EL(express language)
${开头，并以}结束应用方向：访问应用程序数据，可以编写免jsp脚本的JSP代码
例：${a+b}${c+d}
对于文本${}处理 : \${
关键字：
and eq gt true instandor ne false empty
not it ge null div mod
运算符：
[] .
取值：expr-a[expr-b]
expr-a value-a
expr-b value-b
value-a:MAP LISt array javaBean
EL隐式对象：
pageContextimiparam
header
cookies
运算符：
算术运算：*/ % mod
+-
逻辑运算：
&& and
|| or
! not
关系运算：
==
！=
> gt
>= ge
< lt
<= le
${statement?A:B}
${(sessionScope.loggedIn==null)?"tou have not loggged in":"you have Logged in"}
empty运算符：
${empty x}
实例：
<!-- 获取接受的语言 -->
accept-language:${header['accept-language']}
<br/>
<!-- 获取表示 -->
session id:${pageContext.session.id}
<br/>
<!-- 获取员工的姓名信息 -->
employee:${requestScope.em.name}
<br/>
<!-- 获取首都信息 -->
capitals:${capitals["riben"] }
详细如下：
地址类：
package el;
public class Address {
private String Street;
private String city;
public String getStreet() {
return Street;
}
public void setStreet(String street) {
Street = street;
}
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
}
员工类：
package el;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet(name="employeeServlet",urlPatterns= {"/em"})
public class employeeServlet extends HttpServlet{
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//实现一个地址
Address address=new Address();
address.setCity("xian");
address.setStreet("changan");
//实现一个员工
employee em=new employee();
em.setId(3);
em.setName("张三");
em.setAddress(address);
//实现一个MAP对象
Map<String, String> capitals=new HashMap<String, String>();
capitals.put("China", "beijing");
capitals.put("A", "h");
capitals.put("canada", "ottowa");
capitals.put("riben", "dongjing");
//页面分发
RequestDispatcher rd=req.getRequestDispatcher("/employee.jsp");
rd.forward(req, resp);
}
}
员工servlet类：
package el;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet(name="employeeServlet",urlPatterns= {"/em"})
public class employeeServlet extends HttpServlet{
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//实现一个地址
Address address=new Address();
address.setCity("xian");
address.setStreet("changan");
//实现一个员工
employee em=new employee();
em.setId(3);
em.setName("张三");
em.setAddress(address);
//实现一个MAP对象
Map<String, String> capitals=new HashMap<String, String>();
capitals.put("China", "beijing");
capitals.put("A", "h");
capitals.put("canada", "ottowa");
capitals.put("riben", "dongjing");
//页面分发
RequestDispatcher rd=req.getRequestDispatcher("/employee.jsp");
rd.forward(req, resp);
}
}
jsp页面：
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>employee</title>
</head>
<body>
<!-- 获取接受的语言 -->
accept-language:${header['accept-language']}
<br/>
<!-- 获取表示 -->
session id:${pageContext.session.id}
<br/>
<!-- 获取员工的姓名信息 -->
employee:${requestScope.em.name}
<br/>
<!-- 获取首都信息 -->
capitals:${capitals["riben"] }
</body>
</html>