bookId) != null;
+    // user의 장바구니에 특정 책이 담겨있는지 확인
+    private int findBookInCart(String userId, String bookId) {
+        Map<String, Integer> element = bookMapper.findCartByUserId(userId);
+
+        if (element.containsKey(bookId))
+            return element.get(bookId);
+        else
+            return 0;
+    }
+
+    // book이 마켓에 존재하는지 확인
+//    private void verifyBookInList(String bookId) {
+//        if (findByBookId(bookId) == null) {
+//            System.out.println(bookId + "는 도서 목록에 없습니다.");
+//            return;
+//        }
+//    }
+
+    // book을 찾아서 객체 반환
+    public Book findByBookId(String bookId) {
+        return bookMapper.findByBookId(bookId);
     }
 
     // 모든 도서 조회
@@ -46,21 +67,16 @@ public List<Book> getAllBooks() {
     }
 
     // User 장바구니 조회
-    public List<CartElement> getUserCart(String userId) {
-        List<CartElement> bookList = bookMapper.findCartByUserId(userId);
+    public void getUserCart(String userId) {
+        Map<String, Integer> userCart = bookMapper.findCartByUserId(userId);
 
-        if (bookList == null) {
-            System.out.println("장바구니가 비어있습니다.");
-            return new ArrayList<>();
+        try {
+            userCart.entrySet()
+                    .stream()
+                    .forEach(i-> System.out.println(findByBookId(i.getKey()) + " " + i.getValue()));
+        } catch (NullPointerException e) {
+            throw new NullPointerException("장바구니가 비어있습니다.");
         }
-
-        List<CartElement> returnBookList = new ArrayList<>();
-        for (CartElement book: bookList)
-        {
-            returnBookList.add(book);
-        }
-
-        return returnBookList;
     }
 
     public void clearAll(String userId)
@@ -68,4 +84,8 @@ public void clearAll(String userId)
         bookMapper.clear(userId);
         System.out.println("장바구니를 비웠습니다.");
     }
+
+    public void createUserBookCart(String userId) {
+        bookMapper.insertCart(userId);
+    }
 }
\ No newline at end of file
diff --git a/BookCart/src/service/UserService.java b/BookCart/src/service/UserService.java
index 28b3af8..5b9c35a 100644
--- a/BookCart/src/service/UserService.java
+++ b/BookCart/src/service/UserService.java
@@ -1,21 +1,45 @@
 package service;
 
-import mapper.PersonMapper;
-import vo.Person;
+import entity.Person;
+import mapper.PersonMapperImpl;
+
+import java.util.Scanner;
 
 public class UserService{
-    private PersonMapper personMapper = new PersonMapper();
+    private PersonMapperImpl personMapper = new PersonMapperImpl();
+    private BookService bookService = new BookService();
+
+    static Scanner sc = new Scanner(System.in);
 
     // 회원가입 (성공시 1 반환)
-    public int join(Person person) {
-        if (checkPersonInfo(person)) {
-            personMapper.save(person);
-            return 1;
+    public String join() {
+        Person user = inputSignInForm();
+
+        if (checkPersonInfo(user)) {
+            personMapper.save(user);
+            bookService.createUserBookCart(user.getId());
+            System.out.println("회원가입 성공");
+            return user.getId();
         } else {
-            return 0;
+            System.out.println("회원가입 실패");
+            return null;
         }
     }
 
+    private Person inputSignInForm() {
+        //고객 정보 입력
+        System.out.print("당신의 이름을 입력하세요 : ");
+        String name = sc.nextLine();
+        System.out.print("연락처를 입력하세요 : ");
+        String phoneNumber = sc.nextLine();
+        System.out.print("아이디를 입력하세요 : ");
+        String id = sc.nextLine();
+        System.out.print("비밀번호를 입력하세요 : ");
+        String password = sc.nextLine();
+
+        return new Person.Builder(id, password, name, phoneNumber).build();
+    }
+
     // 사용자 정보 유효성 검사
     public boolean checkPersonInfo(Person person) {
         if (personMapper.findById(person.getId()) == null) {
@@ -28,8 +52,11 @@ public boolean checkPersonInfo(Person person) {
     }
 
     // 사용자 정보 출력
-    public void menuGuestInfo(Person person) {
+    public void menuGuestInfo(String userId) {
+        Person person = personMapper.findById(userId);
         System.out.println("현재 고객 정보 : ");
-        System.out.println("이름 " + person.getName() + "연락처 " + person.getPhoneNumber());
+        System.out.println("이름 " + person.getName() +
+                            " 연락처 " + person.getPhoneNumber() +
+                            " 아이디 " + person.getId());
     }
 }
diff --git a/BookCart/src/vo/CartElement.java b/BookCart/src/vo/CartElement.java
index 1e5ee09..22ce707 100644
--- a/BookCart/src/vo/CartElement.java
+++ b/BookCart/src/vo/CartElement.java
@@ -1,28 +1,18 @@
 package vo;
 
 public class CartElement {
-    private Book book;
+    private String bookId;
     private int amount;
 
-    public CartElement(Book book) {
-        this.book = book;
-        this.amount++;
+    public CartElement(String bookId, int amount) {
+        this.bookId = bookId;
+        this.amount = amount;
     }
 
-    public Book getBook() {
-        return book;
+    public String getBookId() {
+        return bookId;
     }
-
     public int getAmount() {
         return amount;
     }
-
-    public void plusAmount()
-    {
-        this.amount++;
-    }
-
-    public String toString() {
-        return (getBook() + "" + getAmount() + "권");
-    }
 }
diff --git a/BookCart/src/vo/Person.java b/BookCart/src/vo/Person.java
deleted file mode 100644
index a1549f3..0000000
--- a/BookCart/src/vo/Person.java
+++ /dev/null
@@ -1,34 +0,0 @@
-package vo;
-
-public class Person {
-    private String id;
-    private String password;
-    private String name;
-    private String phoneNumber;
-    private String address;
-
-    public Person() {}
-
-    public Person(String name, String phoneNumber) {
-        this.name = name;
-        this.phoneNumber = phoneNumber;
-    }
-
-    public Person(String name, String phoneNumber, String address) {
-        this.name = name;
-        this.phoneNumber = phoneNumber;
-        this.address = address;
-    }
-
-    public String getId() {
-        return id;
-    }
-    public String getName() {
-        return name;
-    }
-    public String getPhoneNumber() {
-        return phoneNumber;
-    }
-    public String getPassword() { return password; }
-    public String getAddress() { return address; }
-}
diff --git a/BookCart/src/vo/User.java b/BookCart/src/vo/User.java
deleted file mode 100644
index 38e72ed..0000000
--- a/BookCart/src/vo/User.java
+++ /dev/null
@@ -1,11 +0,0 @@
-package vo;
-
-public class User extends Person {
-    public User(String name, String phoneNumber) {
-        super(name, phoneNumber);
-    }
-
-    public User(String username, String phoneNumber, String address) {
-        super(username, phoneNumber, address);
-    }
-}