JTree - Creating JTree From YAML data

Following example provides a generic utility to load YAML data and build TreeNode from it. We are going to use SnakeYAML implementation to load data from yml file.

Building TreeNode from YAML

package com.logicbig.uicommon;

import org.yaml.snakeyaml.Yaml;
import javax.swing.tree.DefaultMutableTreeNode;
import java.io.IOException;
import java.io.InputStream;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

public class YamlToTreeNodeCreator {

  public static DefaultMutableTreeNode createTreeNodeFromYaml(String yamlFile) {
      Yaml yaml = new Yaml();
      try (InputStream in = YamlToTreeNodeCreator.class.getResourceAsStream(yamlFile)) {
          Iterable<Object> itr = yaml.loadAll(in);
          for (Object o : itr) {
              if (o instanceof Map) {
                  Map<?, ?> map = (Map) o;
                  for (Map.Entry<?, ?> entry : map.entrySet()) {
                      DefaultMutableTreeNode root = new DefaultMutableTreeNode(entry.getKey());
                      createTreeNode(entry.getValue(), root);
                      return root;
                  }
              }
          }
      } catch (IOException e) {
          throw new RuntimeException(e);
      }
      return null;
  }

  public static void createTreeNode(Object o, DefaultMutableTreeNode parentNode) {
      if (o instanceof Map) {
          Map<?, ?> map = (LinkedHashMap) o;
          for (Map.Entry<?, ?> entry : map.entrySet()) {
              DefaultMutableTreeNode node = new DefaultMutableTreeNode(entry.getKey());
              parentNode.add(node);
              createTreeNode(entry.getValue(), node);
          }
      } else if (o instanceof List) {
          List<?> list = (List<?>) o;
          for (Object e : list) {
              createTreeNode(e, parentNode);
          }
      } else if (o instanceof String) {
          DefaultMutableTreeNode node = new DefaultMutableTreeNode(o);
          parentNode.add(node);
      }
  }
}

Main class

public class TreeExampleMain {
  public static void main(String[] args) {
      TreeNode treeNode =
              YamlToTreeNodeCreator.createTreeNodeFromYaml("/countries.yml");
      JTree tree = new JTree(treeNode);
      tree.setCellRenderer(new CountriesTreeRenderer());
      tree.addTreeSelectionListener(createTreeSelectionListener());
      JFrame frame = createFrame();
      frame.add(new JScrollPane(tree));
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
  }

  private static TreeSelectionListener createTreeSelectionListener() {
      return treeSelectionEvent -> {
          TreePath path = treeSelectionEvent.getPath();
          System.out.println("Path: " + path);
          String nodeType = null;
          Object userObject = null;
          Object[] paths = path.getPath();
          switch (paths.length) {
              case 1:
                  nodeType = "World";
                  userObject = paths[0];
                  break;
              case 2:
                  nodeType = "Continent";
                  userObject = paths[1];
                  break;
              case 3:
                  nodeType = "Country";
                  userObject = paths[2];
                  break;
          }
          System.out.printf("nodeType: %s, userObject: %s%n", nodeType, userObject);
          System.out.println("-------");
      };
  }

  private static JFrame createFrame() {
      JFrame frame = new JFrame("JTree from YAML example");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setSize(new Dimension(500, 400));
      return frame;
  }
}

YAML file

src/main/resources/countries.yml

world:
  - Africa:
      - Nigeria
      - Tanzania
      - Tunisia
      - Zambia
  - North America:
      - Canada
      - USA
      - Mexico
      - Cuba
      - Jamaica
  - Sourth America:
      - Argentina
      - Colombia
      - Ecuador
      - Chile
       -Brazil
  - Europe:
      - Norway
      - France
      - Germany
      - Italy
      - UK
  - Asia:
      - Japan
      - Singapore
      - South Korea
      - Myanmar
  - Australia:
      - Papua New Guinea
      - Australia

Tree Renderer

public class CountriesTreeRenderer extends DefaultTreeCellRenderer {

  @Override
  public Component getTreeCellRendererComponent(JTree tree, Object value, boolean sel, boolean expanded,
                                                boolean leaf, int row, boolean hasFocus) {
      super.getTreeCellRendererComponent(tree, value, sel, expanded, leaf, row, hasFocus);
      DefaultMutableTreeNode node = (DefaultMutableTreeNode) value;
      switch (node.getPath().length) {
          case 1:
              setForeground(Color.BLUE);//world
              break;
          case 2:
              setForeground(Color.MAGENTA);//continent
              break;
          case 3:
              setForeground(Color.GREEN.darker());//country
              break;
      }
      return this;
  }
}

Output

Example Project

Dependencies and Technologies Used:

• snakeyaml 1.21: YAML 1.1 parser and emitter for Java.
• JDK 10
• Maven 3.5.4