커스텀 태그(JSTL) 라이브러리 사용, (EL 표현식)

https://mvnrepository.com/artifact/jakarta.servlet.jsp.jstl/jakarta.servlet.jsp.jstl-api/3.0.0

https://mvnrepository.com/artifact/org.glassfish.web/jakarta.servlet.jsp.jstl/3.0.0

https://docs.oracle.com/javaee/5/jstl/1.1/docs/tlddocs/overview-summary.html

Overview (TLDDoc Generated Documentation)

FRAMES NO FRAMES All Tags

docs.oracle.com

<%@page import="java.util.Date"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/fmt" prefix="fmt"%>

<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>JSTL 예제</title>
</head>
<body>
	<h1>JSTL 예제</h1>
	<% // 스크립트 릿 대신에 <c:set....> 태그를 사용할 수 있다. %>
	<c:set var="message" value="JSTL ~~~ "/>
	<p>메시지 : </p><c:out value="${message}" />
	
	<!-- IF -->
	<c:if test="${message != null}">
		<p>메시지 값이 null 아닙니다</p>
	</c:if>
	
	<!-- foreach  -->
	<c:forEach var="i" begin="1" end="10" >
		<p>Number : ${i}</p>	
	</c:forEach>
	
	<h2>JSTL Formatting Example</h2>
	<c:set var="now" value="<%=new Date() %>"/>
	<fmt:formatDate var="formattedDate"  value="${now}" pattern="yyyy-MM-dd HH:mm:ss" />
	
	<p>현재 시간 : ${formattedDate} </p>
	
	<c:set var="price" value="12345.678"/>
	<fmt:formatNumber value="${price}" type="currency" var="formatPrice" />
	<p>Format Price : ${formatPrice} </p>
	
		
</body>
</html>

User 클래스 생성(DTO)

package com.tenco.mdels;

import lombok.Data;

@Data
public class User {
	private int id; 
	private String username;
	private String password; 
	private String email;
}

UserDAOImpl 생성

package com.tenco.repository;

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

import com.mysql.cj.protocol.Resultset;
import com.tenco.mdels.User;

/**
 * 인터페이스 설계 생략.. 
 */
public class UserDAOImpl {

	private static final String URL = "jdbc:mysql://localhost:3306/demo3?serverTimezone=Asia/Seoul";
	private static final String USER = "root";
	private static final String PASSWORD = "asd123";
	
	
	public UserDAOImpl() {
		try {
			Class.forName("com.mysql.cj.jdbc.Driver");
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		}
	}
	
	private Connection getConnection() throws SQLException {
		return DriverManager.getConnection(URL, USER, PASSWORD);
	}
	public List<User> getAUsers() {
		List<User> list = new ArrayList<>();
		String sql = " SELECT * FROM users " ;
		try(Connection conn = getConnection();
			PreparedStatement pstmt = conn.prepareStatement(sql);
			ResultSet rs = pstmt.executeQuery()) {
			while (rs.next()) {
				User user = new User();
				user.setId(rs.getInt("id"));
				user.setUsername(rs.getString("username"));
				user.setEmail(rs.getString("email"));
				list.add(user);
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
		return list;
	}
}

package com.tenco.controller;

import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;

import com.tenco.mdels.User;
import com.tenco.repository.UserDAOImpl;


@WebServlet("/user/*")
public class UserController extends HttpServlet {
	
	private static final long serialVersionUID = 1L;
    private UserDAOImpl userDAOImpl;
    
    public UserController() {
    	userDAOImpl = new UserDAOImpl();
    }

    // http://localhost:8080/jstl/user/list?id=123&name=길동
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		
		// 전체 URL 를 문자를 반환 할려면 
		String fullURL = request.getRequestURL().toString();
		System.out.println("fullURL : " + fullURL);
		
		// URL의 쿼리 문자열을 반환 합니다.(쿼리 문자열이 없으면 null 을 반환)
		String queryString = request.getQueryString();
		System.out.println("queryString : " + queryString);
		
		// 컨텍스트 루트 경로를 반환 받고 싶다면 
		String contextPath = request.getContextPath();
		System.out.println("contextPath : " + contextPath);
		
		// URL 마지막 경로(엔드포인트)를 반환 받고 싶다면
		String pathInfo = request.getPathInfo();
		System.out.println("pathInfo : " + pathInfo);
		
		switch (pathInfo) {
		case "/list":
			userListPage(request, response);
			break;

		default:
			break;
		}
	}

	private void userListPage(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		
		List<User> userList = userDAOImpl.getAUsers();
		request.setAttribute("userList", userList);
		request.getRequestDispatcher("/WEB-INF/user/userList.jsp").forward(request, response);
	}

	/**
	 * @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);
	}

}

<%@page import="java.util.List"%>
<%@page import="com.tenco.mdels.User"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
	
	<h1>USERLIST PAGE</h1>
	<%
		List<User> userList = (List<User>)request.getAttribute("userList");
	%>
	
	<table border="1">
		<tr>
			<th>ID</th>
			<th>이름</th>
			<th>이메일</th>
		</tr>
		<%
			for(User user : userList) { %> 
			<td><%=user.getId()%></td>
			<td><%=user.getUsername()%></td>
			<td><%=user.getPassword()%></td>
				
		<%} %>
		
	</table>
	
	
</body>
</html>

<%@page import="java.util.List"%>
<%@page import="com.tenco.mdels.User"%>
<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
	<h1>USERLIST PAGE</h1>
	<c:choose>
		<c:when test="${not empty userList}">
			<table border="1">
				<tr>
					<th>ID</th>
					<th>이름</th>
					<th>이메일</th>
				</tr>
				<c:forEach var="user" items="${userList}" >
					<tr>
						<td><c:out value="${user.id}"/> </td>
						<td><c:out value="${user.username}"/> </td>
						<td><c:out value="${user.email}"/> </td>
					</tr>
				</c:forEach>
			</table>					
		</c:when>
		<c:otherwise>
			<p>등록된 사용자가 없습니다.</p>
		</c:otherwise>
	</c:choose>
	
</body>
</html>

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커스텀 태그(JSTL) 라이브러리 사용, (EL 표현식)

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