将struts扩展到面向对象的hibernate
译者按：
在看这篇文章之前: 如果你还不清楚hibernate的or/m工作机制， hibernate注释，以及一对多，多对一的机制，请先看hibernate文档
如果你不清楚struts的mvc，请先看struts文档,
你也要大概了解javabean和jakarta commons beanutil是干什么的）
版权声明：任何获得matrix授权的网站，转载时请务必保留以下作者信息和链接
作者:ted he;alilo(作者的blog:http://blog.matrix.org.cn/page/alilo)
原文:http://www.matrix.org.cn/resource/article/44/44391_struts+hibernate.html
关键字:struts;hibernate
摘要
hibernate和struts是当前市面上几个最流行的开源的库之一。它们很有效率，是程序员在开发java企业应用，挑选几个竞争的库的首选。虽然它们经常被一起应用，但是hibernate的设计目标并不是和struts一起使用，而struts在hibernate诞生好多年之前就发布了。为了让它们在一起工作，仍然有很多挑战。这篇文章点明了struts和hibernate之间的一些鸿沟，尤其关系到面向对象建模方面。文章也描述了如何在两者间搭起桥梁，给出了一个基于扩展struts的解决方案。所有的基于struts和hibernate构建的web应用都能从这个通用的扩展中获益。
在hibernate in action（manning,2004十月）这本书里，作者christian bauer和gavin king揭示了面向对象世界的模型和关系数据模型，两个世界的范例是不一致的。hibernate非常成功地在存储层(persistence layer)将两者粘合在一起。但是领域模型(domain model)(也就是model-view-controller的model layer)和html页面(mvc的view layer)仍然存在不一致。在这篇文章中，我们将检查这种不一致，并且探索解决的方案。
范例不一致的再发现
让我们先看一个经典的parent-child关系例子（看下面的代码）：product和category。category类定义了一个类型为long的标示符id和一个类型为string的属性name。product类也有一个类型为long的标示符id和一个类型为category的属性category，表示了多对一的关系（也就是说很多product可以属于一个category)
/**
* @hibernate.class table="category"
*/
public class category {
private long id;
private string name;
/**
* @hibernate.id generator-class="native" column="category_id"
*/
public long getid() {
return id;
}
public void setid(long id) {
this.id = id;
}
/**
* @hibernate.property column="name"
*/
public string getname() {
return name;
}
public void setname(long name) {
this.name = name;
}
}
/**
* @hibernate.class table="product"
*/
public class product {
private long id;
private category category;
/**
* @hibernate.id generator-class="native" column="product_id"
*/
public long getid() {
return id;
}
public void setid(long id) {
this.id = id;
}
/**
* @hibernate.many-to-one
* column="category_id"
* class="category"
* cascade="none"
* not-null="false"
*/
public category getcategory() {
return category;
}
public void setcategory(category category) {
this.category = category;
}
}
<select name="categoryid">
<option value="">no category</option>
<option value="1">category 1</option>
<option value="2">category 2</option>
<option value="3">category 3</option>
</select>
<html:select property="category.id">
<option value="">no category</option>
<html:options collection="categories" property="id" labelproperty="name"/>
</html:select>
public class productform extends actionform {
private long id;
private category category;
...
} public class productform extends actionform {
private long id;
private category category;
...
public void reset(actionmapping mapping, httpservletrequest request)
{
super.reset( mapping, request );
if ( category == null ) { category = new category(); }
}
} public class editproductaction extends action {
public final actionforward execute( actionmapping mapping, actionform form,
httpservletrequest request, httpservletresponse response ) throws exception
{
...
product product = createorloadproduct();
productform productform = (productform)form;
propertyutils.copyproperties( productform, product );
productform.reset( mapping, request );
...
}
} product product = createorloadproduct();
propertyutils.copyproperties( form, product );
form.reset( mapping, request );
public class productform extends actionform {
private long id;
private category category;
...
public void reset(actionmapping mapping, httpservletrequest request) {
super.reset( mapping, request );
if ( category == null ) { category = new category(); }
}
public void cleanupemptyobjects() {
if ( category.getid() == null ) { category = null; }
}
}public class saveproductaction extends action {
public final actionforward execute( actionmapping mapping, actionform form,
httpservletrequest request, httpservletresponse response ) throws exception
{
...
product product = new product();
((productform)form).cleanupemptyobjects();
propertyutils.copyproperties( product, form );
saveproduct( product );
...
}
} public class category {
...
private set products;
...
/**
* @hibernate.set
* table="product"
* lazy="true"
* outer-join="auto"
* inverse="true"
* cascade="all-delete-orphan"
*
* @hibernate.collection-key
* column="category_id"
*
* @hibernate.collection-one-to-many
* class="product"
*/
public set getproducts() {
return products;
}
public void setproducts(set products) {
this.products = products;
}
} public class categoryform extends actionform {
private set productforms;
...
public void reset(actionmapping mapping, httpservletrequest request) {
super.reset( mapping, request );
for ( int i = 0; i < max_product_num_on_page; i++ ) {
productform productform = new productform();
productform.reset( mapping, request );
productforms.add( productform );
}
}
public void cleanupemptyobjects() {
for ( iterator i = productforms.iterator(); i.hasnext(); ) {
productform productform = (productform) i.next();
productform.cleanupemptyobjects();
}
}
} import java.beans.propertydescriptor;
import org.apache.commons.beanutils.propertyutils;
import org.hibernate.metadata.classmetadata;
public abstract class abstractform extends actionform {
public void reset(actionmapping mapping, httpservletrequest request) {
super.reset( mapping, request );
// get propertydescriptor of all bean properties
propertydescriptor descriptors[] =
propertyutils.getpropertydescriptors( this );
for ( int i = 0; i < descriptors.length; i++ ) {
class propclass = descriptors[i].getpropertytype();
classmetadata classmetadata = hibernateutil.getsessionfactory()
.getclassmetadata( propclass );
if ( classmetadata != null ) { // this is a hibernate object
string propname = descriptors[i].getname();
object propvalue = propertyutils.getproperty( this, propname );
// evaluate property, create new instance if it is null
if ( propvalue == null ) {
propertyutils.setproperty( this, propname, propclass.newinstance() );
}
}
}
}
public void cleanupemptyobjects() {
// get propertydescriptor of all bean properties
propertydescriptor descriptors[] =
propertyutils.getpropertydescriptors( this );
for ( int i = 0; i < descriptors.length; i++ ) {
class propclass = descriptors[i].getpropertytype();
classmetadata classmetadata = hibernateutil.getsessionfactory()
.getclassmetadata( propclass );
if ( classmetadata != null ) { // this is a hibernate object
serializable id = classmetadata.getidentifier( this, entitymode.pojo );
// if the object id has not been set, release the object.
// define application specific rules of not-set id here,
// e.g. id == null, id == 0, etc.
if ( id == null ) {
string propname = descriptors[i].getname();
propertyutils.setproperty( this, propname, null );
}
}
}
}
}
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