为什么我应该使用createComponent而不是自己创建实例? [英] Why should I use createComponent instead of creating the instance myself?

问题描述

这更多是一个概念性问题.

This is more of a conceptual question.

我必须处理必须创建动态h:dataTable的功能.每当我创建一个组件时，我都会做类似的事情:

I had to work on a functionality that had to create a dynamic h:dataTable. And whenever I created a component, I did something similar to this:

DataTable table = (DataTable) FacesContext.getCurrentInstance().getApplication()
                      .createComponent(DataTable.COMPONENT_TYPE);

使用FacesContext为我创建所有内容.

Using the FacesContext to create everything for me.

但是我可以简单地做到这一点:

However I could just as simply have done this:

DataTable table = new DataTable();

我之所以采用第一种方式，是因为我在开发时阅读的所有教程和材料都采用了这种方式，但是我却没有清楚的答案.

The reason I did it in the first way is that all the tutorials and material I read while developing did it that way, but I never got a clear answer why.

有没有一个真正的原因，为什么第一个要比第二个好?

Is there an actual reason why the first is better than the second?

推荐答案

Application#createComponent()添加了一个额外的抽象层，允许运行时多态性和可插入性.具体实现可以通过faces-config.xml中的<component>条目进行配置，而该条目又可以通过JAR提供.这允许更改实现而无需重写/重新编译代码.

The Application#createComponent() adds an extra abstract layer allowing runtime polymorphism and pluggability. The concrete implementation is configurable by <component> entry in faces-config.xml which could in turn be provided via a JAR. This allows changing implementation without rewriting/recompiling the code.

就像JDBC API的工作方式一样:您不执行new SomeDriver()，但是您执行Class.forName(someDriverClassName)，这允许驱动程序不成为编译时依赖性，因此JDBC代码可在许多DB供应商之间移植而无需重写/重新编译.

It's exactly like as how JDBC API works: you don't do new SomeDriver(), but you do Class.forName(someDriverClassName) which allows the driver to not be a compiletime dependency and thus your JDBC code to be portable across many DB vendors without rewriting/recompiling.

但是，如果应用程序仅用于内部使用"并且不打算分发(因此所有代码始终在您的控制之下)，那么运行时多态性就没有太大的优势，而且可能会增加(非常小) )的开销.

However, if the application is for "internal usage" only and not intented to be distributable (and thus all the code is always full under you control), then runtime polymorphism has not a so big advantage and may add (very minor) overhead.

• 是什么关系在组件系列，组件类型和渲染器类型之间?

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