Modify a Node of tree

<?page title="new page title" contentType="text/html;charset=UTF-8"?>
<zk>
	<window id="win" border="0" apply="ctrl.Composer">
		<tree id="tree">
			<treechildren>
				<treeitem>
					<treerow>
						<treecell label="Hospital" />
					</treerow>
					<treechildren>
						<treeitem>
							<treerow>
								<treecell label="Hosp1" />
							</treerow>
							<treechildren>
								<treeitem>
									<treerow>
										<treecell label="Hosp1.1" />
									</treerow>
								</treeitem>
							</treechildren>
						</treeitem>
						<treeitem>
							<treerow draggable="true">
								<treecell label="Hosp2" />
							</treerow>
						</treeitem>
					</treechildren>
				</treeitem>
			</treechildren>
		</tree>
		<textbox id="textbox" />
		<button label="modify" id="modifyBtn" />
		<separator />
		<label id="msgLabel" style="color : red;" />
	</window>
</zk>

package ctrl;

import org.zkoss.lang.Strings;
import org.zkoss.zk.ui.Component;
import org.zkoss.zk.ui.util.GenericForwardComposer;
import org.zkoss.zul.*;


public class Composer extends GenericForwardComposer {
	private Tree tree;
	private Textbox textbox;
	private Label msgLabel;
	@Override
	public void doAfterCompose(Component comp) throws Exception {
		super.doAfterCompose(comp);
	}

	public void onClick$modifyBtn(){
		String value = textbox.getValue();	
		Treeitem item = tree.getSelectedItem();
		
		msgLabel.setValue("");
		
		if(item == null){
			msgLabel.setValue("please select an item");	
			return;
		}
		if(Strings.isBlank(value)||Strings.isEmpty(value)){
			msgLabel.setValue("please input a name");
			return;
		}				
		
		Treecell treeCell = (Treecell)item.getTreerow().getFirstChild();
		treeCell.setLabel(value);		
	}
	
	public void onSelect$tree(){
		Treeitem item = tree.getSelectedItem();
		Treecell treeCell = (Treecell)item.getTreerow().getFirstChild();
		
		textbox.setValue(treeCell.getLabel());
	}
	
}