Multi-line pretty-printing of (nested) collections in Java

Question

I want to be able to (pretty-)print the contents of my maps.

They should have newlines and indentation rather than on a single line; ignoring the toString methods of

Answer 1

I was looking for a printing of nested collections in Java which brought me here. However the answers only work for Maps therefore I thought I'd add my solution for nested Collections. It produces a JSON like output, if you want newlines add "]\n" rather than ']'.

Note that this will not produce pretty output if the Object[] contains nested elements. You would need to write a separate method to deal with nested arrays. Also it will not pretty print primitive arrays, for that you'd need an else statement for every primitive array type.

private static , B> String nestedToString(A collection) {
    if (collection == null)
        return "null";

    String ret = "";

    Iterator colIterator = collection.iterator();
    if (colIterator.hasNext()) {
        ret += '[';
        while (colIterator.hasNext()) {
            B object = colIterator.next();
            if (object == null) {
                ret += "null";
            } else if (object instanceof Collection) {
                ret += nestedToString((Collection) object);
            } else if (object instanceof Object[]) {
                ret += Arrays.deepToString((Object[]) object);
            } else {
                ret += object;
            }
            if (colIterator.hasNext()) {
                ret += ", ";
            }
        }
        ret += ']';
    }
    return ret;
}