Is there a general "backend" library for Java reflection

Try the FEST Reflection module. It's a fluent way to do Java reflection. For example:

 String name = method("get").withReturnType(String.class)
                         .withParameterTypes(int.class)
                         .in(names)
                         .invoke(8);

Just a comment to your own answer; actually beanutils has support for getting "a close match" given a set of parameters. See getMatchingAccessibleMethod()

BeanUtils is really powerful and has lots of utility methods for inspecting classes. The same support is naturally available for constructors.

If you're looking for simplicity, I have created a simple library called jOOR in order to facilitate access to the reflection API in Java. It supports the most essential actions without building up a huge API. Here's an example of what jOOR code looks like:

String world = 
on("java.lang.String") // Like Class.forName()
.create("Hello World") // Call the most specific matching constructor
.call("substring", 6)  // Call the most specific matching substring() method
.call("toString")      // Call toString()
.get()                 // Get the wrapped object, in this case a String