一种计算UIComponent clientID的有效方法? [英] An efficient way to compute a UIComponent clientID?

问题描述

实际上，在我的JSF应用程序中，我有这段代码可以根据其ID计算组件 clientId :

Actually in my JSF application I have this code to compute a component clientId from its id:

public static String getComponentClientId(String id) {
  try {
    FacesContext fctx = FacesContext.getCurrentInstance();
    UIComponent found = getComponentWithId(fctx.getViewRoot(), id);
    if (found!=null)
      return found.getClientId(fctx);           
    else
      return null;
  } catch (Exception e) {
    return null;
  }     
}
public static UIComponent getComponentWithId(UIComponent parent, String id) {
  for (Iterator<UIComponent> chs = parent.getFacetsAndChildren(); chs.hasNext();) {
    UIComponent ch = chs.next();
    if (ch.getId().equalsIgnoreCase(id))
     return ch;     
    else {
     UIComponent found = getComponentWithId(ch, id);
     if (found!=null)
       return found;
    }
  }
  return null;
}

该方法有效，但它会在视图组件树中导航，因此效率可能非常低，尤其是在存在人口众多的页面的情况下.我不知道有什么聪明的方法或API可以使工作更快/更轻松?

The method works, but it navigate through the view component tree, so it can be very inefficient, specially in presence of highly populated pages. There is a clever way or an API that I don't know to make the job faster/easier?

推荐答案

我不知道.

很难缓存此信息，因为:

It is difficult to cache this information, because:

1. UIComponent之间的关系及其 clientId 可以为1:N.对于 UIData 管理孩子的状态.来自 getClientId 可能与上下文有关.
2. UIComponent 实例的生存期可能不会超过请求. StateManager 的某些实现可以是配置为在会话中保存视图状态，在这种情况下，对象可能的生存期更长，但是使代码依赖于此将使其变得脆弱，并且很容易引入内存泄漏. /li>
3. 视图可以是动态的.诚然，这是一个极端的情况，但是可以以编程方式添加，删除和移动组件.

1. The relationship between an instance of UIComponent and its clientIds can be 1:N. This is required for components like UIData that manage the state of their children. The return value from getClientId can be context-sensitive.
2. The lifetime of a UIComponent instance probably won't exceed the request. Some implementations of StateManager can be configured to save the view state in the session, in which case the lifetime of the objects might be longer, but making your code rely on this makes it fragile and it would be easy to introduce memory leaks.
3. Views can be dynamic. Admittedly, this is an edge case, but it is possible to add, remove and move components programmatically.

在尝试其他方法之前，我将证明这是一个问题.

I would prove that this is a problem before trying another approach.

您没有说 clientId 的用途，但我猜想它是对某种形式的JavaScript支持的.考虑编写自定义组件并通过发出标记它的渲染器.可以与 for 属性，类似于标签控件.在相同的 NamingContainer 比较容易.您可以在渲染器实现中使用如下代码:

You don't say what you need the clientIds for, but I'm guessing it is for some form of JavaScript support. Consider writing a custom component and emitting your markup via its renderer. This could be used with a for attribute, similar to the label control. Finding a neighbour in the same NamingContainer is relatively easy. You might use code like this in your renderer implementation:

// untested code!
String clientId = mycomponent.getClientId(context);
// get id of target control
String _for = mycomponent.getFor();
int n = clientId.lastIndexOf(NamingContainer.SEPARATOR_CHAR);
String targetClientId = clientId.substring(0, n)
        + NamingContainer.SEPARATOR_CHAR + _for;
ResponseWriter writer = context.getResponseWriter();
// write markup

组件通常通常需要共享一个命名容器以利用彼此的 clientId ，因此这并不是一个很大的限制.如果您可以将该组件作为子组件，则找到父组件会更容易.

Components usually need to share a naming container to make use of each other's clientId anyway, so this isn't a big constraint. If you can make the component a child, it is easier to find a parent.

当然，这种方法也有问题.它使您的UI树变得更大，对生命周期处理和状态管理产生连锁反应.权衡是否值得进行测试.

Of course, this approach has problems too. It makes your UI tree even bigger, with a knock-on effect on lifecycle processing and state-management. Whether the trade-off is worth it would require testing.

我在周末想到了这个.由于50％的JSF查询似乎都是关于如何使用ID的，所以我写了一篇文章，以便我可以介绍一下人们-

I thought about this over the weekend. Since 50% of JSF queries seem to be about how to work with IDs, I wrote a post so I can just refer people to it - JSF: working with component IDs. In includes a mechanism for caching the IDs (sort of!) with some sample code.

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