外部资源

XML, Schema, and XSLT standards support the following constructs that require external resources. The default behavior of the JDK XML processors is to make a connection and fetch the external resources as specified.

• External DTD: references an external Document Type Definition (DTD), example: <!DOCTYPE root_element SYSTEM "url">
• External Entity Reference: refer to external data, syntax: <!ENTITY name SYSTEM "url">
  General entity reference such as the following:

   
  <?xml version="1.0" standalone="no" ?>
  <!DOCTYPE doc [<!ENTITY otherFile SYSTEM "otherFile.xml">]>
  <doc>
      <foo>
      <bar>&otherFile;</bar>
      </foo>
  </doc>
  

• External Parameter Entities, syntax <!ENTITY % name SYSTEM uri>. 例如：

  <?xml version="1.0" standalone="no"?>
      <!DOCTYPE doc [
        <!ENTITY % foo SYSTEM "http://www.example.com/student.dtd"<
        %foo;
      ]>
  

• XInclude: include an external infoset in an XML document
• Reference to XML Schema components using schemaLocation attribute, and import and include elements. Example: schemaLocation="http://www.example.com/schema/bar.xsd"
• Combining style sheets using import or include elements: syntax: <xsl:include href="include.xsl"/>
• xml-stylesheet processing instruction: used to include a stylesheet in an xml document, syntax:
• XSLT document() function: used to access nodes in an external XML document. For example, <xsl:variable name="dummy" select="document('DocumentFunc2.xml')"/>.