How do I cast a HashMap to a concrete class?

The second is not possible because a HashMap is not a Fruit. You could do the first by providing a constructor that takes a Map<String, String> argument.

public Fruit(Map<String, String> map) {
  this.name = map.get("name");
  this.color = map.get("color");
}

It seems like you can use reflection for this

Fruit f = new Fruit();
Class aClass = f.getClass();
for(Field field : aClass.getFields()){
  if(map.containsKey(field.getName())){
    field.set(f,map.get(field.getName()));
  }
}