<h3>存取是普通的单值数据</h3>

<%

    //pageContext.setAttribute("name", "pValue");

    //request.setAttribute("name", "rValue");

    //session.setAttribute("name", "sValue");

    application.setAttribute("name", "aValue");

%>

<%=pageContext.getAttribute("name") %> <!-- 如果没找到 返回null -->

<%=request.getAttribute("name") %>

<%=session.getAttribute("name") %>

<%=application.getAttribute("name") %>

<hr/>

${ pageScope.name } <!-- 返回的是"" -->

${ requestScope.name }

${ sessionScope.name }

${ applicationScope.name }

<hr/>

${ name } <!-- 类似findAttribute("name") 先从page域中查找,没找到去request域中查询,没有找到去session域中找，没有找到就去application域中找 -->

<h3>获取数组的数据</h3>

<%

    String[] arrs = {"李旭华","李冠希","杨凤","杨如花"};

    pageContext.setAttribute("arrs", arrs);

%>

${ arrs[0] }

${ arrs[1] }

${ arrs[2] }

${ arrs[3] }

<h3>获取List集合的数据</h3>

<%

    List<String> list = new ArrayList<String>();

    list.add("李芙蓉");

    list.add("杨芙蓉");

    list.add("王凤");

    pageContext.setAttribute("list", list);

%>

${ list[0] }

${ list[1] }

${ list[2] }

<h3>获取Map集合的数据</h3>

<%

    Map<String,String> map = new HashMap<String,String>();

    map.put("aaa","李旭华");

    map.put("bbb","杨久君");

    map.put("ccc","李芮");

    map.put("ddd","李凤");

    pageContext.setAttribute("map", map);

%>

${ map.aaa }

${ map.bbb }

${ map.ccc }

${ map.ddd }

<h3>获取对象的数据</h3>

<%

    User user = new User(1,"aaa","123");

    pageContext.setAttribute("user", user);

%>

${ user.id }

${ user.username }

${ user.password }

当对象里的成员变量又有嵌套对象的时候,user.detailuser.name

<h3>获取对象的集合的数据</h3>

<%

    User user1 = new User(1,"aaa","123");

    User user2 = new User(2,"bbb","123");

    User user3 = new User(3,"ccc","123");

    List<User> userList = new ArrayList<User>();

    userList.add(user1);

    userList.add(user2);

    userList.add(user3);

    pageContext.setAttribute("userList", userList);

%>

${ userList[0].id } - ${ userList[0].username } - ${ userList[0].password }<br/>

${ userList[1].id } - ${ userList[1].username } - ${ userList[1].password }<br/>

${ userList[2].id } - ${ userList[2].username } - ${ userList[2].password }<br/>

***** .和[]的区别.

    * []用于有下标的数据(数组,list集合) .用于有属性的数据(map,对象)

    * 如果属性名中包含有特殊的字符.必须使用[]

<h1>EL的功能二:执行运算</h1>

<h3>EL执行算数运算</h3>

<%

    pageContext.setAttribute("n1", "10");

    pageContext.setAttribute("n2", "20");

    pageContext.setAttribute("n3", "30");

    pageContext.setAttribute("n4", "40");

%>

${ n1 + n2 + n3 }

<h3>EL执行逻辑运算</h3>

${ n1 < n2 } - ${ n1 lt n2 } <!-- less than --><br/>

${ n1 > n2 } - ${ n1 gt n2 } <!-- great than --><br/>

${ n1 <= n2 } - ${ n1 le n2 } <!-- less equal --><br/>

${ n1 >= n2 } - ${ n1 ge n2 } <!-- great equal --><br/>

${ n1 == n2 } - ${ n1 eq n2 } <!-- equal --><br/>

<h3>EL执行关系运算</h3>

${ n1<n2 && n3 < n4 } - ${ n1<n2 and n3 < n4 }<br/>

${ n1<n2 || n3 < n4 } - ${ n1<n2 or n3 < n4 }<br/>

${ !(n1 < n2) } - ${ not(n1<n2) }

<h3>EL执行三元运算</h3>

${ n1 < n2 ? "正确":"错误" }

<h3>empty运算</h3>

${ user == null } - ${ empty user }

${ user != null } - ${ not empty user }

<h1>EL功能三:操作WEB开发常用的对象</h1>

<!--

    pageScope,requestScope,sessionScope,applicationScope - 获取JSP中域中的数据

    param,paramValues     - 接收参数.

    header,headerValues - 获取请求头信息

    initParam            - 获取全局初始化参数

    cookie                - WEB开发中cookie

    pageContext            - WEB开发中的pageContext.

PageScope和pageContext的区别:pageScope是专门用来获取page域中的数据;pageContext可以获取request等其他八个域对象.

 -->

<h3>接收请求的参数</h3>

<%= request.getParameter("id") %>

<%= request.getParameter("name") %>

<%= Arrays.toString(request.getParameterValues("hobby")) %>

<hr/>

${ param.id }

${ param.name }

${ paramValues.hobby[0] }

${ paramValues.hobby[1] }

<h3>获取请求头</h3>

<%= request.getHeader("User-Agent") %>

<hr/>

${ header["User-Agent"] }

<h3>获取全局初始化参数</h3>

${ initParam.username }

<h3>获取Cookie中的值</h3>

${ cookie.history.value }    如果没有值返回的是””,而不是null

<h3>获取PageContext中的对象</h3>

IP地址：${ pageContext.request.remoteAddr }

工程路径:${ pageContext.request.contextPath }

<c:set var="n1" value="10" scope="page"></c:set>

<c:set var="n2" value="20" scope="page"></c:set>

<c:if test="${ n1 < n2 }" var="flag" scope="page">

    n1 小于 n2

</c:if>

<c:if test="${ n1 >= n2 }">

    n1 大于等于 n2

</c:if>

<c:if test="${ flag }">

    n1 小于 n2

</c:if>

<h1>JSTL的常用标签:forEach</h1>

<%

    String[] arrs = {"李旭华","李冠希","董阳阳"};

    pageContext.setAttribute("arrs", arrs);

%>

<c:forEach var="i" items="${ arrs }">

    ${ i }

</c:forEach>

<h3>遍历List集合</h3>

<%

    List<String> list = new ArrayList<String>();

    list.add("李旭华");

    list.add("李冠希");

    list.add("董阳阳");

    pageContext.setAttribute("list", list);

%>

<c:forEach var="i" items="${ list }">

    ${ i }

</c:forEach>

<h3>遍历Map集合</h3>

<%

    Map<String,String> map = new HashMap<String,String>();

    map.put("aaa","李旭华");

    map.put("bbb","叽里咕噜");

    map.put("ccc","咿咿呀呀");

    pageContext.setAttribute("map", map);

%>

<c:forEach var="entry" items="${ map }">

    ${ entry.key }-${ entry.value }

</c:forEach>

<h3>遍历从1到10</h3>

<c:forEach var="i" begin="1" end="10" step="2">

    ${ i }

</c:forEach>

<h3>遍历从100到300</h3>

<c:forEach var="i" begin="100" end="300" step="5" varStatus="status">

    <c:if test="${ status.count % 3 == 0 }">

        <font color="red">${ i }</font>

    </c:if>

    <c:if test="${ status.count % 3 != 0 }">

        ${ i }

    </c:if>

</c:forEach>

<h1>JSTL提供的EL的函数库</h1>

${ fn:contains("Hello World","Hello") }

${ fn:length("HelloWorld") }

${ fn:toLowerCase("ABCDE") }

<c:forEach var="i" items='${ fn:split("a-b-c-d","-") }'>

    ${ i }

</c:forEach>

创建数据库：

CREATE TABLE `product` (

  `pid` varchar(32) NOT NULL,

  `pname` varchar(50) DEFAULT NULL,

  `market_price` double DEFAULT NULL,

  `shop_price` double DEFAULT NULL,

  `pimage` varchar(200) DEFAULT NULL,

  `pdate` date DEFAULT NULL,

  `is_hot` int(11) DEFAULT NULL,

  `pdesc` varchar(255) DEFAULT NULL,

  `pflag` int(11) DEFAULT NULL,

  `cid` varchar(32) DEFAULT NULL,

  PRIMARY KEY (`pid`)

) ENGINE=InnoDB DEFAULT CHARSET=utf8;

页面显示:

    <c:forEach var="p" items="${list }">

    <tr>

        <td>${ p.pid }</td>

        <td>${ p.pname }</td>

        <td>${ p.shop_price }</td>

        <td>

            <c:if test="${ p.is_hot == 1 }">

                是

            </c:if>

            <c:if test="${ p.is_hot != 1 }">

                否

            </c:if>

        </td>

        <td>${ p.pdesc }</td>

    </tr>

    </c:forEach>