在JSF中，我们可以处理<h:inputText>或<h:selectOneMenu>的值变化的事件。
要注册事件处理程序侦听器，请在UI组件的valueChangeListener属性中传递托管bean方法的名称。
或者实现ValueChangeListener接口，并将实现类名传递给UI组件的valueChangeListener属性。
以下代码显示了如何将托管Bean的方法注册到valueChangeListener方法。
public void localeChanged(ValueChangeEvent e){
//assign new value to country
selectedCountry = e.getNewValue().toString();
}
注册方法
<h:selectOneMenu value="#{userData.selectedCountry}" onchange="submit()"
valueChangeListener="#{userData.localeChanged}" >
<f:selectItems value="#{userData.countries}" />
</h:selectOneMenu>
以下代码显示了如何实现ValueChangeListener监听器方法。
public class LocaleChangeListener implements ValueChangeListener {
@Override
public void processValueChange(ValueChangeEvent event)
throws AbortProcessingException {
//access country bean directly
UserData userData = (UserData) FacesContext.getCurrentInstance().
getExternalContext().getSessionMap().get("userData");
userData.setSelectedCountry(event.getNewValue().toString());
}
}
并注册到<f:valueChangeListener>标签。
<h:selectOneMenu value="#{userData.selectedCountry}" onchange="submit()">
<f:valueChangeListener type="com.zaixian.test.LocaleChangeListener"
/>
<f:selectItems value="#{userData.countries}" />
</h:selectOneMenu>
实例
打开NetBeans，创建一个名称为：ValueChangedEvent 的Web项目，其结构如下所示 -
以下是文件：User.java 文件中的代码 -
/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package com.zaixian;
/**
*
* @author Maxsu
*/
import java.io.Serializable;
import java.util.LinkedHashMap;
import java.util.Map;
import javax.faces.bean.ManagedBean;
import javax.faces.bean.SessionScoped;
import javax.faces.event.ValueChangeEvent;
@ManagedBean(name = "country")
@SessionScoped
public class User implements Serializable {
private static final long serialVersionUID = 1L;
private static Map<String, String> countries;
private String localeCode = "en"; //default value
static {
countries = new LinkedHashMap<String, String>();
countries.put("United Kingdom", "en"); //label, value
countries.put("French", "fr");
countries.put("German", "de");
}
public void countryLocaleCodeChanged(ValueChangeEvent e) {
localeCode = e.getNewValue().toString();
}
public Map<String, String> getCountryInMap() {
return this.countries;
}
public String getLocaleCode() {
return localeCode;
}
public void setLocaleCode(String localeCode) {
this.localeCode = localeCode;
}
}
以下是文件：MyValueChangedListener.java 文件中的代码 -
/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package com.zaixian;
/**
*
* @author Maxsu
*/
import javax.faces.context.FacesContext;
import javax.faces.event.AbortProcessingException;
import javax.faces.event.ValueChangeEvent;
import javax.faces.event.ValueChangeListener;
public class MyValueChangedListener implements ValueChangeListener {
@Override
public void processValueChange(ValueChangeEvent event)
throws AbortProcessingException {
User country = (User) FacesContext.getCurrentInstance().
getExternalContext().getSessionMap().get("country");
country.setLocaleCode(event.getNewValue().toString());
}
}
以下是文件：index.xhtml 文件中的代码 -
<?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:h="http://java.sun.com/jsf/html"
xmlns:f="http://java.sun.com/jsf/core"
xmlns:ui="http://java.sun.com/jsf/facelets">
<h:body>
<h:form>
Selected country locale :
<h:inputText id="country" value="#{country.localeCode}" size="20" />
Select a country {method binding}:
<h:selectOneMenu value="#{country.localeCode}" onchange="submit()"
valueChangeListener="#{country.countryLocaleCodeChanged}">
<f:selectItems value="#{country.countryInMap}" />
</h:selectOneMenu>
Select a country:
<h:selectOneMenu value="#{country.localeCode}" onchange="submit()">
<f:valueChangeListener type="com.zaixian.MyValueChangedListener" />
<f:selectItems value="#{country.countryInMap}" />
</h:selectOneMenu>
</h:form>
</h:body>
</html>
运行项目
在ValueChangedEvent 项目上点击右键，选择 【运行】，在Tomcat启动完成后，打开浏览器访问以下地址：
http://localhost:8084/ValueChangedEvent/
如果程序没有错误，应该会看到如下界面 -
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