用分治法解决级联对象与相应XML之间的互相转化

　　如果我们有一个group对象,它底下有一堆company对象,company底下有一堆employee对象,我们可称这三个对象为级联对象,如果要求将对象从以下XML文件中转化过来该怎么做呢?

＜?xml version="1.0" encoding="UTF-8"?＞
＜root＞
＜group name="citigroup"＞
＜location＞New york＜/location＞
＜company name="citibank"＞
＜location＞Paris＜/location＞
＜employee name="andy"＞
＜age＞29＜/age＞
＜/employee＞
＜employee name="bill"＞
＜age＞30＜/age＞
＜/employee＞
＜employee name="cindy"＞
＜age＞31＜/age＞
＜/employee＞
＜/company＞
＜company name="citisoft"＞
＜location＞Dalian＜/location＞
＜employee name="doll"＞
＜age＞32＜/age＞
＜/employee＞
＜employee name="edin"＞
＜age＞33＜/age＞
＜/employee＞
＜employee name="felix"＞
＜age＞34＜/age＞
＜/employee＞
＜/company＞
＜/group＞
＜/root＞

　　如果集中解析XML的话,解析XML的代码和创建对象的代码将混杂在在一块,级联关系越深,代码将越冗长难懂而难以修改,使代码可维护性不佳;

　　如果我们让一个对象与相应的XML节点关联起来的话,只需要在构造函数中处理有关部分的XML.拿Group对象举例来说,它只需要知道如何从一个＜group＞...＜/group＞节点中提取name,location以及下级的company就行了,从XML的角度来说,它只需要辨认＜group＞节点下的＜name＞属性,＜location＞子节点和＜company＞子节点就行了,转化为对象时只需转化这些内容,而下级节点如＜company＞的内容则交给Company类去处理.对一个类来说,它只需要知道和成员变量有关的节点就行了,其它部分自有上级或下级类处理,这样一层层分治开来,代码结构将清晰和简化起来.

　　下面是代码,请注意观察下面Group,Company,Employee三个类的构造函数:

Group类:
package com.sitinspring.objectxml;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import org.dom4j.Element;

public class Group {
private String name;

private String location;

private List＜Company＞ companies;

public Group(Element element){
this.name=element.attributeValue("name");
this.location=element.elementText("location");

companies=new ArrayList＜Company＞();
List companyNodes = element.elements("company");
for (Iterator it = companyNodes.iterator(); it.hasNext(); ) {
Element companyElm = (Element) it.next();
companies.add(new Company(companyElm));
}
}

public Element makeElement(Element parentElm){
Element element=parentElm.addElement("group");

element.addAttribute("name", this.name);
Element ageElm = element.addElement("location");
ageElm.setText(this.location);

for (Iterator it = companies.iterator(); it.hasNext(); ) {
Company company = (Company) it.next();

company.makeElement(element);
}

return element;
}

public List＜Company＞ getCompanies() {
return companies;
}

public String getLocation() {
return location;
}

public void setLocation(String location) {
this.location = location;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}
}

Company类:

package com.sitinspring.objectxml;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import org.dom4j.Element;

public class Company {
private String name;

private String location;

private List＜Employee＞ employees;

public Company(Element element){
this.name=element.attributeValue("name");
this.location=element.elementText("location");

employees=new ArrayList＜Employee＞();
List employeeNodes = element.elements("employee");
for (Iterator it = employeeNodes.iterator(); it.hasNext(); ) {
Element employeeElm = (Element) it.next();
employees.add(new Employee(employeeElm));
}
}

public Element makeElement(Element parentElm){
Element element=parentElm.addElement("company");

element.addAttribute("name", this.name);
Element ageElm = element.addElement("location");
ageElm.setText(this.location);

for (Iterator it = employees.iterator(); it.hasNext(); ) {
Employee employee = (Employee) it.next();
employee.makeElement(element);
}

return element;
}

public String getLocation() {
return location;
}

public void setLocation(String location) {
this.location = location;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public List＜Employee＞ getEmployees() {
return employees;