Why should I use createComponent instead of creating the instance myself?

问题

This is more of a conceptual question.

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);

Using the FacesContext to create everything for me.

However I could just as simply have done this:

DataTable table = new DataTable();

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.

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

回答1:

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.

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.

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.

See also:

• What is the relationship between component family, component type and renderer type?

来源：https://stackoverflow.com/questions/16610655/why-should-i-use-createcomponent-instead-of-creating-the-instance-myself