EL運算式，
1、EL是JSP內建的運算式語言。
2、EL運算式來讀取四大域
3、JavaBean導航
1 <%@ page contentType="text/html;charset=UTF-8" language="java" %> 2 <%@ page import="domain.Employee,domain.Address" %> 3 <html> 4 <head> 5 <title>Title</title> 6 </head> 7 <body> 8 <% 9 Address address = new Address();10 address.setCity("深圳");11 address.setStreet("南山");12 13 Employee emp = new Employee();14 emp.setName("張三");15 emp.setSalary(12312);16 emp.setAddress(address);17 18 request.setAttribute("emp",emp);19 %>20 <h3>使用el擷取request域的emp</h3>21 ${requestScope.emp.address.street}22 <!-- request.getAttribute("emp").getAddress().getStreet--><br/>23 ${emp.hehe}24 </body>25 </html>
1 package domain; 2 public class Employee { 3 private String name; 4 private double salary; 5 private Address address; 6 7 public String getName() { return name; } 8 public void setName(String name) { this.name = name; } 9 public double getSalary() { return salary; }10 public void setSalary(double salary) { this.salary = salary; }11 public Address getAddress() { return address; }12 public void setAddress(Address address) { this.address = address; }13 @Override14 public String toString() {15 return "Employee{" +16 "name='" + name + '\'' +17 ", salary=" + salary +18 ", address=" + address +19 '}';20 }21 public String getHehe() { return "呵呵"; }22 }
1 package domain; 2 3 public class Address { 4 private String city; 5 private String street; 6 7 public String getCity() { return city; } 8 public void setCity(String city) { this.city = city; } 9 public String getStreet() { return street; }10 public void setStreet(String street) { this.street = street; }11 @Override12 public String toString() {13 return "Address{" +14 "city='" + city + '\'' +15 ", street='" + street + '\'' +16 '}';17 }18 }
4、EL可以輸出的東西都11個內建對象中:其中10個是Map，不是map的是PageContext類型，一個頂9個。
<body>
<%-- map.key這是el的文法，map['key']也可以操作map --%>
${param.username}<br/>
${paramValues.hobby[0]}
${paramValues.hobby[1]}
</body>
<body> ${header['User-Agent']}<br/> </body>
<context-param> <param-name>xxx</param-name> <param-value>XXX</param-value></context-param> <context-param> <param-name>yyy</param-name> <param-value>YYY</param-value></context-param>
<body>
${initParam.xxx}
</body>
<body>${cookie.JSESSIONID}<br/>${cookie.JSESSIONID.name}<br/>${cookie.JSESSIONID.value}<br/></body> 1 <body> 2 <!-- 擷取項目名，無則為"/" --> 3 ${pageContext.request.contextPath} 4 <hr/> 5 <a href="${pageContext.request.contextPath}/el/a.jsp">點擊這裡</a> 6 <form action="${pageContext.request.contextPath}/cookie/a.jsp" method="post"> 7 <input type="submit" value="xxx"> 8 </form> 9 <hr/>10 ${pageContext.session.id}11 </body>
| EL運算式 | 說明 | 描述 |
| ${pageContext.request.queryString} | pageContext.getRequest().getQueryString(); | 取得請求的參數字串 |
| ${pageContext.request.requestURL} | pageContext.getRequest().getRequestURL(); | 取得請求的URL，但不包括請求之參數字串 |
| ${pageContext.request.contextPath} | pageContext.getRequest().getContextPath(); | 服務的web application 的名稱 |
| ${pageContext.request.method} | pageContext.getRequest().getMethod(); | 取得HTTP 的方法(GET、POST) |
| ${pageContext.request.protocol} | pageContext.getRequest().getProtocol(); | 取得使用的協議(HTTP/1.1、HTTP/1.0) |
| ${pageContext.request.remoteUser} | pageContext.getRequest().getRemoteUser(); | 取得使用者名稱稱 |
| ${pageContext.request.remoteAddr } | pageContext.getRequest().getRemoteAddr(); | 取得使用者的IP 位址 |
| ${pageContext.session.new} | pageContext.getSession().isNew(); | 判斷session 是否為新的 |
| ${pageContext.session.id} | pageContext.getSession().getId(); | 取得session 的ID |
| ${pageContext.servletContext.serverInfo} | pageContext.getServletContext().getServerInfo(); | 取得主機端的服務資訊 |
5、EL函數庫（由JSTL提供的）
<%@taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions"%>
${fn:contains("abc","a")}<!-- true -->
| 函數 | 描述 |
| boolean contains(String input,String substring) | 測試輸入的字串是否包含指定的子串 |
| boolean containsIgnoreCase(String input,String substring) | 測試輸入的字串是否包含指定的子串，大小寫不敏感 |
| int indexOf(String input,String substring) | 返回指定字串在輸入字串中出現的位置 |
| String toLowerCase(String input) | 將字串中的字元轉為小寫 |
| String toUpperCase(String input) | 將字串中的字元轉為大寫 |
| boolean startsWith(String input,String substring) | 測試輸入字串是否以指定的首碼開始 |
| boolean endsWith(String input,String substring) | 測試輸入的字串是否以指定的尾碼結尾 |
| String substring(String input,int beginIndex,int endIndex) | 返回字串的子集 |
| String substringAfter(String input,String substring) | 返回字串在指定子串之後的子集 |
| String substringBefore(String input,String substring) | 返回字串在指定子串之前的子集 |
| String escapeXml(String input) | 跳過可以作為XML標記的字元("<"、">"、"&"、" ' "、“ " ”),即進行轉義 |
| String trim(String input) | 移除首尾的空白符 |
| String replace(String input,String substringBefore,String substringAfter) | 將輸入字串中指定的位置替換為指定的字串然後返回 |
| String[] split(String input,String delimiters) | 將字串用指定的分隔字元分隔然後組成一個子字串數組並返回 |
| int length(Object obj) | 返回字串、數組、各種集合的長度 |
| String join(String array[] ,String separator) | 將數組中的元素合成一個字串然後輸出 |
6、自訂函數庫
①寫一個java類，類中可以定義0~N個方法，但必須是static，而且有傳回值的。
②在WEB-INF目錄下建立一個tld檔案
<function> <name>fun</name> <function-class>fn.MyFunction</function-class> <function-signature>java.lang.String fun()</function-signature></function>
③在jsp頁面中匯入標籤庫
<%@ taglib prefix="it" uri="/WEB-INF/tlds/itcast.tld"%>
④在jsp頁面中使用自訂的函數：${it:fun()}
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