List to Tree (using whitespaces to indent) with Groovy

Supose you have a structure like this:

id	name	father
1	N1	null
11	N11	1
12	N12	1
121	N121	12
122	N122	12
13	N13	1
131	N131	13
1311	N1311	131
13111	N13111	1311
14	N14	1
2	N2	null

public class Node {
    def id
    def name
    def father
}

public class NodePrinter {
    private void printLeftPad(def source,int pad)
    {
        for(int i=0;i<pad;i++) print " ";
        println source;
    }
    
    public int indent(List items,int index,int pad)
    {
        printLeftPad("${items.get(index).name}",pad);

        def current= items.get(index);
        int i=index+1;
        for(;i<items.size();i++)
        {
            if( items.get(i).father==current.id )
            {
                printLeftPad("{",pad);
                i=indent(items,i,pad+4);
                printLeftPad("}",pad);
            }
            else
            {
                if( current.father==items.get(i).father )
                {
                    printLeftPad("${items.get(i).name}",pad);
                    current=items.get(i);
                }
                else
                {
                    return i-1;
                }
            }
        }

        return i;
    }

}

def nodes=[ new Node(id:1,name:'N1',father:null),
            new Node(id:11,name:'N11',father:1),
            new Node(id:12,name:'N12',father:1),
            new Node(id:121,name:'N121',father:12),
            new Node(id:122,name:'N122',father:12),
            new Node(id:13,name:'N13',father:1),
            new Node(id:131,name:'N131',father:13),
            new Node(id:1311,name:'N1311',father:131),
            new Node(id:13111,name:'N13111',father:1311),
            new Node(id:14,name:'N14',father:1),
            new Node(id:2,name:'N2',father:null)
          ];
          
def printer=new NodePrinter();
printer.indent(nodes,0,4);

This will give us the following result:

    N1
    {
        N11
        N12
        {
            N121
            N122
        }
        N13
        {
            N131
            {
                N1311
                {
                    N13111
                }
            }
        }
        N14
    }
    N2

Enjoy it!