用分治法解决级联对象与相应XML之间的互相转化问题

用分治法解决级联对象与相应XML之间的互相转化问题

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;
    }

    public void setEmployees(List<Employee> employees) {
        this.employees = employees;
    }
}

Employee类:

package  com.sitinspring.objectxml;

import  org.dom4j.Element;

public   class  Employee  {
    private String name;

    private int age;

    public Employee(Element element) {
        this.name = element.attributeValue("name");
        this.age = Integer.parseInt(element.elementText("age"));
    }

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

        element.addAttribute("name", this.name);
        Element ageElm = element.addElement("age");
        ageElm.setText(String.valueOf(this.age));

        return element;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

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

从上面三个构造函数我们可以发现,传入一个节点,程序会解析这个节点并生成一个对象.

从对象生成XML是构造函数的逆过程,思想是一样的,这里就不赘述了,大家观察三个类中的makeElement函数即可.

调用过程:

package  com.sitinspring.objectxml;

import  java.io.File;
import  java.io.FileWriter;

import  org.dom4j.Document;
import  org.dom4j.DocumentHelper;
import  org.dom4j.Element;
import  org.dom4j.io.SAXReader;
import  org.dom4j.io.XMLWriter;

public   class  Test {
    public static void main(String[] args){
        try{
            // 从XML得到对象
            SAXReader reader = new SAXReader();
            Document document= reader.read(new File("group1.xml"));
            Element groupElm=document.getRootElement().element("group");
            Group group=new Group(groupElm);
            
            // 从对象得到XML
            Document document2 = DocumentHelper.createDocument();
            Element root = document2.addElement("root");
            Element groupElm2=group.makeElement(root);

            XMLWriter writer = new XMLWriter(new FileWriter("group2.xml"));
            writer.write(document2);
            writer.close();
        }
        catch(Exception ex){
            ex.printStackTrace();
        }
    }
}

源码下载(请大家自行加入dom4j包):
http://www.blogjava.net/Files/sitinspring/ObjectXml20070917002818.rar