XML的解析技术

Xml解析方式分为两种:

1.dom
document object model 即文档对象模型，它是w3c组织推荐的解析xml的一种方式。

2.sax
simple api for xml 不是官方标准，它是xml 社区事实上的标准，几乎所有的xml解析器都支持它

Jaxp解析
Java api for xml programming 是sun公司的一套操作xml的API. Jaxp很好的支持了dom与sax解析方式。Jaxp开发包是javase的一部分，它是由javax.xml org.w3c.domoirg.xml.saq包及其子包组成
需要类：DocumentBuilderFactory
DocumentBuilder
Document element node 这三个属性是理解xml的关键类，分别指dom, 元素，<node> </node> 开头的内容

• 要xml文件代码

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

<bookstore>
    <book catgrory="computer">
        <title>java从入门到放弃</title>
        <author>王二</author>
        <year>1009</year>
        <price>43.5</price>
    </book>
    <book catgrory="story">
        <title>mysql从入门到放弃</title>
        <author>龙达</author>
        <year>2011</year>
        <price>23.5</price>
    </book>
    
</bookstore>

• dom代码
  当出现了#text ........ 是由于文档间空格换行，需要写逻辑进行处理。

package org.dgw.net;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;

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.NamedNodeMap;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

public class demo1 {
    public static void main(String[] args) throws ParserConfigurationException,
            FileNotFoundException, SAXException, IOException {
        // 构建dom解析工厂
        DocumentBuilderFactory dom = DocumentBuilderFactory.newInstance();
        // 得到解决对象
        DocumentBuilder builder = dom.newDocumentBuilder();
        // 拿到dom对象
        Document document = builder
                .parse(new FileInputStream(new File("d://xmldemo.xml")));
        // 获取根节点
        Element root = document.getDocumentElement();
        System.out.println(root.getNodeName());

        // 读取database节点NodeList接口提供对节点的有序集合的抽象
        NodeList nodeList = root.getElementsByTagName("book");
        for (int i = 0; i < nodeList.getLength(); i++) {
            // 获取一个节点
            Node node = nodeList.item(i);
            // 获取该节点所有属性
            NamedNodeMap attributes = node.getAttributes();
            for (int j = 0; j < attributes.getLength(); j++) {
                Node attribute = attributes.item(j);
                System.out.println(attribute.getNodeName() + ":"
                        + attribute.getNodeValue());
            }
            // 获取所有子节点数据
            NodeList childNodes = node.getChildNodes();
            for (int j = 0; j < childNodes.getLength(); j++) {
                Node childNode = childNodes.item(j);
                if (childNode.getNodeType()==Document.ELEMENT_NODE) {
                    System.out.println(childNode.getNodeName() + ":"
                            + childNode.getTextContent());
                }
            }
        }
    }
}

• 生成一个简单文档

类：TransformerFactory Transformer DOMSource StreamResult

package org.xml.tech;

import java.io.File;

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.TransformerFactoryConfigurationError;
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;

public class domcreate {
    private static File file;
    private final static String path = "D://demo.xml";

    public static void main(String[] args) throws ParserConfigurationException,
            Exception, TransformerFactoryConfigurationError {
        DocumentBuilder builder = DocumentBuilderFactory.newInstance()
                .newDocumentBuilder();
        Document dom = builder.newDocument();
        // 标注xml信息
        dom.setXmlVersion("1.0");
        dom.setXmlStandalone(true);
        // 开始构建
        Element root = dom.createElement("root");
        root.setAttribute("lang", "zh");
        dom.appendChild(root);
        // 子节点
        Element book = dom.createElement("book");
        Element title = dom.createElement("title");
        String textContent = "hell wold";
        title.setTextContent(textContent);
        book.appendChild(title);
        root.appendChild(book);
        createXml(dom);

    }

    private static void createXml(Node dom)
            throws TransformerFactoryConfigurationError, TransformerException {
        Transformer transformer = TransformerFactory.newInstance()
                .newTransformer();
        DOMSource source = new DOMSource(dom);
        file = new File(path);
        StreamResult result = new StreamResult(file);
        transformer.transform(source, result);

    }
}

Sax解析
Sax是基于事件驱动（事件是预定义的，读到什么内容即可触发相关事件）的方式来对xml进行处理。Sax它只能进行读操作。它是读取一行解析一行。大的xml文档采用此读取方式，是不可往复的，不可逆的

相关类： SAXParserFactory SAXParser XMLReader ContentHandler DefaultHandler

package org.xml.tech;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;

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.SAXException;
import org.xml.sax.XMLReader;
import org.xml.sax.helpers.DefaultHandler;

public class SaxDemo {
    public static void main(String[] args) throws ParserConfigurationException,
            SAXException, FileNotFoundException, IOException {
        SAXParser parser = SAXParserFactory.newInstance().newSAXParser();
        XMLReader reader = parser.getXMLReader();
        reader.setContentHandler(new DefaultHandler() {

            @Override
            public void startDocument() throws SAXException {
                System.out.println("开始解析");
            }

            @Override
            public void endDocument() throws SAXException {
                System.out.println("结束解析");
            }

            @Override
            public void startElement(String uri, String localName, String qName,
                    Attributes attributes) throws SAXException {
                System.out.println("开始解析节点[" + qName + "]...");
                System.out.println("共有[" + attributes.getLength() + "]个属性");
            }

            @Override
            public void characters(char[] ch, int start, int length)
                    throws SAXException {
                // 内容解析
                /*
                 * String string = new String(ch, start, length);
                 * System.out.println(string);
                 */
                System.out.println(start);
                System.out.println(length);
                String string = new String(ch);
                System.out.println(string);

            }

            @Override
            public void endElement(String uri, String localName, String qName)
                    throws SAXException {
                System.out.println("结束解析XML节点...");
            }

        });
        // 文件源必须写在末尾
        reader.parse(
                new InputSource(new FileInputStream(new File("D://demo.xml"))));
    }

}

Dom4j介绍
Dom4j它是一个优秀操作xml的工具，在很开源的框架中大量使用dom4j, 例如Struts2 hibernate sping框架。dom4j是一个简单的开源库，用于处理XML、 XPath和XSLT，它基于Java平台，使用Java的集合框架，全面集成了DOM，SAX和JAXP，是目前比较流行XML文档解析方法。

要想使用dom4j必须下载dom4j jar包才可以使用。
链接：：：http://www.dom4j.org/dom4j-1.6.1/

package org.xml.tech;

import java.io.FileOutputStream;
import java.util.List;

import org.dom4j.Attribute;
import org.dom4j.Document;
import org.dom4j.DocumentHelper;
import org.dom4j.Element;
import org.dom4j.io.OutputFormat;
import org.dom4j.io.SAXReader;
import org.dom4j.io.XMLWriter;

public class Dom4jHandler {
    public void add() throws Exception {
        // 1.创建一个Document
        Document document = DocumentHelper.createDocument();
        // 2.给Document添加数据
        Element root = document.addElement("DataSource");
        // 添加注释
        root.addComment("这是注释信息");
        // 在root根节点下面添加一个子节点
        Element database = root.addElement("database");
        database.addAttribute("name", "mysql");
        database.addAttribute("version", "5.0");
        // 添加子节点
        database.addElement("driver").setText("com.mysql.jdbc.Driver");
        database.addElement("url")
                .setText("jdbc:mysql://localhost:3306/myjdbc");
        database.addElement("user").setText("root");
        database.addElement("password").setText("root");
        // 3.将Document写出文件
        OutputFormat format = OutputFormat.createPrettyPrint();
        format.setEncoding("utf-8");
        // FileOutputStream默认生成的路径在根路径
        XMLWriter xw = new XMLWriter(new FileOutputStream("db.xml"), format);
        xw.write(document);
        xw.close();
    }

    public void update(String fileName) throws Exception {
        // sax解析器
        SAXReader saxReader = new SAXReader();
        // 读到对象
        Document document = saxReader
                .read(this.getClass().getResourceAsStream("/" + fileName));
        Element root = document.getRootElement();
        List<Element> databases_node = root.elements("database");
        for (Element database_node : databases_node) {
            if (database_node.attributeValue("name")
                    .equalsIgnoreCase("mysql")) {
                System.out
                        .println("old:" + database_node.attributeValue("name"));
                database_node.attribute("name").setText("Oracle");
                System.out.println(
                        "update:" + database_node.attributeValue("name"));

                database_node.element("driver").setText("oracel");
                database_node.element("url").setText("jdbc");

                // 删除password节点
                database_node.remove(database_node.element("password"));

                // 删除属性
                database_node.remove(database_node.attribute("version"));
            }
        }

        OutputFormat format = OutputFormat.createPrettyPrint();
        format.setEncoding("utf-8");
        // FileOutputStream默认生成的路径在根路径
        XMLWriter xw = new XMLWriter(new FileOutputStream("db2.xml"), format);
        xw.write(document);
        xw.close();
    }

    public void read(String fileName) throws Exception {
        // sax解析器
        SAXReader saxReader = new SAXReader();
        // 读到对象
        Document document = saxReader
                .read(this.getClass().getResourceAsStream("/" + fileName));
        Element root = document.getRootElement();
        System.out.println("根节点：" + root.getName());

        // List<Element> childElements=root.elements();
        List<Element> childElements = root.elements("database");
        for (Element child : childElements) {
            // 获取属性 不知道属性名称时的遍历方法
            List<Attribute> attributes = child.attributes();
            // for (Attribute attribute : attributes) {
            // System.out.println(attribute.getName()+":"+attribute.getValue());
            // }
            String name = child.attributeValue("name");
            // String version = child.attributeValue("version");
            String version = child.attribute("version").getValue();
            System.out.println(name + ":" + version);

            // //获取子节点
            // List<Element> childs=child.elements();
            // for (Element element : childs) {
            // System.out.println(element.getName()+":"+element.getText());
            // }
            System.out.println(child.elementText("driver"));
            System.out.println(child.element("url").getText());
            System.out.println(child.elementTextTrim("user"));
            System.out.println(child.element("password").getTextTrim());

        }
    }

    public static void main(String[] args) throws Exception {
        // new Dom4jHandler().read("data-source.xml");
        // new Dom4jHandler().add();
        new Dom4jHandler().update("data-source.xml");
    }
}