Example analysis of various applications of EL expression in JSP
- 2021-10-11 19:15:23
- OfStack
EL operator:
<%@page language="java" contentType="text/html;charset=gb2312"%>
<%@page import="java.sql.*" %>
<!DOCTYPE html>
<html>
<head>
<title>El Arithmetic operator </title>
</head>
<body>
<table border=1>
<tr>
<td> Arithmetic operator </td>
<td> Results </td>
</tr>
<tr>
<td> Addition operator \${1 + 1}</td>
<td> Results ${1+1}</td>
</tr>
<tr>
<td> Subtraction operator \${1 - 1}</td>
<td> Results ${1-1}</td>
</tr>
<tr>
<td> Multiplication operator \${1 * 2}</td>
<td> Results ${1 * 1}</td>
</tr>
<tr>
<td> Division operator \${3 / 2}</td>
<td> Results ${3 / 2}</td>
</tr>
<tr>
<td> Coherence operator \${3 % 2}</td>
<td> Results ${3 % 2}</td>
</tr>
</table>
<table border=1>
<tr>
<td> Relational operator </td>
<td> Results </td>
</tr>
<tr>
<td> Equal operator \${1 == 1}</td>
<td> Results ${1==1}</td>
</tr>
<tr>
<td> Not equal to operator \${1 != 1}</td>
<td> Results ${1!=1}</td>
</tr>
<tr>
<td> Less than operator \${1 < 2}</td>
<td> Results ${1 < 2}</td>
</tr>
<tr>
<td> Greater than operator \${3 > 2}</td>
<td> Results ${3 > 2}</td>
</tr>
<tr>
<td> Less than or equal to operator \${1 <= 2}</td>
<td> Results ${1 <= 2}</td>
</tr>
<tr>
<td> Greater than or equal to operator \${3 >= 2}</td>
<td> Results ${3 >= 2}</td>
</tr>
</table>
<table border=1>
<tr>
<td> Logical operator </td>
<td> Results </td>
</tr>
<tr>
<td colspan="2"> Logical operator &&</td>
</tr>
<tr>
<td>\${true && true}</td>
<td> Results ${true && true}</td>
</tr>
<tr>
<td>\${true && false}</td>
<td> Results ${true && false}</td>
</tr>
<tr>
<td>\${false && false}</td>
<td> Results ${false && false}</td>
</tr>
<tr>
<td colspan="2"> Logical operator ||</td>
</tr>
<tr>
<td>\${true || true}</td>
<td> Results ${true || true}</td>
</tr><tr>
<td>\${true || false}</td>
<td> Results ${true || false}</td>
</tr><tr>
<td>\${false || false}</td>
<td> Results ${false || false}</td>
</tr>
<tr>
<td colspan="2"> Logical operator !</td>
</tr>
<tr>
<td>\${!true}</td>
<td> Results ${!true}</td>
</tr><tr>
<td>\${!false}</td>
<td> Results ${!false}</td>
</tr>
</table>
<table border=1>
<tr>
<td> Conditional operator </td>
<td> Results </td>
</tr>
<tr>
<td>\${2>1?"Yes":"No"}</td>
<td> Results ${2>1?"Yes":"No"}</td>
</tr>
<tr>
<td>\${2<1?"Yes":"No"}</td>
<td> Results ${2<1?"Yes":"No"}</td>
</tr>
</table>
<table border=1>
<tr>
<td> Validation operator </td>
<td> Results </td>
</tr>
<tr>
<td>\${empty param.username}</td>
<td> Results ${empty param.username}</td>
</tr>
<tr>
<td>\${empty param.password}</td>
<td> Results ${empty param.password}</td>
</tr>
</table>
<table border=1>
<tr>
<td> Parenthesis Operator and Operator Priority </td>
<td> Results </td>
</tr>
</table>
</body>
</html>
EL handles built-in objects:
The "." and "[]" symbols are used to access data
${applicationScope.user.username}
${applicationScope.user[0].username}
${applicationScope.user["user-name"]}
To pass a value through a variable, you must use []
${applicationScope.user["data"]}
Built-in objects related to storage
<!DOCTYPE html>
<html>
<head>
<title> Built-in objects related to storage </title>
</head>
<body>
<%
//application Range setting properties name With a value of application_name
application.setAttribute("name","application_name");
//session Range setting properties name With a value of session_name
session.setAttribute("name","session_name");
//request Range setting properties name With a value of request_name
request.setAttribute("name","request_name");
//page Range setting properties name With a value of page_name
pageContext.setAttribute("name","page_name");
%>
<%-- Get page Within the scope name Attribute --%>
page The value of the property within the scope is: ${pageScope.name}<br />
<%-- Get request Within the scope name Properties of --%>
request The value of the property within the scope is: ${requestScope.name}<br />
<%-- Get session Within the scope name Properties of --%>
session The value of the property within the scope is: ${sessionScope.name}<br />
<%-- Get application Within the scope name Attribute --%>
application The value of the property within the scope is: ${applicationScope.name}<br />
</body>
</html>
Built-in objects related to input
<!DOCTYPE html>
<html>
<head>
<title> User form </title>
</head>
<body>
<form action="UserDemo.jsp" method="post">
User name: <input type="text" name="username" /><br />
Password: <input type="password" name="password" /><br />
Name: <input type="text" name="name" /><br />
Gender: <input type="radio" name="sex" value=" Male "> Male <input type="radio" name="sex" value=" Female "> Female <br />
Hobbies: <br />
<input type="checkbox" name="interest" value=" Play basketball "> Play basketball <br />
<input type="checkbox" name="interest" value=" Read a book "> Read a book <br />
<input type="checkbox" name="interest" value=" Travel "> Travel <br />
<input type="checkbox" name="interest" value=" Programming "> Programming <br />
<input type="submit" value=" Submit ">
<input type="reset" value=" Reset ">
</form>
</body>
</html>
<!DOCTYPE html>
<html>
<head>
<title> Receive user parameters </title>
</head>
<body>
<%
// Format page encoding
request.setCharacterEncoding("gb2312");
%>
<%-- Receive user parameters --%>
User name: ${<span style="color:#003399;">param</span>.username}<br />
Password: ${<span style="color:#003399;">param</span>.password}<br />
Name: ${<span style="color:#003399;">param</span>.name}<br />
Gender: ${<span style="color:#003399;">param</span>.sex}<br />
Hobbies: ${<span style="color:#003399;">paramValues</span>.interest[0]}
${<span style="color:#003399;">paramValues</span>.interest[1]}
</body>
</html>
cookie built-in object
<!DOCTYPE html>
<html>
<head>
<title> Settings cookie Value of </title>
</head>
<body>
<%
// Settings cookie Value of
Cookie c = new Cookie("username","root");
// Add cookie To the client
response.addCookie(c);
%>
<a href="getCookieDemo.jsp"> Display cookie Value of </a>
</body>
</html>
<span style="color:#000000;"><%@page language="java" contentType="text/html;charset=gb2312"%>
<!DOCTYPE html>
<html>
<head>
<title> Acquire cookie Value of </title>
</head>
<body>
cookie In username The value of is: ${cookie.username.value}
</body>
</html>
header Built-in Object
<!DOCTYPE html>
<html>
<head>
<title> Acquire header Value of </title>
</head>
<body>
${header["host"]}<br />
${header["user-agent"]}<br />
</body>
</html>
initParam Built-in Object: Gets the environment variables set in the web site
<%@page language="java" contentType="text/html;charset=gb2312"%>
<!DOCTYPE html>
<html>
<head>
<title> Obtain environmental parameters </title>
</head>
<body>
username Parameter values: ${initParam.username}<br />
</body>
</html>
<?xml version="1.0" encoding="ISO-8859-1"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
version="2.5">
<context-param>
<param-name>username</param-name>
<param-value>Zhangdapeng</param-value>
</context-param>
</web-app>
pageContex Built-in Object
Used to get detailed information about user requests and pages
<%@page language="java" contentType="text/html;charset=gb2312"%>
<!DOCTYPE html>
<html>
<head>
<title>pageContext Demo </title>
</head>
<body>
<table border="1">
<tr>
<td> Gets the string of the requested parameters </td>
<td>${pageContext.request.queryString}</td>
</tr><tr>
<td> Acquisition request URL</td>
<td>${pageContext.request.requestURL}</td>
</tr><tr>
<td> Acquire web Application name </td>
<td>${pageContext.request.contextPath}</td>
</tr><tr>
<td> Acquire HTTP Request mode ( POST/GET ) </td>
<td>${pageContext.request.method}</td>
</tr><tr>
<td> Obtain the agreement for use </td>
<td>${pageContext.request.protocol}</td>
</tr><tr>
<td> Obtain users IP Address </td>
<td>${pageContext.request.remoteAddr}</td>
</tr><tr>
<td> Judge session Is it new </td>
<td>${pageContext.session.new}</td>
</tr><tr>
<td> Acquire session Adj. id</td>
<td>${pageContext.session.id}</td>
</tr>
</table>
</body>
</html>
EL accessor:
Read data in JavaBean using accessor
package com.javaweb.ch08;
import java.util.*;
//1 A simple one JavaBean Example
public class Person{
//name Attribute
private String name;
//age Attribute
private int age;
//sex Attribute
private String sex;
//friends Attribute
private ArrayList friends;
// Parametric construction method
public Person(){
}
// Custom constructed methods
public Person(String name,int age,String sex){
this.name = name;
this.age = age;
this.sex = sex;
}
// Get name Attribute value of
public String getName(){
return name;
}
// Get age Attribute value
public int getAge(){
return age;
}
// Get sex Attribute value of
public String getSex(){
return sex;
}
// Settings name Properties of
public void setName(String name){
this.name = name;
}
// Settings age Attribute value of
public void setAge(int age){
this.age = age;
}
// Settings sex Attribute value of
public void setSex(String sex){
this.sex = sex;
}
// Settings friends Value of
public void setFriends(ArrayList friends){
this.friends = friends;
}
// Get friends Attribute value of
public ArrayList getFriends(){
return friends;
}
}
${applicationScope.user.username}
${applicationScope.user[0].username}
${applicationScope.user["user-name"]}
Using memory to read data in Map
${applicationScope.user.username}
${applicationScope.user[0].username}
${applicationScope.user["user-name"]}
Using memory to read data from an array
${applicationScope.user.username}
${applicationScope.user[0].username}
${applicationScope.user["user-name"]}
Complex application of memory
<%@page language="java" contentType="text/html;charset=gb2312"%>
<%@page import="java.util.*,com.javaweb.ch08.*" %>
<!DOCTYPE html>
<html>
<head>
<title> Settings Array Page </title>
</head>
<body>
<%
ArrayList<Person> persons = new ArrayList<Person>();
Person person1 = new Person("wang wu",24," Male ");
Person person2 = new Person("wang liu",24," Female ");
persons.add(person1);
persons.add(person2);
session.setAttribute("persons",persons);
%>
<a href="GetMapDemo.jsp"> Jump to GetArrayDemo.jsp</a>
</body>
</html>
<%@page language="java" contentType="text/html;charset=gb2312"%>
<!DOCTYPE html>
<html>
<head>
<title> Read using memory map Data in </title>
</head>
<body>
User name 1 : ${sessionScope.persons[0].name},${sessionScope.persons[0].age},${sessionScope.persons[0].sex}<br />
User name 2 : ${sessionScope.persons[1].name},${sessionScope.persons[1].age},${sessionScope.persons[1].sex}<br />
</body>
</html>