在TestNG中运行时，即使对于内置类型，使用反射创建类也会引发java.lang.ClassNotFoundException

Question

I have some code that is using reflection at a particular place to instantiate a few objects like this:

String className = type.toString();
Class klass = Class.forName(className);

This bit of code works fine when running in the normal environment. However when I try to unit test the set of methods that run these two lines, I keep getting java.lang.ClassNotFoundException exceptions.

At first I thought it had to do with the fact that the class I was trying to instantiate wasn't being included on the classpath for some strange reason. So I then did this:

// Where type variable points to java.lang.String rather than my own class
String className = type.toString();
Class klass = Class.forName(className);

And yet it still fails:

 java.lang.ClassNotFoundException: class java.lang.String
     at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
     at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
     at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
     at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
     at java.lang.Class.forName0(Native Method)
     at java.lang.Class.forName(Class.java:348)

I've been looking into the ClassLoader and trying to determine why it can't seem to find any classes but to no avail.

Does anyone know why this is happening only when TestNG is running the code and what to do about it?

Answer 1

Okay, I was able to figure it out. And of course it was incredibly dumb and makes you question all of your years being a software engineer.

The problem was this line:

String className = type.toString();

The value type was of class java.lang.reflect.Type .

Can you see the issue? Don't feel bad if you can't because I couldn't either.

If you run this code:

System.out.println(type.toString());
System.out.println(type.getTypeName());

You end up with the following output:

class java.lang.String
java.lang.String

The issue is quite obvious seeing that, I should be using getTypeName() not toString() . Of course it will throw ClassNotFoundException because class<SPACE> precedes the actual class name.

Yet when I looked at the stacktrace, I overlooked it had class<SPACE> before the name of the class.

Sigh. Good times were had learning about class loaders though.