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 ->
*
* 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