Java SAX解析XML

　　SAX解析XML采用的是从上而下的基于事件驱动的解析方式，在解析过程中会视情况自动调用startDocument()、startElement()、characters()、endElement()、endDocument()等相关的方法。

由编译执行的结果来看：

• startDocument()方法只会在文档开始解析的时候被调用，每次解析只会调用一次。
• startElement()方法每次在开始解析一个元素，即遇到元素标签开始的时候都会调用。
• characters()方法也是在每次解析到元素标签携带的内容时都会调用，即使该元素标签的内容为空或换行。而且如果元素内嵌套元素，在父元素结束标签前， characters()方法会再次被调用，此处需要注意。
• endElement()方法每次在结束解析一个元素，即遇到元素标签结束的时候都会调用。
• endDocument() startDocument()方法只会在文档解析结束的时候被调用，每次解析只会调用一次。

oracle官方解析教程 http://docs.oracle.com/javase/tutorial/jaxp/sax/parsing.html

package com.demo.test;

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

import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Result;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.sax.SAXTransformerFactory;
import javax.xml.transform.sax.TransformerHandler;
import javax.xml.transform.stream.StreamResult;

import org.xml.sax.Attributes;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.AttributesImpl;
import org.xml.sax.helpers.DefaultHandler;

public class XmlDemo {

    private static class SAXHandler extends DefaultHandler {

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

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

        @Override
        public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
            System.out.println("startElement, uri=" + uri + ", localName=" + localName + ", qName=" + qName + ", attributes.getLength()=" + attributes.getLength());
            if (attributes.getLength() > 0) {
                for (int i = 0; i < attributes.getLength(); i++) {
                    System.out.println("startElement attributes(" + i + "): " + attributes.getQName(i) + "=" + attributes.getValue(i));
                }
            }
        }

        @Override
        public void endElement(String uri, String localName, String qName) throws SAXException {
            System.out.println("endElement, uri=" + uri + ", localName=" + localName + ", qName=" + qName);
        }

        @Override
        public void characters(char[] ch, int start, int length) throws SAXException {
            System.out.println("characters, start=" + start + ", length=" + length + ", ch=" + new String(ch, start, length));
        }

    }

    private static void parseXml(String xmlPath) {
        SAXParserFactory saxParserFactory = SAXParserFactory.newInstance();
        FileInputStream fis = null;
        try {
            fis = new FileInputStream(xmlPath);
            InputSource is = new InputSource(fis);
            // SAX会自动从流中检测正确的字符编码，但是如果流中没有明确指定编码，可能会导致转换错误
            is.setEncoding("UTF-8");
            SAXParser saxParser = saxParserFactory.newSAXParser();
            saxParser.parse(is, new SAXHandler());
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (ParserConfigurationException e) {
            e.printStackTrace();
        } catch (SAXException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (fis != null) {
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    private static void generateXml(String filePath) {
        SAXTransformerFactory saxTransformerFactory = (SAXTransformerFactory) SAXTransformerFactory.newInstance();
        FileOutputStream fos = null;
        try {
            TransformerHandler transformerHandler = saxTransformerFactory.newTransformerHandler();
            Transformer transformer = transformerHandler.getTransformer();
            transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
            // 如果是yes，那么会自动换行但不会缩进；如果是no，则不会换行。默认是no
//          transformer.setOutputProperty(OutputKeys.INDENT, "no");
            //不省略的话，会自动添加<?xml version="1.0" encoding="UTF-8"?>。默认是no
            transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "no");
            fos = new FileOutputStream(filePath);
            Result result = new StreamResult(fos);
            transformerHandler.setResult(result);
            transformerHandler.startDocument();
            AttributesImpl attr = new AttributesImpl();
            attr.addAttribute(null, null, "class", String.class.getName(), "value");
            startElement(transformerHandler, "html", null);
            startElement(transformerHandler, "head", null);
            endElement(transformerHandler, "head");
            startElement(transformerHandler, "body", null);
            selfEndElement(transformerHandler, "p", attr, "characters");
            endElement(transformerHandler, "body");
            endElement(transformerHandler, "html");
            transformerHandler.endDocument();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (TransformerConfigurationException e) {
            e.printStackTrace();
        } catch (SAXException e) {
            e.printStackTrace();
        } finally {
            if (fos != null) {
                try {
                    fos.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    // SAX默认不自动缩进，因此需要手动根据元素层次进行缩进控制
    private static int indent = 0;
    private static String uri = "http://www.chy.uri";
    private static String localname = "localname";
//  private static String uri = null;
//  private static String localname = null;

    private static void startElement(TransformerHandler transformerHandler, String qName, Attributes atts) throws SAXException {
        System.out.println("startElement " + qName);
        indent++;
        addTabs(transformerHandler);
        transformerHandler.startElement(uri, localname, qName, atts);
    }

    private static void endElement(TransformerHandler transformerHandler, String qName) throws SAXException {
        System.out.println("endElement " + qName);
        addTabs(transformerHandler);
        indent--;
        transformerHandler.endElement(uri, localname, qName);
    }

    /**
     * 自封闭式标签
     */
    private static void selfEndElement(TransformerHandler transformerHandler, String qName, Attributes atts, String str) throws SAXException {
        System.out.println("endElement " + qName);
        indent++;
        addTabs(transformerHandler);
        indent--;
        transformerHandler.startElement(uri, localname, qName, atts);
        if (str != null) {
            char[] charArr = str.toCharArray();
            transformerHandler.characters(charArr, 0, charArr.length);
        }
        transformerHandler.endElement(uri, localname, qName);
    }

    /**
     * SAX不会添加缩进，要自己添加
     */
    private static void addTabs(TransformerHandler transformerHandler) throws SAXException {
        System.out.println("addTabs " + indent);
        char[] ch = new char[indent];
        ch[0] = '\n';
        if (indent > 1) {
            for (int i = 1; i < ch.length; i++) {
                ch[i] = '\t';
            }
        }
        transformerHandler.characters(ch, 0, ch.length);
    }

    public static void main(String[] args) {
        String xmlPath = "test.xml";
        parseXml(xmlPath);
        generateXml("test.xml");
    }
}

生成的XML如下

<?xml version="1.0" encoding="UTF-8"?>
<html xmlns="http://www.chy.uri">
    <head>
    </head>
    <body>
        <p class="value">characters</p>
    </body>
</html>

这里如果uri变量设置为空，会自动生成一个无结束标签的META标签，并且indent设置为no也无效，还是会自动换行

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

<head>
<META http-equiv="Content-Type" content="text/html; charset=UTF-8">

</head>

<body>

<p class="value">characters</p>

</body>

</html>

右击项目 –> Properties（Alt + Enter）–> Java Build Path –> Libraries –> 双击JRE System Library
注意：这里如果选择OSGi/Minimum-1.2是找不到”javax.xml.“或”org.xml.sax.”的相关包的。最低版本必须是J2SE-1.5。