在專案中，有大量的諸如“產品型別”這樣的下拉選擇框，為了保證專案後期的可維護性，除了相對固化的類別可以在程式碼中直接寫死外，這些下拉選擇框應當儘量從系統的資料字典表中進行動態讀取和展現。但在展現時候存在一個問題，如果分類存在多級時候，一種方案是採用幾個下拉框進行級聯操作，也即所謂的DoubleSelect，但這種情況只適用與兩級級聯選單的情況，在處理上也不具有通用性。例如典型的需求：

對於產品類別，結構如下：

產品類別（頂級節點：root,型別：product_type）:

　|-娛樂（產品大類1:product_type1,型別:product_type）

　　　|-音樂（產品分類11,product_type11）

　　　　　|-流行音樂（子分類111,product_type111）

　　　　　|-搖滾音樂（子分類112,product_type112）

　　　|-產品分類12

　|-商務（產品大類2）

1、資料庫儲存策略

鑑於此，在專案中，對於這樣的需求的實現方法如下：

對於一種類別（例如對於產品類別product_type）的子類別在oss_category(類別表)中儲存方案如下：

1、在oss_category表中插入一條記錄用於標識“產品類別”對應的頂級節點，其

category_id=1,parent_id=-1,category_type=”product_type”,category_name=”root”

2、在oss_category表中插入一條記錄用於標識“product_type11”2級節點，其

category_id=2,parent_id=1,category_type=”product_type”,category_name=”product_type1”

3、在oss_category表中插入一條記錄用於標識“product_type11”3級節點，其

category_id=3,parent_id=2,category_type=”product_type”,category_name=”product_type11”

整個資料庫指令碼如下：

CREATE TABLE `oss_category` (

`category_id` int(11) NOT NULL auto_increment,

`parent_id` int(11) default ‘-1′,

`level` smallint(6) default NULL,

`is_leaf` tinyint(1) default NULL,

`category_title` varchar(100) default NULL,

`category_name` varchar(100) default NULL,

`category_code` varchar(100) default NULL,

`category_type` varchar(30) default NULL,

`image` varchar(255) default NULL,

`status` varchar(20) default NULL,

`creator` varchar(50) default NULL,

`create_date` datetime default NULL,

`modify_user` varchar(50) default NULL,

`modify_date` datetime default NULL,

`description` text,

PRIMARY KEY(`category_id`)

) ENGINE=MyISAM AUTO_INCREMENT=1 DEFAULT CHARSET=gbk;

INSERT INTO `oss_category` VALUES (’1′, ‘-1′, ’1′, ’0′, ‘root’, ‘root’, ‘root’, ‘product_type’, null, ’1′, null, null, null, null, null);

INSERT INTO `oss_category` VALUES (’2′, ’1′, ’2′, ’0′, ‘<input type=\’checkbox\’ name=\’product_type1\’id=\’product_type1\’/><b>product_type1</b>’, ‘product_type1′, ‘product_type1′, ‘product_type’, null, ’1′, null, null, null, null, null);

INSERT INTO `oss_category` VALUES (’3′, ’1′, ’2′, ’0′, ‘<input type=\’checkbox\’ name=\’product_type2\’ id=\’product_type2\’class=\’treeCheckBox\’/><b>product_typ’, ‘product_type2′, ‘product_type2′, ‘product_type’, null, ’1′, null, null, null, null, null);

INSERT INTO `oss_category` VALUES (’4′, ’3′, ’3′, ’0′, ‘<input type=\’checkbox\’ name=\’product_type21\’id=\’product_type21\’/><b>product_type21</b>’, ‘product_type21′, ‘product_type21′, ‘product_type’, null, ’1′, null, null, null, null, null);

INSERT INTO `oss_category` VALUES (’5′, ’2′, ’3′, ’0′, ‘<input type=\’checkbox\’ name=\’product_type11\’id=\’product_type11\’/><b>product_type11</b>’, ‘product_type11′, ‘product_type11′, ‘product_type’, null, ’1′, null, null, null, null, null);

INSERT INTO `oss_category` VALUES (’6′, ’5′, ’4′, ’1′, ‘<input type=\’checkbox\’ name=\’product_type111\’id=\’product_type111\’/><b>product_type111</b>’, ‘product_type111′, ‘product_type111′, ‘product_type’, null, ’1′, null, null, null, null, null);

INSERT INTO `oss_category` VALUES (’7′, ’3′, ’2′, ’0′, ‘<input type=\’checkbox\’ name=\’product_type22\’ id=\’product_type22\’/><b>product_type22</b>’, ‘product_type22′, ‘product_type22′, ‘product_type’, null, ’1′, null, null, null, null, null);

INSERT INTO `oss_category` VALUES (’8′, ’2′, ’3′, ’0′, ‘<input type=\’checkbox\’ name=\’product_type12\’id=\’product_type12\’/><b>product_type12</b>’, ‘product_type12′, ‘product_type12′, ‘product_type’, null, ’1′, null, null, null, null, null);

INSERT INTO `oss_category` VALUES (’9′, ’4′, ’4′, ’1′, ‘<input type=\’checkbox\’ name=\’product_type211\’id=\’product_type211\’/><b>product_type211</b>’, ‘product_type211′, ‘product_type211′, ‘product_type’, null, ’1′, null, null, null, null, null);

INSERT INTO `oss_category` VALUES (’10′, ’7′, ’4′, ’1′, ‘<input type=\’checkbox\’ name=\’product_type221\’id=\’product_type221\’/><b>product_type221</b>’, ‘product_type221′, ‘product_type221′, ‘product_type’, null, ’1′, null, null, null, null, null);

2、下拉框展現樹形結構策略

為了保證跨瀏覽器的相容性，不採用任何控制元件來實現在下拉框中展現樹形結構，而採用最為原始的拼湊出如下形式的select 框

<select>

<option value=”1″>1</option>

<option value=”11″>&nbsp;&nbsp;|-11</option>

<option value=”12″>&nbsp;&nbsp;|-12</option>

<option value=”2″>2</option>

<option value=”21″>&nbsp;&nbsp;|-21</option>

<option value=”22″>&nbsp;&nbsp;|-22</option>

</select>

也即用&nbsp;來實現縮排來達到樹形結構的效果，在實現上只需要在程式中拼湊出這樣的字串到介面展現即可。

在Struts2中，採用標籤展現結果時候，注意property的選項escape=”false”,讓Struts2不要對字串進行轉義。

<s:property value=”#request.selectResult” escape=”false”/>

3、程式碼實現

程式碼基本上沿用了原來的樹形結構的程式碼，由於原來與OssCategory及ossCategoryDAO存在衝突，拷貝OssCategory.hbm.xml為Tree.hbm.xml。

3.1、Model層

package com.mobilesoft.framework.tree.model;

import java.util.Date;

import java.util.List;

import java.util.Set;

import com.mobilesoft.framework.common.model.BaseObject;

/**

* OssCategory entity.

*

* @author MyEclipse Persistence Tools

*/

public class Tree extends BaseObject

implements java.io.Serializable {

// Fields

private Integer categoryId;

private Integer parentId;

private Short level;

private Byte isLeaf;

private String categoryTitle;

private String categoryName;

private String categoryCode;

private String categoryType;

private String image;

private String status;

private String creator;

private Date createDate;

private String modifyUser;

private Date modifyDate;

private String description;

private Tree[] childCategories;

// Constructors

/** default constructor */

public Tree() {

}

/** full constructor */

public Tree(Integer parentId, Short level, Byte isLeaf,

String categoryTitle, String categoryName, String categoryCode,

String categoryType, String image, String status, String creator,

Date createDate, String modifyUser, Date modifyDate,

String description) {

this.parentId = parentId;

this.level = level;

this.isLeaf = isLeaf;

this.categoryTitle = categoryTitle;

this.categoryName = categoryName;

this.categoryCode = categoryCode;

this.categoryType = categoryType;

this.image = image;

this.status = status;

this.creator = creator;

this.createDate = createDate;

this.modifyUser = modifyUser;

this.modifyDate = modifyDate;

this.description = description;

}

// Property accessors

public Integer getCategoryId() {

return this.categoryId;

}

public void setCategoryId(Integer categoryId) {

this.categoryId = categoryId;

}

public Integer getParentId() {

return this.parentId;

}

public void setParentId(Integer parentId) {

this.parentId = parentId;

}

public Short getLevel() {

return this.level;

}

public void setLevel(Short level) {

this.level = level;

}

public Byte getIsLeaf() {

return this.isLeaf;

}

public void setIsLeaf(Byte isLeaf) {

this.isLeaf = isLeaf;

}

public String getCategoryTitle() {

return this.categoryTitle;

}

public void setCategoryTitle(String categoryTitle) {

this.categoryTitle = categoryTitle;

}

public String getCategoryName() {

return this.categoryName;

}

public void setCategoryName(String categoryName) {

this.categoryName = categoryName;

}

public String getCategoryCode() {

return this.categoryCode;

}

public void setCategoryCode(String categoryCode) {

this.categoryCode = categoryCode;

}

public String getCategoryType() {

return this.categoryType;

}

public void setCategoryType(String categoryType) {

this.categoryType = categoryType;

}

public String getImage() {

return this.image;

}

public void setImage(String image) {

this.image = image;

}

public String getStatus() {

return this.status;

}

public void setStatus(String status) {

this.status = status;

}

public String getCreator() {

return this.creator;

}

public void setCreator(String creator) {

this.creator = creator;

}

public Date getCreateDate() {

return this.createDate;

}

public void setCreateDate(Date createDate) {

this.createDate = createDate;

}

public String getModifyUser() {

return this.modifyUser;

}

public void setModifyUser(String modifyUser) {

this.modifyUser = modifyUser;

}

public Date getModifyDate() {

return this.modifyDate;

}

public void setModifyDate(Date modifyDate) {

this.modifyDate = modifyDate;

}

public String getDescription() {

return this.description;

}

public void setDescription(String description) {

this.description = description;

}

public Tree[] getChildCategories() {

return childCategories;

}

public void setChildCategories(Tree[] childCategories) {

this.childCategories = childCategories;

}

}

3.2、DAO層

package com.mobilesoft.framework.tree.dao.hibernate;

import org.apache.log4j.Logger;

import java.util.ArrayList;

import java.util.Iterator;

import java.util.List;

import org.apache.commons.logging.Log;

import org.apache.commons.logging.LogFactory;

import org.hibernate.LockMode;

import org.springframework.context.ApplicationContext;

import org.springframework.orm.hibernate3.support.HibernateDaoSupport;

import com.mobilesoft.framework.tree.model.Tree;

/**

* A data access object (DAO) providing persistence and search support for

* Tree entities. Transaction control of the save(), update() and

* delete() operations can directly support Spring container-managed

* transactions or they can be augmented to handle user-managed Spring

* transactions. Each of these methods provides additional information for how

* to configure it for the desired type of transaction control.

*

* @see com.mobilesoft.esales.model.Tree

* @author MyEclipse Persistence Tools

*/

public class TreeDAO extends HibernateDaoSupport {

/**

* Logger for this class

*/

private static final Logger logger = Logger.getLogger(TreeDAO.class);

private static final Log log = LogFactory.getLog(TreeDAO.class);

// property constants

public static final String PARENT_ID = “parentId”;

public static final String LEVEL = “level”;

public static final String IS_LEAF = “isLeaf”;

public static final String tree_TITLE = “categoryTitle”;

public static final String tree_NAME = “categoryName”;

public static final String tree_CODE = “categoryCode”;

public static final String tree_TYPE = “categoryType”;

public static final String IMAGE = “image”;

public static final String STATUS = “status”;

public static final String CREATOR = “creator”;

public static final String MODIFY_USER = “modifyUser”;

public static final String DESCRIPTION = “description”;

public String delimiter;

protected void initDao() {

// do nothing

}

/*

省略掉其他方法

*/

public static TreeDAO getFromApplicationContext(

ApplicationContext ctx) {

return (TreeDAO) ctx.getBean(“treeDAO”);

}

public Tree[] getAlltree() {

ArrayList<Tree> resultList=new ArrayList<Tree>();

String queryString=”from Tree as tree where tree.parentId=1″;

List<Tree> queryList =getHibernateTemplate().find(queryString);

Iterator iterator=queryList.iterator();

while(iterator.hasNext()){

Tree tree=(Tree)iterator.next();

Tree[] childrenArray=getChildCategoriesById(tree.getCategoryId());

logger.debug(“getAlltree() – Tree[] childrenList=” + childrenArray.length);

tree.setChildCategories(childrenArray);

resultList.add(tree);

}

Tree[] resultArray=(Tree[])resultList.toArray(new Tree[resultList.size()]);

return resultArray;

}

public String getChildrenByType(String type,boolean includeRoot,String delimiter ){

this.delimiter=delimiter;

StringBuffer resultBuffer=new StringBuffer();

resultBuffer.append(“<select>”);

StringBuffer queryBuffer=new StringBuffer(“from Tree as tree where tree.categoryType=’”);

queryBuffer.append(type);

queryBuffer.append(“‘ order by tree.categoryId asc “);

logger.fatal(queryBuffer);

List<Tree> queryList =getHibernateTemplate().find(queryBuffer.toString());

if(queryList.size()>0){

Tree[] treeArray=(Tree[])queryList.toArray(new Tree[queryList.size()]);

int start;

if(includeRoot)

start=0;

else

start=1;

resultBuffer.append(“<option value=’”);

resultBuffer.append(treeArray[start].getCategoryId());

resultBuffer.append(“‘>”);

resultBuffer.append(treeArray[start].getCategoryName());

resultBuffer.append(“</option>”);

String childrenStr=getChildCategories4Select(treeArray[start].getCategoryId(),treeArray[start].getLevel());

logger.debug(“getChildrenByType( String ) – start String=” + start +”,level is :”+treeArray[start].getLevel());

resultBuffer.append(childrenStr);

logger.fatal(“getChildrenByType(String) – StringBuffer resultBuffer11111=” + resultBuffer);

resultBuffer.append(“</select>”);

return resultBuffer.toString();

}else{

return “</select>”;

}

}

public Tree[] getChildCategoriesById(int treeId) {

String queryString=”from Tree as tree where tree.parentId=”+treeId;

List<Tree> queryList =getHibernateTemplate().find(queryString);

logger.debug(“getChildCategoriesById(int) – List<Tree> queryList=” + queryList.size());

ArrayList<Tree> resultList=new ArrayList<Tree>();

Iterator iterator=queryList.iterator();

while(iterator.hasNext()){

Tree tree=(Tree)iterator.next();

Tree[] childrenList=getChildCategoriesById(tree.getCategoryId());

logger.debug(“getChildCategoriesById(int) – Tree[] childrenList=” + childrenList+”parentid is “+treeId);

tree.setChildCategories(childrenList);

resultList.add(tree);

}

Tree[] resultArray=(Tree[])resultList.toArray(new Tree[resultList.size()]);

return resultArray;

}

/*

* @return 要拼湊出如下形式的select 框

* <select>

* <option value=”1″>1</option>

* <option value=”11″>&nbsp;&nbsp;|-11</option>

* <option value=”12″>&nbsp;&nbsp;|-12</option>

* <option value=”2″>2</option>

* <option value=”21″>&nbsp;&nbsp;|-21</option>

* <option value=”22″>&nbsp;&nbsp;|-22</option>

* </select>

*

* @param treeId節點的id號

* @param rootLevel所在類別子樹根節點在整棵樹中的層級

*/

public String getChildCategories4Select(int treeId,int rootLevel) {

StringBuffer childBuffer=new StringBuffer();

String queryString=”from Tree as tree where tree.parentId=”+treeId;

List<Tree> queryList =getHibernateTemplate().find(queryString);

logger.debug(“getChildCategories4Select(int,int) – List<Tree> queryList=” + queryList.size());

ArrayList<Tree> resultList=new ArrayList<Tree>();

Iterator iterator=queryList.iterator();

while(iterator.hasNext()){

Tree tree=(Tree)iterator.next();

int childLevel=tree.getLevel();

childBuffer.append(“<option value=’”);

childBuffer.append(tree.getCategoryId());

childBuffer.append(” ‘>”);

for(int i=0;i<=childLevel-rootLevel;i++)

childBuffer.append(“&nbsp;&nbsp;”);

childBuffer.append(this.delimiter+tree.getCategoryName());

childBuffer.append(“</option>”);

String childrenStr=getChildCategories4Select(tree.getCategoryId(),rootLevel);

childBuffer.append(childrenStr);

logger.debug(“getChildCategories4Select(int,int) – childBuffer=” + childBuffer);

}

return childBuffer.toString();

}

}

3.3、Service層

TreeService.java

package com.mobilesoft.framework.tree.service;

import java.util.List;

import java.util.Set;

import com.mobilesoft.framework.tree.model.Tree;

public interface TreeService {

/**

* @return 獲取下級子節點

*/

//public Set getChildren(int rootId);

/**

* @return 遞迴指定級別的所有子節點

*

*/

//public Set getChildrenByLevel(int rootId,int level);

/**

* 用於獲取資料字典中指定類別的所有型別的節點，

* 類別表節點的樹形結構

* |– ROOT 根類別（-1）

* 　|–類別型別：套餐類別 bundle_type

* 　　|–3 套餐類別1

* 　　|–4 套餐類別2

*　|–類別型別：產品類別 product_type

* 　　|–產品大類1

*　　　　|–產品大類11

*　　　　　|—產品大類別111

*　　　　　|—產品大類別112

*　　　　|–產品大類12

* @return 獲取指定型別的所有子節點

* 在實現上，對於諸如”產品類別“等下拉框可能為樹形結構的元素，

* 為了避免由於瀏覽器相容性問題，在形式上是樹形結構，

* 實際上就是從字典表（目前樹形結構仍然採用oss_category作為字典表）動態取出資料，然後拼湊成字串形式展現，例如：

* <select>

* <option value=”1″>1</option>

*<option value=”11″>&nbsp;&nbsp;|-11</option>

*<option value=”12″>&nbsp;&nbsp;|-12</option>

*<option value=”2″>2</option>

*<option value=”21″>&nbsp;&nbsp;|-21</option>

*<option value=”22″>&nbsp;&nbsp;|-22</option>

*</select>

* @param type:節點的型別

* @param levle:節點相對於所屬型別的節點的級別 -1表示獲取所屬型別的根節點的所有級別的子節點

*/

public String getChildrenByType( String type);

public String getChildrenByType( String type,boolean includeRoot);

public String getChildrenByType( String type,boolean includeRoot,String delimiter);

/**

* @return 獲取指定根節點的所有子節點

*/

public Tree[]getAllTree();

}

TreeServiceImpl.java

package com.mobilesoft.framework.tree.service.impl;

import java.util.List;

import java.util.Set;

import com.mobilesoft.framework.tree.dao.hibernate.TreeDAO;

import com.mobilesoft.framework.tree.model.Tree;

import com.mobilesoft.framework.tree.service.TreeService;

public class TreeServiceImpl implements TreeService {

TreeDAO treeDAO;

String delimiter;

public Set getChildren(int rootId) {

// TODO Auto-generated method stub

return null;

}

public Set getLevelChildren(int rootId, int level) {

// TODO Auto-generated method stub

return null;

}

public String getChildrenByType( String type){

return treeDAO.getChildrenByType(type,true,this.delimiter);

}

public String getChildrenByType( String type,boolean includeRoot){

return treeDAO.getChildrenByType(type,includeRoot,this.delimiter);

}

public String getChildrenByType( String type,boolean includeRoot,String delimiter){

return treeDAO.getChildrenByType(type,includeRoot,delimiter);

}

public Tree[]getAllTree(){

return treeDAO.getAlltree();

}

public TreeDAO gettreeDAO() {

return treeDAO;

}

public void settreeDAO(TreeDAO treeDAO) {

this.treeDAO = treeDAO;

}

public String getDelimiter() {

return delimiter;

}

public void setDelimiter(String delimiter) {

this.delimiter = delimiter;

}

}

3.4、呼叫方法

以Action中為例：

private TreeService treeService;

public String getChildrenByType(){

String selectResult=treeService.getChildrenByType(“product_type”);

getRequest().setAttribute(“selectResult”, selectResult);

returnSUCCESS;

}

public TreeService getTreeService() {

returntreeService;

}

publicvoid setTreeService(TreeService treeService) {

this.treeService = treeService;

}

注意：getChildrenByType方法有三個過載（overload）方法，

public String getChildrenByType( String type);

public String getChildrenByType( String type,boolean includeRoot);

public String getChildrenByType( String type,boolean includeRoot,String delimiter);

但實際上最後還是呼叫的是getChildrenByType( String type,boolean includeRoot,String delimiter)，

引數說明：

type: 類別的型別，例如product_type

includeRoot：是否包含所在類別的根節點，例如查詢product_type是否，是否需要匯出所在類別的root節點

delimiter：在下拉框選擇時候，分隔符型別，預設為“|-”,可以在applicationContext-service.xml中修改或呼叫時候傳遞引數。

3.5、配置檔案

applicationContext-resources.xml

<property name=”mappingResources”>

<list>

<value>com/mobilesoft/framework/tree/model/Tree.hbm.xml</value>

</list>

</property>

applicationContext-dao.xml

<bean id=”treeDAO”

class=”com.mobilesoft.framework.tree.dao.hibernate.TreeDAO”>

<property name=”sessionFactory”>

<ref bean=”sessionFactory” />

</property>

</bean>

applicationContext-service.xml

<bean id=”treeService”

class=”com.mobilesoft.framework.tree.service.impl.TreeServiceImpl”>

<property name=”treeDAO”>

<ref bean=”treeDAO” />

</property>

<property name=”delimiter” value=”|-”/>

</bean>

action-servlet.xml

<bean id=”treeAction” scope=”prototype”

class=”com.mobilesoft.esales.webapp.action.TreeAction”>

<property name=”treeService”>

<ref bean=”treeService” />

</property>

</bean>

struts.xml

<action name=”treeAction” method=”execute” class=”treeAction”>

<result name=”success”>test/treetest.jsp</result>

</action>