EL表达式的详细用法
EL与JSTL作为JAVA WEB开发者来说,熟练的运用它们,在View模式下效率更高.因为它们的存在,基本上在视图页是不会出现 JAVA 代码的!它们的强大之处将在下面一一列举!至于概念性的就不多说了,就以例子来介绍!
target.jsp
<%@ page language="java" contentType="text/html; charset=GB2312" import="cn.itcast.el.*,
java.util.*"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'target.jsp.jsp' starting page</title>
</head>
<body>
<%--
Object obj = session.getAttribute("person");
if(obj != null){
Person p = (Person)obj;
%>
name: <%= p.getName() %><br>
email: <%= p.getEmail() %><br>
password: <%= p.getPassword() %>
<%
}
--%>
1. <br>
name: ${sessionScope.person.name } -- ${sessionScope["person"].name }<br>
email: ${sessionScope.person.email }<br>
password: ${sessionScope.person.password }<br><br>
2.
<%
//pageContext.setAttribute("username", "Bob");
application.setAttribute("username", "Bob");
%>
<br>依次从 page request session application 中寻找指定的属性值<br>
username: ${username } -- (原理: <%= pageContext.findAttribute("username") %>)
<br><br>
3.<br>
<%
String age = request.getParameter("age");
out.println("age + 12(error): " + (age + 12) + ", (right): " + (Integer.parseInt(age) +
12));
%>
<br>
age + 12: ${param.age + 12}
<br><br>
4. <br>
<%
Person p = new Person();
p.setEmail("email123");
p.setName("Tom123");
p.setPassword("123456123");
request.setAttribute("person123", p);
%>
requestScope.person.email: ((强转成 javaBean 类型)request.getAttribute("person123")).getEmail
();<br>
email: ${requestScope.person123.email }
<br><br>
5. <br>
<%
int i = 0;
%>
<%= i %>
name: ${param.name} --- <%= request.getParameter("name") %><br>
age: ${param.age} --- <%= request.getParameter("age") %><br>
interesing: ${paramValues.interesing[0] } ${paramValues.interesing[1] }
---
<%= request.getParameterValues("interesing")[0] %>
<%= request.getParameterValues("interesing")[1] %>
<br><br>
6. <br>
initParam: ${initParam.initParam } --- <%= application.getInitParameter("initParam") %>
<br><br>
7. <br>
method: ${pageContext.request.method } --- <%= ((HttpServletRequest)pageContext.getRequest
()).getMethod() %><br>
localAddr: ${pageContext.request.localAddr }<br>
remoteHost: ${pageContext.request.remoteHost }<br>
contentType: ${pageContext.response.contentType }<br>
<br><br>
8. <br>
<%
request.setAttribute("number", 100);
%>
number + 12: ${requestScope.number + 12 } (不是: ${requestScope.number} + 12)
<br><br>
9. <br>
number > 12: ${requestScope.number > 12 }
<br><br>
10. <br>
<%
List list = new ArrayList();
request.setAttribute("list", list);
request.setAttribute("flag", null);
%>
empty list: ${empty requestScope.list }<br>
empty flag: ${empty requestScope.flag }<br>
<%
request.setAttribute("flag", "flagValue");
list.add("^^");
%>
empty flag: ${empty requestScope.flag }<br>
empty list: ${empty requestScope.list }<br>
和 10 比 : ${requestScope.number > 10 ? " > 10" : " < 10" }
</body>
</html>
target.jsp
<%@ page language="java" contentType="text/html; charset=GB2312" import="cn.itcast.el.*,
java.util.*"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>My JSP 'target.jsp.jsp' starting page</title>
</head>
<body>
<%--
Object obj = session.getAttribute("person");
if(obj != null){
Person p = (Person)obj;
%>
name: <%= p.getName() %><br>
email: <%= p.getEmail() %><br>
password: <%= p.getPassword() %>
<%
}
--%>
1. <br>
name: ${sessionScope.person.name } -- ${sessionScope["person"].name }<br>
email: ${sessionScope.person.email }<br>
password: ${sessionScope.person.password }<br><br>
2.
<%
//pageContext.setAttribute("username", "Bob");
application.setAttribute("username", "Bob");
%>
<br>依次从 page request session application 中寻找指定的属性值<br>
username: ${username } -- (原理: <%= pageContext.findAttribute("username") %>)
<br><br>
3.<br>
<%
String age = request.getParameter("age");
out.println("age + 12(error): " + (age + 12) + ", (right): " + (Integer.parseInt(age) +
12));
%>
<br>
age + 12: ${param.age + 12}
<br><br>
4. <br>
<%
Person p = new Person();
p.setEmail("email123");
p.setName("Tom123");
p.setPassword("123456123");
request.setAttribute("person123", p);
%>
requestScope.person.email: ((强转成 javaBean 类型)request.getAttribute("person123")).getEmail
();<br>
email: ${requestScope.person123.email }
<br><br>
5. <br>
<%
int i = 0;
%>
<%= i %>
name: ${param.name} --- <%= request.getParameter("name") %><br>
age: ${param.age} --- <%= request.getParameter("age") %><br>
interesing: ${paramValues.interesing[0] } ${paramValues.interesing[1] }
---
<%= request.getParameterValues("interesing")[0] %>
<%= request.getParameterValues("interesing")[1] %>
<br><br>
6. <br>
initParam: ${initParam.initParam } --- <%= application.getInitParameter("initParam") %>
<br><br>
7. <br>
method: ${pageContext.request.method } --- <%= ((HttpServletRequest)pageContext.getRequest
()).getMethod() %><br>
localAddr: ${pageContext.request.localAddr }<br>
remoteHost: ${pageContext.request.remoteHost }<br>
contentType: ${pageContext.response.contentType }<br>
<br><br>
8. <br>
<%
request.setAttribute("number", 100);
%>
number + 12: ${requestScope.number + 12 } (不是: ${requestScope.number} + 12)
<br><br>
9. <br>
number > 12: ${requestScope.number > 12 }
<br><br>
10. <br>
<%
List list = new ArrayList();
request.setAttribute("list", list);
request.setAttribute("flag", null);
%>
empty list: ${empty requestScope.list }<br>
empty flag: ${empty requestScope.flag }<br>
<%
request.setAttribute("flag", "flagValue");
list.add("^^");
%>
empty flag: ${empty requestScope.flag }<br>
empty list: ${empty requestScope.list }<br>
和 10 比 : ${requestScope.number > 10 ? " > 10" : " < 10" }
</body>
</html>