读取XML文件

   JAVA操作XML文档主要有四种方式，分别是DOM、SAX、JDOM和DOM4J，DOM和SAX是官方提供的，而JDOM和DOM4J则是引用第三方库的，其中用的最多的是DOM4J方式。运行效率和内存使用方面最优的是SAX，但是由于SAX是基于事件的方式，所以SAX无法在编写XML的过程中对已编写内容进行修改，但对于不用进行频繁修改的需求，还是应该选择使用SAX。

   下面基于这四种方式来读取XML文件。

 

   第一，以DOM的方式实现。

package xmls;
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;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import java.io.File;
import java.io.IOException;
/**
 * Created by lenovo on 2017-6-3.
 */
public class DOMReadDemo {
    public static void main(String[] args){
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        try{
            DocumentBuilder db = dbf.newDocumentBuilder();
            Document document = db.parse("src/xmls/DOM.xml");
            NodeList booklist = document.getElementsByTagName("book");
            for(int i = 0; i < booklist.getLength(); i++){
                System.out.println("--------第" + (i+1) + "本书----------");
                Element ele = (Element) booklist.item(i);
                NodeList childNodes= ele.getChildNodes();
                for(int j = 0; j < childNodes.getLength(); j++){
                    Node n = childNodes.item(j);
                    if(n.getNodeName() != "#text"){
                        System.out.println(n.getNodeName() + ":" + n.getTextContent());
                    }
                }
                System.out.println("---------------------------------");
            }
        }catch (ParserConfigurationException e){
            e.printStackTrace();
        }catch (IOException e){
            e.printStackTrace();
        }catch (SAXException e){
            e.printStackTrace();
        }
    }
}

    第二，以SAX的方式实现。

package xmls;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
/**
 * Created by lenovo on 2017-6-1.
 */
public class xmlTest2 {
    public static void main(String[] args){
        SAXParserFactory spf = SAXParserFactory.newInstance();
        try{
            SAXParser sp = spf.newSAXParser();
            SAXParserHandler handler = new SAXParserHandler();
            sp.parse("src\xmls\book.xml", handler);
        }catch (Exception e){
            e.printStackTrace();
        }
    }
}

package xmls;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
/**
 * Created by lenovo on 2017-6-1.
 */
public class SAXParserHandler extends DefaultHandler {
    @Override
    public void startDocument() throws SAXException {
        super.startDocument();
        System.out.println("SAX解析开始");
    }
    @Override
    public void endDocument() throws SAXException {
        super.endDocument();
        System.out.println("SAX解析结束");
    }
    @Override
    public void startElement(String s, String s1, String s2, Attributes attributes) throws SAXException {
        super.startElement(s, s1, s2, attributes);
        System.out.println(s2);
        for(int i = 0; i < attributes.getLength(); i++){
            String name = attributes.getQName(i);
            String value = attributes.getValue(name);
            System.out.println("属性值：" + name + "=" + value);
        }
    }
    @Override
    public void endElement(String s, String s1, String s2) throws SAXException {
        super.endElement(s, s1, s2);
        if(s2.equals("book")){
            System.out.println("-----------------------");
        }
    }
    @Override
    public void characters(char[] ch, int start, int length) throws SAXException {
        super.characters(ch, start, length);
        String value = new String(ch, start, length);
        if(value.trim().equals("")){
            return;
        }
        System.out.println(value);
    }
}

    第三，以JDOM的方式实现。

package xmls;
import org.jdom2.Attribute;
import org.jdom2.Document;
import org.jdom2.Element;
import org.jdom2.JDOMException;
import org.jdom2.input.JDOMParseException;
import org.jdom2.input.SAXBuilder;
import java.io.*;
import java.util.List;
/**
 * Created by lenovo on 2017-6-2.
 */
public class JDOMTest {
    public static void main(String[] args){
        SAXBuilder saxBuilder = new SAXBuilder();
        InputStream in;
        try{
            in = new FileInputStream(new File("src\xmls\book.xml"));
            Document document = saxBuilder.build(in);
            Element rootElement = document.getRootElement();
            List<Element> bookList = rootElement.getChildren();
            for(Element book: bookList){
                System.out.println("第" + (bookList.indexOf(book)+1) + "本书！");
                List<Attribute> attrs = book.getAttributes();
                for(Attribute attr: attrs){
                    System.out.println(attr.getName() + "=" + attr.getValue());
                }
                for(Element item: book.getChildren()){
                    System.out.println(item.getName() + ":" + item.getValue());
                }
                System.out.println("------------------------------------");
            }
        }catch (FileNotFoundException e){
            e.printStackTrace();
        }catch (JDOMException e){
            e.printStackTrace();
        }catch (IOException e){
            e.printStackTrace();
        }
    }
}

    第四，以DOM4J的方式实现。

package xmls;
import org.dom4j.*;
import org.dom4j.io.OutputFormat;
import org.dom4j.io.SAXReader;
import org.dom4j.io.XMLWriter;
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Iterator;
import java.util.List;
/**
 * Created by lenovo on 2017-6-2.
 */
public class DOM4JTest {
    public void parseXML(){
        SAXReader saxReader = new SAXReader();
        try{
            Document document = saxReader.read(new File("src\xmls\book.xml"));
            Element rootElement = document.getRootElement();
            Iterator it = rootElement.elementIterator();
            while (it.hasNext()){
                Element book = (Element)it.next();
                List<Attribute> attrs = book.attributes();
                for(Attribute attr: attrs){
                    System.out.println("属性名：" + attr.getName() + "---- 属性值：" + attr.getValue() );
                }
                Iterator cit = book.elementIterator();
                while (cit.hasNext()){
                    Element child = (Element) cit.next();
                    System.out.println("子节点：" + child.getName());
                }
            }
        }catch (DocumentException e){
            e.printStackTrace();
        }
    }
    public static void main(String[] args){
        DOM4JTest dom4JTest = new DOM4JTest();
        dom4JTest.parseXML();
    }
}