EL式

EL式(Expression Language)は、Jspにデータ表示するの使います。
データ表示には<%=XXX%>も使えますが、EL式の方が少し便利で少し見やすいです。

サーブレット

				
package test;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
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 javax.servlet.http.HttpSession;

@WebServlet("/Count")
public class Count extends HttpServlet {
	private static final long serialVersionUID = 1L;

	public Count() {
		super();
	}

	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		// Sessionを取得
		HttpSession session = request.getSession();

		// Applicationを取得
		ServletContext application = getServletContext();

		String hdn = (String) request.getParameter("hdn");

		// クリアボタンで各情報をクリア
		if (hdn != null && hdn.equals("clear")) {
			session.invalidate();
			application.removeAttribute("count2");
			response.sendRedirect("count.jsp");
			return;
		}

		// requestを処理
		String count0 = request.getParameter("count0");
		if (count0 == null || count0.length() == 0 || count0.equals("null")) {
			count0 = "1";
			TestBean reqBean = new TestBean();
			reqBean.setName("Request");
			request.setAttribute("count0", count0);
			request.setAttribute("req", reqBean);
		} else {
			count0 = "" + (Integer.parseInt(count0) + 1);
		}
		request.setAttribute("count0", count0);

		// sessionを処理
		Integer count1 = (Integer) session.getAttribute("count1");
		if (count1 == null) {
			count1 = 1;
			TestBean sesBean = new TestBean();
			sesBean.setName("Session");
			session.setAttribute("ses", sesBean);
		} else {
			count1++;
		}
		session.setAttribute("count1", count1);

		// applicationを処理
		Integer count2 = (Integer) application.getAttribute("count2");
		if (count2 == null) {
			count2 = 1;
			TestBean appBean = new TestBean();
			appBean.setName("Application");
			application.setAttribute("app", appBean);
		} else {
			count2++;
		}
		application.setAttribute("count2", count2);

		RequestDispatcher dispatch = request.getRequestDispatcher("count.jsp");
		dispatch.forward(request, response);
	}
}

Jsp

				
<%@page import="test.TestBean"%>
<%@ page language="java" contentType="text/html; charset=UTF8"
	pageEncoding="UTF8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF8">
<title>セッション、アプリケーション</title>
<script type="text/javascript">
	//テキスト読み込み時に実行
	document.addEventListener("DOMContentLoaded", function() {

		//+1ボタン押下時
		document.getElementById("id1").onclick = function() {
			document.getElementById("id3").value = "count";
			frm.submit();
		};

		//クリアボタン押下時
		document.getElementById("id2").onclick = function() {
			document.getElementById("id3").value = "clear";
			frm.submit();
		};
	}, false);
</script>
</head>
<body>
	<form action="/test/Count" method="post" name="frm">

		<input type="button" id="id1" value="+1" />
		<input type="button" id="id2" value="クリア" /> <br /> 
		<input type="hidden" id="id3" name="hdn" />
		リクエスト：<input type="text" name="count0" value="${count0}" /> <br /> 
		セッション：${count1} <br />
		アプリケーション：${count0}
		<hr />
		${req.name} <br />
		${ses.name} <br /> 
		${app.name}
	</form>
</body>
</html>

実行

http://localhost:8080/test/count.jsp にアクセスすると実行できます。

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