1.5 JSP标准标签库(JSTL)(核心标签 outsetremoveifchooseforEachforTokensredirect)

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JSTL(JavaServer Page Standard Tag  Library):JSP标准标签库。它封装了JSP应用的通用核心功能。

 

1.准备工作

使用JSTL前需要下载所需文件,下载地址及安装教材可参阅:http://www.runoob.com/jsp/jsp-jstl.html

 

测试类 Person.java

public class Person {
    private String name;
    private String sex;
    private int age;
    
    public String getName() {
        return name;
    }
    
    public void setName(String name) {
        this.name = name;
    }
    public String getSex() {
        return sex;
    }
    public void setSex(String sex) {
        this.sex = sex;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
}

 

2、c:out标签:类似out.printf(xxx)

<%@ 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> 
    
    <%
        request.setAttribute("requestAttribute", "requestValue");
    %>
    
    <jsp:useBean id = "per" class = "com.myclass.Person" scope = "request" />  <!-- Person per = new Person()-->
    
    <jsp:setProperty name = "per" property = "name" value = "zhansan"/>         
    
    <c:out value = "zhansan"/><br>                         <!-- out标签直接输出字符串 -->
    <c:out value = "${requestAttribute}"></c:out><br>      <!-- out标签输出属性-->
    <c:out value = "${per.name}"></c:out><br>              <!-- out标签输出对象中属性 -->
    
    <!-- 当输出为空时,输出默认值-->
    <c:out value = "${requestAttri}" default = "该属性不存在!"/><br>     <!-- default设置默认值 -->
    <c:out value = "${requestAttri}">该属性不存在</c:out><br>             <!-- 标签体设置默认值 -->
    <c:out value = "<%=null %>" default = "该属性不存在!"/> 
        
</body>
</html>

 

 

 

 

3、c:set标签:主要用于设置属性、对象中属性的值。类似setXXX,setAttribute(var,value);

 

<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body> 
    
    <%
        request.setAttribute("requestAttri", "requestValue");
    %> 
    
    <jsp:useBean id = "per" class = "com.myclass.Person" scope = "request" />  <!-- Person per = new Person()-->
    
    <c:set var = "test" value = "test"/>   <!-- 没有指定属性范围,默认是pageScope -->
    ${pageScope.test}
    
    <!-- <c:set var = "属性名称" value = "属性值"  scope = "属性作用域" /> -->
    <c:set var = "sessionName" value = "sessionValue" scope = "session"/>  <!-- 在指定范围中设置属性 (value属性设置值) -->
    <!-- 相当于session.setAttribute("sessionName","sessionValue")  -->
    <c:out value = "${sessionName}" />
    
  <!-- <c:set var = "属性名称" scope = "属性作用域"> 属性值 </c:set> --> <c:set var = "requestName" scope = "request">requestValue</c:set>   <!--在指定范围中设置属性 (标签体设置值)--> <!-- 相当于request.setAttribute("requestName","requestValue") --> <c:out value = "${requestName}" />
  <!-- <c:set target = "对象名称" property = "属性名" value = "属性值"> --> <c:set target = "${per}" property = "name" value = "zhangsan"/>   <!--通过标签 设置对象属性 类似 per.name = "zhangsan"--> <c:out value="${per.name}"></c:out> <c:out value="${per}"></c:out> <!-- 此处的${per} 类似 System.out.print(per)--> </body> </html>

 

 

4、c:remove标签:移除属性,类似(xxx.remove(name))

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ page import = "java.util.*,com.myclass.*" %>
<%@ 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:set var = "testRemove" value = "value" scope = "session"/>
    <!-- <c:remove var = "属性名" scoep = "[page|request|session|application]" /> 删除指定作用域中的var属性-->
    <c:remove var="testRemove" scope="session"/>  <!-- 类似 session.removeAttribute("testRemove") -->
    <c:out value = "${tempRemove }" default="该属性不存在"/>        
</body>
</html>

 

 

5、c:if 标签:用于判断,类似if(test == [true | false]){语句}

 

<%@ 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:set var = "age" value = "19" scope = "session"/>
        <%--   <c:if test = "判断条件" var = "属性名" scope = "设置保存范围"  />   --%>
        <!-- 判断的结果(true|false)会存储在var中 -->
        <c:if test = "${age >= 18 }" var="isAdult" scope = "session" >
            <h2> 成年</h2>  <!-- 满足条件执行的语句 -->
        </c:if>
        <c:if test = "${!isAdult}" >  <!-- !isAdult 和isAdult互反所以只会执行一个 -->
            未成年
        </c:if>
        是否成年:${isAdult}
        
</body>
</html>

 

 

6、c:choose标签:分支选择,类似switch。

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<%@ page import = "java.util.*,com.myclass.*" %>
<%@ 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:set var = "score" value = "60" scope = "session"/>
        <c:choose >
            <c:when test="${score >= 90}"> 优秀</c:when>     <!-- test为true则执行对应语句并跳出choose -->
            <c:when test="${score >= 80}"> 良好</c:when>
            <c:when test="${score >= 70}"> 一般</c:when>
            <c:when test="${score >= 60}"> 及格</c:when>
            <c:otherwise>不及格</c:otherwise>                   <!-- 所有选项都不满足则执行otherwise中的语句 -->
        </c:choose>
        
</body>
</html>

 

 

7、c: forEach标签:主要用于输出可迭代对象和控制迭代次数(for)

 实现了Collection接口的对象,都可以使用forEach输出。

<%@ 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> 
    <!-- forEach输出list -->
    <%
        List<String> list = new LinkedList<String>();
        for(int i = 0; i < 5; i++){
            list.add("" + i);
        }
        request.setAttribute("list", list);
    %>
    
    <c:forEach items = "${list}" var = "li">
        <c:out value = "${li}"/><!-- li就代表链表中一个对象(String) -->
    </c:forEach><br>
    
    <!-- forEach输出map -->
    <%
        Map<String,Person> map = new HashMap<String,Person>();
        for(int i = 0; i < 5; i++){
            map.put("" + i,new Person("" + i, i % 2 == 0 ? "man" : "woman", i));
        }
        request.setAttribute("map",map);
    %>
    <c:forEach items = "${map}" var = "m" ><!-- m代表map中一个对象,可通过m.key获取键,m.value获取值(person对象) -->
        ${m.key } ${m.value.name} ${m.value.sex} ${m.value.age}<br> 
    </c:forEach><br>
    
    <!-- 控制迭代次数 并输出状态-->
    <table>
        <td></td><td> 是否是第一个</td><td>是否是最后一个</td><td>计数(当前是第几个)</td>
        <c:forEach var = "i" begin="1" end = "11" step = "2" varStatus="st"> <!-- 步长(step)为2 for(i = 1; i <= 11 ; i += 2 ) -->
                <tr><!-- 迭代的属性           当前属性是否是第一个       当前属性是否是最后一个     计数是第几个属性,从1开始-->    
                    <td>${i }</td><td> ${st.first}</td><td>${st.last }</td><td>${st.count}</td>
                </tr>
        </c:forEach>
    </table>
        
</body>
</html>

 

8、forTokens标签: 将字符串分割成子串然后迭代。类“www.google.com”.split(".")

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