JavaEE-08 JSTL和EL

<!-- 设置之前应该是空值 -->
设置变量之前的值是：msg=
<c:out value="${msg}" default="null" />
<!-- 给变量msg设值 -->
<c:set var="msg" value="Hello JSP!" scope="page"></c:set>
<!-- 此时msg的值应该是上面设置的"已经不是空值了" -->
<br>设置新值以后：msg=
<c:out value="${msg}"></c:out>
<!-- 把 msg变量从page范围内移除-->
<c:remove var="msg" scope="page" />
<!-- 此时msg的值应该显示null -->
<br>移除变量msg以后：msg=
<c:out value="${msg}" default="null"></c:out>

<c:if test="<boolean>" var="<string>" scope="<string>">
...
</c:if>

/**User类*/
public class User {
private String name;
private String password;
private String role;
private String[] habits;
//……
}

/**login.jsp*/<%
String userName = request.getParameter("userName");//用户名
String password = request.getParameter("passWord");//密码
String cmdStr = request.getParameter("cmdStr");//cmdStr
if ("post".equals(cmdStr)) {
if ("admin".equals(userName) && "admin".equals(password)) {
//登录成功
User user = new User();
user.setName(userName);
user.setPassword(password);
//设置session属性
request.getSession().setAttribute("user", user);
} else {
request.setAttribute("errMsg", "用户名或密码不正确");
}
}
%>
<c:set var="isLogin" value="${empty sessionScope.user}" />
<c:if test="${isLogin}">
<form id="login" method="post" action="login_2.jsp">
<input type="hidden" value="post" name="cmdStr">
<c:if test="${not empty errMsg}">
<div style="color:red;">${errMsg}</div>
<c:remove var="errMsg" />
</c:if>
<table>
<tr>
<td>用户名:</td>
<td><input id="userName" name="userName" type="text"></td>
</tr>
<tr>
<td>密码:</td>
<td><input id="passWord" name="passWord"
type="password"></td>
</tr>
</table>
<input type="submit" value="登录">
</form>
</c:if>
<c:if test="${!isLogin}">
欢迎 ${user.name},您已经登录成功!
<c:remove var="user" scope="session"/>
</c:if>

<c:choose >
<c:when test="<boolean>"/>
...
</c:when>
<c:when test="<boolean>"/>
...
</c:when>
...
...
<c:otherwise>
...
</c:otherwise>
</c:choose>

<c:set var="salary" scope="session" value="${2000*2}" />
<p>
你的工资为 :
<c:out value="${salary}" />
</p>
<c:choose>
<c:when test="${salary <= 0}">
太惨了。
</c:when>
<c:when test="${salary > 1000}">
不错的薪水，还能生活。
</c:when>
<c:otherwise>
什么都没有。
</c:otherwise>
</c:choose>

<%
//用户名
String userName = request.getParameter("userName");
//密码
String password = request.getParameter("passWord");
//cmdStr
String cmdStr = request.getParameter("cmdStr");if ("post".equals(cmdStr)) {
if ("accp_user".equals(userName) && "accp_pass".equals(password)) {
//登录成功
User user = new User();
user.setName(userName);
user.setPassword(password);
user.setRole("部门经理");
//设置session属性
request.getSession().setAttribute("user", user);
} else {
request.setAttribute("errMsg", "用户名或密码不正确");
}
}
%>
<c:choose>
<c:when test="${empty user}">
<form id="login" method="post" action="login_3.jsp">
<input type="hidden" value="post" name="cmdStr">
<c:if test="${not empty errMsg}">
<div style="color:red;">${errMsg}</div>
<c:remove var="errMsg" />
</c:if>
<table>
<tr>
<td>用户名:</td>
<td><input id="userName" name="userName"
type="text"></td>
</tr>
<tr>
<td>密码:</td>
<td><input id="passWord" name="passWord"
type="password"></td>
</tr>
</table>
<input type="submit" value="登录">
</form>
</c:when>
<c:otherwise>
<c:choose>
<c:when test="${user.role eq '总监'}">
总监页面
</c:when>
<c:when test="${user.role eq '部门经理'}">
部门经理页面
</c:when>
<c:otherwise>
员工页面
</c:otherwise>
</c:choose>
</c:otherwise>
</c:choose>

<c:forEach items="<object>" begin="<int>" end="<int>" step="<int>"
var="<string>" varStatus="<string>">
//循环体
</c:forEach>

<c:forEach var="i" begin="1" end="5">
Item<c:out value="${i}"/><p>
</c:forEach>

<c:forEach begin="1" end="5" step= "2">
<c:out value="*"></c:out>
</c:forEach>

<%
Map<String, String> map = new HashMap<String, String>();
map.put("tom", "美国");
map.put("lily", "英国");
map.put("jack", "中国");
request.setAttribute("map", map);
%>
<c:forEach var="entry" items="${map}">
${entry.key}
${entry.value}<p>
</c:forEach>

<%
List products = GoodsDao.getAllProducts();
request.setAttribute("products", products);
%>
<!-- 循环输出商品信息 -->
<c:forEach var="product" items="${requestScope.products}" varStatus="status">
<!-- 如果是偶数行，为该行换背景颜色 -->
<tr <c:if test="${status.index % 2 == 1}">style="background-color:rgb(219,241,212);"</c:if>>
<td>${product.name }</td>
<td>${product.area }</td>
<td>${product.price }</td>
</tr>
</c:forEach>