struts2：OGNL表达式，遍历List、Map集合；投影的使用
OGNL是Object-Graph Navigation Language的缩写，它是一种功能强大的表达式语言（Expression Language，简称为EL），通过它简单一致的表达式语法，可以存取对象的任意属性，调用对象的方法，遍历整个对象的结构图，实现字段类型转化等功能。它使用相同的表达式去存取对象的属性。
片头（ognl.jsp）
<% request.setAttribute("para", "request scope attribute"); request.getSession().setAttribute("para", "session scope attribute"); request.getSession().getServletContext().setAttribute("para", "aplication scope attribute"); List<Student> listStudent = new ArrayList<Student>(); listStudent.add(new Student(1, "张三", new Date())); listStudent.add(new Student(2, "李四", new Date())); listStudent.add(new Student(3, "赵五", new Date())); listStudent.add(new Student(4, "孙六", new Date())); listStudent.add(new Student(5, "钱七", new Date())); pageContext.setAttribute("listStudent", listStudent); %>
调用
http://127.0.0.1:8080/st/ssh/demo6/ognl.jsp?para=hello
1. 通过OGNL表达式获取属性范围中的值
<br/> HTTP parameters para = <s:property value="#parameters.para" /> <br/> request attribute para = <s:property value="#request.para" /> <br/> session attribute para = <s:property value="#session.para" /> <br/> application attribute para = <s:property value="#application.para" /> <br/> attr attribute para = <s:property value="#attr.para" /> <br/> <hr>
输出：
HTTP parameters para = hello
request attribute para = request scope attribute
session attribute para = session scope attribute
application attribute para = aplication scope attribute
attr attribute para = request scope attribute
2. 通过OGNL表达式创建list集合，并且遍历出集合中的值
<br> <s:set name="list" value="{'eeeee','ddddd','ccccc','bbbbb','aaaaa'}"></s:set> <s:iterator value="#list" var="o"> ${o}<br/> <!--<s:property />--> </s:iterator> <br/> <hr>
输出：
eeeee
ddddd
ccccc
bbbbb
aaaaa
3. 通过OGNL表达式创建Map集合，并且遍历出集合中的值
<br> <s:set name="map" value="#{'1':'eeeee','2':'ddddd','3':'ccccc','4':'bbbbb','5':'aaaaa'}"></s:set> <s:iterator value="#map" var="o"> ${o.key}->${o.value}<br/> <!-- <s:property value="#o.key"/>-><s:property value="#o.value"/><br/> --> <!-- <s:property value="key" />-><s:property value="value" /> --> </s:iterator> <br/> <hr>
输出：
1->eeeee
2->ddddd
3->ccccc
4->bbbbb
5->aaaaa
4. 通过OGNL表达式，进行逻辑判断
<br> <s:if test="'aaa' in {'aaa','bbb'}"> aaa 在 集合{'aaa','bbb'}中； </s:if> <s:else> aaa 不在 集合{'aaa','bbb'}中； </s:else> <br/> <s:if test="#request.req not in #list"> 不 在 集合list中； </s:if> <s:else> 在 集合list中； </s:else> <br/> <hr>
输出：
aaa 在 集合{'aaa','bbb'}中；
不 在 集合list中；
5. 通过OGNL表达式的投影功能进行数据筛选
<s:iterator value="#attr.listStudent.{?#this.id % 2 != 0}" var="cur"> <s:property value="#cur.username"/> </s:iterator> <br/> <s:iterator value="#attr.listStudent.{^#this.id % 2 != 0}" var="cur"> <s:property value="#cur.username"/> </s:iterator> <br/> <s:iterator value="#attr.listStudent.{$#this.id % 2 != 0}" var="cur"> <s:property value="#cur.username"/> </s:iterator> <br/> <s:property value="#attr.listStudent.{username}[0]"/> <br/> <s:property value="#attr.listStudent.{$#this.id == 3}.{username}[0]"/> <br/>
输出：
张三 赵五 钱七
张三
钱七
张三
赵五
6. 通过OGNL表达式访问某个类的静态方法和值
<br> <s:property value="@java.lang.Maths@floor(32.56)" /> <br/> <hr>
输出：
32.0
7. OGNL表达式 迭代标签 详细
<br> <s:set name="list2" value="{'aa','bb','cc','dd','ee','ff','gg','hh','ii','jj'}"></s:set> <table border="1"> <tr> <td> 索引 </td> <td> 值 </td> <td> 奇？ </td> <td> 偶？ </td> <td> 首？ </td> <td> 尾？ </td> <td> 当前迭代数量 </td> </tr> <s:iterator value="#list2" var="o" status="s"> <tr bgcolor="<s:if test="#s.even">pink</s:if>"> <td> <s:property value="#s.getIndex()" /> </td> <td> <s:property /> </td> <td> <s:if test="#s.odd">Y</s:if> <s:else>N</s:else> </td> <td> <s:if test="#s.even">Y</s:if> <s:else>N</s:else> </td> <td> <s:if test="#s.first">Y</s:if> <s:else>N</s:else> </td> <td> <s:if test="#s.isLast()">Y</s:if> <s:else>N</s:else> </td> <td> <s:property value="#s.getCount()"/> </td> </tr> </s:iterator> </table>
输出：
8. 完整代码（ognl.jsp）
<%@ page language="java" import="java.util.*,com.clzhang.ssh.demo6.Student" pageEncoding="utf-8"%> <%@ taglib uri="/struts-tags" prefix="s"%> <% request.setAttribute("para", "request scope attribute"); request.getSession().setAttribute("para", "session scope attribute"); request.getSession().getServletContext().setAttribute("para", "aplication scope attribute"); List<Student> listStudent = new ArrayList<Student>(); listStudent.add(new Student(1, "张三", new Date())); listStudent.add(new Student(2, "李四", new Date())); listStudent.add(new Student(3, "赵五", new Date())); listStudent.add(new Student(4, "孙六", new Date())); listStudent.add(new Student(5, "钱七", new Date())); pageContext.setAttribute("listStudent", listStudent); %> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <body> 1. 通过OGNL表达式获取属性范围中的值 <br/> HTTP parameters para = <s:property value="#parameters.para" /> <br/> request attribute para = <s:property value="#request.para" /> <br/> session attribute para = <s:property value="#session.para" /> <br/> application attribute para = <s:property value="#application.para" /> <br/> attr attribute para = <s:property value="#attr.para" /> <br/> <hr> 2. 通过OGNL表达式创建list集合，并且遍历出集合中的值 <br> <s:set name="list" value="{'eeeee','ddddd','ccccc','bbbbb','aaaaa'}"></s:set> <s:iterator value="#list" var="o"> ${o}<br/> <!--<s:property />--> </s:iterator> <br/> <hr> 3. 通过OGNL表达式创建Map集合，并且遍历出集合中的值 <br> <s:set name="map" value="#{'1':'eeeee','2':'ddddd','3':'ccccc','4':'bbbbb','5':'aaaaa'}"></s:set> <s:iterator value="#map" var="o"> ${o.key}->${o.value}<br/> <!-- <s:property value="#o.key"/>-><s:property value="#o.value"/><br/> --> <!-- <s:property value="key" />-><s:property value="value" /> --> </s:iterator> <br/> <hr> 4. 通过OGNL表达式，进行逻辑判断 <br> <s:if test="'aaa' in {'aaa','bbb'}"> aaa 在 集合{'aaa','bbb'}中； </s:if> <s:else> aaa 不在 集合{'aaa','bbb'}中； </s:else> <br/> <s:if test="#request.req not in #list"> 不 在 集合list中； </s:if> <s:else> 在 集合list中； </s:else> <br/> <hr> 5. 通过OGNL表达式的投影功能进行数据筛选 <br> <s:iterator value="#attr.listStudent.{?#this.id % 2 != 0}" var="cur"> <s:property value="#cur.username"/> </s:iterator> <br/> <s:iterator value="#attr.listStudent.{^#this.id % 2 != 0}" var="cur"> <s:property value="#cur.username"/> </s:iterator> <br/> <s:iterator value="#attr.listStudent.{$#this.id % 2 != 0}" var="cur"> <s:property value="#cur.username"/> </s:iterator> <br/> <s:property value="#attr.listStudent.{username}[0]"/> <br/> <s:property value="#attr.listStudent.{$#this.id == 3}.{username}[0]"/> <br/> <hr> 6. 通过OGNL表达式访问某个类的静态方法和值 <br> <s:property value="@java.lang.Math@floor(32.56)" /> <br/> <hr> 7. OGNL表达式 迭代标签 详细 <br> <s:set name="list2" value="{'aa','bb','cc','dd','ee','ff','gg','hh','ii','jj'}"></s:set> <table border="1"> <tr> <td> 索引 </td> <td> 值 </td> <td> 奇？ </td> <td> 偶？ </td> <td> 首？ </td> <td> 尾？ </td> <td> 当前迭代数量 </td> </tr> <s:iterator value="#list2" var="o" status="s"> <tr bgcolor="<s:if test="#s.even">pink</s:if>"> <td> <s:property value="#s.getIndex()" /> </td> <td> <s:property /> </td> <td> <s:if test="#s.odd">Y</s:if> <s:else>N</s:else> </td> <td> <s:if test="#s.even">Y</s:if> <s:else>N</s:else> </td> <td> <s:if test="#s.first">Y</s:if> <s:else>N</s:else> </td> <td> <s:if test="#s.isLast()">Y</s:if> <s:else>N</s:else> </td> <td> <s:property value="#s.getCount()"/> </td> </tr> </s:iterator> </table> </body> </html>
Student.java（只用到部分方法）
package com.clzhang.ssh.demo6; import java.util.*; public class Student { private int id; private String username; private int grade; private Date birthday; //只要是重写一个类的构造方法，就必须要为这个类保留空的构造方法 //因为框架默认的都会去调用无参的空的构造方法 public Student(){}; public Student(int id, String username, Date birthday) { this.id = id; this.username = username; this.birthday = birthday; } public Student(String username,int grade){ this.username = username; this.grade = grade; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public int getGrade() { return grade; } public void setGrade(int grade) { this.grade = grade; } public int getId() { return id; } public void setId(int id) { this.id = id; } public Date getBirthday() { return birthday; } public void setBirthday(Date birthday) { this.birthday = birthday; } @Override public String toString() { //如果不重写它的toString()方法的话，默认调用toString()将输出【类型+@+内存地址的哈希值】 return "{学生姓名：" + username + "，成绩：" + grade + "}"; } }