[JAVA] SingleTon

SingleTon

• 인스턴스(객체)가 한개만 만들어지는 것
• new 명령을 외부에서 사용하지 못하게 한다.
• 리소스(자원)을 아낄 수 있다
• 데이터에 대한 일관성을 유지할 수 있다, 신뢰성을 가질 수 있음
• 클래스 만드는 방법
  1. 자신 class의 참조값이 저장될 변수를 private static으로 선언한다.
  2. 모든 생성자의 접근 제한자를 private으로 한다. (new명령 외부 사용 불가능)
  3. 자신 class의 인스턴스를 생성하고 반환하는 메서드를 public static으로 작성한다.
     (이 메서드의 이름은 보통 getInstance로 한다.)

---

singleton 생성 예제

public class MySingleton {
	// 1번
	private static MySingleton single;
	
	// 2번
	private MySingleton() {
		System.out.println("싱글톤 클래스의 생성자");
	}
	
	// 3번
	public static MySingleton getInstance() {
		// 1번의 변수 null이면 현재 클래스의 객체를 생성해서 1번 변수에 저장한다
		// 그리고 1번의 변수값을 반환한다.
		if(single==null) {
			single = new MySingleton();
		}
		return single;
	}
	
	// 기타 이 클래스가 처리할 내용들을 작성한다.
	public void displayTest() {
		System.out.println("싱글톤 클래스의 메서드 호출입니다");
	}
}

singleton 사용 예제

public class SingletonTest {
	public static void main(String[] args) {
//		MySingleton test = new MySingleton(); // 외부에서 new 명령으로 생성 불가
		
		MySingleton test2 = MySingleton.getInstance();
		MySingleton test3 = MySingleton.getInstance();
		
		// 참조값 동일
		System.out.println("test2 => "+test2);	// test2 => kr.or.ddit.singleton.MySingleton@15db9742
		System.out.println("test3 => "+test3);	// test3 => kr.or.ddit.singleton.MySingleton@15db9742
		System.out.println();
		System.out.println(test2==test3); // true
		System.out.println(test2.equals(test3)); // true
		
		test2.displayTest(); // 싱글톤 클래스의 메서드 호출입니다
	}
}

실제로 적용하기

MemberDaoImpl.java

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

import kr.or.ddit.member.vo.MemberVO;
import kr.or.ddit.util.DBUtil;

public class MemberDaoImpl implements IMemberDao{
	private static MemberDaoImpl dao;
	
	private MemberDaoImpl() {
		// TODO Auto-generated constructor stub
	}
	
	public static MemberDaoImpl getInstance() {
		if(dao==null) {
			dao = new MemberDaoImpl();
		}
		return dao;
	}

	@Override
	public int insertMember(MemberVO memVo) {
		Connection conn = null;
		PreparedStatement pstmt = null;
		int cnt = 0; // 반환값이 저장될 변수
		
		try {
			conn = DBUtil.getConnection();
			String sql = "insert into mymember"
					+ "(mem_id, mem_pass, mem_name, mem_tel, mem_addr) " 
					+ " values(?, ?, ?, ?, ?) ";
			pstmt = conn.prepareStatement(sql);
			pstmt.setString(1, memVo.getMem_id());
			pstmt.setString(2, memVo.getMem_pass());
			pstmt.setString(3, memVo.getMem_name());
			pstmt.setString(4, memVo.getMem_tel());
			pstmt.setString(5, memVo.getMem_addr());		
			
			cnt = pstmt.executeUpdate();
			
		} catch (Exception e) {
			// TODO: handle exception
		} finally {
			if(pstmt!=null) try{pstmt.close();} catch(SQLException e) {}
			if(conn!=null) try{conn.close();} catch(SQLException e) {}
		}
		return cnt;
	}

	@Override
	public int deleteMember(String mem_id) {
		Connection conn = null;
		PreparedStatement pstmt = null;
		int cnt = 0; // 반환값이 저장될 변수
		
		try {
			conn = DBUtil.getConnection();
			String sql = "delete from mymember where mem_id=?";
			pstmt = conn.prepareStatement(sql);
			pstmt.setString(1, mem_id);
			cnt = pstmt.executeUpdate();
			
		} catch (Exception e) {
			// TODO: handle exception
		} finally {
			if(pstmt!=null) try{pstmt.close();} catch(SQLException e) {}
			if(conn!=null) try{conn.close();} catch(SQLException e) {}
		}
		return cnt;
	} 

	@Override
	public int updateMember(MemberVO memVo) {
		Connection conn = null;
		PreparedStatement pstmt = null;
		int cnt = 0; // 반환값이 저장될 변수
		
		try {
			conn = DBUtil.getConnection();
			String sql = "update mymember set mem_pass=?, mem_name=?, mem_tel=?, mem_addr=? where mem_id=?";
			pstmt = conn.prepareStatement(sql);
			pstmt.setString(1, memVo.getMem_pass());
			pstmt.setString(2, memVo.getMem_name());
			pstmt.setString(3, memVo.getMem_tel());
			pstmt.setString(4, memVo.getMem_addr());
			pstmt.setString(5, memVo.getMem_id());
			
			cnt = pstmt.executeUpdate();
			
		} catch (Exception e) {
			// TODO: handle exception
		} finally {
			if(pstmt!=null) try{pstmt.close();} catch(SQLException e) {}
			if(conn!=null) try{conn.close();} catch(SQLException e) {}
		}
		return cnt;
	}

	@Override
	public List<MemberVO> getAllMember() {
		List<MemberVO> list = new ArrayList<MemberVO>();
		Connection conn = null;
		PreparedStatement pstmt = null;
		ResultSet rs = null;
		try {
			conn = DBUtil.getConnection();
			String sql = "select * from mymember";
			pstmt = conn.prepareStatement(sql);
			rs = pstmt.executeQuery();
			while (rs.next()) {
				MemberVO memVo = new MemberVO();
				memVo.setMem_id(rs.getString("mem_id"));
				memVo.setMem_pass(rs.getString("mem_pass"));
				memVo.setMem_name(rs.getString("mem_name"));
				memVo.setMem_tel(rs.getString("mem_tel"));
				memVo.setMem_addr(rs.getString("mem_addr"));
				list.add(memVo);
			}
		} catch (Exception e) {
			// TODO: handle exception
		} finally {
			if(rs!=null) try{rs.close();} catch(SQLException e) {}
			if(pstmt!=null) try{pstmt.close();} catch(SQLException e) {}
			if(conn!=null) try{conn.close();} catch(SQLException e) {}
		}
		return list;
	}

	@Override
	public int getMemIdCount(String mem_id) {
		Connection conn = null;
		PreparedStatement pstmt = null;
		ResultSet rs = null;
		int count = 0;
		
		try {
			conn = DBUtil.getConnection();
			String sql = "select count(*) count from mymember where mem_id=?";
			pstmt = conn.prepareStatement(sql);
			pstmt.setString(1, mem_id);
			rs = pstmt.executeQuery();
			if (rs.next()) {
				count = rs.getInt("count");
			}
		} catch (Exception e) {
			// TODO: handle exception
		} finally {
			if(rs!=null) try{rs.close();} catch(SQLException e) {}
			if(pstmt!=null) try{pstmt.close();} catch(SQLException e) {}
			if(conn!=null) try{conn.close();} catch(SQLException e) {}
		}
		
		return count;
	}

	@Override
	public MemberVO getMemInfo(String mem_id) {
		MemberVO memVo = new MemberVO();
		Connection conn = null;
		PreparedStatement pstmt = null;
		ResultSet rs = null;
		int count = 0;
		
		try {
			conn = DBUtil.getConnection();
			String sql = "select * from mymember where mem_id=?";
			pstmt = conn.prepareStatement(sql);
			pstmt.setString(1, mem_id);
			rs = pstmt.executeQuery();
			if (rs.next()) {
				memVo.setMem_id(rs.getString("mem_id"));
				memVo.setMem_pass(rs.getString("mem_pass"));
				memVo.setMem_name(rs.getString("mem_name"));
				memVo.setMem_tel(rs.getString("mem_tel"));
				memVo.setMem_addr(rs.getString("mem_addr"));
			}
		} catch (Exception e) {
			// TODO: handle exception
		} finally {
			if(rs!=null) try{rs.close();} catch(SQLException e) {}
			if(pstmt!=null) try{pstmt.close();} catch(SQLException e) {}
			if(conn!=null) try{conn.close();} catch(SQLException e) {}
		}
		return memVo;
	}

	@Override
	public int updateMember2(Map<String, String> paramMap) {
		Connection conn = null;
		PreparedStatement pstmt = null;
		int cnt = 0; // 반환값이 저장될 변수
		
		try {
			conn = DBUtil.getConnection();
			String sql = "update mymember set "+paramMap.get("FIELD")+"=? where mem_id=?";
			pstmt = conn.prepareStatement(sql);
			pstmt.setString(1, paramMap.get("VALUE"));
			pstmt.setString(2, paramMap.get("MEMID"));
			
			cnt = pstmt.executeUpdate();
		} catch (Exception e) {
			// TODO: handle exception
		} finally {
			if(pstmt!=null) try{pstmt.close();} catch(SQLException e) {}
			if(conn!=null) try{conn.close();} catch(SQLException e) {}
		}
		return cnt;
	}


}

MemberServiceImpl.java

import java.util.List;
import java.util.Map;

import kr.or.ddit.member.dao.IMemberDao;
import kr.or.ddit.member.dao.MemberDaoImpl;
import kr.or.ddit.member.vo.MemberVO;

public class MemberServiceImpl implements IMemberService {
	private static MemberServiceImpl service;
	private IMemberDao dao; // DAO객체가 저장될 변수 선언
	// 생성자
	private MemberServiceImpl() {
		dao = MemberDaoImpl.getInstance();
	}
	
	public static MemberServiceImpl getInstance() {
		if(service==null) service = new MemberServiceImpl();
		return service;
	}

	@Override
	public int insertMember(MemberVO memVo) {
		return dao.insertMember(memVo);
	}

	@Override
	public int deleteMember(String mem_id) {
		return dao.deleteMember(mem_id);
	}

	@Override
	public int updateMember(MemberVO memVo) {
		return dao.updateMember(memVo);
	}

	@Override
	public List<MemberVO> getAllMember() {
		return dao.getAllMember();
	}

	@Override
	public int getMemIdCount(String mem_id) {
		return dao.getMemIdCount(mem_id);
	}

	@Override
	public MemberVO getMemInfo(String mem_id) {
		return dao.getMemInfo(mem_id);
	}

	@Override
	public int updateMember2(Map<String, String> paramMap) {
		return dao.updateMember2(paramMap);
	}

}

MemberController.java

import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Scanner;

import kr.or.ddit.member.service.IMemberService;
import kr.or.ddit.member.service.MemberServiceImpl;
import kr.or.ddit.member.vo.MemberVO;

public class MemberController {
	private Scanner scan;
	private IMemberService service;

	public MemberController() {
		service = MemberServiceImpl.getInstance();
		scan = new Scanner(System.in);
	}

	public static void main(String[] args) {
		new MemberController().memberStart();
	}

	// 시작 메서드
	public void memberStart() {
		while (true) {
			int sel = displayMenu();
			switch (sel) {
			case 1:
				insert();
				break;
			case 2:
				delete();
				break;
			case 3:
				update();
				break;
			case 4:
				update2();
				break;
			case 5:
				update_part();
				break;
			case 6:
				print();
				break;
			case 0:
				System.out.println("시스템을 종료합니다");
				return;
			default:
				break;
			}
		}
	}

	private void update2() {
		String mem_id = "";
		System.out.print("ID >> ");
		mem_id = scan.next();
		int count = service.getMemIdCount(mem_id);
		if (count == 0) {
			System.out.println("존재하지 않는 아이디입니다.");
			return;
		}
		int sel = displayUpdateMenu2();
		
		Map<String, String> paramMap = new HashMap<String, String>();
		
		if (sel==1) {
			System.out.print("PW >> ");
			paramMap.put("FIELD", "mem_pass");
			paramMap.put("VALUE", scan.next());
		}

		if (sel==2) {
			System.out.print("이름 >> ");
			paramMap.put("FIELD", "mem_name");
			paramMap.put("VALUE", scan.next());
		}

		if (sel==3) {
			System.out.print("전화번호 >> ");
			paramMap.put("FIELD", "mem_tel");
			paramMap.put("VALUE", scan.next());
		}

		if (sel==4) {
			scan.nextLine();
			System.out.print("주소 >> ");
			paramMap.put("FIELD", "mem_addr");
			paramMap.put("VALUE", scan.nextLine());
		}
		paramMap.put("MEMID", mem_id);
		service.updateMember2(paramMap);
		
	}
	
	public int displayUpdateMenu2() {
		System.out.println("업데이트할 내용을 선택해주세요");
		System.out.println();
		System.out.println("1. 비밀번호 수정");
		System.out.println("2. 이름 수정");
		System.out.println("3. 전화번호 수정");
		System.out.println("4. 주소 수정");
		return scan.nextInt();
	}

	private void update_part() {
		String mem_id = "";
		System.out.print("ID >> ");
		mem_id = scan.next();
		int count = service.getMemIdCount(mem_id);
		if (count == 0) {
			System.out.println("존재하지 않는 아이디입니다.");
			return;
		}
		String sel = displayUpdateMenu();

		MemberVO memVo = service.getMemInfo(mem_id);
		if (sel.contains("1")) {
			System.out.print("PW >> ");
			memVo.setMem_pass(scan.next());
		}

		if (sel.contains("2")) {
			System.out.print("이름 >> ");
			memVo.setMem_name(scan.next());
		}

		if (sel.contains("3")) {
			System.out.print("전화번호 >> ");
			memVo.setMem_tel(scan.next());
		}

		if (sel.contains("4")) {
			scan.nextLine();
			System.out.print("주소 >> ");
			memVo.setMem_addr(scan.nextLine());
		}

		service.updateMember(memVo);

	}

	public String displayUpdateMenu() {
		System.out.println("업데이트할 내용을 선택해주세요");
		System.out.println("중복선택이 가능합니다");
		System.out.println("ex. 123 >  비밀번호/이름/전화번호 수정");
		System.out.println();
		System.out.println("1. 비밀번호 수정");
		System.out.println("2. 이름 수정");
		System.out.println("3. 전화번호 수정");
		System.out.println("4. 주소 수정");
		return scan.next();
	}

	private void print() {
		List<MemberVO> list = service.getAllMember();

		System.out.println("-- 전체 자료 출력 --");
		System.out.println();
		if (list == null || list.size() == 0) {
			System.out.println("회원정보가 없습니다.");
			System.out.println("메인화면으로 돌아갑니다.");
			System.out.println();
			return;
		}
		System.out.println("-------------------------------------------------");
		System.out.println("회원아이디\t비밀번호\t회원이름\t전화번호\t\t주소");
		System.out.println("-------------------------------------------------");

		for (MemberVO memVo : list) {
			System.out.println(memVo.getMem_id() + "\t" + memVo.getMem_pass() + "\t" + memVo.getMem_name() + "\t"
					+ memVo.getMem_tel() + "\t" + memVo.getMem_addr());
		}
		System.out.println("-------------------------------------------------");

	}

	private void update() {
		String mem_id = "";
		System.out.print("ID >> ");
		mem_id = scan.next();
		int count = service.getMemIdCount(mem_id);
		if (count == 0) {
			System.out.println("존재하지 않는 아이디입니다.");
			return;
		}
		System.out.println("변경할 정보를 입력해주세요");

		MemberVO memVo = new MemberVO();

		memVo.setMem_id(mem_id);

		System.out.print("PW >> ");
		memVo.setMem_pass(scan.next());

		System.out.print("이름 >> ");
		memVo.setMem_name(scan.next());

		System.out.print("전화번호 >> ");
		memVo.setMem_tel(scan.next());
		// 버퍼 삭제
		scan.nextLine();
		System.out.print("주소 >> ");
		memVo.setMem_addr(scan.nextLine());

		service.updateMember(memVo);

	}

	private void delete() {
		String mem_id = "";
		System.out.print("ID >> ");
		mem_id = scan.next();
		int count = service.getMemIdCount(mem_id);
		if (count == 0) {
			System.out.println("존재하지 않는 아이디입니다.");
			return;
		}
		service.deleteMember(mem_id);
		System.out.println("삭제가 완료되었습니다.");

	}

	private void insert() {
		String mem_id = "";
		int count;
		do {
			count = 0;
			System.out.print("ID >> ");
			mem_id = scan.next();
			count = service.getMemIdCount(mem_id);
			if (count > 0) {
				System.out.println("중복된 아이디입니다");
			}
		} while (count > 0);

		MemberVO memVo = new MemberVO();

		memVo.setMem_id(mem_id);

		System.out.print("PW >> ");
		memVo.setMem_pass(scan.next());

		System.out.print("이름 >> ");
		memVo.setMem_name(scan.next());

		System.out.print("전화번호 >> ");
		memVo.setMem_tel(scan.next());
		// 버퍼 삭제
		scan.nextLine();
		System.out.print("주소 >> ");
		memVo.setMem_addr(scan.nextLine());

		service.insertMember(memVo);
	}

	private int displayMenu() {
		System.out.println("1. 자료 추가");
		System.out.println("2. 자료 삭제");
		System.out.println("3. 자료 수정");
		System.out.println("4. 부분 수정");
		System.out.println("5. 부분 다중 수정");
		System.out.println("6. 전체 자료 출력");
		System.out.println("0. 작업 끝");
		System.out.print("메뉴 >> ");
		int sel = scan.nextInt();
		return sel;
	}

}