JSTL简单教程--JSTL核心标签（JSTL Tutorial with Examples – JSTL Core Tags）

JSP Standard Tag Library (JSTL)是一个标准的标签库用来控制jsp的行为、迭代和控制表现、国际化以及sql等。

JSTL是javaEE的一部分并被绝大部分servlet容易所包含，但当我们用到时需要下载jstl的jar才能在容器中使用。大部分时间，我们可以在事例程序下找到他们，你需要把他们放到你工程的WEB-INF/lib目录下就可以了。这些jar就会被容器所找到，例如在tomcat下你需要jstl.jar 和 standard.jar。并加入到build path下才可以。

JSTL包含以下五类：
1、Core Tags:核心标签提供包含迭代、逻辑判断、异常、url、以及跳转等。你只需要在你的jsp页面包含以下代码就可以：

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

2、Formatting and Localization Tags:这个是用来提供格式化数字、日期i18n从本地。只需要加入下面代码

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

3、SQL Tags:这个是对关系型数据库的支持。例如mysql、oracle等等。之需要加入以下代码：

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

4、XML Tags： 主要用户XML文档。例如解析XML，转换xml数据和Xpath表达式等。需要加入如下代码：

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

5、JSTL Functions Tags：function 标签用于一些操作逻辑，多数用于String 操作，例如spli等：需要加入以下代码：

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

 

所有的标签都是以http://java.sun.com/jsp/jstl/开始的。

JSTL Core Tags

Tag	Description
	To write something in JSP page, we can use EL also with this tag
	Same as or include directive
	redirect request to another resource
	To set the variable value in given scope.
	To remove the variable from given scope
	To catch the exception and wrap it into an object.
	Simple conditional logic, used with EL and we can use it to process the exception from
	Simple conditional tag that establishes a context for mutually exclusive conditional operations, marked by and
	Subtag of that includes its body if its condition evalutes to ‘true’.
	Subtag of that includes its body if its condition evalutes to ‘false’.
	for iteration over a collection
	for iteration over tokens separated by a delimiter.
	used with to pass parameters
	to create a URL with optional query string parameters

来看事例：

Employee.java

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package com.journaldev.model;

public class Employee {

    private int id;
    private String name;
    private String role;
    public Employee() {
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getRole() {
        return role;
    }
    public void setRole(String role) {
        this.role = role;
    }

}

 

HomeServlet.java

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package com.journaldev.servlet;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.RequestDispatcher;
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 com.journaldev.model.Employee;

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

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        List empList = new ArrayList();
        Employee emp1 = new Employee();
        emp1.setId(1); emp1.setName("Pankaj");emp1.setRole("Developer");
        Employee emp2 = new Employee();
        emp2.setId(2); emp2.setName("Meghna");emp2.setRole("Manager");
        empList.add(emp1);empList.add(emp2);
        request.setAttribute("empList", empList);

        request.setAttribute("htmlTagData", " creates a new line.");
        request.setAttribute("url", "http://www.journaldev.com");
        RequestDispatcher rd = getServletContext().getRequestDispatcher("/home.jsp");
        rd.forward(request, response);
    }

}

 

home.jsp

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<%@ page language="java" contentType="text/html; charset=US-ASCII"
    pageEncoding="US-ASCII"%>

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<title>Home Pagetitle>

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<style>
table,th,td
{
border:1px solid black;
}
style>

head>

<body>
<%-- Using JSTL forEach and out to loop a list and display items in table --%>
<table>
<tbody>
<tr><th>IDth><th>Nameth><th>Roleth>tr>

<c:forEach items="${requestScope.empList}" var="emp">
<tr><td><c:out value="${emp.id}">c:out>td>

<td><c:out value="${emp.name}">c:out>td>

<td><c:out value="${emp.role}">c:out>td>tr>

c:forEach>

tbody>

table>

<br><br>
<%-- simple c:if and c:out example with HTML escaping --%>
<c:if test="${requestScope.htmlTagData ne null }">
<c:out value="${requestScope.htmlTagData}" escapeXml="true">c:out>

c:if>

<br><br>
<%-- c:set example to set variable value --%>
<c:set var="id" value="5" scope="request">c:set>

<c:out value="${requestScope.id }" >c:out>

<br><br>
<%-- c:catch example --%>
<c:catch var ="exception">
   <% int x = 5/0;%>
c:catch>

<c:if test = "${exception ne null}">
   <p>Exception is : ${exception} <br />
   Exception Message: ${exception.message}p>

c:if>

<br><br>
<%-- c:url example --%>
<a href="${requestScope.url }">c:url>">JournalDeva>

body>

html>

 

 

当访问http://localhost:8080/JSTLExample/HomeServlet这个servlet的时候，我们会看到下面的结果