Web开发框架中的架构模式比较(三)

类别:VC语言 点击:0 评论:0 推荐:
页面内容和表现风格的分离,(XSLT)

页面内容和表现风格分离的第一步,是CSS风格文件和HTML页面的分离,但是,HTML的页面内容和显示元素还是紧紧捆绑在一起。XML推广之后,XSLT也大行其道,大量地应用在web发布系统中。ASP.Net和java web框架都在朝这个方向走,只是java web框架走得更快,更远。下面进行说明。

在处理XSLT时,SAX接口要比DOM接口快得多,而且几乎不占据内存空间。令人不安的是,.Net框架到现在还没有提供SAX接口。微软提供了一套MSXML SDK,其中包含了基于COM组件的SAX实现,并提供了在VB和VC中应用的实例。MSXML SAX的VC用例中,需要包含头文件msxml2.h。这就是说,.Net框架无法以一种自然的方式调用MSXML SAX。还有,.Net框架的XSLT是如何实现的,即,System.Xml.Xsl.XslTransform是用什么方式实现的,是调用SAX接口,还是DOM接口。如何使用.Net框架组成一条XSLT的处理管道?我也找不到方法。也没有发现这方面的例子。

Apache Xerce项目支持XML处理,提供Java和C++版本,并提供了调用MSXML的封装;Apache Xalan项目支持XSLT处理;Apache Cocoon2.0,使用SAX接口,组成XSLT的处理管道。

Apache Xalan项目的一个例子文件UseXMLFilters.java

UseXMLFilters.java。(节录,文件头部分省略)

 

public class UseXMLFilters

{

  public static void main(String[] args)

       throws TransformerException, TransformerConfigurationException,

         SAXException, IOException         

       {

    // Instantiate  a TransformerFactory.

      TransformerFactory tFactory = TransformerFactory.newInstance();

    // Determine whether the TransformerFactory supports The use uf SAXSource

    // and SAXResult

    if (tFactory.getFeature(SAXSource.FEATURE) && tFactory.getFeature(SAXResult.FEATURE))

    {

      // Cast the TransformerFactory to SAXTransformerFactory.

      SAXTransformerFactory saxTFactory = ((SAXTransformerFactory) tFactory);

        // Create an XMLFilter for each stylesheet.

      XMLFilter xmlFilter1 = saxTFactory.newXMLFilter(new StreamSource("foo1.xsl"));

      XMLFilter xmlFilter2 = saxTFactory.newXMLFilter(new StreamSource("foo2.xsl"));

      XMLFilter xmlFilter3 = saxTFactory.newXMLFilter(new StreamSource("foo3.xsl"));

   

      // Create an XMLReader.

           XMLReader reader = XMLReaderFactory.createXMLReader();

   

      // xmlFilter1 uses the XMLReader as its reader.

      xmlFilter1.setParent(reader);

   

      // xmlFilter2 uses xmlFilter1 as its reader.

      xmlFilter2.setParent(xmlFilter1);

   

      // xmlFilter3 uses xmlFilter2 as its reader.

      xmlFilter3.setParent(xmlFilter2);

   

      // xmlFilter3 outputs SAX events to the serializer.

      Serializer serializer = SerializerFactory.getSerializer

                                   (OutputProperties.getDefaultMethodProperties("xml"));       

      serializer.setOutputStream(System.out);

      xmlFilter3.setContentHandler(serializer.asContentHandler());

 

        // Perform the series of transformations as follows:

           //   - transformer3 gets its parent (transformer2) as the XMLReader/XMLFilter

           //     and calls transformer2.parse(new InputSource("foo.xml")).

      //   - transformer2 gets its parent (transformer1) as the XMLReader/XMLFilter

           //     and calls transformer1.parse(new InputSource("foo.xml")).

      //   - transformer1 gets its parent (reader, a SAXParser) as the XMLReader

      //     and calls reader.parse(new InputSource("foo.xml")).

           //   - reader parses the XML document and sends the SAX parse events to transformer1,

           //     which performs transformation 1 and sends the output to transformer2.

        //   - transformer2 parses the transformation 1 output, performs transformation 2, and

           //     sends the output to transformer3.

           //   - transformer3 parses the transformation 2 output, performs transformation 3,

        //     and sends the output to the serializer.

      xmlFilter3.parse(new InputSource("foo.xml"));

    }

  }

}

 

Apache Cocoon项目的一个配置文件例子sitemap.xmap

Apache Cocoon项目的sitemap.xmap定义了XSLT处理管道。见下例中的<map:handle-errors>部分,错误信息经过两次XSLT处理," error2document.xsl" 和"apache.xsl"。

/sample/tutorial/sitemap.xmap (节录,无关部分省略)

 

<map:pipelines>

  <map:pipeline>

 

<map:match pattern="*-dept.xml">

  <map:act set="process">

    <map:parameter name="descriptor" value="context://tutorial/docs/department-form.xml"/>

    <map:generate type="serverpages" src="docs/confirm-dept.xsp"/>

    <map:serialize type="xml"/>

  </map:act>

  <map:generate type="serverpages" src="docs/{1}-dept.xsp"/>

  <map:serialize type="xml"/>

</map:match>

...

   <map:handle-errors>

    <map:transform src="stylesheets/system/error2document.xsl"/>

    <map:transform src="stylesheets/apache.xsl"/>

    <map:serialize status-code="500"/>

   </map:handle-errors>

 

  </map:pipeline>

...

 </map:pipelines>

 

ASP.Net的Xml Web控件例子

下面的示例从.Net框架文当中摘录,说明如何使用 Xml 控件通过示例 XSL 转换文件来显示示例 XML 文件。示例 XML 文件名为 People.xml,示例 XSL 转换文件名为 Peopletable. xsl。可以看到,asp:Xml控间只能进行一步XSLT转换。

 

<html>

<body>

   <h3>Xml Example</h3>

   <form runat="server">

      <asp:Xml id="xml1"

           DocumentSource="people.xml"

           TransformSource="peopletable.xsl"

           runat="server" />

   </form>

</body>

</html>

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