Struts2學習筆記(OGNL表達式)
Struts 2支持以下幾種表達式語言:
OGNL(Object-Graph Navigation Language),可以方便地操作對象屬性的開源表達式語言;
JSTL(JSP Standard Tag Library),JSP 2.0集成的標準的表達式語言;
Groovy,基於Java平臺的動態語言,它具有時下比較流行的動態語言(如Python、Ruby和Smarttalk等)的一些起特性;
Velocity,嚴格來說不是表達式語言,它是一種基於Java的模板匹配引擎,具說其性能要比JSP好。
Struts 2默認的表達式語言是OGNL,原因是它相對其它表達式語言具有下面幾大優勢:
支持對象方法調用,如xxx.doSomeSpecial();
支持類靜態的方法調用和值訪問,表達式的格式爲@[類全名(包括包路徑)]@[方法名 | 值名],例如:@java.lang.String@format('foo %s', 'bar')或@tutorial.MyConstant@APP_NAME;
支持賦值操作和表達式串聯,如price=100, discount=0.8, calculatePrice(),這個表達式會返回80;
訪問OGNL上下文(OGNL context)和ActionContext;
操作集合對象
OGNL是通常要結合Struts 2的標誌一起使用,如<s:property value="xx" />等。大家經常遇到的問題是#、%和$這三個符號的使用。
訪問OGNL上下文和Action上下文,#相當於ActionContext.getContext();下表有幾個ActionContext中有用的屬性:
用於過濾和投影(projecting)集合,如books.{?#this.price<100}。
構造Map,如#{'foo1':'bar1', 'foo2':'bar2'}。
個人覺得OGNL真的很簡單,即使有的表達方式忘了也沒關係,一查就搞定了,尚學堂的教學中有個例子不錯,基本上常用的都包括了。
下面是OGNL表達式的使用例子。
<?xml version="1.0" encoding="GB18030" ?> <%@ page language="java" contentType="text/html; charset=GB18030" pageEncoding="GB18030"%> <%@ taglib uri="/struts-tags" prefix="s" %> <!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"> <head> <meta http-equiv="Content-Type" content="text/html; charset=GB18030" /> <title>OGNL表達式語言學習</title> </head> <body> <ol> <li>訪問值棧中的action的普通屬性: username = <s:property value="username"/> </li> <li>訪問值棧中對象的普通屬性(get set方法):<s:property value="user.age"/> | <s:property value="user['age']"/> | <s:property value="user[\"age\"]"/> | wrong: <%--<s:property value="user[age]"/>--%></li> <li>訪問值棧中對象的普通屬性(get set方法): <s:property value="cat.friend.name"/></li> <li>訪問值棧中對象的普通方法:<s:property value="password.length()"/></li> <li>訪問值棧中對象的普通方法:<s:property value="cat.miaomiao()" /></li> <li>訪問值棧中action的普通方法:<s:property value="m()" /></li> <hr /> <li>訪問靜態方法:<s:property value="@com.bjsxt.struts2.ognl.S@s()"/></li> <li>訪問靜態屬性:<s:property value="@com.bjsxt.struts2.ognl.S@STR"/></li> <li>訪問Math類的靜態方法:<s:property value="@@max(2,3)" /></li> <hr /> <li>訪問普通類的構造方法:<s:property value="new com.bjsxt.struts2.ognl.User(8)"/></li> <hr /> <li>訪問List:<s:property value="users"/></li> <li>訪問List中某個元素:<s:property value="users[1]"/></li> <li>訪問List中元素某個屬性的集合:<s:property value="users.{age}"/></li> <li>訪問List中元素某個屬性的集合中的特定值:<s:property value="users.{age}[0]"/> | <s:property value="users[0].age"/></li> <li>訪問Set:<s:property value="dogs"/></li> <li>訪問Set中某個元素:<s:property value="dogs[1]"/></li> <li>訪問Map:<s:property value="dogMap"/></li> <li>訪問Map中某個元素:<s:property value="dogMap.dog101"/> | <s:property value="dogMap['dog101']"/> | <s:property value="dogMap[\"dog101\"]"/></li> <li>訪問Map中所有的key:<s:property value="dogMap.keys"/></li> <li>訪問Map中所有的value:<s:property value="dogMap.values"/></li> <li>訪問容器的大小:<s:property value="dogMap.size()"/> | <s:property value="users.size"/> </li> <hr /> <li>投影(過濾):<s:property value="users.{?#this.age==1}[0]"/></li> <li>投影:<s:property value="users.{^#this.age>1}.{age}"/></li> <li>投影:<s:property value="users.{$#this.age>1}.{age}"/></li> <li>投影:<s:property value="users.{$#this.age>1}.{age} == null"/></li> <hr /> <li>[]:<s:property value="[0].username"/></li> </ol> <s:debug></s:debug> </body> </html>
下面是對應的java,都是最簡單的class
OgnlAction.java
package com.bjsxt.struts2.ognl; import java.util.ArrayList; import java.util.HashMap; import java.util.HashSet; import java.util.List; import java.util.Map; import java.util.Set; import com.opensymphony.xwork2.ActionSupport; public class OgnlAction extends ActionSupport { private Cat cat; private Map<String, Dog> dogMap = new HashMap<String, Dog>(); private Set<Dog> dogs = new HashSet<Dog>(); private String username; private String password; private User user; private List<User> users = new ArrayList<User>(); public OgnlAction() { users.add(new User(1)); users.add(new User(2)); users.add(new User(3)); dogs.add(new Dog("dog1")); dogs.add(new Dog("dog2")); dogs.add(new Dog("dog3")); dogMap.put("dog100", new Dog("dog100")); dogMap.put("dog101", new Dog("dog101")); dogMap.put("dog102", new Dog("dog102")); } public String execute() { return SUCCESS; } public String m() { return "hello"; } public User getUser() { return user; } public void setUser(User user) { this.user = user; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } public Cat getCat() { return cat; } public void setCat(Cat cat) { this.cat = cat; } public Map<String, Dog> getDogMap() { return dogMap; } public void setDogMap(Map<String, Dog> dogMap) { this.dogMap = dogMap; } public Set<Dog> getDogs() { return dogs; } public void setDogs(Set<Dog> dogs) { this.dogs = dogs; } public List<User> getUsers() { return users; } public void setUsers(List<User> users) { this.users = users; } }
Dog.java
package com.bjsxt.struts2.ognl;public class Dog { private String name; public Dog() { } public Dog(String name) { super(); this.name = name; } public String getName() { return name; } public void setName(String name) { this.name = name; } @Override public String toString() { return "dog: " + name; } }
Cat.java
package com.bjsxt.struts2.ognl;public class Cat { private Dog friend; public Dog getFriend() { return friend; } public void setFriend(Dog friend) { this.friend = friend; } public String miaomiao() { return "miaomiao"; } }
User.java
package com.bjsxt.struts2.ognl;public class User { private int age = 8; public User() { } public User(int age) { super(); this.age = age; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } @Override public String toString() { return "user" + age; } }
S.java
package com.bjsxt.struts2.ognl;public class S { public static String STR = "STATIC STRING"; public static String s() { return "static method"; } }