笔记:XML-解析文档-流机制解析器(SAX、StAX)

DOM
解析器完整的读入XML文档,然后将其转换成一个树型的数据结构,对于大多数应用,DOM 都运行很好,但是,如果文档很大,并且处理算法又非常简单,可以在运行时解析节点,而不必看到完整的树形结构,那么我们应该使用流机制解析器(streaming parser),Java 类库提供的流解析机制有 SAX 解析器和 StAX 解析器,SAX 解析器是基于事件回调机制,而 StAX解析器提供了解析事件的迭代器。

  1. 使用SAX解析器

    SAX
    解析器在解析XML 输入的组成部分时会报告事件,在使用 SAX 解析器时,需要一个处理器来为不同的解析器事件定义事件动作,ContentHandler 接口定义了若干个在解析文档时解析器会调用的回调方法,我们可以使用
    DefaultHandler
    类,该类继承与
    ContentHandler
    并提供了默认实现,重要的方法如下:

  • startDocument:在文档开始时调用一次
  • endDocument:在文档结束时调用一次
  • startElement:在遇到起始标签时调用,有3个描述元素名的参数,其中qName参数标识标签限定名,如果命名空间处理特性打开,则
    uri
    表示的是命名空间,localName 表示的是本地名。
  • endElement:在遇到结束标签时调用,其参数和
    startElement
    一致
  • characters:在每当遇到字符数据时调用,如果标签没有内容,但有子标签时,其中的空格会作为字符数据返回

示例代码如下:

  • 事件处理类

    public class CustomDefaultHandler extends DefaultHandler {

            @Override

            public
    void
    startDocument() throws SAXException {

                    super.startDocument();

     
     

                    System.out.println("call startDocument");

            }

     
     

            @Override

            public
    void
    endDocument() throws SAXException {

                    super.endDocument();

                    System.out.println("call endDocument");

            }

     
     

            @Override

            public
    void
    characters(char[] ch, int start, int length) throws SAXException {

                    super.characters(ch, start, length);

     
     

                    String chs = new
    String(ch, start, length);

                    System.out.println("characters ch=" + chs + " start=" + start + " length=" + length);

            }

     
     

            @Override

            public
    void
    startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {

                    super.startElement(uri, localName, qName, attributes);

     
     

                    StringBuilder sb = new
    StringBuilder();

                    for (int i = 0; i < attributes.getLength(); i++) {

                            sb.append(attributes.getLocalName(i) + "=\"" + attributes.getValue(i) + "\"
    ");

                    }

     
     

                    System.out.println("startElement qName=" + qName + " Uri=" + uri + " localName=" + localName + " "

    + sb.toString());

            }

     
     

            @Override

            public
    void
    endElement(String uri, String localName, String qName) throws SAXException {

                    super.endElement(uri, localName, qName);

     
     

                    System.out.println("endElement " + qName);

            }

    }

  • 调用类

    try {

            Path xmlPath = Paths.get("E:\\IDEA Workspace\\exampleiostream\\src\\main\\java\\org\\drsoft\\examples\\xml", "appParse.xml");

            InputStream xmlStream = Files.newInputStream(xmlPath, StandardOpenOption.READ);

            SAXParserFactory saxParserFactory = SAXParserFactory.newInstance();

            SAXParser saxParser = saxParserFactory.newSAXParser();

            saxParser.parse(xmlStream, new
    CustomDefaultHandler());

    } catch (SAXException e) {

              e.printStackTrace();

    } catch (ParserConfigurationException e) {

              e.printStackTrace();

    } catch (IOException e) {

              e.printStackTrace();

    }

  1. 使用StAX解析器

    StAX
    解析器时一种拉解析器(pull
    parser),与安装事件处理器不同,只需要使用基本的循环来迭代所有事件,示例代码如下:

    try {

          Path xmlPath = Paths.get("E:\\IDEA Workspace\\exampleiostream\\src\\main\\java\\org\\drsoft\\examples\\xml", "appParse.xml");

          InputStream xmlStream = Files.newInputStream(xmlPath, StandardOpenOption.READ);

     
     

          XMLInputFactory factory = XMLInputFactory.newFactory();

          XMLStreamReader parser = factory.createXMLStreamReader(xmlStream);

     
     

          while (parser.hasNext()) {

                      int event = parser.next();

                      switch (event) {

                              case XMLStreamConstants.START_DOCUMENT:

                                        System.out.println("START_DOCUMENT Call");

                                        break;

     
     

                              case XMLStreamConstants.END_DOCUMENT:

                                        System.out.println("END_DOCUMENT Call");

                                        break;

     
     

                              case XMLStreamConstants.START_ELEMENT:

                                        StringBuilder sb = new
    StringBuilder();

                                        for (int i = 0; i < parser.getAttributeCount(); i++) {

                                                sb.append(parser.getAttributeName(i) + "=\"" + parser.getAttributeValue(i) + "\"
    ");

                                        }

                                        System.out.println("START_ELEMENT qName=" + parser.getName() + " Uri="

    + parser.getNamespaceURI() + " localName=" + parser.getLocalName() + " attribute="

    + sb.toString());

                                        break;

     
     

                              case XMLStreamConstants.END_ELEMENT:

                                        System.out.println("END_ELEMENT qName=" + parser.getName() + " Uri=" + parser.getNamespaceURI()

                                                         + " localName=" + parser.getLocalName());

                                        break;

     
     

                              case XMLStreamConstants.CHARACTERS:

                                        int start = parser.getTextStart();

                                        int length = parser.getTextLength();

                                        System.out.println("CHARACTERS text=" + new
    String(parser.getTextCharacters(), start, length));

                                        break;

                    }

          }

    } catch (IOException e) {

            e.printStackTrace();

    } catch (XMLStreamException e) {

          e.printStackTrace();

    }

     
     

     
     

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