Question

While I was digging an issue in spring’s sources, I found the following:

public abstract class RequestContextHolder {
    private static final boolean jsfPresent = 
        ClassUtils.isPresent("javax.faces.context.FacesContext", 
        RequestContextHolder.class.getClassLoader());

and then in a method:

if (jsfPresent) {
    attributes = FacesRequestAttributesFactory.getFacesRequestAttributes();
}

Where the factory is defined as :

/**
 * Inner class to avoid hard-coded JSF dependency.
 */
private static class FacesRequestAttributesFactory

This works obviously, as the inner class is not ‘touched’ until it is required, and at that moment it is certain that JSF exists on the classpath.

Now, I wonder if this is a good approach to apply in a other cases. For example this method means a compile time dependency.

So, two questions:

• are there any drawbacks to this approach, other than the compile time dependency
• are there better ways to prevent explicit dependency on an API, while still using it.

Answer 1

The code in the question looks quite clean to me.
The only way I can think of to avoid compile time dependancy is to use reflection. Try and load the class by name, if present search for the method you are after.

Reflection sounds worse to me.