JavaWeb入门—引用JSTL核心库

引用JSTL核心库

1.介绍

JSTL安装功能分为5类标签库

类别

核心标签库——core

格式化输出标签库——fmt

SQL操作标签库——sql

XML操作标签库——xml

函数标签库——functions

2.抒写规则

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

JSTL标签库在taglibs-standard-impl.jar由META-INF/c.tld定义。

3.使用JSTL

导入相对应的jar和在JSP中抒写对应规则，然后在<body>标签中抒写"<c:"就会出现如下选项，说明配置成功。

JavaWeb入门—引用JSTL核心库

4.判断标签

JSTL核心库提供了两种判断的标签

<c:if>——单分支判断

<c:choose>、<c:when>、<c:otherwise>——多分支判断

JstlServlet.java

package com.imooc.jstl;

import java.io.IOException;
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 JstlServlet
 */
@WebServlet("/jstl")
public class JstlServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public JstlServlet() {
        super();
    }

	protected void doGet(HttpServletRequest request, HttpServletResponse response) 
			throws ServletException, IOException {
		request.setAttribute("score", 46);
		request.setAttribute("grade", "B");
		request.getRequestDispatcher("/core.jsp").forward(request, response);
	}
}

core.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>JSTL</title>
</head>
<body>
	<h1>${requestScope.score }</h1>
	<c:if test="${requestScope.score>=60 }">
		<h2 style="color:green">成绩合格!</h2>
	</c:if>
	<c:if test="${requestScope.score<60 }">
		<h2 style="color:red">成绩不合格!</h2>
	</c:if>
</body>
</html>

JavaWeb入门—引用JSTL核心库

虽然实现了功能，但是使用单分支判断对于程序的可读性来说太差了。JSTL提供了多分支判断的语句

<%@ 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>JSTL</title>
</head>
<body>
	<h1>${requestScope.score }</h1>
	<c:if test="${requestScope.score>=60 }">
		<h2 style="color:green">成绩合格!</h2>
	</c:if>
	<c:if test="${c.score<60 }">
		<h2 style="color:red">成绩不合格!</h2>
	</c:if>
	
	<!-- 多分支判断  choose when otherwise-->
	<c:choose>
		<c:when test="${requestScope.grade == 'A'}">
			<h2>优秀</h2>
		</c:when>
		<c:when test="${requestScope.grade == 'B'}">
			<h2>良</h2>
		</c:when>
		<c:when test="${requestScope.grade == 'C'}">
			<h2>中</h2>
		</c:when>
		<c:when test="${requestScope.grade == 'D'}">
			<h2>差</h2>
		</c:when>
		<c:otherwise>
			<h2>GG</h2>
		</c:otherwise>
	</c:choose>
	
</body>
</html>

5.JSTL遍历集合

<c:forEach>标签用于遍历集合中的每一个对象

JavaWeb入门—引用JSTL核心库

items:遍历是集合

var：集合中的内容

varStatus：集合遍历的次数——idx.index=0为初始值

Company.java

package com.imooc.company;

public class Company {
	private String cname;
	private String url;
	
	//构造方法,方便写入数据
	public Company(String cname,String url) {
		this.cname = cname;
		this.url = url;
	}
	public String getCname() {
		return cname;
	}
	public void setCname(String cname) {
		this.cname = cname;
	}
	public String getUrl() {
		return url;
	}
	public void setUrl(String url) {
		this.url = url;
	}
	
}

CompanySevlet.java

package com.imooc.company;

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

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 CompanySevlet
 */
@WebServlet("/CompanySevlet")
public class CompanySevlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public CompanySevlet() {
        super();
    }

	/**
	 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doGet(HttpServletRequest request, HttpServletResponse response) 
			throws ServletException, IOException {
		
		//创建集合
		List<Company> list = new ArrayList<Company>();
		
		//存入信息
		list.add(new Company("百度","www.baidu.com"));
		list.add(new Company("腾讯", "www.tencent.com"));
		list.add(new Company("网易", "www.imooc.com"));
		
		//将集合存入request作用域
		request.setAttribute("companys", list);
		
		//进行转发
		request.getRequestDispatcher("/company.jsp").forward(request, response);
	}

}

company.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>Company</title>
</head>
<body>
	<!-- 通过forEach循环
		List companylist = request.getAttribute("companys");
		for(Company c : companylist){
			out.println("...");
		}
	 -->
	<c:forEach items="${requestScope.companys }" var="c" varStatus="idx">
		<h2>${idx.index+1}.${c.cname } ${c.url }</h2>
	</c:forEach>
</body>
</html>