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关于SAX解析Xml的1点心得体会

2012-09-08 
关于SAX解析Xml的一点心得体会本人新手,也就随便写写,有兴趣的可以看下!SAX解析XML十分简单,可是将解析出

关于SAX解析Xml的一点心得体会
本人新手,也就随便写写,有兴趣的可以看下!

SAX解析XML十分简单,可是将解析出来的数据分类存储就不那么容易了!我的XML源文件如下:

XML code
<?xml version="1.0" encoding="UTF-8"?><config>   <Vms total_Vms="5">      <Vm>          <Vm_ID>0</Vm_ID>          <Vm_mips>278</Vm_mips>      </Vm>      <Vm>          <Vm_ID>1</Vm_ID>          <Vm_mips>289</Vm_mips>      </Vm>      <Vm>          <Vm_ID>2</Vm_ID>          <Vm_mips>132</Vm_mips>      </Vm>      <Vm>          <Vm_ID>3</Vm_ID>          <Vm_mips>209</Vm_mips>      </Vm>      <Vm>          <Vm_ID>4</Vm_ID>          <Vm_mips>286</Vm_mips>      </Vm>   </Vms>   <Cloudlets total_Cloudlets="10">      <Cloudlet>          <Cloudlet_ID>0</Cloudlet_ID>           <Cloudlet_length>19365</Cloudlet_length>       </Cloudlet>      <Cloudlet>          <Cloudlet_ID>1</Cloudlet_ID>           <Cloudlet_length>49809</Cloudlet_length>       </Cloudlet>      <Cloudlet>          <Cloudlet_ID>2</Cloudlet_ID>           <Cloudlet_length>30218</Cloudlet_length>       </Cloudlet>      <Cloudlet>          <Cloudlet_ID>3</Cloudlet_ID>           <Cloudlet_length>44157</Cloudlet_length>       </Cloudlet>      <Cloudlet>          <Cloudlet_ID>4</Cloudlet_ID>           <Cloudlet_length>16754</Cloudlet_length>       </Cloudlet>      <Cloudlet>          <Cloudlet_ID>5</Cloudlet_ID>           <Cloudlet_length>18336</Cloudlet_length>       </Cloudlet>      <Cloudlet>          <Cloudlet_ID>6</Cloudlet_ID>           <Cloudlet_length>20045</Cloudlet_length>       </Cloudlet>      <Cloudlet>          <Cloudlet_ID>7</Cloudlet_ID>           <Cloudlet_length>31493</Cloudlet_length>       </Cloudlet>      <Cloudlet>          <Cloudlet_ID>8</Cloudlet_ID>           <Cloudlet_length>30727</Cloudlet_length>       </Cloudlet>      <Cloudlet>          <Cloudlet_ID>9</Cloudlet_ID>           <Cloudlet_length>31017</Cloudlet_length>       </Cloudlet>         </Cloudlets></config>


我用了4个List(vmId、vmMips、CloudletId、CloudletLength)来保存解析出来的数据。saxParse会读取InputStream来一行一行的解析xml文件中的数据,saxParse解析xml文件的核心方法是parse(InputStream in,DefaultsHandler dh),我们只需要用这个方法就好。DefaultHandler里面的方法全部都是空的,我们需要设计自己的handler通过继承来重写里面一些比较重要的方法,在我的代码里面重写了5个方法,其中后面3个是必须的!

Java code
import java.io.FileInputStream;import java.io.InputStream;import java.util.ArrayList;import java.util.List;import javax.xml.parsers.SAXParser;import javax.xml.parsers.SAXParserFactory;import org.xml.sax.Attributes;import org.xml.sax.SAXException;import org.xml.sax.helpers.DefaultHandler;public class SAXParseUtil {      static List<String> vmId=new ArrayList<String>();     static List<String> vmMips=new ArrayList<String>();     static List<String> cloudletId=new ArrayList<String>();     static List<String> cloudletLength=new ArrayList<String>();          private class MyHandle extends DefaultHandler{         String qqName=null;         String temp=null;                    @Override        public void startDocument() throws SAXException {            // TODO Auto-generated method stub            super.startDocument();            System.out.println("开始解析!");        }                     @Override        public void endDocument() throws SAXException {            // TODO Auto-generated method stub            super.endDocument();            System.out.println("解析结束!");        }                      @Override        public void startElement(String uri, String localName, String qName,                Attributes attributes) throws SAXException {            // TODO Auto-generated method stub            super.startElement(uri, localName, qName, attributes);            if(qName.equals("Vm_ID"))                   qqName=qName;            if(qName.equals("Vm_mips"))                  qqName=qName;            if(qName.equals("Cloudlet_ID"))                  qqName=qName;            if(qName.equals("Cloudlet_length"))                  qqName=qName;        }                      @Override        public void endElement(String uri, String localName, String qName)                throws SAXException {            // TODO Auto-generated method stub             super.endElement(uri, localName, qName);             if(qName=="Vm_ID"){                    vmId.add(temp);                    System.out.println(qName+":"+temp);             }             if(qName=="Vm_mips"){                vmMips.add(temp);                    System.out.println(qName+":"+temp);             }                                  if(qName=="Cloudlet_ID"){                    cloudletId.add(temp);                    System.out.println(qName+":"+temp);             }                                  if(qName=="Cloudlet_length"){                    cloudletLength.add(temp);                    System.out.println(qName+":"+temp);             }                            }                      @Override        public void characters(char[] ch, int start, int length)                throws SAXException {            // TODO Auto-generated method stub            super.characters(ch, start, length);            //System.out.println(new String(ch,start,length));            if(qqName=="Vm_ID")                temp=new String(ch,start,length);            if(qqName=="Vm_mips")                temp=new String(ch,start,length);            if(qqName=="Cloudlet_ID")                temp=new String(ch,start,length);            if(qqName=="Cloudlet_length")                temp=new String(ch,start,length);        }     }          public void parseXML(String fileName) {         try {             SAXParserFactory saxfac=SAXParserFactory.newInstance();             SAXParser parse=saxfac.newSAXParser();             InputStream in=new FileInputStream(fileName);             parse.parse(in, new MyHandle());        } catch (Exception e) {            // TODO: handle exception            e.printStackTrace();        }     }     public static void main(String[] args) {        new SAXParseUtil().parseXML("/Users/apple/documents/configuration.xml");        System.out.println();        System.out.print("vmId:");        for(String s:vmId)System.out.print(s+" ");    System.out.println();        System.out.print("vmMips:");        for(String s:vmMips)System.out.print(s+" ");    System.out.println();        System.out.print("cloudletId:");        for(String s:cloudletId)System.out.print(s+" ");    System.out.println();        System.out.print("cloudletLength:");            for(String s:cloudletLength)System.out.print(s+" ");    System.out.println();        System.out.println();            System.out.println("The size of vmId is:"+vmId.size()+"\n"+"The size of vmMips is:"+vmMips.size()+"\n"+                           "The size of CloudletId is:"+cloudletId.size()+"\n"+"The size of " +                           "CloudletLength is:"+cloudletLength.size());    }} 



数据的保存要放在endElement()方法中,要不然,解析器会一直解析导致保存的数据失真(我测试过,里面会保存很多的空格)

下面是程序运行的结果:

开始解析!
Vm_ID:0
Vm_mips:278
Vm_ID:1
Vm_mips:289
Vm_ID:2
Vm_mips:132
Vm_ID:3
Vm_mips:209
Vm_ID:4
Vm_mips:286
Cloudlet_ID:0
Cloudlet_length:19365
Cloudlet_ID:1
Cloudlet_length:49809
Cloudlet_ID:2
Cloudlet_length:30218
Cloudlet_ID:3
Cloudlet_length:44157
Cloudlet_ID:4
Cloudlet_length:16754
Cloudlet_ID:5
Cloudlet_length:18336
Cloudlet_ID:6
Cloudlet_length:20045
Cloudlet_ID:7
Cloudlet_length:31493
Cloudlet_ID:8
Cloudlet_length:30727
Cloudlet_ID:9
Cloudlet_length:31017
解析结束!

vmId:0 1 2 3 4 
vmMips:278 289 132 209 286 
cloudletId:0 1 2 3 4 5 6 7 8 9 
cloudletLength:19365 49809 30218 44157 16754 18336 20045 31493 30727 31017 

The size of vmId is:5
The size of vmMips is:5
The size of CloudletId is:10
The size of CloudletLength is:10


SAX解析的优点的简单明了,但是,在解析的过程中,它需要把整个的xml结构树都放在内存中,比较耗费内存。还有一种比较好的基于事件的实时解析方法,我在这里就不过多的赘述,我给出一个解析Vm_ID的简单示例:
Java code
    public String[] getVmsID(String fileName)throws XMLStreamException, IOException{    XMLInputFactory xmlif=XMLInputFactory.newInstance();    XMLEventReader xmler=xmlif.createXMLEventReader(new FileReader(new File(fileName)));    XMLEvent event;    int i=0;    String VmsName []=new String[getVmsNumber(fileName)+1];    while(xmler.hasNext()){        event=xmler.nextEvent();        if(event.isCharacters()){            //如果解析字段为字符,则用数组将其保存            VmsName[i]=event.asCharacters().getData();        }        else if(event.isEndElement()){         EndElement ee=event.asEndElement();         if(ee.getName().getLocalPart().equals("Vm_ID")){             //如果结束标签为Vm_ID则进入下一次循环             i++;             continue;         }        }    }    return VmsName;  }


[解决办法]
JDK 中 XML 基本上有三种方式:DOM、SAX 和 StAX

SAX 是 push 模式
StAX 是 pull 模式

SAX 只能读,而 StAX 既能读又能写,处理速度比 SAX 快,呵呵。 

StAX 原本是 Java EE 中的,从 JDK 6 加到 Java SE 中去了,类库位于 javax.xml.stream.* 有兴趣的话可以去看看。

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