While working on a project that uses Hibernate, my team was getting a little frustrated while trying to interrogate a tree structure in our data model since all collections are mapped as java.util.HashSets. We wanted a simple function that could print the tree to the log, so I took a free hour and wrote this. It was a little more complicated than I anticipated because it had to handle situations like these.
root
|
|- child
|
|- child
root
|
|- child
|
|- child
and the infamous (to me) …
root | |- child | | | |- child | | | |- child | |- child
There’s a subtle difference. Notice that in the middle one, the line for the first child stops because there aren’t any more children, but in the last one, the line continues? I could have created some kind of 2D text buffer and gone back to draw the line, but that would be boring. Here’s what I came up with. I don’t know whether it’s pretty, but it works!
/**
* Creates a tree representation of the node
* @param node The node, which may not be null
* @return A string containing the formatted tree
*/
public static String toStringTree(Node node) {
final StringBuilder buffer = new StringBuilder();
return toStringTreeHelper(node, buffer, new LinkedList<Iterator<Node>>()).toString();
}
private static void toStringTreeDrawLines(List<Iterator<Node>> parentIterators, boolean amLast) {
StringBuilder result = new StringBuilder();
Iterator<Iterator<Node>> it = parentIterators.iterator();
while (it.hasNext()) {
Iterator<Node> anIt = it.next();
if (anIt.hasNext() || (!it.hasNext() && amLast)) {
result.append(" |");
}
else {
result.append(" ");
}
}
return result.toString();
}
private static StringBuilder toStringTreeHelper(Node node, StringBuilder buffer, List<Iterator<Node>>
parentIterators) {
if (!parentIterators.isEmpty()) {
boolean amLast = !parentIterators.get(parentIterators.size() - 1).hasNext();
buffer.append("\n");
String lines = toStringTreeDrawLines(parentIterators, amLast);
buffer.append(lines);
buffer.append("\n");
buffer.append(lines);
buffer.append("- ");
}
buffer.append(node.toString());
if (node.hasChildren()) {
Iterator<Node> it = node.getChildNodes().iterator();
parentIterators.add(it);
while (it.hasNext()) {
Node child = it.next();
toStringTreeHelper(child, buffer, parentIterators);
}
parentIterators.remove(it);
}
return buffer;
}