Question

I’m trying to catch a ClassCastException when deserializing an object from xml.

So,

try {     restoredItem = (T) decoder.readObject(); } catch (ClassCastException e){     //don't need to crash at this point,    //just let the user know that a wrong file has been passed. } 

And yet this won’t as the exception doesn’t get caught. What would you suggest?

Answer 1

The code in the question should give you an unchecked cast warning. Listen to -Xlint.

All the compiler knows about T is its bounds, which it probably doesn’t have (other than explicitly extending Object and a super of the null type). So effectively the cast at runtime is (Object) – not very useful.

What you can do is pass in an instance of the Class of the parameterised type (assuming it isn’t generic).

class MyReader<T> {     private final Class<T> clazz;     MyReader(Class<T> clazz) {         if (clazz == null) {             throw new NullPointerException();         }         this.clazz = clazz;     }     public T restore(String from) {         ...         try {             restoredItem = clazz.cast(decoder.readObject());             ...             return restoredItem;         } catch (ClassCastException exc) {             ...         }     } } 

Or as a generic method:

    public <T> T restore(Class<T> clazz, String from) {         ...         try {             restoredItem = clazz.cast(decoder.readObject());             ...