[JavaWeb] JSTL tag library

JSTL tag library

JSTL Standard Label Library;

JSTL is used to simplify JSP development and improve code readability and maintainability.

JSTL is defined by SUN(Oracle) and implemented by Apache Tomcat team.

Reference to JSTL Core Library

Core is the most important tag library of JSTL, which provides the basic functions of JSTL.
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
JSTL Core Label Library is defined by META-INF/c.tld in taglibs-standard-impl.jar

Conditional judgement

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Insert title here</title>
</head>
<body>
    <%
        int x = 15;
        request.setAttribute("x", x);
    %>
    <c:if test="${ requestScope.x > 0 && requestScope.x <= 10 }">
        <div style="color:blue;font-weight:bold;">1-10 Integers between</div>
    </c:if>
    <c:if test="${ requestScope.x > 10 && requestScope.x <= 20 }">
        <div style="color:red;font-weight:bold;">11-20 Integers between</div>
    </c:if>
</body>
</html>

Multiple Conditional Judgment

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Insert title here</title>
</head>
<body>
    <c:choose>
        <c:when test="${ param.day == 'MONDAY' }">
            <h2 style="color:blue;">Monday</h2>
        </c:when>
        <c:when test="${ param.day == 'TUESDAY' }">
            <h2 style="color:blue;">Tuesday</h2>
        </c:when>
        <c:when test="${ param.day == 'WEDNESDAY' }">
            <h2 style="color:blue;">Wednesday</h2>
        </c:when>
        <c:when test="${ param.day == 'THURSDAY' }">
            <h2 style="color:blue;">Thursday</h2>
        </c:when>
        <c:when test="${ param.day == 'FRIDAY' }">
            <h2 style="color:blue;">Friday</h2>
        </c:when>
        <c:when test="${ param.day == 'SATURDAY' }">
            <h2 style="color:blue;">Saturday</h2>
        </c:when>
        <c:when test="${ param.day == 'SUNDAY' }">
            <h2 style="color:blue;">Sunday</h2>
        </c:when>
        <c:otherwise>
            <h2 style="color:red;">The content is not right!</h2>
        </c:otherwise>
    </c:choose>
</body>
</html>

Ergodic cycle

MonthServlet.java

package jstl;

import java.io.IOException;
import java.util.HashSet;
import java.util.Set;
 
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
 
/**
 * Servlet implementation class MonthServlet
 */
@WebServlet("/month")
public class MonthServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
        
    /**
     * @see HttpServlet#HttpServlet()
     */
    public MonthServlet() {
        super();
        // TODO Auto-generated constructor stub
    }
 
    /**
    * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
    */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        Set<String> setMonths = new HashSet();
        setMonths.add("January");
        setMonths.add("February");
        setMonths.add("March");
        setMonths.add("April");
        setMonths.add("May");
        request.setAttribute("months", setMonths);
        request.getRequestDispatcher("/month.jsp").forward(request, response);
    }
 
}

month.jsp

<%@ 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>
    <c:forEach items="${requestScope.months }" var="c" varStatus="idx">
        <h2>${idx.index + 1} - ${c }</h2>
    </c:forEach>
</body>
</html>

c:out

Belong to Core
<c:out value="${nothing}" default="none"> </c:out> (nothing=null) converts the original null value to "none"
<c:out value="${html}" escapeXml= "true"> </c:out> Browser will display HTML source code without explanation.

fmt formatted tag library

FMT formatted tag library URI:http://java.sun.com/jsp/jstl/fmt
<fmt: formatDate value="" pattern="> formatted date label
<fmt: formatNumber value="" pattern="> formatted numeric label

formatDate pattern

yyyy	Four years
MM	Two months
dd	Two days
HH	24 hour system
hh	12 hour system
mm	Minute
ss	Seconds
SSS	Millisecond

formatNumber pattern

"0.00": Keep two decimal places
"0,000.00": Separated by three-one, with two decimal digits reserved

Posted by farel on Sat, 12 Oct 2019 12:10:36 -0700

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