笔记:XML-解析文档-DOM

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要处理XML文档,就要先解析(parse)他,解析器时这样一个程序,读入一个文件,确认整个文件具有正确的格式,然后将其分解成各种元素,使得程序员能够访问这些元素,Java库提供了两种XML解析器:

  • 像文档对象模型(Document Object Model,DOM)解析器这样的树型解析器,他们将读入的XML文档转换成树结构
  • 像XML简单API(Simple API for XML,SAX)解析器这样的流机制解析器,他们读入XML文档时生成相应的事件

DOM解析器对于实现我们的大多数目的来说都更容易一些,如果需要处理很长的文档,用他来生成树结构会消耗大量的内存,或者只需要对于某些元素感兴趣,而不关心他们的上下文,那么可以考虑使用SAX解析器。DOM解析器的接口已经被W3C标准化了,org.w3c.dom包中包含了这些接口类型的定义,比如:Document、Element等,不同的实现者都编写了实现这些接口的DOM解析器,Java XML 处理API(Java API for XML Processing,JAXP)库使得实际上可以以插件形式使用这些解析器中的任意一个。要读入一个XML文档,首先需要一个DocumentBuilder对象,可以从 DocumentBuilderFactory 中得到这个对象,代码如下:

DocumentBuilderFactory factory=DocumentBuilderFactory.newInstance();

DocumentBuilder builder=factory.newDocumentBuilder();

现在,可以从文件中读入某个文档:

 File f = …;

Document doc = builder.parse(f);

或者,可以用一个URL:

URL u = …;

Document doc = builder.parse(u);

甚至可以使用一个任意的输入流:

InputStream in = …;

Document doc = builder.parse(in);

Document 对象时XML文档的树型结构在内存的表现,他由实现了 Node 接口及其各子接口的类对象构成,子接口层次结构如下:

DOM 解析XML文档的代码示例如下:

  • XML文档内容:

    <?xml version="1.0" encoding="utf-8" ?>

    <root>

            <title>

                    <font enabled="false">

                            <!-- 字体名称 -->

                            <name>Helvetica</name>

                            <size>36</size>

                    </font>

                    <data>

                            <![CDATA[xml document root node <root.../>]]>

                    </data>

            </title>

    </root>

  • 解析代码:

    public static void main(String[] args) {

                    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

                    try {

                            DocumentBuilder builder = factory.newDocumentBuilder();

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

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

                            Document xmlDocument = builder.parse(xmlStream);

                            StringBuilder sb = new StringBuilder();

                            sb.append("<?xml version=\\"" + xmlDocument.getXmlVersion() + "\\" encodin=\\""

    + xmlDocument.getXmlEncoding() + "\\" ?>");

                            Element root = xmlDocument.getDocumentElement();

                            sb.append("<" + root.getTagName() + ">");

                            NodeList nodeList = root.getChildNodes();

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

                                    if (nodeList.item(i) instanceof Element) {

                                            sb.append(parseChildNodes((Element) nodeList.item(i)));

                                    }

                            }

                            sb.append("</" + root.getTagName() + ">");

                            System.out.println(sb.toString());

                    } catch (ParserConfigurationException e) {

                            e.printStackTrace();

                    } catch (IOException ex) {

                            ex.printStackTrace();

                    } catch (SAXException e) {

                            e.printStackTrace();

                    }

            }

       

            private static String parseChildNodes(Element element) {

                    StringBuilder sb = new StringBuilder();

                    sb.append("<" + element.getTagName());

                    NamedNodeMap map = element.getAttributes();

                    for (int j = 0; j < map.getLength(); j++) {

                            sb.append(" " + map.item(j).getNodeName() + "=\\"" + map.item(j).getNodeValue() + "\\"");

                    }

                    sb.append(" >");

                    if (element.hasChildNodes()) {

                            NodeList list = element.getChildNodes();

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

                                    if (list.item(i) instanceof Element) {

                                            Element curElement = (Element) list.item(i);

                                            sb.append(parseChildNodes(curElement));

                                            continue;

                                    }

                                    if (list.item(i) instanceof CDATASection) {

                                            CDATASection cdataSection = (CDATASection) list.item(i);

                                            sb.append("<![CDATA[").append(cdataSection.getData()).append("]]>");

                                            continue;

                                    }

                                    if (list.item(i) instanceof Comment) {

                                            Comment comment = (Comment)list.item(i);

                                            sb.append("<!-- "+comment.getData()+" -->");

                                            continue;

                                    }

                                    if (list.item(i) instanceof Text) {

                                            Text curText = (Text) list.item(i);

                                            sb.append(curText.getData().trim());

                                            continue;

                                    }

                            }

                    }

                    sb.append("</" + element.getTagName() + ">");

                    return sb.toString();

            }

       

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