EL#{bean.id}如何调用托管bean方法bean.getId() [英] How does EL #{bean.id} call managed bean method bean.getId()
问题描述
我并不真正理解吸气剂和吸气剂的工作原理，尽管这是一个基本概念.我有以下代码，属性id如何发送到Managed Bean?是通过吸气剂方法捕获的吗?
I do not really understand how getter and setter work althougth it is a basic concept. I have the following code, how is the attribute id sent to Managed Bean? Is it captured by getter method?
我的面孔
<p:inputText id="id" value="#{bean.id}">
我的托管bean
private String id;
public void setId(String id) {
this.id = id;
}
public String getId() {
return id;
}
推荐答案
#{}表达式对getter和setter方法的调用不是JSF的一部分，而是
The call of getter and setter methods by #{} expressions is not part of JSF but Expression Language (most known as EL). JSF takes advantage of EL to bind the data of the HTML components to the fields of a bean through proper getters and setters. This is:
- 如果该bean存在，则表达式语言将在适当的范围内执行已注册bean的适当getter.
- 如果客户端执行表单提交或ajax请求，则发送到服务器的组件(通常是
<h:form>中的所有组件，如果有ajax请求，则可以声明要发送到服务器的组件)将包含一个新值，并将使用适当的setter方法将该值设置为该字段.
- If the bean exists, Expression Language will execute the proper getter of the registered bean in the proper scope.
- If client performs a form submission or an ajax request, then the components that are sent to the server (usually all the components in the
<h:form>, in case of ajax requests you can state which components to send to the server) will contain a new value, and this value will be set to the field with the proper setter method.
例如，您有一个属于请求范围的SayHelloBean:
For example, you have a SayHelloBean which belongs to request scope:
@RequestScoped
@ManagedBean
public class LoginBean {
private String name;
//proper getter
public String getName() {
return this.name;
}
//proper setter
public void setName(String name) {
this.name = name;
}
}
这两个facelets页面(因为这是一个示例，因此我避免声明<html>，<h:head>，<h:body>和其他元素，而只关注相关代码)
And these 2 facelets pages (since it's an example I avoid declaring <html>, <h:head>, <h:body> and other elements, just focusing on the relevant code)
Page1.xhtml:
Page1.xhtml:
<h:form>
Please tell me your name
<h:inputText value="#{loginBean.name}" />
<h:commandButton action="page2" />
</h:form>
Page2.xhtml:
Page2.xhtml:
Hello #{loginBean.name}
这是幕后发生的事情:
-
当加载Page1.xhtml时，JSF将创建一个新的
LoginBean实例(我们称为loginBean)并将其注册到JSP请求范围中.由于<h:inputText />的值绑定到LoginBean#name(将其读取为LoginBean类的字段name的字段)，因此EL将显示loginBean#name的值(即读为实例loginBean的字段name)，由于未初始化，因此EL将显示null为空字符串.
When Page1.xhtml is loaded, a new instance of
LoginBean, which we may callloginBean, will be created by JSF and registered into JSP request scope. Since the value of<h:inputText />is bound toLoginBean#name(which is read as the fieldnameofLoginBeanclass), then EL will display the value ofloginBean#name(which is read as the fieldnameof instanceloginBean), and since that is not initialized, EL will displaynull, as an empty string.
当您提交Page1.xhtml的格式时，由于LoginBean是@RequestScoped，因此JSF将创建一个LoginBean的新实例，我们可以将其称为loginBean2(在其中添加2最后，因为此实例与之前创建的loginBean完全不同)，并将其注册到JSP请求范围中.由于<h:inputText />的值绑定到LoginBean#name，因此JSF将通过调用适当的setter来验证和设置数据.这将使loginBean2#name具有由<h:inputText/>呈现的<input type="text">的值.
When you submit the form of Page1.xhtml, since LoginBean is @RequestScoped then JSF will create a new instance of LoginBean, which we may call it loginBean2 (adding 2 in the end because this instance is totally different from the loginBean previously created) and will register it in JSP request scope. Since the value of <h:inputText /> is bound to LoginBean#name, JSF will validate and set the data by calling the proper setter. This will make loginBean2#name have the value of the <input type="text"> that was rendered by <h:inputText/>.
最后，JSF将确保向前导航到Page2.xhtml，在进行处理时，它将找到#{loginBean.name}，EL将检查loginBean2#name的值并将其替换.
At last, JSF will make sure to navigate to Page2.xhtml through forward, where when processing it, it will find #{loginBean.name} and EL will check for the value of loginBean2#name and replace it.
这里解释的步骤只是对JSF生命周期的一个很小的解释(很多元素没有解释)，以及JSF如何使用getter和setters.
The steps explained here are a very small explanation (and with lot of elements not explained) of the JSF lifecycle and how JSF uses getters and setters.
更多信息:
- How to pass parameter to jsp:include via c:set? What are the scopes of the variables in JSP?
- How to choose the right bean scope?
- The Lifecycle of a JavaServer Faces Application
- Differences between Forward and Redirect
附加说明:由于您正在学习JSF，因此请避免将任何业务逻辑代码放入getter/setter中.这在这里得到了很大的解释:为什么JSF多次调用getters
Additional note: since you're learning JSF, avoid putting any business logic code in getters/setters. This is greatly explained here: Why JSF calls getters multiple times
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