<f:metadata>、<f:viewParam>和 <f:viewAction>用于? [英] What can <f:metadata>, <f:viewParam> and <f:viewAction> be used for?

问题描述

谁能解释一下我们一般如何使用这个片段，或者在现实世界中如何使用这个片段?

Can anyone clarify how we can use in general, or a in real world example, this snippet?

<f:metadata>
    <f:viewParam id="id" value="#{bean.id}" />
    <f:viewAction action="#{bean.init}" />
</f:metadata>

推荐答案

处理GET参数

管理 GET 参数的设置、转换和验证.就像 <h:inputText>，但是对于 GET 参数.

Process GET parameters

The <f:viewParam> manages the setting, conversion and validation of GET parameters. It's like the <h:inputText>, but then for GET parameters.

下面的例子

<f:metadata>
    <f:viewParam name="id" value="#{bean.id}" />
</f:metadata>

基本上执行以下操作:

• 通过名称id获取请求参数值.
• 如有必要，转换并验证它(您可以使用 required、validator 和 converter 属性并嵌套一个 <f:转换器> 和 就像 )
• 如果转换和验证成功，则将其设置为由 #{bean.id} 值表示的 bean 属性，或者如果 value 属性不存在，则设置它作为名称 id 上的请求属性，以便它在视图中通过 #{id} 可用.

• Get the request parameter value by name id.
• Convert and validate it if necessary (you can use required, validator and converter attributes and nest a <f:converter> and <f:validator> in it like as with <h:inputText>)
• If conversion and validation succeeds, then set it as a bean property represented by #{bean.id} value, or if the value attribute is absent, then set it as request attribtue on name id so that it's available by #{id} in the view.

因此，当您以 foo.xhtml?id=10 的形式打开页面时，参数值 10 以这种方式在 bean 中设置，就在视图呈现之前.

So when you open the page as foo.xhtml?id=10 then the parameter value 10 get set in the bean this way, right before the view is rendered.

至于验证，以下示例将参数设置为 required="true" 并仅允许 10 到 20 之间的值.任何验证失败都会导致显示一条消息.

As to validation, the following example sets the param to required="true" and allows only values between 10 and 20. Any validation failure will result in a message being displayed.

<f:metadata>
    <f:viewParam id="id" name="id" value="#{bean.id}" required="true">
        <f:validateLongRange minimum="10" maximum="20" />
    </f:viewParam>
</f:metadata>
<h:message for="id" />

---

对 GET 参数执行业务操作

您可以使用 为此.

<f:metadata>
    <f:viewParam id="id" name="id" value="#{bean.id}" required="true">
        <f:validateLongRange minimum="10" maximum="20" />
    </f:viewParam>
    <f:viewAction action="#{bean.onload}" />
</f:metadata>
<h:message for="id" />

与

public void onload() {
    // ...
}

然而自 JSF 2.2 以来是新的( 自 JSF 2.0 以来已经存在).如果您无法升级，那么您最好的选择是使用 代替.

The <f:viewAction> is however new since JSF 2.2 (the <f:viewParam> already exists since JSF 2.0). If you can't upgrade, then your best bet is using <f:event> instead.

<f:event type="preRenderView" listener="#{bean.onload}" />

然而，这是在每个请求时调用的.您需要明确检查请求是否不是回发:

This is however invoked on every request. You need to explicitly check if the request isn't a postback:

public void onload() {
    if (!FacesContext.getCurrentInstance().isPostback()) {
        // ...
    }
}

当您想跳过转换/验证失败"时情况一样，然后执行以下操作:

When you would like to skip "Conversion/Validation failed" cases as well, then do as follows:

public void onload() {
    FacesContext facesContext = FacesContext.getCurrentInstance();
    if (!facesContext.isPostback() && !facesContext.isValidationFailed()) {
        // ...
    }
}

使用 <f:event> 这种方式本质上是一种解决方法/hack，这正是在 JSF 2.2 中引入 <f:viewAction> 的原因.

Using <f:event> this way is in essence a workaround/hack, that's exactly why the <f:viewAction> was introduced in JSF 2.2.

您可以通过"通过将 includeViewParams 属性设置为 true 或通过添加 includeViewParams=true 请求参数来获取导航链接中的视图参数.

You can "pass-through" the view parameters in navigation links by setting includeViewParams attribute to true or by adding includeViewParams=true request parameter.

<h:link outcome="next" includeViewParams="true">
<!-- Or -->
<h:link outcome="next?includeViewParams=true">

用上面的<f:metadata>示例生成基本上如下链接

which generates with the above <f:metadata> example basically the following link

<a href="next.xhtml?id=10">

使用原始参数值.

这种方法只要求next.xhtml也在完全一样的参数，否则不会通过.

This approach only requires that next.xhtml has also a <f:viewParam> on the very same parameter, otherwise it won't be passed through.

也可以与plain HTML"结合使用.获取表单.

The <f:viewParam> can also be used in combination with "plain HTML" GET forms.

<f:metadata>
    <f:viewParam id="query" name="query" value="#{bean.query}" />
    <f:viewAction action="#{bean.search}" />
</f:metadata>
...
<form>
    <label for="query">Query</label>
    <input type="text" name="query" value="#{empty bean.query ? param.query : bean.query}" />
    <input type="submit" value="Search" />
    <h:message for="query" />
</form>
...
<h:dataTable value="#{bean.results}" var="result" rendered="#{not empty bean.results}">
     ...
</h:dataTable>

基本上使用这个 @RequestScoped bean:

With basically this @RequestScoped bean:

private String query;
private List<Result> results;

public void search() {
    results = service.search(query);
}

请注意， 是用于 ，而不是纯 HTML ！另请注意，当 #{bean.query} 为空时，输入值会显示 #{param.query}，因为否则提交的值根本不会显示验证或转换错误.请注意，此构造对于 JSF 输入组件无效(它已经在幕后"这样做了).

Note that the <h:message> is for the <f:viewParam>, not the plain HTML <input type="text">! Also note that the input value displays #{param.query} when #{bean.query} is empty, because the submitted value would otherwise not show up at all when there's a validation or conversion error. Please note that this construct is invalid for JSF input components (it is doing that "under the covers" already).

• ViewParam vs @ManagedProperty(value = "#{param.id}")
• JSF 2.0 中的通信 - 处理 GET 请求参数

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