Spring dependency injection - reflection / byte code instrumentation

Question

When I want to use dependency injection with some non-default constructor, i.e. with parameters, spring must be using byte code instrumentation for that, right? Because AFAIK reflection only supports default constructor?

Answer 1

Reflections supports any number of arguments, say for instance I have a class TestClass which takes two arguments in one of its constructors:

public TestClass(int test1, String test) {
    System.out.println(test1 + test);
}

I would invoke this constructor, through reflection, like so:

    Constructor<TestClass> constructor = TestClass.class.getConstructor(Integer.class, String.class);
    TestClass test = constructor.newInstance(1, "test");

Answer 2

Reflection.

Please check source code for the class

org.springframework.beans.factory.support.ConstructorResolver Method: protected BeanWrapper autowireConstructor(...)

invokes =>

org.springframework.beans.factory.support.SimpleInstantiationStrategy Method: public Object instantiate(...)

invokes =>

org.springframework.beans.BeanUtils Method: public static Object instantiateClass(Constructor ctor, Object[] args)

which uses Reflection to create the bean