객체지향 (OOP)

Java Application - 싱글톤 패턴(Singleton pattern) (2 - Web 버젼)

고인돌개발자 2021. 4. 30. 10:27

학습목표 : 웹 시스템을 통해 서버에서 싱글톤이 구현되는 부분을 확인한다.
부제 : 여러 사용자의 접근을 통해 웹에서 싱글톤을 확인하자.

 

1. 웹 프로젝트 실행 (New - Dynamic Web Project)

<웹 패키지 구조>

 

2. NaSingleClass.java 생성 (싱글톤 객체)

package singleton;


public class NaSingleClass {
private String strName;
	
	// 클래스 참조 변수 선언 
	// 해당 값을 static 으로 선언하여, 메모리에 올려, 모두가 참조하게 함(포인터)
	private static NaSingleClass singleInstance;
	
	// 생성자가 private , new 접근 할 수 없음
	private NaSingleClass() {		
	}
	
	// 해당 함수를 통해서만, 객체화가능,,,
	// 해당 함수를 통해서만, 객체화가능,,,
		//public static NaSingleClass getSingleInstance() {
		//public static synchronized NaSingleClass getSingleInstance() {
		public static synchronized NaSingleClass getSingleInstance() {
			if(singleInstance ==null) {
				synchronized (NaSingleClass.class) {
					if(singleInstance ==null) {
						singleInstance = new NaSingleClass();
					}
				}			
			}
			return singleInstance;
		}
	
	public String getStrName() {
		return strName;
	}
	
	public void setStrName(String strName) {
		this.strName = strName;
	}
}

3. NaSingleClassNo.java (일반 자바 클래스, static 변수)

package no_singleton;

public class NaSingleClassNo {
	
	private static String strName;
	
	public NaSingleClassNo() {	
	}	
	
	public String getStrName() {
		return strName;
	}
	
	public void setStrName(String strName) {
		this.strName = strName;
	}

}

4. hello.java (Servlet , 생성) , parameter (name=~~)

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import singleton.NaSingleClass;
import no_singleton.NaSingleClassNo;

/**
 * Servlet implementation class hello
 */
@WebServlet("/hello")
public class hello extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public hello() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.getWriter().append("Served at: ").append(request.getContextPath());
		
				String strIp   = request.getRemoteAddr();
				String strName = request.getParameter("name");				
		
				System.out.println("\n\n\n\n ================ No Single =========================="+strIp);				
				
				// No Single
				NaSingleClassNo na = new NaSingleClassNo();
				NaSingleClassNo na2 = new NaSingleClassNo();
				NaSingleClassNo na3 = new NaSingleClassNo();
				
				na.setStrName("Kim");
				if(strName !=null) {
					na.setStrName(strName);
				}				
				
				System.out.printf("na ,  %s , %s \n", na, na.getStrName());
				System.out.printf("na2 , %s , %s \n", na2, na2.getStrName());
				System.out.printf("na3 , %s , %s \n", na3, na3.getStrName());				
				
				System.out.println("\n ================ Single =========================="+strIp);
		
				// Single
				NaSingleClass naS = NaSingleClass.getSingleInstance();
				NaSingleClass naS2 = NaSingleClass.getSingleInstance();
				NaSingleClass naS3 = NaSingleClass.getSingleInstance();
				
				naS.setStrName("Kim");
				if(strName !=null) {
					naS.setStrName(strName);
				}
				
				System.out.printf("naS ,  %s , %s \n", naS, naS.getStrName());
				System.out.printf("naS2 , %s , %s \n", naS2, naS2.getStrName());;
				System.out.printf("naS3 , %s , %s \n", naS3, naS3.getStrName());;				
				
				/* 아래가 바로 초창기 Servlet 의 위엄... */
				response.setContentType("text/html");
				response.setCharacterEncoding("utf-8");
				PrintWriter w = response.getWriter();
				
				w.write("<html>\n" +
				"<head>\n" +
				"<meta charset=\"UTF-8\">\n" +
				"</head>\n" +
				"<body>\n" +
				"<p> =============== No Single =========================="+strIp+
				"<ul>\n" +
				" <li>na Address  = "+na +" , _______Name: "+na.getStrName()  +"</li>\n" +
				" <li>na2 Address  ="+na2+" , _______Name: "+na2.getStrName()   +"</li>\n" +
				" <li>na3 Address  ="+na3+" , _______Name: "+na3.getStrName()+"</li>\n" +
				"</ul>\n" +
				"<p> ===============  Single =========================="+strIp+
				"<ul>\n" +
				" <li>naS Address  = "+naS +" , _______Name: "+naS.getStrName()  +"</li>\n" +
				" <li>naS2 Address  ="+naS2+" , _______Name: "+naS2.getStrName()   +"</li>\n" +
				" <li>naS3 Address  ="+naS3+" , _______Name: "+naS3.getStrName()+"</li>\n" +
				"</ul>\n" +
				"</body>\n" +
				"</html>");				
				
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

5. hello_2.java (Servlet , 생성) 단순 조회 



import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import no_singleton.NaSingleClassNo;
import singleton.NaSingleClass;

/**
 * Servlet implementation class hello_2
 */
@WebServlet("/hello_2")
public class hello_2 extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public hello_2() {
        super();
        // TODO Auto-generated constructor stub
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		response.getWriter().append("Served at: ").append(request.getContextPath());
		
		String strIp   = request.getRemoteAddr();
		
		System.out.println("\n\n\n\n ================ No Single =========================="+strIp);
		// No Single
		NaSingleClassNo na  = new NaSingleClassNo();
		NaSingleClassNo na2 = new NaSingleClassNo();
		NaSingleClassNo na3 = new NaSingleClassNo();
		
		
		
		 System.out.printf("na ,  %s , %s \n", na, na.getStrName());
		 System.out.printf("na2 , %s , %s \n", na2, na2.getStrName());
		 System.out.printf("na3 , %s , %s \n", na3, na3.getStrName());
		 
		
		System.out.println("\n ================ No Single =========================="+strIp);
		
		// Single		
		NaSingleClass naS = NaSingleClass.getSingleInstance();
		NaSingleClass naS2 = NaSingleClass.getSingleInstance();
		NaSingleClass naS3 = NaSingleClass.getSingleInstance();
		
		
		 System.out.printf("naS ,  %s , %s \n", naS, naS.getStrName());
		 System.out.printf("naS2 , %s , %s \n", naS2, naS2.getStrName());;
		 System.out.printf("naS3 , %s , %s \n", naS3, naS3.getStrName());;
		 
		
		/* 아래가 바로 초창기 Servlet 의 위엄... */
		response.setContentType("text/html");
		response.setCharacterEncoding("utf-8");
		PrintWriter w = response.getWriter();
		
		w.write("<html>\n" +
		"<head>\n" +
		"<meta charset=\"UTF-8\">\n" +
		"</head>\n" +
		"<body>\n" +
		"<p> =============== No Single =========================="+strIp+
		"<ul>\n" +
		" <li>na Address  = "+na +" , _______Name: "+na.getStrName()  +"</li>\n" +
		" <li>na2 Address  ="+na2+" , _______Name: "+na2.getStrName()   +"</li>\n" +
		" <li>na3 Address  ="+na3+" , _______Name: "+na3.getStrName()+"</li>\n" +
		"</ul>\n" +
		"<p> ===============  Single =========================="+strIp+
		"<ul>\n" +
		" <li>naS Address  = "+naS +" , _______Name: "+naS.getStrName()  +"</li>\n" +
		" <li>naS2 Address  ="+naS2+" , _______Name: "+naS2.getStrName()   +"</li>\n" +
		" <li>naS3 Address  ="+naS3+" , _______Name: "+naS3.getStrName()+"</li>\n" +
		"</ul>\n" +
		"</body>\n" +
		"</html>");
		
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

 

# Test : http://localhost:8080/SingleTonWebTest/hello?name=KIM

# Test : http://localhost:8080/SingleTonWebTest/hello_2

 

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