从String className获取可抛出的类对象

Question

Given a string like com.abc.XYZException I'd like to get a throwable class that can be resolved from the class path with that string as class name.

private Class<? extends Throwable> getExceptionClass(String className){
    return Class.forName(className);
}

This snippets cant be compiled because Class.forName(className) returns Class<?> but Class<? extends Throwable> Class<? extends Throwable> is required. How do I return Class<? extends Throwable> Class<? extends Throwable> ?

Answer 1

The unchecked cast is unavoidable but you could do things safer by checking that the input is conform before casting it.
You could indeed use isAssignableFrom() method of Class to check that the Class instance loaded is a subclass of the Throwable class.

  public Class<? extends Throwable> getExceptionClass(String className) {
    try {
        Class<?> clazz = Class.forName(className);
        if (!Throwable.class.isAssignableFrom(clazz)) {
            throw new IllegalArgumentException("error in the provided classname");
        }
        return (Class<? extends Throwable>) clazz;
    } catch (ClassNotFoundException e) {
        // handling the exception
    }
  }

Answer 2

As also suggested in a comment (unchecked cast of the returned class), this should be what you require in order to let it be compiled:

private Class<? extends Throwable> getExceptionClass(String className) throws ClassNotFoundException {
    return (Class<? extends Throwable>) Class.forName(className);
}

Answer 3

This should do the trick;

private Class<? extends Throwable> getExceptionClass(String className) throws ClassNotFoundException{
    return (Class<? extends Throwable>) Class.forName(className);
    }

Answer 4

Or without class cast you could make it return any class type using wildcard :

   private Class<?> getExceptionClass(String className) throws ClassNotFoundException{
            return Class.forName(className);    
   }