我们通常会在应用中碰到树形结构的内容,比如 文件夹/文件模型, 部门组织结构,目录树等等,通常在设计模式中叫做 compose 模式。

在数据库中常常这样表示: 我们以Catalog (分级目录) 为例子

Catalog (分级目录)

字段名称

字段

类型

备注

目录ID

catalog_id

varchar(36)

pk, not null

目录名称

catalog_name

varchar(50)

not null

父目录ID

parent_id

varchar(36)

fk

创建时间

create_datetime

datetime

not null

目录描述

description

varchar(200)

 


我们考虑在数据库中一次将所有数据读入内存,然后在内存中生成一个Tree,这样可以减少数据库的访问,增加性能,并且只有的数据方式改变的时候,全部重新从数据库中生成Tree,否则一直保持在内存中。

我们使用标准的DAO模式先生成 POJO类(Catalog)和DAO类(CatalogDAO)。

然后我们建立相对通用的 Tree 和 TreeNode 类。

Tree.java

package com.humpic.helper.tree;

import java.util.*;

import org.apache.commons.lang.StringUtils;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

public abstract class Tree {
   
protected static Log log = LogFactory.getLog(Tree.class);

   
private Map treeNodeMaps = new Hashtable();
   
private TreeNode root;

   
/**
     * root if it's parent is empty
    
*/
   
protected void reload(List nodes) {
        log.info(
"tree will start reload all data");
       
       
synchronized (this) {
           
// initialize
            treeNodeMaps.clear();
            root
= null;

            List treeNodes
= new Vector(nodes.size());
           
for (int i = 0; i < nodes.size(); i++) {
                TreeNode node
= this.transform(nodes.get(i)); // transform
                treeNodes.add(node);
                node.setTree(
this);
                treeNodeMaps.put(node.getNodeId(), node);
            }
           
           
for (int i = 0; i < treeNodes.size(); i++) {
                TreeNode node
= (TreeNode) treeNodes.get(i);
                String parentId
= node.getParentId();
               
if (this.isRootNode(node)) {
                    if (root == null) {
                        root
= node;
                    }
else {
                        log.error(
"find more then one root node. ignore.");
                    }

                }
else {
                   
TreeNode parent = (TreeNode) treeNodeMaps.get(parentId);
                   
if (parent != null) {
                        parent.addChild(node);
                        node.setParent(parent);
                    }
else {
                        log.warn(
"node [id=" + node.getNodeId() + "]: missing parent node.");
                    }

                }
            }
        }

       
if (root == null) {
            log.error(
"the root node is not be defined");
        }
    }

    protected boolean isRootNode(TreeNode node) {
       
return StringUtils.isBlank(node.getParentId());
    }

    public TreeNode getRootNode() {
       
return root;
    }

   
public TreeNode getTreeNode(String nodeId) {
       
return (TreeNode) treeNodeMaps.get(nodeId);
    }

   
public void addTreeNode(TreeNode node) {
       
synchronized (this) {
            treeNodeMaps.put(node.getNodeId(), node);

            String parentId
= node.getParentId();
           
if (StringUtils.isNotBlank(parentId)) {
                TreeNode parent
= getTreeNode(parentId);
               
if (parent != null) {
                    parent.addChild(node);
                    node.setParent(parent);
                }
else {
                    log.error(
"parent cannot be found: " + node.getParentId());
                }
            }
else {
               
if (root == null) {
                    root
= node;
                }
else {
                    log.error(
"find more then one root node. ignore.");
                }
            }
        }
    }

   
public void deleteTreeNode(String nodeId) {
       
synchronized (this) {
            TreeNode node
= getTreeNode(nodeId);
           
if (node == null)
               
throw new IllegalArgumentException(nodeId + " cannot be found.");

           
if (node.getParent() == null) {
                root
= null;
                treeNodeMaps.clear();
                log.warn(
"the root node has been removed.");
            }
else {
                node.getParent().getChildren().remove(node);

                treeNodeMaps.remove(nodeId);
                List children
= node.getAllChildren();
               
for (int i = 0; i < children.size(); i++) {
                    TreeNode n
= (TreeNode) children.get(i);
                    treeNodeMaps.remove(n.getNodeId());
                }
            }
        }
    }

   
/**
     * <pre>
     * Usage: Office -&gt;
     *
     * public TreeNode transform(Object info) {
     *     OfficeInfo office_info = (OfficeInfo) info;
     *     TreeNode node = new TreeNode();
     *     node.setNodeId(office_info.getOfficeId());
     *     node.setParentId(office_info.getParentId());
     *     node.setBindData(office_info);
     *     return node;
     * }
     * </pre>
    
*/
   
protected abstract TreeNode transform(Object info);
}

TreeNode.java

package com.humpic.helper.tree;

import java.util.List;
import java.util.Vector;

import org.apache.commons.collections.Predicate;
import org.apache.commons.lang.ObjectUtils;

public class TreeNode {

   
private Tree tree;
   
private TreeNode parent;
   
private List children = new Vector();
   
private List childrenGroup = new Vector();
   
private String nodeId;
   
private String parentId;
   
private Object bindData;

   
public String getNodeId() {
       
return nodeId;
    }

   
public void setNodeId(String nodeId) {
       
this.nodeId = nodeId;
    }

   
public String getParentId() {
       
return parentId;
    }

   
public void setParentId(String parentId) {
       
this.parentId = parentId;
    }

   
public Object getBindData() {
       
return bindData;
    }

   
public void setBindData(Object bindData) {
       
this.bindData = bindData;
    }

   
public Tree getTree() {
       
return tree;
    }

   
public void setTree(Tree tree) {
       
this.tree = tree;
    }

   
public void setParent(TreeNode parent) {
       
this.parent = parent;
    }

   
public TreeNode getParent() {
       
return this.parent;
    }

   
public List getChildren() {
       
return this.children;
    }

   
public void addChild(TreeNode node) {
        children.add(node);
    }

   
/**
     * get all children, and chilren's children
    
*/
   
public List getAllChildren() {
       
if (this.childrenGroup.isEmpty()) {
           
synchronized (this.tree) {
               
for (int i = 0; i < this.children.size(); i++) {
                    TreeNode node
= (TreeNode) this.children.get(i);
                   
this.childrenGroup.add(node);
                   
this.childrenGroup.addAll(node.getAllChildren());
                }
            }
        }
       
return this.childrenGroup;
    }

   
/**
     * get all children, and chilren's children
    
*/
  
 public List getAllChildren(Predicate predicate) {
        List groups
= new Vector();
        fillAllChildren(groups, predicate);
       
return groups;
    }

   
private void fillAllChildren(List groups, Predicate predicate) {
       
for (int i = 0; i < this.children.size(); i++) {
            TreeNode node
= (TreeNode) this.children.get(i);
           
if (predicate.evaluate(node)) {
                groups.add(node);
                node.fillAllChildren(groups, predicate);
            }
        }
    }

    /**
     * get all parents, and parent's parent
    */

   
public List getParents() {
        List results =
new Vector();
        TreeNode parent =
this.getParent();
       
while (parent != null) {
            results.add(parent);
            parent = parent.getParent();
        }
       
return results;
    }

   
/**
     * A.isMyParent(B) == B is A' parent ? <br>
     * root.isMyParent(null) == true; <br>
     * root.isMyParent(*) == false <br>
     * *.isMyParent(null) == false
    
*/
   
public boolean isMyParent(String nodeId) {
        TreeNode target
= tree.getTreeNode(nodeId);
        TreeNode parent
= this.getParent();
       
if (parent == null) {
           
return target == null;
        }
else {
           
return parent.equals(target);
        }
    }

   
/**
     * A.isMyAncestor(B) == B is A' ancestor ? <br>
     * *.isMyAncestor(null) == true;
    
*/
   
public boolean isMyAncestor(String nodeId) {
        TreeNode target
= tree.getTreeNode(nodeId);
       
if (target == null)
           
return true;

       
return target.getAllChildren().contains(this);
    }

   
/**
     * A.isMyBrother(B) == B is A' brother ? <br>
     * *.isMyBrother(null) == false
    
*/
   
public boolean isMyBrother(String nodeId) {
        TreeNode target
= tree.getTreeNode(nodeId);
       
if (target == null)
           
return false;

        TreeNode p1
= this.getParent();
        TreeNode p2
= target.getParent();
       
return ObjectUtils.equals(p1, p2);
    }

}

然后建立业务 Tree

CatalogTree.java

package com.humpic.helper.tree;

import java.util.List;
import org.apache.commons.collections.Predicate;

public class CatalogTree extends Tree {
   
private static CatalogTree instance = null;

   
private CatalogTree() {}
   
   
public static synchronized CatalogTree getInstance() {
       
if (instance == null) {
            instance = new CatalogTree();
            instance.reloadCatalogs();
        }
       
return instance;
    }

   
protected TreeNode transform(Object info) {
        Catalog catalog
= (Catalog) info;
        TreeNode node
= new TreeNode();
        node.setNodeId(catalog.getCatalogId());
        node.setParentId(catalog.getParentId());
        node.setBindData(catalog);
       
return node;
    }

   
public void reloadCatalogs() {
        List nodes
= CatalogDAO.getInstance().findAll();
       
super.reload(nodes);
    }

   
public Catalog getCatalogNode(String catalogId) {
        TreeNode node
= super.getTreeNode(catalogId);
       
return node == null ? null : (Catalog) node.getBindData();
    }
}

最后,我们只要使用以下的语句就可以了:

1. CatalogTree.getInstance().getTreeNode(...)
2. CatalogTree.getInstance().getCatalogNode(...)
3. CatalogTree.getInstance().getRootNode()

然后通过 TreeNode,就可以得到 parent, parents 和 children, allChildren


文章来源:http://x-spirit.spaces.live.com/Blog/cns!CC0B04AE126337C0!367.entry