Question

I have basic knowledge of Java’s reflection API – therefore, this is not only a question of how, it’s a question of whether it’s possible and whether I’m going about a solution the best way.

We’re doing some acceptance testing of multiple, interrelated projects; each of these projects retrieve data from a MongoDB store using an in-house abstraction API. To facilitate this testing, each component needs some pre-loaded data to be available in the database.

I’m building a command-line tool to accept a DTO (pre-compiled class binary), for loading of multiple instances using the morphia ORM library. I would like each member of our team to be able to run the generator passing in via cli their DTO (in jar or directory form), and a file (csv or otherwise) for instantiating a desired amount of records.

I have the class loading working fine with URLClassLoader. Now I’m trying to instantiate an instance of this class using data from a file.

Is this possible? Would serialized objects be a better approach?

Answer 1

That’s perfectly possible using the Java Reflection API :

• Load Class instance by name (Class.forName(className), you don’t really need the ClassLoader instance)
• Grab Constructor instance of constructors have parameters and invoke newInstance(Object… args) on this constructor instance to create an instance of your DTO class.
• Invoke getDeclaredFields() on your Class instance and iterate over them to set their values (field.set(instance, value)). Make sure to invoke field.setAccessible(true) to be able to access private fields.