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解析Xml四種方法
編輯:XML詳解     
【引言】

目前在Java中用於解析XML的技術很多,主流的有DOM、SAX、JDOM、DOM4j,下文主要介紹這4種解析XML文檔技術的使用、優缺點及性能測試。
一、【基礎知識——掃盲】

sax、dom是兩種對xml文檔進行解析的方法(沒有具體實現,只是接口),所以只有它們是無法解析XML文檔的;jaxp只是api,它進一步封裝了sax、dom兩種接口,並且提供了DomcumentBuilderFactory/DomcumentBuilder和SAXParserFactory/SAXParser(默認使用xerces解釋器)。
二、【DOM、SAX、JDOM、DOM4j簡單使用介紹】

1、【DOM(Document Object Model) 】
由W3C提供的接口,它將整個XML文檔讀入內存,構建一個DOM樹來對各個節點(Node)進行操作。
示例代碼:

    <?XML version="1.0" encoding="UTF-8"?>  
    <university name="pku">  
        <college name="c1">  
            <class name="class1">  
                <student name="stu1" sex='male' age="21" />  
                <student name="stu2" sex='female' age="20" />  
                <student name="stu3" sex='female' age="20" />  
            </class>  
            <class name="class2">  
                <student name="stu4" sex='male' age="19" />  
                <student name="stu5" sex='female' age="20" />  
                <student name="stu6" sex='female' age="21" />  
            </class>  
        </college>  
        <college name="c2">  
            <class name="class3">  
                <student name="stu7" sex='male' age="20" />  
            </class>  
        </college>  
        <college name="c3">  
        </college>  
    </university>  

後文代碼中有使用到text.xml(該文檔放在src路徑下,既編譯後在classes路徑下),都是指該XML文檔。

    package test.XML;  
      
    import Java.io.File;  
    import Java.io.FileNotFoundException;  
    import Java.io.FileOutputStream;  
    import Java.io.IOException;  
    import Java.io.InputStream;  
      
    import Javax.XML.parsers.DocumentBuilder;  
    import Javax.XML.parsers.DocumentBuilderFactory;  
    import Javax.XML.parsers.ParserConfigurationException;  
    import Javax.XML.transform.Transformer;  
    import Javax.XML.transform.TransformerConfigurationException;  
    import Javax.XML.transform.TransformerException;  
    import Javax.XML.transform.TransformerFactory;  
    import Javax.XML.transform.dom.DOMSource;  
    import Javax.XML.transform.stream.StreamResult;  
      
    import org.w3c.dom.Document;  
    import org.w3c.dom.Element;  
    import org.w3c.dom.Node;  
    import org.w3c.dom.NodeList;  
    import org.w3c.dom.Text;  
    import org.XML.sax.SAXException;  
      
    /** 
     * dom讀寫XML 
     * @author whwang 
     */  
    public class TestDom {  
          
        public static void main(String[] args) {  
            read();  
            //write();   
        }  
          
        public static void read() {  
            DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();  
            try {  
                DocumentBuilder builder = dbf.newDocumentBuilder();  
                InputStream in = TestDom.class.getClassLoader().getResourceAsStream("test.XML");  
                Document doc = builder.parse(in);  
                // root <university>   
                Element root = doc.getDocumentElement();  
                if (root == null) return;  
                System.err.println(root.getAttribute("name"));  
                // all college node   
                NodeList collegeNodes = root.getChildNodes();  
                if (collegeNodes == null) return;  
                for(int i = 0; i < collegeNodes.getLength(); i++) {  
                    Node college = collegeNodes.item(i);  
                    if (college != null && college.getNodeType() == Node.ELEMENT_NODE) {  
                        System.err.println("\t" + college.getAttributes().getNamedItem("name").getNodeValue());  
                        // all class node   
                        NodeList classNodes = college.getChildNodes();  
                        if (classNodes == null) continue;  
                        for (int j = 0; j < classNodes.getLength(); j++) {  
                            Node clazz = classNodes.item(j);  
                            if (clazz != null && clazz.getNodeType() == Node.ELEMENT_NODE) {  
                                System.err.println("\t\t" + clazz.getAttributes().getNamedItem("name").getNodeValue()); 
                                // all student node   
                                NodeList studentNodes = clazz.getChildNodes();  
                                if (studentNodes == null) continue;  
                                for (int k = 0; k < studentNodes.getLength(); k++) {  
                                    Node student = studentNodes.item(k);  
                                    if (student != null && student.getNodeType() == Node.ELEMENT_NODE) {  
                                        System.err.print("\t\t\t" + student.getAttributes().getNamedItem("name").getNodeValue());  
                                        System.err.print(" " + student.getAttributes().getNamedItem("sex").getNodeValue());  
                                        System.err.println(" " + student.getAttributes().getNamedItem("age").getNodeValue());  
                                    }  
                                }  
                            }  
                        }  
                    }  
                }  
            } catch (ParserConfigurationException e) {  
                e.printStackTrace();  
            } catch (FileNotFoundException e) {  
                e.printStackTrace();  
            } catch (SAXException e) {  
                e.printStackTrace();  
            } catch (IOException e) {  
                e.printStackTrace();  
            }  
              
        }  
          
        public static void write() {  
            DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();  
            try {  
                DocumentBuilder builder = dbf.newDocumentBuilder();  
                InputStream in = TestDom.class.getClassLoader().getResourceAsStream("test.XML");  
                Document doc = builder.parse(in);  
                // root <university>   
                Element root = doc.getDocumentElement();  
                if (root == null) return;  
                // 修改屬性   
                root.setAttribute("name", "tsu");  
                NodeList collegeNodes = root.getChildNodes();  
                if (collegeNodes != null) {  
                    for (int i = 0; i <collegeNodes.getLength() - 1; i++) {  
                        // 刪除節點   
                        Node college = collegeNodes.item(i);  
                        if (college.getNodeType() == Node.ELEMENT_NODE) {  
                            String collegeName = college.getAttributes().getNamedItem("name").getNodeValue();  
                            if ("c1".equals(collegeName) || "c2".equals(collegeName)) {  
                                root.removeChild(college);  
                            } else if ("c3".equals(collegeName)) {  
                                Element newChild = doc.createElement("class");  
                                newChild.setAttribute("name", "c4");  
                                college.appendChild(newChild);  
                            }  
                        }  
                    }  
                }  
                // 新增節點   
                Element addCollege = doc.createElement("college");  
                addCollege.setAttribute("name", "c5");  
                root.appendChild(addCollege);  
                Text text = doc.createTextNode("text");  
                addCollege.appendChild(text);  
                  
                // 將修改後的文檔保存到文件   
                TransformerFactory transFactory = TransformerFactory.newInstance();  
                Transformer transFormer = transFactory.newTransformer();  
                DOMSource domSource = new DOMSource(doc);  
                File file = new File("src/dom-modify.XML");  
                if (file.exists()) {  
                    file.delete();  
                }  
                file.createNewFile();  
                FileOutputStream out = new FileOutputStream(file);           
                StreamResult XMLResult = new StreamResult(out);  
                transFormer.transform(domSource, XMLResult);  
                System.out.println(file.getAbsolutePath());  
            } catch (ParserConfigurationException e) {  
                e.printStackTrace();  
            } catch (SAXException e) {  
                e.printStackTrace();  
            } catch (IOException e) {  
                e.printStackTrace();  
            } catch (TransformerConfigurationException e) {  
                e.printStackTrace();  
            } catch (TransformerException e) {  
                e.printStackTrace();  
            }  
        }  
    }  

該代碼只要稍做修改,即可變得更加簡潔,無需一直寫if來判斷是否有子節點。

2、【SAX (Simple API for XML) 】
SAX不用將整個文檔加載到內存,基於事件驅動的API(Observer模式),用戶只需要注冊自己感興趣的事件即可。SAX提供EntityResolver, DTDHandler, ContentHandler, ErrorHandler接口,分別用於監聽解析實體事件、DTD處理事件、正文處理事件和處理出錯事件,與AWT類似,SAX還提供了一個對這4個接口默認的類DefaultHandler(這裡的默認實現,其實就是一個空方法),一般只要繼承DefaultHandler,重寫自己感興趣的事件即可。
示例代碼:

    package test.XML;  
      
    import Java.io.IOException;  
    import Java.io.InputStream;  
      
    import Javax.XML.parsers.ParserConfigurationException;  
    import Javax.XML.parsers.SAXParser;  
    import Javax.XML.parsers.SAXParserFactory;  
      
    import org.XML.sax.Attributes;  
    import org.XML.sax.InputSource;  
    import org.XML.sax.Locator;  
    import org.XML.sax.SAXException;  
    import org.XML.sax.SAXParseException;  
    import org.XML.sax.helpers.DefaultHandler;  
      
    /** 
     * 
     * @author whwang 
     */  
    public class TestSAX {  
      
        public static void main(String[] args) {  
            read();  
            write();  
        }  
          
        public static void read() {  
            try {  
                SAXParserFactory factory = SAXParserFactory.newInstance();  
                SAXParser parser = factory.newSAXParser();  
                InputStream in = TestSAX.class.getClassLoader().getResourceAsStream("test.XML");  
                parser.parse(in, new MyHandler());  
            } catch (ParserConfigurationException e) {  
                e.printStackTrace();  
            } catch (SAXException e) {  
                e.printStackTrace();  
            } catch (IOException e) {  
                e.printStackTrace();  
            }  
        }  
          
        public static void write() {  
            System.err.println("純SAX對於寫操作無能為力");  
        }  
          
    }  
      
    // 重寫對自己感興趣的事件處理方法   
    class MyHandler extends DefaultHandler {  
      
        @Override  
        public InputSource resolveEntity(String publicId, String systemId)  
                throws IOException, SAXException {  
            return super.resolveEntity(publicId, systemId);  
        }  
      
        @Override  
        public void notationDecl(String name, String publicId, String systemId)  
                throws SAXException {  
            super.notationDecl(name, publicId, systemId);  
        }  
      
        @Override  
        public void unparsedEntityDecl(String name, String publicId,  
                String systemId, String notationName) throws SAXException {  
            super.unparsedEntityDecl(name, publicId, systemId, notationName);  
        }  
      
        @Override  
        public void setDocumentLocator(Locator locator) {  
            super.setDocumentLocator(locator);  
        }  
      
        @Override  
        public void startDocument() throws SAXException {  
            System.err.println("開始解析文檔");  
        }  
      
        @Override  
        public void endDocument() throws SAXException {  
            System.err.println("解析結束");  
        }  
      
        @Override  
        public void startPrefixMapping(String prefix, String uri)  
                throws SAXException {  
            super.startPrefixMapping(prefix, uri);  
        }  
      
        @Override  
        public void endPrefixMapping(String prefix) throws SAXException {  
            super.endPrefixMapping(prefix);  
        }  
      
        @Override  
        public void startElement(String uri, String localName, String qName,  
                Attributes attributes) throws SAXException {  
            System.err.print("Element: " + qName + ", attr: ");  
            print(attributes);  
        }  
      
        @Override  
        public void endElement(String uri, String localName, String qName)  
                throws SAXException {  
            super.endElement(uri, localName, qName);  
        }  
      
        @Override  
        public void characters(char[] ch, int start, int length)  
                throws SAXException {  
            super.characters(ch, start, length);  
        }  
      
        @Override  
        public void ignorableWhitespace(char[] ch, int start, int length)  
                throws SAXException {  
            super.ignorableWhitespace(ch, start, length);  
        }  
      
        @Override  
        public void processingInstruction(String target, String data)  
                throws SAXException {  
            super.processingInstruction(target, data);  
        }  
      
        @Override  
        public void skippedEntity(String name) throws SAXException {  
            super.skippedEntity(name);  
        }  
      
        @Override  
        public void warning(SAXParseException e) throws SAXException {  
            super.warning(e);  
        }  
      
        @Override  
        public void error(SAXParseException e) throws SAXException {  
            super.error(e);  
        }  
      
        @Override  
        public void fatalError(SAXParseException e) throws SAXException {  
            super.fatalError(e);  
        }  
          
        private void print(Attributes attrs) {  
            if (attrs == null) return;  
            System.err.print("[");  
            for (int i = 0; i < attrs.getLength(); i++) {  
                System.err.print(attrs.getQName(i) + " = " + attrs.getValue(i));  
                if (i != attrs.getLength() - 1) {  
                    System.err.print(", ");  
                }  
            }  
            System.err.println("]");  
        }  
    }  

3、【JDOM】
JDOM與DOM非常類似,它是處理XML的純Java API,API大量使用了Collections類,且JDOM僅使用具體類而不使用接口。 JDOM 它自身不包含解析器。它通常使用 SAX2 解析器來解析和驗證輸入 XML 文檔(盡管它還可以將以前構造的 DOM 表示作為輸入)。它包含一些轉換器以將 JDOM 表示輸出成 SAX2 事件流、DOM 模型或 XML 文本文檔
示例代碼:

    package test.XML;  
      
    import Java.io.File;  
    import Java.io.FileOutputStream;  
    import Java.io.IOException;  
    import Java.io.InputStream;  
    import Java.util.List;  
      
    import org.jdom.Attribute;  
    import org.jdom.Document;  
    import org.jdom.Element;  
    import org.jdom.JDOMException;  
    import org.jdom.input.SAXBuilder;  
    import org.jdom.output.XMLOutputter;  
      
    /** 
     * JDom讀寫XML 
     * @author whwang 
     */  
    public class TestJDom {  
        public static void main(String[] args) {  
            //read();   
            write();  
        }  
          
        public static void read() {  
            try {  
                boolean validate = false;  
                SAXBuilder builder = new SAXBuilder(validate);  
                InputStream in = TestJDom.class.getClassLoader().getResourceAsStream("test.XML");  
                Document doc = builder.build(in);  
                // 獲取根節點 <university>   
                Element root = doc.getRootElement();  
                readNode(root, "");  
            } catch (JDOMException e) {  
                e.printStackTrace();  
            } catch (IOException e) {  
                e.printStackTrace();  
            }  
        }  
          
        @SuppressWarnings("unchecked")  
        public static void readNode(Element root, String prefix) {  
            if (root == null) return;  
            // 獲取屬性   
            List<Attribute> attrs = root.getAttributes();  
            if (attrs != null && attrs.size() > 0) {  
                System.err.print(prefix);  
                for (Attribute attr : attrs) {  
                    System.err.print(attr.getValue() + " ");  
                }  
                System.err.println();  
            }  
            // 獲取他的子節點   
            List<Element> childNodes = root.getChildren();  
            prefix += "\t";  
            for (Element e : childNodes) {  
                readNode(e, prefix);  
            }  
        }  
          
        public static void write() {  
            boolean validate = false;  
            try {  
                SAXBuilder builder = new SAXBuilder(validate);  
                InputStream in = TestJDom.class.getClassLoader().getResourceAsStream("test.XML");  
                Document doc = builder.build(in);  
                // 獲取根節點 <university>   
                Element root = doc.getRootElement();  
                // 修改屬性   
                root.setAttribute("name", "tsu");  
                // 刪除   
                boolean isRemoved = root.removeChildren("college");  
                System.err.println(isRemoved);  
                // 新增   
                Element newCollege = new Element("college");  
                newCollege.setAttribute("name", "new_college");  
                Element newClass = new Element("class");  
                newClass.setAttribute("name", "ccccc");  
                newCollege.addContent(newClass);  
                root.addContent(newCollege);  
                XMLOutputter out = new XMLOutputter();  
                File file = new File("src/jdom-modify.XML");  
                if (file.exists()) {  
                    file.delete();  
                }  
                file.createNewFile();  
                FileOutputStream fos = new FileOutputStream(file);  
                out.output(doc, fos);  
            } catch (JDOMException e) {  
                e.printStackTrace();  
            } catch (IOException e) {  
                e.printStackTrace();  
            }  
        }  
          
    }  

4、【DOM4j】
dom4j是目前在xml解析方面是最優秀的(Hibernate、Sun的JAXM也都使用dom4j來解析XML),它合並了許多超出基本 XML 文檔表示的功能,包括集成的 XPath 支持、XML Schema 支持以及用於大文檔或流化文檔的基於事件的處理
示例代碼:

    package test.XML;  
      
    import Java.io.File;  
    import Java.io.FileWriter;  
    import Java.io.IOException;  
    import Java.io.InputStream;  
    import Java.util.List;  
      
    import org.dom4j.Attribute;  
    import org.dom4j.Document;  
    import org.dom4j.DocumentException;  
    import org.dom4j.DocumentHelper;  
    import org.dom4j.Element;  
    import org.dom4j.ProcessingInstruction;  
    import org.dom4j.VisitorSupport;  
    import org.dom4j.io.SAXReader;  
    import org.dom4j.io.XMLWriter;  
      
    /** 
     * Dom4j讀寫XML 
     * @author whwang 
     */  
    public class TestDom4j {  
        public static void main(String[] args) {  
            read1();  
            //read2();   
            //write();   
        }  
      
        public static void read1() {  
            try {  
                SAXReader reader = new SAXReader();  
                InputStream in = TestDom4j.class.getClassLoader().getResourceAsStream("test.XML");  
                Document doc = reader.read(in);  
                Element root = doc.getRootElement();  
                readNode(root, "");  
            } catch (DocumentException e) {  
                e.printStackTrace();  
            }  
        }  
          
        @SuppressWarnings("unchecked")  
        public static void readNode(Element root, String prefix) {  
            if (root == null) return;  
            // 獲取屬性   
            List<Attribute> attrs = root.attributes();  
            if (attrs != null && attrs.size() > 0) {  
                System.err.print(prefix);  
                for (Attribute attr : attrs) {  
                    System.err.print(attr.getValue() + " ");  
                }  
                System.err.println();  
            }  
            // 獲取他的子節點   
            List<Element> childNodes = root.elements();  
            prefix += "\t";  
            for (Element e : childNodes) {  
                readNode(e, prefix);  
            }  
        }  
          
        public static void read2() {  
            try {  
                SAXReader reader = new SAXReader();  
                InputStream in = TestDom4j.class.getClassLoader().getResourceAsStream("test.XML");  
                Document doc = reader.read(in);  
                doc.accept(new MyVistor());  
            } catch (DocumentException e) {  
                e.printStackTrace();  
            }  
        }  
          
        public static void write() {  
            try {  
                // 創建一個XML文檔   
                Document doc = DocumentHelper.createDocument();  
                Element university = doc.addElement("university");  
                university.addAttribute("name", "tsu");  
                // 注釋   
                university.addComment("這個是根節點");  
                Element college = university.addElement("college");  
                college.addAttribute("name", "cccccc");  
                college.setText("text");  
                  
                File file = new File("src/dom4j-modify.XML");  
                if (file.exists()) {  
                    file.delete();  
                }  
                file.createNewFile();  
                XMLWriter out = new XMLWriter(new FileWriter(file));  
                out.write(doc);  
                out.flush();  
                out.close();  
            } catch (IOException e) {  
                e.printStackTrace();  
            }  
        }  
    }  
      
    class MyVistor extends VisitorSupport {  
        public void visit(Attribute node) {  
            System.out.println("Attibute: " + node.getName() + "="  
                    + node.getValue());  
        }  
      
        public void visit(Element node) {  
            if (node.isTextOnly()) {  
                System.out.println("Element: " + node.getName() + "="  
                        + node.getText());  
            } else {  
                System.out.println(node.getName());  
            }  
        }  
      
        @Override  
        public void visit(ProcessingInstruction node) {  
            System.out.println("PI:" + node.getTarget() + " " + node.getText());  
        }  
    }  

 
三、【性能測試】

環境:AMD4400+ 2.0+GHz主頻 JDK6.0
運行參數:-Xms400m -Xmx400m
XML文件大小:10.7M
結果:
DOM: >581297ms
SAX: 8829ms
JDOM: 581297ms
DOM4j: 5309ms
時間包括IO的,只是進行了簡單的測試,僅供參考!!!!

四、【對比】

1、【DOM】
DOM是基於樹的結構,通常需要加載整文檔和構造DOM樹,然後才能開始工作。
優點:
    a、由於整棵樹在內存中,因此可以對XML文檔隨機訪問
    b、可以對XML文檔進行修改操作
    c、較sax,dom使用也更簡單。
缺點:
    a、整個文檔必須一次性解析完
    a、由於整個文檔都需要載入內存,對於大文檔成本高
2、【SAX】
SAX類似流媒體,它基於事件驅動的,因此無需將整個文檔載入內存,使用者只需要監聽自己感興趣的事件即可。
優點:
    a、無需將整個XML文檔載入內存,因此消耗內存少
    b、可以注冊多個ContentHandler
缺點:
    a、不能隨機的訪問XML中的節點
    b、不能修改文檔
3、【JDOM】
JDOM是純Java的處理XML的API,其API中大量使用Collections類,
優點:
    a、DOM方式的優點
    b、具有SAX的Java規則
缺點
    a、DOM方式的缺點
4、【DOM4J】
這4中XML解析方式中,最優秀的一個,集易用和性能於一身。

五、【小插曲XPath】

XPath 是一門在 XML 文檔中查找信息的語言, 可用來在 XML 文檔中對元素和屬性進行遍歷。XPath 是 W3C XSLT 標准的主要元素,並且 XQuery 和 XPointer 同時被構建於 XPath 表達之上。因此,對 XPath 的理解是很多高級 XML 應用的基礎。
XPath非常類似對數據庫操作的SQL語言,或者說JQuery,它可以方便開發者抓起文檔中需要的東西。(dom4j也支持xpath)
示例代碼:

    package test.XML;  
      
    import Java.io.IOException;  
    import Java.io.InputStream;  
      
    import Javax.XML.parsers.DocumentBuilder;  
    import Javax.XML.parsers.DocumentBuilderFactory;  
    import Javax.XML.parsers.ParserConfigurationException;  
    import Javax.XML.xpath.XPath;  
    import Javax.XML.xpath.XPathConstants;  
    import Javax.XML.xpath.XPathExpression;  
    import Javax.XML.xpath.XPathExpressionException;  
    import Javax.XML.xpath.XPathFactory;  
      
    import org.w3c.dom.Document;  
    import org.w3c.dom.NodeList;  
    import org.XML.sax.SAXException;  
      
    public class TestXPath {  
      
        public static void main(String[] args) {  
            read();  
        }  
          
        public static void read() {  
            try {  
                DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();  
                DocumentBuilder builder = dbf.newDocumentBuilder();  
                InputStream in = TestXPath.class.getClassLoader().getResourceAsStream("test.XML");  
                Document doc = builder.parse(in);  
                XPathFactory factory = XPathFactory.newInstance();  
                XPath xpath = factory.newXPath();  
                // 選取所有class元素的name屬性   
                // XPath語法介紹: http://w3school.com.cn/xpath/   
                XPathExpression expr = xpath.compile("//class/@name");  
                NodeList nodes = (NodeList) expr.evaluate(doc, XPathConstants.NODESET);  
                for (int i = 0; i < nodes.getLength(); i++) {  
                    System.out.println("name = " + nodes.item(i).getNodeValue());  
                        }  
            } catch (XPathExpressionException e) {  
                e.printStackTrace();  
            } catch (ParserConfigurationException e) {  
                e.printStackTrace();  
            } catch (SAXException e) {  
                e.printStackTrace();  
            } catch (IOException e) {  
                e.printStackTrace();  
            }  
        }  
          
    }  

 

六、【補充】

注意4種解析方法對TextNode(文本節點)的處理:

1、在使用DOM時,調用node.getChildNodes()獲取該節點的子節點,文本節點也會被當作一個Node來返回,如:

 

    <?XML version="1.0" encoding="UTF-8"?>  
    <university name="pku">  
        <college name="c1">  
            <class name="class1">  
                <student name="stu1" sex='male' age="21" />  
                <student name="stu2" sex='female' age="20" />  
                <student name="stu3" sex='female' age="20" />  
            </class>  
        </college>  
    </university>  

 

    package test.XML;  
      
    import Java.io.FileNotFoundException;  
    import Java.io.IOException;  
    import Java.io.InputStream;  
    import Java.util.Arrays;  
      
    import Javax.XML.parsers.DocumentBuilder;  
    import Javax.XML.parsers.DocumentBuilderFactory;  
    import Javax.XML.parsers.ParserConfigurationException;  
      
    import org.w3c.dom.Document;  
    import org.w3c.dom.Element;  
    import org.w3c.dom.Node;  
    import org.w3c.dom.NodeList;  
    import org.XML.sax.SAXException;  
      
    /** 
     * dom讀寫XML 
     * @author whwang 
     */  
    public class TestDom2 {  
          
        public static void main(String[] args) {  
            read();  
        }  
          
        public static void read() {  
            DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();  
            try {  
                DocumentBuilder builder = dbf.newDocumentBuilder();  
                InputStream in = TestDom2.class.getClassLoader().getResourceAsStream("test.XML");  
                Document doc = builder.parse(in);  
                // root <university>   
                Element root = doc.getDocumentElement();  
                if (root == null) return;  
    //          System.err.println(root.getAttribute("name"));   
                // all college node   
                NodeList collegeNodes = root.getChildNodes();  
                if (collegeNodes == null) return;  
                System.err.println("university子節點數:" + collegeNodes.getLength());  
                System.err.println("子節點如下:");  
                for(int i = 0; i < collegeNodes.getLength(); i++) {  
                    Node college = collegeNodes.item(i);  
                    if (college == null) continue;  
                    if (college.getNodeType() == Node.ELEMENT_NODE) {  
                        System.err.println("\t元素節點:" + college.getNodeName());  
                    } else if (college.getNodeType() == Node.TEXT_NODE) {  
                        System.err.println("\t文本節點:" + Arrays.toString(college.getTextContent().getBytes()));  
                    }  
                }  
            } catch (ParserConfigurationException e) {  
                e.printStackTrace();  
            } catch (FileNotFoundException e) {  
                e.printStackTrace();  
            } catch (SAXException e) {  
                e.printStackTrace();  
            } catch (IOException e) {  
                e.printStackTrace();  
            }  
              
        }  
    }  

輸出的結果是:

 

 

    university子節點數:3  
    子節點如下:  
        文本節點:[10, 9]  
        元素節點:college  
        文本節點:[10]  

 

其中\n的ASCII碼為10,\t的ASCII碼為9。結果讓人大吃一驚,university的子節點數不是1,也不是2,而是3,這3個子節點都是誰呢?為了看得更清楚點,把XML文檔改為:

 

 

    <?XML version="1.0" encoding="UTF-8"?>  
    <university name="pku">11  
        <college name="c1">  
            <class name="class1">  
                <student name="stu1" sex='male' age="21" />  
                <student name="stu2" sex='female' age="20" />  
                <student name="stu3" sex='female' age="20" />  
            </class>  
        </college>22  
    </university>  

還是上面的程序,輸出結果為:

 

 

    university子節點數:3  
    子節點如下:  
        文本節點:[49, 49, 10, 9]  
        元素節點:college  
        文本節點:[50, 50, 10]  

其中數字1的ASCII碼為49,數字2的ASCII碼為50。

 

2、使用SAX來解析同DOM,當你重寫它的public void characters(char[] ch, int start, int length)方法時,你就能看到。

3、JDOM,調用node.getChildren()只返回子節點,不包括TextNode節點(不管該節點是否有Text信息)。如果要獲取該節點的Text信息,可以調用node.getText()方法,該方法返回節點的Text信息,也包括\n\t等特殊字符。

4、DOM4j同JDOM
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