在struts2，<s:doubleselect>标签用于创建两个html下拉框，第一个下拉列表中选择后，第二个下拉列表将根据第一个选择发生相应的变化。一个非常典型的例子是“国家”，“国家”下拉选项，不同的“状态”列表是根据所选择的“国家”。
这里创建一个web工程：strut2sdoubleselect，来演示在多个复选框如何设置的默认值，整个项目的结构如下图所示：
<s:doubleselect> 标签示例
<s:doubleselect label="fruits (ognl) "
name="fruit1" list="{'fruit','meat'}"
doublename="fruit2"
doublelist="top == 'fruit' ? {'apple', 'orange','banana'} : {'chicken', 'pig'}" />
产生下面的html代码...
<tr>
<td class="tdlabel">
<label for="resultaction_fruit1" class="label">
fruits (ognl) :
</label>
</td>
<td>
<select name="fruit1" id="resultaction_fruit1"
onchange="resultaction_fruit1redirect(this.options.selectedindex)">
<option value="fruit">fruit</option>
<option value="meat">meat</option>
</select>
<br />
<select name="fruit2" id="resultaction_fruit2">
</select>
<script type="text/javascript">
var resultaction_fruit1group = new array(2 + 0);
for (i = 0; i < (2 + 0); i++)
resultaction_fruit1group[i] = new array();
resultaction_fruit1group[0][0] = new option("apple", "apple");
resultaction_fruit1group[0][1] = new option("orange", "orange");
resultaction_fruit1group[0][2] = new option("banana", "banana");
resultaction_fruit1group[1][0] = new option("chicken", "chicken");
resultaction_fruit1group[1][1] = new option("pig", "pig");
var resultaction_fruit1temp = document.resultaction.resultaction_fruit2;
resultaction_fruit1redirect(0);
function resultaction_fruit1redirect(x) {
var selected = false;
for (m = resultaction_fruit1temp.options.length - 1; m >= 0; m--) {
resultaction_fruit1temp.options[m] = null;
}
for (i = 0; i < resultaction_fruit1group[x].length; i++) {
resultaction_fruit1temp.options[i] =
new option(
resultaction_fruit1group[x][i].text, resultaction_fruit1group[x][i].value
);
}
if ((resultaction_fruit1temp.options.length > 0) && (! selected)) {
resultaction_fruit1temp.options[0].selected = true;
}
}
</script>
</td>
</tr>
好了，<s:doubleselect>标签是真正产生大量的代码。它会创建两个下拉列表， 很多javascript代码背后做魔术（第一选择，第二个变化），并且还附上了“onchange()”行为，以第一个下拉框。
<s:doubleselect name="" list="" doublename="" doublelist="" />
“name”和“list”是指第一个下拉列表。“doublename”和“doublelist”是指所述第二下拉列表。数据群和“<s:select>”标签是一样的。
在一个完整的例子，例如<s：doubleselect>标签，表示使用ognl或java列出数据来填充到下拉列表中。
action类来生成两个下拉列表。
doubleselectaction.java
package com.h3.common.action;
import java.util.arraylist;
import java.util.arrays;
import java.util.hashmap;
import java.util.map;
import java.util.set;
import com.opensymphony.xwork2.actionsupport;
public class doubleselectaction extends actionsupport{
private string fruit1;
private string fruit2;
private string server1;
private string server2;
private string language1;
private string language2;
map languagemap;
public string getfruit1() {
return fruit1;
}
public void setfruit1(string fruit1) {
this.fruit1 = fruit1;
}
public string getfruit2() {
return fruit2;
}
public void setfruit2(string fruit2) {
this.fruit2 = fruit2;
}
public string getserver1() {
return server1;
}
public void setserver1(string server1) {
this.server1 = server1;
}
public string getserver2() {
return server2;
}
public void setserver2(string server2) {
this.server2 = server2;
}
public string getlanguage1() {
return language1;
}
public void setlanguage1(string language1) {
this.language1 = language1;
}
public string getlanguage2() {
return language2;
}
public void setlanguage2(string language2) {
this.language2 = language2;
}
public map getlanguagemap() {
return languagemap;
}
public void setlanguagemap(map languagemap) {
this.languagemap = languagemap;
}
public doubleselectaction(){
languagemap =new hashmap();
languagemap.put("java",
new arraylist<string>(arrays.aslist("spring", "hibernate", "struts 2")));
languagemap.put(".net", new arraylist<string>(arrays.aslist("vb.net", "c#")));
languagemap.put("javascript", new arraylist<string>(arrays.aslist("jquery")));
}
public string execute() {
return success;
}
public string display() {
return none;
}
}
渲染两个下拉下拉框，通过“<s:doubleselect>”标签，并通过java列表，ognl列表填充
doubleselect.jsp
<%@ taglib prefix="s" uri="/struts-tags" %>
<html>
<head>
</head>
<body>
<h1>struts2 <s:doubleselect> 示例</h1>
<s:form action="resultaction" namespace="/">
<s:doubleselect label="fruits (ognl) "
name="fruit1" list="{'fruit','meat'}"
doublename="fruit2"
doublelist="top == 'fruit' ? {'apple', 'orange','banana'} : {'chicken', 'pig'}" />
<s:set name="serverlist"
value="#{
'appserver': {'apache', 'tomcat', 'jboss'},
'database': {'oracle', 'mysql'}
}" />
<s:doubleselect label="server (ognl) "
name="server1" list="#serverlist.keyset()"
doublename="server2" doublelist="#serverlist[top]" />
<s:doubleselect label="language (java list) "
name="language1" list="languagemap.keyset()"
doublename="language2" doublelist="languagemap.get(top)" />
<s:submit value="submit" name="submit" />
</s:form>
</body>
</html>
result.jsp
<%@ taglib prefix="s" uri="/struts-tags" %> <html> <body> <h1>struts2 <s:doubleselect> 示例</h1> <h2> test #1 : <s:property value="fruit1"/> , <s:property value="fruit2"/> </h2> <h2> test #2 : <s:property value="server1"/> , <s:property value="server2"/> </h2> <h2> test #2 : <s:property value="language1"/> , <s:property value="language2"/> </h2> </body> </html>
<?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="default" namespace="/" extends="struts-default">
<action name="doubleselectaction"
class="com.h3.common.action.doubleselectaction" method="display">
<result name="none">/pages/doubleselect.jsp</result>
</action>
<action name="resultaction" class="com.h3.common.action.doubleselectaction">
<result name="success">/pages/result.jsp</result>
</action>
</package>
</struts>
http://localhost:8080/strut2sdoubleselect/doubleselectaction.action
http://localhost:8080/strut2sdoubleselect/resultaction.action
