Java创建树形结构算法实例代码

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.Date;
import java.util.Iterator;
import java.util.List;

/**
 * <Description> 菜单扩展<br>
 */
public class MenuExt implements Serializable {

  /**
   * 菜单ID
   */
  private Long id;

  /**
   * 菜单名称
   */
  private String name;

  /**
   * 菜单地址
   */
  private String url;

  /**
   * 菜单图标
   */
  private String icon;

  /**
   * 父菜单ID
   */
  private Long parentId;

  /**
   * 子菜单
   */
  private List<MenuExt> children = new ArrayList<MenuExt>();

  /**
   * 菜单顺序
   */
  private Integer ordby;

  /**
   * 菜单状态
   */
  private String state;

  //省略Getter和Setter


  /**
   * 
   * <Description> 孩子节点排序<br>
   * 
   */
  public void sortChildren() {
    Collections.sort(children, new Comparator<MenuExt>() {
      @Override
      public int compare(MenuExt menu1, MenuExt menu2) {
        int result = 0;

        Integer ordby1 = menu1.getOrdby();
        Integer ordby2 = menu2.getOrdby();

        Long id1 = menu1.getId();
        Long id2 = menu2.getId();
        if (null != ordby1 && null != ordby2) {
          result = (ordby1 < ordby2 ? -1 : (ordby1 == ordby2 ? 0 : 1));
        } else {
          result = (id1 < id2 ? -1 : (id1 == id2 ? 0 : 1));
        }
        return result;
      }

    });
    // 对每个节点的下一层节点进行排序
    for (Iterator<MenuExt> it = children.iterator(); it.hasNext();) {
      it.next().sortChildren();
    }
  }

  public List<MenuExt> getChildren() {
    return children;
  }

  public void setChildren(List<MenuExt> children) {
    this.children = children;
  }
}

public static List<MenuExt> createTreeMenus(List<MenuExt> menus) {
    List<MenuExt> treeMenus = null;
    if (null != menus && !menus.isEmpty()) {
      // 创建根节点
      MenuExt root = new MenuExt();
      root.setName("菜单根目录");

      // 组装Map数据
      Map<Long, MenuExt> dataMap = new HashMap<Long, MenuExt>();
      for (MenuExt menu : menus) {
        dataMap.put(menu.getId(), menu);
      }

      // 组装树形结构
      Set<Entry<Long, MenuExt>> entrySet = dataMap.entrySet();
      for (Entry<Long, MenuExt> entry : entrySet) {
        MenuExt menu = entry.getValue();
        if (null == menu.getParentId() || 0 == menu.getParentId()) {
          root.getChildren().add(menu);
        } else {
          dataMap.get(menu.getParentId()).getChildren().add(menu);
        }
      }

      // 对树形结构进行二叉树排序
      root.sortChildren();
      treeMenus = root.getChildren();
    }
    return treeMenus;
  }