How do I address unchecked cast warnings?

Question

Eclipse is giving me a warning of the following form:

Type safety: Unchecked cast from Object to HashMap

This is from a call to

Answer 1

Almost every problem in Computer Science can be solved by adding a level of indirection*, or something.

So introduce a non-generic object that is of a higher-level that a Map. With no context it isn't going to look very convincing, but anyway:

public final class Items implements java.io.Serializable {
    private static final long serialVersionUID = 1L;
    private Map map;
    public Items(Map map) {
        this.map = New.immutableMap(map);
    }
    public Map getMap() {
        return map;
    }
    @Override public String toString() {
        return map.toString();
    }
}

public final class New {
    public static  Map immutableMap(
        Map original
    ) {
        // ... optimise as you wish...
        return Collections.unmodifiableMap(
            new HashMap(original)
        );
    }
}

static Map getItems(HttpSession session) {
    Items items = (Items)
        session.getAttribute("attributeKey");
    return items.getMap();
}

*Except too many levels of indirection.