JSF - Expression Language

JSF提供了豐富的表達式語言。我們可以使用{operation expression}符號來編寫正常操作。以下是JSF表達式語言的一些優點。

可以引用be an屬性，其中bean可以是存儲在請求、會話或應用程式範圍中的對象，也可以是託管bean。
提供對集合元素（可以是列表、映射或數組）的輕鬆訪問。
提供對預定義對象（如請求）的輕鬆訪問。
算術、邏輯和關係操作可以使用表達式語言完成。
自動類型轉換。
將缺少的值顯示爲空字符串，而不是NullPointerException。

Example Application

讓我們創建一個測試JSF應用程式來測試表達式語言。

Step	Description
1	Create a project with a name helloworld under a package com.tutorialspoint.test as explained in the JSF - First Application chapter.
2	Modify UserData.java under package com.tutorialspoint.test as explained below.
3	Modify home.xhtml as explained below. Keep the rest of the files unchanged.
4	Compile and run the application to make sure the business logic is working as per the requirements.
5	Finally, build the application in the form of war file and deploy it in Apache Tomcat Webserver.
6	Launch your web application using appropriate URL as explained below in the last step.

UserData.java

package com.tutorialspoint.test;

import java.io.Serializable;
import java.util.Date;

import javax.faces.bean.ManagedBean;
import javax.faces.bean.SessionScoped;

@ManagedBean(name = "userData", eager = true)
@SessionScoped
public class UserData implements Serializable {
   private static final long serialVersionUID = 1L;
   private Date createTime = new Date();
   private String message = "Hello World!";

   public Date getCreateTime() {
      return(createTime);
   }
   
   public String getMessage() {
      return(message);
   }
}

home.xhtml

<?xml version = "1.0" encoding = "UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" 
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns = "http://www.w3.org/1999/xhtml"
   xmlns:f = "http://java.sun.com/jsf/core"    
   xmlns:h = "http://java.sun.com/jsf/html">
   
   <h:head>
      <title>JSF Tutorial!</title>
   </h:head>
   
   <h:body>
      <h2>Expression Language Example</h2>
      Creation time: 
      <h:outputText value = "#{userData.createTime}"/>
      <br/><br/>
      Message: 
      <h:outputText value = "#{userData.message}"/>
   </h:body>
</html>

完成所有更改後，讓我們像在JSF-First應用程式一章中那樣編譯和運行應用程式。如果您的應用程式一切正常，這將產生以下結果。