Accessing Map attached to Servlet using JSP Expression Language and JSTL Tag Library

 

 Servlet Code:

java

import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class ServletExpression extends HttpServlet {

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

        response.setContentType("text/html;charset=UTF-8");

        // Prepare data
        ArrayList<String> instituteList = new ArrayList<>();
        instituteList.add("Institute-1");
        instituteList.add("Institute-2");
        instituteList.add("Institute-3");
        instituteList.add("Institute-4");

        Map<String, Integer> accountMap = new HashMap<>();
        accountMap.put("abc", 200000);
        accountMap.put("xyz", 100000);
        accountMap.put("pqr", 300000);
        accountMap.put("lmn", 400000);

        // Store in session
        HttpSession session = request.getSession();
        session.setAttribute("instname", instituteList);

        // Store in application scope
        ServletContext application = request.getServletContext();
        application.setAttribute("acctname", accountMap);

        // Output HTML
        try (PrintWriter out = response.getWriter()) {
            out.println("""
                <html>
                    <head>
                        <title>First Servlet</title>
                    </head>
                    <body>
                        <h1>Welcome to JAVA</h1>
                    </body>
                </html>
                """);
        }
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws IOException, ServletException {
        doPost(request, response);
    }
}

JSP (displayApplication.jsp)

jsp
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>

<h2>JSTL Tag Example</h2>
<hr/>

<!-- Direct index access -->
1: ${instname[0]} <br/>
2: ${instname[1]} <br/>
3: ${instname[2]} <br/>
4: <c:out value="${instname[3]}" default="Institute-1"/> <br/>
5: <c:out value="${instname[4]}" default="Institute-2"/> <br/>
6: <c:out value="${instname[5]}" default="Institute-3"/> <br/>

<hr/>

<b>Using JSTL to iterate ArrayList:</b><br/><br/>

<c:forEach var="item" items="${instname}">
    ${item} <br/>
</c:forEach>

<hr/>

<b>&lt;c:forEach&gt; examples:</b><br/>

<c:forEach var="i" begin="1" end="10">
    ${i}
    <c:if test="${i < 3}"> less than 3 </c:if>
    <c:if test="${i < 6}"> less than 6 </c:if>
    <c:if test="${i < 8}"> less than 8 </c:if>
    <br/>
</c:forEach>

<hr/>

<b>&lt;c:choose&gt; example:</b><br/>

<c:forEach var="i" begin="1" end="10">
    ${i}
    <c:choose>
        <c:when test="${i < 3}"> less than 3 </c:when>
        <c:when test="${i < 6}"> less than 6 </c:when>
        <c:when test="${i < 8}"> less than 8 </c:when>
        <c:when test="${i == 8}"> equal to 8 </c:when>
        <c:otherwise> greater than 8 </c:otherwise>
    </c:choose>
    <br/>
</c:forEach>

<hr/>

<b>HashMap example:</b><br/>

<c:forEach var="entry" items="${acctname}">
    ${entry.key} has account balance US $ ${entry.value} <br/>
</c:forEach>

<hr/>

<b>Reverse Order Print:</b><br/>

<c:forEach var="i" begin="1" end="10" step="2">
    <c:set var="revorder" value="${11 - i}" />
    ${revorder} <br/>
</c:forEach>

<hr/>