关于数据映射

一个笔记：
1 关于marshal类：（对映射文件的处理）
Marshaller类用来将一个Java类转换为XML数据。UnMarshaller类转换一个XML文档成Java对象。

对映射文件处理的简单例子的代码片断：
Marshaller marshaller;

Mapping _mapping;

PrintWriter writer;

MyClass myObject;

………………

// 创建marshaller对象并载入Mapping映射规则

marshaller = new Marshaller( writer );

marshaller.setMapping( _mapping );





// OO对象到XML数据 (可以是流，DOM树节点，或是SAX遍历句柄)
的映射转换

java.io.Writer out;

marshaller.marshal(myObject, out);





org.w3c.dom.Node node

marshaller.marshal(myObject, node);





org.xml.sax.DocumentHandler handler

marshaller.marshal(myObject, handler);

………………

几个重要概念:

编组（Marshalling）是把内存中的数据转化到存储媒介上的过程。因此在 Java 和 XML 环境中，编组就是把一些 Java 对象转化成一个（或多个） XML 文档。在数据库环境中，则是把 Java 表示的数据存入数据库。显然，编组的秘密在于把 Java 实例中的面向对象结构转化成适用于 XML 的扁平结构，或者 RDBMS 中的关系结构（使用 Java 技术转换到 OODBMS 实际上很简单）。

解组（Unmarshalling）是把数据从存储媒介转换到内存中的过程——正好与编组相反。因此需要把 XML 文档解组到 Java VM 中。这里的复杂性不是在扁平数据中，因为这不是必需的，而在于从正确的数据到正确的 Java 代码变量的映射。如果映射是错误的，就不可能正确地访问数据。当然，如果再尝试重新编组还会造成更大的问题，并且问题传播得很快。

往返（Round-tripping）可能是最重要也最容易误解的数据绑定术语。往返用于描述从存储媒介到内存然后回到存储媒介的完整循环。在 XML 和 Java 技术环境中，这就意味着从 XML 文档到 Java 实例变量，然后再回到 XML 文档。正确的往返要求，如果中间没有修改数据，XML 输入和 XML 输出应该是等同的。

Castor 框架：

Castor XML 数据绑定很容易上手，甚至不需要定义 XML 文档格式。只要您的数据用类 JavaBean 的对象表示，Castor 就能自动生成表示这些数据的文档格式，然后从文档重构原始数据。

用一个例子(Castor)来说明：Jbuilder中调试

This bean was auto generated from a schema

清单 1. XmlEmployeeType信息 bean

package com.borland.samples.xml.databinding.castor;

import java.io.IOException;

import java.io.Reader;

import java.io.Serializable;

import java.io.Writer;

import org.exolab.castor.xml.MarshalException;

import org.exolab.castor.xml.Marshaller;

import org.exolab.castor.xml.Unmarshaller;

import org.exolab.castor.xml.ValidationException;

import org.xml.sax.ContentHandler;

/**

* Class XmlEmployeeType.

* @version $Revision$ $Date$

*/

public class XmlEmployeeType implements java.io.Serializable {

      private java.lang.String _empNo;

      private java.lang.String _firstName;

      private java.lang.String _lastName;

    private java.lang.String _phoneExt;

    private java.lang.String _hireDate;

    private java.lang.String _deptNo;

    private java.lang.String _jobCode;

    private java.lang.String _jobGrade;

    private java.lang.String _jobCountry;

      private java.lang.String _salary;

     private java.lang.String _fullName;

    public XmlEmployeeType() {

        super();

      }

     public java.lang.String getDeptNo()

     {

        return this._deptNo;

      }

      public java.lang.String getEmpNo()

    {

        return this._empNo;

    }

  

    public java.lang.String getFirstName()

    {

        return this._firstName;

    }

  

    public java.lang.String getFullName()

    {

        return this._fullName;

    }

  

    public java.lang.String getHireDate()

    {

        return this._hireDate;

}



    public java.lang.String getJobCode()

    {

        return this._jobCode;

    } tJobCode()



       public java.lang.String getJobCountry()

    {

        return this._jobCountry;

    }

  

    public java.lang.String getJobGrade()

    {

        return this._jobGrade;

    }

  

    public java.lang.String getLastName()

    {

        return this._lastName;

    }

  

    public java.lang.String getPhoneExt()

    {

        return this._phoneExt;

    }

  

    public java.lang.String getSalary()

    {

        return this._salary;

    } //-- java.lang.String getSalary()





    public boolean isValid()

    {

        try {

            validate();

        }

        catch (org.exolab.castor.xml.ValidationException vex) {

            return false;

        }

        return true;

    }

 

    public void marshal(java.io.Writer out)

        throws org.exolab.castor.xml.MarshalException, org.exolab.castor.xml.ValidationException

    {

       

        Marshaller.marshal(this, out);

}

 

    public void marshal(org.xml.sax.ContentHandler handler)

        throwsjava.io.IOException,org.exolab.castor.xml.MarshalException, org.exolab.castor.xml.ValidationException

    {

         Marshaller.marshal(this, handler);

    }

   

    public void setDeptNo(java.lang.String deptNo)

    {

        this._deptNo = deptNo;

    }

    public void setEmpNo(java.lang.String empNo)

    {

        this._empNo = empNo;

    }

    public void setFirstName(java.lang.String firstName)

    {

        this._firstName = firstName;

    } //-- void setFirstName(java.lang.String)





    public void setFullName(java.lang.String fullName)

    {

        this._fullName = fullName;

    } //-- void setFullName(java.lang.String)



  

    public void setHireDate(java.lang.String hireDate)

    {

        this._hireDate = hireDate;

    } //-- void setHireDate(java.lang.String)



  

    public void setJobCode(java.lang.String jobCode)

    {

        this._jobCode = jobCode;

} //-- void setJobCode(java.lang.String)



    public void setJobCountry(java.lang.String jobCountry)

    {

        this._jobCountry = jobCountry;

    } //-- void setJobCountry(java.lang.String)





    public void setJobGrade(java.lang.String jobGrade)

    {

        this._jobGrade = jobGrade;

    } //-- void setJobGrade(java.lang.String)



  

    public void setLastName(java.lang.String lastName)

    {

        this._lastName = lastName;

    } //-- void setLastName(java.lang.String)



 

    public void setPhoneExt(java.lang.String phoneExt)

    {

        this._phoneExt = phoneExt;

    } //-- void setPhoneExt(java.lang.String)



 

    public void setSalary(java.lang.String salary)

    {

        this._salary = salary;

    } //-- void setSalary(java.lang.String)



    public static java.lang.Object unmarshal(java.io.Reader reader)

        throws org.exolab.castor.xml.MarshalException, org.exolab.castor.xml.ValidationException

    {

        Return(com.borland.samples.xml.databinding.castor.XmlEmployeeType) Unmarshaller.unmarshal(com.borland.samples.xml.databinding.castor.XmlEmployeeType.class, reader);

    } //-- java.lang.Object unmarshal(java.io.Reader)



   

    public void validate()

        throws org.exolab.castor.xml.ValidationException

    {

        org.exolab.castor.xml.Validator validator = new org.exolab.castor.xml.Validator();

        validator.validate(this);

    } //-- void validate()

}

清单 2. 测试默认的数据绑定

/**

* Title:        XML Tutorial

* Description:  XML Tutorial for JBuilder

* Company:      Borland Software Coporation

* @author

* @version 1.0

*/

import java.io.*;

import org.exolab.castor.xml.*;

public class DB_Castor {

public DB_Castor() {

  }

public static void main(String[] args) {

    try {

       String fileName = "Employees.xml";

       System.out.println("== unmarshalling \"" + fileName + "\" ==");

       //Unmarshal XML file.

       XmlEmployees xmlEmployees = (XmlEmployees)XmlEmployees.unmarshal(new FileReader(fileName));

       System.out.println("TotalNumber of XmlEmployees read = " + xmlEmployees.getXmlEmployeeCount());

       System.out.println("FirstXmlEmployee's Full Name is " + xmlEmployees.getXmlEmployee(0).getFullName());

       System.out.println("LastXmlEmployee's Full Name is " + xmlEmployees.getXmlEmployee(xmlEmployees.getXmlEmployeeCount()-1).getFullName());

       // Add an XmlEmployee.

       xmlEmployees.addXmlEmployee(getXmlEmployee("8000","400","Charlie","Castor","3/3/2001","VP","USA","2","1993","155000.00"));



       // Modify the last XmlEmployee.

       xmlEmployees.setXmlEmployee(xmlEmployees.getXmlEmployeeCount()-1, getXmlEmployee("8000","600","Peter","Castor","3/3/2001","VP","USA","3","2096","125000.00"));



       // Marshal out the data to the same XML file.

       xmlEmployees.marshal(new java.io.FileWriter(fileName));

      }

       catch (Exception ex) {

         ex.printStackTrace();

    }

  }

  private static XmlEmployee getXmlEmployee(String XmlEmployeeNumber,String departmentNumber,String firstName,String lastName,String hireDate,String jobCode,String jobCountry,String jobGrade,String phoneExt,String salary){

    XmlEmployee xmlEmployee = new XmlEmployee();

    xmlEmployee.setEmpNo(XmlEmployeeNumber);

    xmlEmployee.setDeptNo(departmentNumber);

    xmlEmployee.setFirstName(firstName);

    xmlEmployee.setLastName(lastName);

    xmlEmployee.setFullName(lastName+", "+firstName);

    xmlEmployee.setHireDate(hireDate);

    xmlEmployee.setJobCode(jobCode);

    xmlEmployee.setJobCountry(jobCountry);

    xmlEmployee.setJobGrade(jobGrade);

    xmlEmployee.setPhoneExt(phoneExt);

    xmlEmployee.setSalary(salary);

    return xmlEmployee;

  }

}



最后，看看运行的效果;XML是不是变化了；此篇仅仅描述了一个Castor框架，还有JAXB(Sun的框架)；以及其他开源的框架需要不断的去学习。

==========================
Castor 学习笔记
Castor XML
http://www.castor.org/xml-framework.html

Castor XML 是XML数据绑定的framework。
与两种主要的XML API(DOM及SAX)不同，它们主要是处理XML文件的结构，
而Castor能够通过表现数据的对象，处理XML文件中的数据。

Castor XML能处理几乎所有java bean格式的java对象，从xml读取或生成xml。
大多数情况下，marshalling框架使用ClassDescriptors和FieldDescriptors来描述
一个对象怎么marshal成xml文件，或从xml文件中unmarshal。
术语marshal 和unmarshal，是表示转换数据流从/到一个对象的行为。
marshalling转换对象到stream，unmarshalling从stream到一个对象。

The marshalling framework
负责执行java和xml之间的转换。
包含两个主要的类：
org.exolab.castor.xml.Marshaller and org.exolab.castor.xml.Unmarshaller.
假设有一个Member类，marshal一个对象，只需要简单的调用Marshaller如下：
Member Member = new Member("Ryan 'Mad Dog' Madden");
writer = new FileWriter("test.xml");
Marshaller.marshal(Member, writer);
unmarshal需要调用Unmarshaller如下：
reader = new FileReader("test.xml");
Member Member = (Member)Unmarshaller.unmarshal(Member.class, reader);
注意：当使用mapping文件时，以上代码是不够的：
Mapping mapping = new Mapping();
mapping.loadMapping("mapping.xml");
reader = new FileReader("test.xml");
Unmarshaller unmarshaller = new Unmarshaller(Member.class);
unmarshaller.setMapping(mapping);
Member Member = (Member)unmarshaller.unmarshal(reader);


Using Existing Classes/Objects
Castor能marshal几乎所有任意的对象从/到xml。
当特殊类的描述不可用时，
marshalling framework使用reflection得到对象的信息。

把描述放在java 源文件中，比放在内存中，修改和编译所花的工作更小。

如果class文件中存在描述，则Castor使用这些描述来控制marshalling。
marshalling对象时，一个主要的约束，是要有一个缺省的无参的构造方法。
并且要有get和set方法来进行marshalling和unmarshalling。

Class Descriptors
class descriptors提供了Castor框架必须的信息，
这样class才能正确的marshalling和unmarshalling。
class descriptors包含了field descriptors的集合。

XML格式的class descriptors提供castor框架marshalling所需的信息。
XMLClassDescriptor的实现类是：org.exolab.castor.xml.XMLClassDescriptor.

XML Class Descriptors有四种方法创建，两种基于运行时，两种基于编译时。

Compile-Time Descriptors
使用compile time descriptors，方法之一是实现org.exolab.castor.xml.XMLClassDescriptor，
或者用Source Code Generator来创建描述。



Run-Time Descriptors
使用run tiem descriptors,方法之一是提供一个mapping文件，
让Castor introspect(应该翻译成内省？)
或者组合使用缺省的introspection和特殊的mapping文件。

评论

5 楼 jefferson 2007-03-28  

xml与javabean的隐射实现都多个开源的选择
1、XStream，XStream是codehaus上的一个开源项目，用于将Javabean serialize为xml格式，以及从xml中生成javabean。
2、castor、xmlbeans，castor和xmlbeans这种都是先定义schema，然后根据schema来generate java class，然后调用marshall和unmarshall方法来序列化javabean。这是属于重量级的方法，虽然功能强大，使用却不方便。如果你改了schema，势必要重新generate，这样你就不能在generate的java class上加上自己的方法。导致生成的java class纯粹用于serialize。
3、 commons的betwikt也具有类似的功能，但好像需要配置rule，显得还是稍微麻烦些。

根据xml 的schema生成对应的数据映射类示例,利用Castor

schema文件：
<?xml version="1.0" encoding="UTF-8"?>
<!-- edited with XMLSpy v2006 sp2 U (http://www.altova.com) by chris (grt) -->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" elementFormDefault="qualified" attributeFormDefault="unqualified">
<xs:element name="ExportedFile">
<xs:annotation>
<xs:documentation>Comment describing your root element</xs:documentation>
</xs:annotation>
<xs:complexType>
<xs:sequence>
<xs:element name="username" type="xs:string"/>
<xs:element name="userpass" type="xs:string"/>
<xs:element ref="columnNames" minOccurs="0" maxOccurs="1"/>
<xs:element ref="records" minOccurs="0" maxOccurs="1"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="columnNames">
<xs:complexType>
<xs:sequence>
<xs:element name="columnName" type="xs:string" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="records">
<xs:complexType>
<xs:sequence>
<xs:element ref="record" minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="record">
<xs:complexType>
<xs:sequence>
<xs:element name="field" maxOccurs="unbounded">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute name="name" type="xs:string"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
知识点：
Schema共有8种元素：<Schema>、<ElementType>、<element>、<group>、<AttributeType>、<attribute>、<datatype>和<description>。这些元素对XML中允许的语法和结构进行了定义。Schema文件与其他的XML文档结构非常相似，根元素为<Schema>，表明文档类型。 其中属性name指定Schema名称，xmlns指定所属名称空间。第一个xmlns指定全文的缺省名称空间，第二个定义了文档中可使用的数据类型的名称空间。

<element>元素与〈ElementType〉中的name属性完全一致。minOccurs和maxOccurs属性分别指定了元素出现的最少和最多次数，默认值都为1。minOccurs为0说明元素是可选的，maxOccurs为*说明元素出现的次数不受限制。

<attribute>元素取值要与<AttributeType>中的name属性完全一致; required说明该属性对于引用它的元素是否为必要的; default指定属性类型的缺省值。如果对同一属性的<AttributeType>和<attribute>中相对应的default和required属性都给出了定义，那么<attribute>的优先级别更高，以它的取值为准。

其对应的xml文件格式，如下：
<?xml version="1.0" encoding="GB2312"?>
<!--Sample XML file edited by lizongbo-->
<userinfo xmlns="user" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<ExportedFile>
<username>d</username>
<userpass>dd</userpass>
<columnNames>
<columnName>d</columnName>
<columnName>dd</columnName>
</columnNames>
<record>
<records>
<field>
<name>dd</name>
</field>
</record>
</records>
</ExportedFile>


利用ant生成,其代码段示例为：

<target name="generateCastorClasses" depends=".">
<java classname="org.exolab.castor.builder.SourceGenerator">
<arg line="-dest '${dir}/source' -i '${dir}/config/Export.xsd' -f -package com.object" />
<classpath>
<fileset dir="${dir}/lib">
<include name="*.jar" />
</fileset>
</classpath>
</java>
</target>
其中，dir为工程目录,schema文件放在工程目录下的config目录中。生成的java文件放在工程目录下的source目录中，名字空间为com.object

把xml转换成映射类，调用生产类的方法unmarshal（根据xml实例化映射对象）或者marshal（根据映射对象生成xml文件）
前者的简单示例代码为：
ExportedFile exportedFile = (ExportedFile) TWIssues.unmarshal(new InputStreamReader(file
.getInputStream(),"GBK"));
其中，file为xml文件

4 楼 jefferson 2006-11-20  

对于xml的读取，一般用SAXBuilder；那么如果要对文件流的内容进行格式化（自定义的），则会用到：XMLFilter，
我们可以自己继承并实现XMLFilter，例如：自定义的filter类的对象实例是myFilter，只要 new SAXBuilder().setXMLFilter（myFileter）即可。
一个XMLFilter实现的简单例子：

public class XMLFilterBase extends XMLFilterImpl implements LexicalHandler
{


    ////////////////////////////////////////////////////////////////////
    // Constructors.
    ////////////////////////////////////////////////////////////////////


    /**
     * Construct an XML filter with no parent.
     *
     * <p>This filter will have no parent: you must assign a parent
     * before you start a parse or do any configuration with
     * setFeature or setProperty.</p>
     *
     * @see org.xml.sax.XMLReader#setFeature
     * @see org.xml.sax.XMLReader#setProperty
     */
    public XMLFilterBase()
    {
    }


    /**
     * Create an XML filter with the specified parent.
     *
     * <p>Use the XMLReader provided as the source of events.</p>
     *
     * @param xmlreader The parent in the filter chain.
     */
    public XMLFilterBase(XMLReader parent)
    {
        super(parent);
    }



    ////////////////////////////////////////////////////////////////////
    // Convenience methods.
    ////////////////////////////////////////////////////////////////////


    /**
     * Start a new element without a qname or attributes.
     *
     * <p>This method will provide a default empty attribute
     * list and an empty string for the qualified name. It invokes
     * {@link #startElement(String, String, String, Attributes)}
     * directly.</p>
     *
     * @param uri The element's Namespace URI.
     * @param localName The element's local name.
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
     * @see org.xml.sax.ContentHandler#startElement
     */
    public void startElement (String uri, String localName)
    throws SAXException
    {
        startElement(uri, localName, "", EMPTY_ATTS);
    }


    /**
     * Start a new element without a Namespace URI or qname.
     *
     * <p>This method will provide an empty string for the
     * Namespace URI, and empty string for the qualified name.
     * It invokes
     * {@link #startElement(String, String, String, Attributes)}
     * directly.</p>
     *
     * @param localName The element's local name.
     * @param atts The element's attribute list.
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
     * @see org.xml.sax.ContentHandler#startElement
     */
    public void startElement (String localName, Attributes atts)
    throws SAXException
    {
        startElement("", localName, "", atts);
    }


    /**
     * Start a new element without a Namespace URI, qname, or attributes.
     *
     * <p>This method will provide an empty string for the
     * Namespace URI, and empty string for the qualified name,
     * and a default empty attribute list. It invokes
     * {@link #startElement(String, String, String, Attributes)}
     * directly.</p>
     *
     * @param localName The element's local name.
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
     * @see org.xml.sax.ContentHandler#startElement
     */
    public void startElement (String localName)
    throws SAXException
    {
        startElement("", localName, "", EMPTY_ATTS);
    }


    /**
     * End an element without a qname.
     *
     * <p>This method will supply an empty string for the qName.
     * It invokes {@link #endElement(String, String, String)}
     * directly.</p>
     *
     * @param uri The element's Namespace URI.
     * @param localName The element's local name.
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
     * @see org.xml.sax.ContentHandler#endElement
     */
    public void endElement (String uri, String localName)
    throws SAXException
    {
        endElement(uri, localName, "");
    }


    /**
     * End an element without a Namespace URI or qname.
     *
     * <p>This method will supply an empty string for the qName
     * and an empty string for the Namespace URI.
     * It invokes {@link #endElement(String, String, String)}
     * directly.</p>
     *
     * @param localName The element's local name.
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
     * @see org.xml.sax.ContentHandler#endElement
     */
    public void endElement (String localName)
    throws SAXException
    {
        endElement("", localName, "");
    }


    /**
     * Add an empty element.
     *
     * Both a {@link #startElement startElement} and an
     * {@link #endElement endElement} event will be passed on down
     * the filter chain.
     *
     * @param uri The element's Namespace URI, or the empty string
     *        if the element has no Namespace or if Namespace
     *        processing is not being performed.
     * @param localName The element's local name (without prefix).  This
     *        parameter must be provided.
     * @param qName The element's qualified name (with prefix), or
     *        the empty string if none is available.  This parameter
     *        is strictly advisory: the writer may or may not use
     *        the prefix attached.
     * @param atts The element's attribute list.
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
     * @see org.xml.sax.ContentHandler#startElement
     * @see org.xml.sax.ContentHandler#endElement
     */
    public void emptyElement (String uri, String localName,
    String qName, Attributes atts)
    throws SAXException
    {
        startElement(uri, localName, qName, atts);
        endElement(uri, localName, qName);
    }


     /**
      * Add an empty element without a qname or attributes.
      *
      * <p>This method will supply an empty string for the qname
      * and an empty attribute list.  It invokes
      * {@link #emptyElement(String, String, String, Attributes)}
      * directly.</p>
      *
      * @param uri The element's Namespace URI.
      * @param localName The element's local name.
      * @exception org.xml.sax.SAXException If a filter
      *            further down the chain raises an exception.
      * @see #emptyElement(String, String, String, Attributes)
      */
    public void emptyElement (String uri, String localName)
    throws SAXException
    {
        emptyElement(uri, localName, "", EMPTY_ATTS);
    }


    /**
     * Add an empty element without a Namespace URI or qname.
     *
     * <p>This method will provide an empty string for the
     * Namespace URI, and empty string for the qualified name.
     * It invokes
     * {@link #emptyElement(String, String, String, Attributes)}
     * directly.</p>
     *
     * @param localName The element's local name.
     * @param atts The element's attribute list.
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
     * @see org.xml.sax.ContentHandler#startElement
     */
    public void emptyElement (String localName, Attributes atts)
    throws SAXException
    {
        emptyElement("", localName, "", atts);
    }


    /**
     * Add an empty element without a Namespace URI, qname or attributes.
     *
     * <p>This method will supply an empty string for the qname,
     * and empty string for the Namespace URI, and an empty
     * attribute list.  It invokes
     * {@link #emptyElement(String, String, String, Attributes)}
     * directly.</p>
     *
     * @param localName The element's local name.
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
      * @see #emptyElement(String, String, String, Attributes)
     */
    public void emptyElement (String localName)
    throws SAXException
    {
        emptyElement("", localName, "", EMPTY_ATTS);
    }


    /**
     * Add an element with character data content.
     *
     * <p>This is a convenience method to add a complete element
     * with character data content, including the start tag
     * and end tag.</p>
     *
     * <p>This method invokes
     * {@link @see org.xml.sax.ContentHandler#startElement},
     * followed by
     * {@link #characters(String)}, followed by
     * {@link @see org.xml.sax.ContentHandler#endElement}.</p>
     *
     * @param uri The element's Namespace URI.
     * @param localName The element's local name.
     * @param qName The element's default qualified name.
     * @param atts The element's attributes.
     * @param content The character data content.
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
     * @see org.xml.sax.ContentHandler#startElement
     * @see #characters(String)
     * @see org.xml.sax.ContentHandler#endElement
     */
    public void dataElement (String uri, String localName,
                             String qName, Attributes atts,
                             String content)
    throws SAXException
    {
        startElement(uri, localName, qName, atts);
        characters(content);
        endElement(uri, localName, qName);
    }


    /**
     * Add an element with character data content but no qname or attributes.
     *
     * <p>This is a convenience method to add a complete element
     * with character data content, including the start tag
     * and end tag.  This method provides an empty string
     * for the qname and an empty attribute list. It invokes
     * {@link #dataElement(String, String, String, Attributes, String)}}
     * directly.</p>
     *
     * @param uri The element's Namespace URI.
     * @param localName The element's local name.
     * @param content The character data content.
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
     * @see org.xml.sax.ContentHandler#startElement
     * @see #characters(String)
     * @see org.xml.sax.ContentHandler#endElement
     */
    public void dataElement (String uri, String localName, String content)
    throws SAXException
    {
        dataElement(uri, localName, "", EMPTY_ATTS, content);
    }


    /**
     * Add an element with character data content but no Namespace URI or qname.
     *
     * <p>This is a convenience method to add a complete element
     * with character data content, including the start tag
     * and end tag.  The method provides an empty string for the
     * Namespace URI, and empty string for the qualified name. It invokes
     * {@link #dataElement(String, String, String, Attributes, String)}}
     * directly.</p>
     *
     * @param localName The element's local name.
     * @param atts The element's attributes.
     * @param content The character data content.
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
     * @see org.xml.sax.ContentHandler#startElement
     * @see #characters(String)
     * @see org.xml.sax.ContentHandler#endElement
     */
    public void dataElement (String localName, Attributes atts, String content)
    throws SAXException
    {
        dataElement("", localName, "", atts, content);
    }


    /**
     * Add an element with character data content but no attributes
     * or Namespace URI.
     *
     * <p>This is a convenience method to add a complete element
     * with character data content, including the start tag
     * and end tag.  The method provides an empty string for the
     * Namespace URI, and empty string for the qualified name,
     * and an empty attribute list. It invokes
     * {@link #dataElement(String, String, String, Attributes, String)}}
     * directly.</p>
     *
     * @param localName The element's local name.
     * @param content The character data content.
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
     * @see org.xml.sax.ContentHandler#startElement
     * @see #characters(String)
     * @see org.xml.sax.ContentHandler#endElement
     */
    public void dataElement (String localName, String content)
    throws SAXException
    {
        dataElement("", localName, "", EMPTY_ATTS, content);
    }


    /**
     * Add a string of character data, with XML escaping.
     *
     * <p>This is a convenience method that takes an XML
     * String, converts it to a character array, then invokes
     * {@link @see org.xml.sax.ContentHandler#characters}.</p>
     *
     * @param data The character data.
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
     * @see @see org.xml.sax.ContentHandler#characters
     */
    public void characters (String data)
    throws SAXException
    {
        char ch[] = data.toCharArray();
        characters(ch, 0, ch.length);
    }



    ////////////////////////////////////////////////////////////////////
    // Override org.xml.sax.helpers.XMLFilterImpl methods.
    ////////////////////////////////////////////////////////////////////


    /**
     * Set the value of a property.
     *
     * <p>This will always fail if the parent is null.</p>
     *
     * @param name The property name.
     * @param state The requested property value.
     * @exception org.xml.sax.SAXNotRecognizedException When the
     *            XMLReader does not recognize the property name.
     * @exception org.xml.sax.SAXNotSupportedException When the
     *            XMLReader recognizes the property name but
     *            cannot set the requested value.
     * @see org.xml.sax.XMLReader#setProperty
     */
    public void setProperty (String name, Object value)
    throws SAXNotRecognizedException, SAXNotSupportedException
    {
        for (int i = 0; i < LEXICAL_HANDLER_NAMES.length; i++) {
            if (LEXICAL_HANDLER_NAMES[i].equals(name)) {
                setLexicalHandler((LexicalHandler) value);
                return;
            }
        }
        super.setProperty(name, value);
    }


    /**
     * Look up the value of a property.
     *
     * @param name The property name.
     * @return The current value of the property.
     * @exception org.xml.sax.SAXNotRecognizedException When the
     *            XMLReader does not recognize the feature name.
     * @exception org.xml.sax.SAXNotSupportedException When the
     *            XMLReader recognizes the property name but
     *            cannot determine its value at this time.
     * @see org.xml.sax.XMLReader#setFeature
     */
    public Object getProperty (String name)
    throws SAXNotRecognizedException, SAXNotSupportedException
    {
        for (int i = 0; i < LEXICAL_HANDLER_NAMES.length; i++) {
            if (LEXICAL_HANDLER_NAMES[i].equals(name)) {
                return getLexicalHandler();
            }
        }
        return super.getProperty(name);
    }


    /**
     * Parse a document.
     *
     * @param input The input source for the document entity.
     * @exception org.xml.sax.SAXException Any SAX exception, possibly
     *            wrapping another exception.
     * @exception java.io.IOException An IO exception from the parser,
     *            possibly from a byte stream or character stream
     *            supplied by the application.
     * @see org.xml.sax.XMLReader#parse(org.xml.sax.InputSource)
     */
    public void parse (InputSource input)
    throws SAXException, IOException
    {
        installLexicalHandler();
        super.parse(input);
    }



    ////////////////////////////////////////////////////////////////////
    // Registration of org.xml.sax.ext.LexicalHandler.
    ////////////////////////////////////////////////////////////////////


    /**
     * Set the lexical handler.
     *
     * @param handler The new lexical handler.
     * @exception java.lang.NullPointerException If the handler
     *            is null.
     */
    public void setLexicalHandler (LexicalHandler handler)
    {
        if (handler == null) {
            throw new NullPointerException("Null lexical handler");
        } else {
            lexicalHandler = handler;
        }
    }


    /**
     * Get the current lexical handler.
     *
     * @return The current lexical handler, or null if none was set.
     */
    public LexicalHandler getLexicalHandler ()
    {
        return lexicalHandler;
    }



    ////////////////////////////////////////////////////////////////////
    // Implementation of org.xml.sax.ext.LexicalHandler.
    ////////////////////////////////////////////////////////////////////


    /**
     * Filter a start DTD event.
     *
     * @param name The document type name.
     * @param publicId The declared public identifier for the
     *        external DTD subset, or null if none was declared.
     * @param systemId The declared system identifier for the
     *        external DTD subset, or null if none was declared.
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
     * @see org.xml.sax.ext.LexicalHandler#startDTD
     */
    public void startDTD(String name, String publicId, String systemId)
    throws SAXException {
        if (lexicalHandler != null) {
            lexicalHandler.startDTD(name, publicId, systemId);
        }
    }


    /**
     * Filter a end DTD event.
     *
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
     * @see org.xml.sax.ext.LexicalHandler#endDTD
     */
    public void endDTD()
    throws SAXException {
        if (lexicalHandler != null) {
            lexicalHandler.endDTD();
        }
    }


    /*
     * Filter a start entity event.
     *
     * @param name The name of the entity.  If it is a parameter
     *        entity, the name will begin with '%', and if it is the
     *        external DTD subset, it will be "[dtd]".
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
     * @see org.xml.sax.ext.LexicalHandler#startEntity
     */
    public void startEntity(String name)
    throws SAXException {
        if (lexicalHandler != null) {
            lexicalHandler.startEntity(name);
        }
    }


    /*
     * Filter a end entity event.
     *
     * @param name The name of the entity that is ending.
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
     * @see org.xml.sax.ext.LexicalHandler#endEntity
     */
    public void endEntity(String name)
    throws SAXException {
        if (lexicalHandler != null) {
            lexicalHandler.endEntity(name);
        }
    }


    /*
     * Filter a start CDATA event.
     *
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
     * @see org.xml.sax.ext.LexicalHandler#startCDATA
     */
    public void startCDATA()
    throws SAXException {
        if (lexicalHandler != null) {
            lexicalHandler.startCDATA();
        }
    }


    /*
     * Filter a end CDATA event.
     *
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
     * @see org.xml.sax.ext.LexicalHandler#endCDATA
     */
    public void endCDATA()
    throws SAXException {
        if (lexicalHandler != null) {
            lexicalHandler.endCDATA();
        }
    }


    /*
     * Filter a comment event.
     *
     * @param ch An array holding the characters in the comment.
     * @param start The starting position in the array.
     * @param length The number of characters to use from the array.
     * @exception org.xml.sax.SAXException If a filter
     *            further down the chain raises an exception.
     * @see org.xml.sax.ext.LexicalHandler#comment
     */
    public void comment(char[] ch, int start, int length)
    throws SAXException {
        if (lexicalHandler != null) {
            lexicalHandler.comment(ch, start, length);
        }
    }



    ////////////////////////////////////////////////////////////////////
    // Internal methods.
    ////////////////////////////////////////////////////////////////////


    /**
     * Installs lexical handler before a parse.
     *
     * <p>Before every parse, check whether the parent is
     * non-null, and re-register the filter for the lexical
     * events.</p>
     */
    private void installLexicalHandler ()
    {
        XMLReader parent = getParent();
        if (parent == null) {
            throw new NullPointerException("No parent for filter");
        }
        // try to register for lexical events
        for (int i = 0; i < LEXICAL_HANDLER_NAMES.length; i++) {
            try {
                parent.setProperty(LEXICAL_HANDLER_NAMES[i], this);
                break;
            }
            catch (SAXNotRecognizedException ex) {
                // ignore
            }
            catch (SAXNotSupportedException ex) {
                // ignore
            }
        }
    }



    ////////////////////////////////////////////////////////////////////
    // Internal state.
    ////////////////////////////////////////////////////////////////////


    private LexicalHandler lexicalHandler = null;



    ////////////////////////////////////////////////////////////////////
    // Constants.
    ////////////////////////////////////////////////////////////////////


    protected static final Attributes EMPTY_ATTS = new AttributesImpl();

    protected static final String[] LEXICAL_HANDLER_NAMES = {
        "http://xml.org/sax/properties/lexical-handler",
        "http://xml.org/sax/handlers/LexicalHandler"
    };


}

3 楼 jefferson 2006-11-16  

XMLProperties.java
写得不错，贴上来给自己参考：

public class XMLProperties {

    private File file;
    private Document doc;
    /**
     * Parsing the XML file every time we need a property is slow. Therefore,
     * we use a Map to cache property values that are accessed more than once.
     */
    private Map propertyCache = new HashMap();

    /**
     * Creates a new XMLProperties object.
     *
     * @parm file the full path the file that properties should be read from
     *      and written to.
     */
    public XMLProperties(String file) {
        this.file = new File(file);
        try {
            SAXBuilder builder = new SAXBuilder();
            // Strip formatting
            DataUnformatFilter format = new DataUnformatFilter();
            builder.setXMLFilter(format);
            doc = builder.build(new File(file));
        }
        catch (Exception e) {
            System.err.println("Error creating XML parser in "
                + "PropertyManager.java");
            e.printStackTrace();
        }
    }

    /**
     * Returns the value of the specified property.
     *
     * @param name the name of the property to get.
     * @return the value of the specified property.
     */
    public String getProperty(String name) {
        if (propertyCache.containsKey(name)) {
            return (String)propertyCache.get(name);
        }

        String[] propName = parsePropertyName(name);
        // Search for this property by traversing down the XML heirarchy.
        Element element = doc.getRootElement();
        for (int i = 0; i < propName.length; i++) {
            element = element.getChild(propName[i]);
            if (element == null) {
                // This node doesn't match this part of the property name which
                // indicates this property doesn't exist so return null.
                return null;
            }
        }
        // At this point, we found a matching property, so return its value.
        // Empty strings are returned as null.
        String value = element.getText();
        if ("".equals(value)) {
            return null;
        }
        else {
            // Add to cache so that getting property next time is fast.
            value = value.trim();
            propertyCache.put(name, value);
            return value;
        }
    }

    /**
     * Return all children property names of a parent property as a String array,
     * or an empty array if the if there are no children. For example, given
     * the properties <tt>X.Y.A</tt>, <tt>X.Y.B</tt>, and <tt>X.Y.C</tt>, then
     * the child properties of <tt>X.Y</tt> are <tt>A</tt>, <tt>B</tt>, and
     * <tt>C</tt>.
     *
     * @param parent the name of the parent property.
     * @return all child property values for the given parent.
     */
    public String [] getChildrenProperties(String parent) {
        String[] propName = parsePropertyName(parent);
        // Search for this property by traversing down the XML heirarchy.
        Element element = doc.getRootElement();
        for (int i = 0; i < propName.length; i++) {
            element = element.getChild(propName[i]);
            if (element == null) {
                // This node doesn't match this part of the property name which
                // indicates this property doesn't exist so return empty array.
                return new String [] { };
            }
        }
        // We found matching property, return names of children.
        List children = element.getChildren();
        int childCount = children.size();
        String [] childrenNames = new String[childCount];
        for (int i=0; i<childCount; i++) {
            childrenNames[i] = ((Element)children.get(i)).getName();
        }
        return childrenNames;
    }

    /**
     * Sets the value of the specified property. If the property doesn't
     * currently exist, it will be automatically created.
     *
     * @param name the name of the property to set.
     * @param value the new value for the property.
     */
    public void setProperty(String name, String value) {
        // Set cache correctly with prop name and value.
        propertyCache.put(name, value);

        String[] propName = parsePropertyName(name);
        // Search for this property by traversing down the XML heirarchy.
        Element element = doc.getRootElement();
        for (int i=0; i<propName.length; i++) {
            // If we don't find this part of the property in the XML heirarchy
            // we add it as a new node
            if (element.getChild(propName[i]) == null) {
                element.addContent(new Element(propName[i]));
            }
            element = element.getChild(propName[i]);
        }
        // Set the value of the property in this node.
        element.setText(value);
        // write the XML properties to disk
        saveProperties();
    }

    /**
     * Deletes the specified property.
     *
     * @param name the property to delete.
     */
    public void deleteProperty(String name) {
        String[] propName = parsePropertyName(name);
        // Search for this property by traversing down the XML heirarchy.
        Element element = doc.getRootElement();
        for (int i=0; i<propName.length-1; i++) {
            element = element.getChild(propName[i]);
            // Can't find the property so return.
            if (element == null) {
                return;
            }
        }
        // Found the correct element to remove, so remove it...
        element.removeChild(propName[propName.length-1]);
        // .. then write to disk.
        saveProperties();
    }

    /**
     * Saves the properties to disk as an XML document. A temporary file is
     * used during the writing process for maximum safety.
     */
    private synchronized void saveProperties() {
        OutputStream out = null;
        boolean error = false;
        // Write data out to a temporary file first.
        File tempFile = null;
        try {
            tempFile = new File(file.getParentFile(), file.getName() + ".tmp");
            // Use JDOM's XMLOutputter to do the writing and formatting. The
            // file should always come out pretty-printed.
            XMLOutputter outputter = new XMLOutputter("    ", true);
            out = new BufferedOutputStream(new FileOutputStream(tempFile));
            outputter.output(doc, out);
        }
        catch (Exception e) {
            e.printStackTrace();
            // There were errors so abort replacing the old property file.
            error = true;
        }
        finally {
            try {  out.close();  }
            catch (Exception e) {
                e.printStackTrace();
                error = true;
            }
        }
        // No errors occured, so we should be safe in replacing the old
        if (!error) {
            // Delete the old file so we can replace it.
            file.delete();
            // Rename the temp file. The delete and rename won't be an
            // automic operation, but we should be pretty safe in general.
            // At the very least, the temp file should remain in some form.
            tempFile.renameTo(file);
        }
    }

    /**
     * Returns an array representation of the given Jive property. Jive
     * properties are always in the format "prop.name.is.this" which would be
     * represented as an array of four Strings.
     *
     * @param name the name of the Jive property.
     * @return an array representation of the given Jive property.
     */
    private String[] parsePropertyName(String name) {
        // Figure out the number of parts of the name (this becomes the size
        // of the resulting array).
        int size = 1;
        for (int i=0; i<name.length(); i++) {
            if (name.charAt(i) == '.') {
                size++;
            }
        }
        String[] propName = new String[size];
        // Use a StringTokenizer to tokenize the property name.
        StringTokenizer tokenizer = new StringTokenizer(name, ".");
        int i = 0;
        while (tokenizer.hasMoreTokens()) {
            propName[i] = tokenizer.nextToken();
            i++;
        }
        return propName;
    }
}

2 楼 jefferson 2006-11-14  

注意，如果要在系统中支持上述功能，必须下载JDOM包，还要有DataFormatFilter. java、DataUnformatFilter.java、XMLFilterBase.java和XMLProperties.java支持。这几个类不包含在JDOM标准包中，作为一个应用包含在其Sample中。当然也可以直接从Jive中复制出来使用。

1 楼 jefferson 2006-11-14  

有许多系统的配置是放在Properties文件中，但负责的配置一般都用xml来配置，上述的object与xml的映射是一个良好的方式，不过有些配置也许并不需要包装成类来操作，比如比较简单的：
<email>

　　<fromName>Administrator</fromName>

　　<fromEmail>[e-mail]</fromEmail>

　　<subject>Your thread was updated!</subject>

　　<body>Hello {name}! The thread {threadName} was updated!</body>

　</email>

可用类似与Properties文件的封装类：Property.java  用XMLProperties ：
private static final String JIVE_CONFIG_FILENAME = "jive_config.xml";

private static XMLProperties properties = null;



...

//从配置文件获取配置

　public static String getJiveProperty(String name) {

　　loadProperties();

　　return properties.getProperty(name);

　}

  //用JDOM载入配置文件

　private synchronized static void loadProperties() {

　　if (properties == null) {

　　　properties = new XMLProperties(jiveHome + File.separator +

　　　　　　　　　　　JIVE_CONFIG_FILENAME);

　　}

　}

//将配置保存到配置文件中

public static void setJiveProperty(String name, String value) {

   loadProperties();

   properties.setProperty(name, value);

}

从上面代码看出，对XML文件读写非常方便，使用properties.getProperty(name)就可以获得name的配置值，而properties.setProperty(name, value)一句就可以将name和其值value保存到XML文件中，非常类似Hashtable的读取和存入。