Struts 2 - 迭代器標籤

建立Action類

首先，讓我們建立一個名為Employee.java的簡單類，如下所示：

package com.tutorialspoint.struts2;

import java.util.ArrayList;
import java.util.List;

import org.apache.struts2.util.SubsetIteratorFilter.Decider;

public class Employee {
   private String name;
   private String department;

   public Employee(){}
   public Employee(String name,String department) {
      this.name = name;
      this.department = department;
   }
   
   private List employees;
   private List contractors;
	
   public String execute() {
      employees = new ArrayList();
      employees.add(new Employee("George","Recruitment"));
      employees.add(new Employee("Danielle","Accounts"));
      employees.add(new Employee("Melissa","Recruitment"));
      employees.add(new Employee("Rose","Accounts"));

      contractors = new ArrayList();
      contractors.add(new Employee("Mindy","Database"));
      contractors.add(new Employee("Vanessa","Network"));
      return "success";
   }

   public Decider getRecruitmentDecider() {
      return new Decider() {
         public boolean decide(Object element) throws Exception {
            Employee employee = (Employee)element;
            return employee.getDepartment().equals("Recruitment");
         }
      };
   }
   
   public String getName() {
      return name;
   }
   
   public void setName(String name) {
      this.name = name;
   }
   
   public String getDepartment() {
      return department;
   }
   
   public void setDepartment(String department) {
      this.department = department;
   }
   
   public List getEmployees() {
      return employees;
   }
   
   public void setEmployees(List employees) {
      this.employees = employees;
   }
   
   public List getContractors() {
      return contractors;
   }
   
   public void setContractors(List contractors) {
      this.contractors = contractors;
   }
}

Employee類有兩個屬性 - name 和 department，我們還有兩個employees列表 - permanent員工和合同工。我們有一個名為getRecruitmentDecider的方法，它返回一個Decider物件。

Decider實現如果員工在recruitment部門工作則返回true，否則返回false。

接下來，讓我們建立一個DepartmentComparator來比較Employee物件：

package com.tutorialspoint.struts2;

import java.util.Comparator;

public class DepartmentComparator implements Comparator {
   public int compare(Employee e1, Employee e2) {
      return e1.getDepartment().compareTo(e2.getDepartment());
   }

   @Override
   public int compare(Object arg0, Object arg1) {
      return 0;
   }
}

如上例所示，部門比較器根據部門按字母順序比較員工。

建立檢視

建立一個名為employee.jsp的檔案，內容如下：

<%@ page contentType = "text/html; charset = UTF-8" %>
<%@ taglib prefix = "s" uri = "/struts-tags" %>

<html>
   <head>
      <title>Employees</title>
   </head>
   
   <body>
      <b>Example of Iterator Tag</b><br/>
      
      <s:iterator value = "employees">
         <s:property value = "name"/> , 
         <s:property value = "department"/><br/>
      </s:iterator>
   
      <br/><br/>
   
      <b>Employees sorted by Department</b>
      <br/>

      <s:bean name = "com.tutorialspoint.struts2.DepartmentComparator" 
         var = "deptComparator" />

      <s:sort comparator = "deptComparator" source = "employees">
         
         <s:iterator>
            <s:property value = "name"/> , 
            <s:property value = "department"/><br/>
         </s:iterator>
      </s:sort>
   
      <br/><br/>
   
      <b>SubSet Tag - Employees working in Recruitment department </b><br/>
      <s:subset decider="recruitmentDecider" source = "employees">
         
         <s:iterator>
            <s:property value = "name"/> , 
            <s:property value = "department"/><br/>
         </s:iterator>
      
      </s:subset>
   
      <br/><br/>
   
      <b>SubSet Tag - Employees 2 and 3 </b><br/>
   
      <s:subset start="1" count = "2" source = "employees">
         
         <s:iterator>
            <s:property value = "name"/> , 
            <s:property value = "department"/><br/>
         </s:iterator>
      
      </s:subset>
   </body>
</html>

讓我們逐一瞭解使用的標籤：

迭代器標籤

我們使用iterator標籤遍歷employees列表。我們將"employees"屬性作為源提供給迭代器標籤。在迭代器標籤的主體中，我們現在可以訪問employees列表中的Employee物件。我們列印員工的姓名，然後列印他們的部門。

排序標籤

首先，我們將DepartmentComparator宣告為一個bean。我們給這個bean命名為deptComparator。然後我們使用sort標籤，並將"employees"列表指定為源，並將"deptComparator"指定為要使用的比較器。然後，根據前面的示例，我們迭代列表並列印員工。從輸出中可以看出，這會列印按部門排序的員工列表。

子集標籤

subset標籤用於獲取列表或陣列的子集。我們有兩種型別的subset標籤。在第一個示例中，我們使用recrutimentDecider獲取在招聘部門工作的員工列表（請參閱Employee.java中的getRecruitmentDecider()方法）。

在第二個示例中，我們沒有使用任何決策器，而是獲取列表中第2和第3個元素。subset標籤接受兩個引數"count"和"start"。"start"確定子集的起始點，"count"確定子集的長度。

配置檔案

你的struts.xml應該如下所示：

<?xml version = "1.0" Encoding = "UTF-8"?>
<!DOCTYPE struts PUBLIC
   "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
   "http://struts.apache.org/dtds/struts-2.0.dtd">

<struts>
   <constant name = "struts.devMode" value = "true" />
   <package name = "helloworld" extends = "struts-default">
      <action name = "employee" 
         class = "com.tutorialspoint.struts2.Employee"
         method = "execute">
         <result name = "success">/employee.jsp</result>
      </action>
   </package>

</struts>

你的web.xml應該如下所示：

<?xml version = "1.0" Encoding = "UTF-8"?>
<web-app xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
   xmlns = "http://java.sun.com/xml/ns/javaee" 
   xmlns:web = "http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
   xsi:schemaLocation = "http://java.sun.com/xml/ns/javaee 
   http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
   id = "WebApp_ID" version = "3.0">
   
   <display-name>Struts 2</display-name>
   
   <welcome-file-list>
      <welcome-file>index.jsp</welcome-file>
   </welcome-file-list>
   
   <filter>
      <filter-name>struts2</filter-name>
      <filter-class>
         org.apache.struts2.dispatcher.FilterDispatcher
      </filter-class>
   </filter>

   <filter-mapping>
      <filter-name>struts2</filter-name>
      <url-pattern>/*</url-pattern>
   </filter-mapping>
</web-app>

右鍵單擊專案名稱，然後單擊匯出 > WAR 檔案以建立WAR檔案。然後將此WAR部署到Tomcat的webapps目錄中。最後，啟動Tomcat伺服器並嘗試訪問URL https://:8080/HelloWorldStruts2/employee.action。這將產生以下螢幕：

struts_control_tags.htm

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