Can you inject java classes during script execution?

[Pexien]

I have a class which I am injecting as an object in to the runtime

public class JavaManager {

    private V8 runtime;

    public InjectJava(V8 runtime) {
        this.runtime = runtime;
    }

    public void importClass(String className) {
        try {
            V8JavaAdapter.injectClass(Class.forName(className), runtime);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

so I can inject classes using Java.injectClass('class') in a script, similar to how import and require work, but instead with Java classes. However, when loading the script with J2V8 I get a java.lang.Error: Runtime disposed error error? Any ideas of how to solve this, or am I just missing something?