xpath使用效率探索(转)

                                       XPath使用效率
1.“/”与“//”的效率比较

String xpath1="/broadcast/contentList/item[@sendId=\"99\" and @receiveId=\"100\" and @resId=\"200\"]";
String xpath2="//item[@sendId=\"99\" and @receiveId=\"100\" and @resId=\"200\"]";

读同一个xml文件中，xpath1效率是xpath2效率的2倍到3倍

2.效率与节点层数的关系
“/”与节点层数影响不大，“//”与节点层数影响很大，我理解“/”可以迅速定位，而“//”需要查找整个xml文件

3.效率与记录集的关系

String xpath1="/broadcast/item[@sendId=\"99\" and @receiveId=\"100\" and @resId=\"200\"]"; //记录单一
String xpath2="/broadcast/contentList/item[@sendId=\"20742\" and @receiveId=\"4413033\" and @resId=\"0\"]";//记录多条
String xpath3="/broadcast/contentList/item";

在程序找到记录后，不做任何事情情况下，即光从xpath查找的效率考虑，此三个表达式效率相差不大，我理解是此三个表达式都需要查找所有的item节点。
这结果也同样适合与“//”

4.“//”使用效率

String xpath1="//item[@sendId=\"99\" and @receiveId=\"100\" and @resId=\"200\"]";
String xpath2="//contentList/item[@sendId=\"99\" and @receiveId=\"100\" and @resId=\"200\"]";

"//"定位越准确，效率会稍微提高点

5.xpath二次查找效率问题   
即把一个xpath路径，分为二次查找，第一次查出xml中的部分节点，然后在查找出的节点下，查处所有的记录集   

String xpath1="/broadcast/contentList/item[@sendId=\"20742\" and @receiveId=\"4413033\" and @resId=\"0\"]";
//String xpath1="/broadcast/contentList/item";

String path1="/broadcast";        
//String path2="./item[@sendId=\"99\" and @receiveId=\"100\" and @resId=\"200\"]";
String path2="./contentList/item";
xpathTwice(fileName,path1,path2);

与"/"直接路径查找相比，影响不大，效率基本上相同。

测试程序：

package com.corry.test;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Date;
import java.util.Iterator;
import java.util.List;

import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.Node;
import org.dom4j.XPath;
import org.dom4j.io.OutputFormat;
import org.dom4j.io.SAXReader;
import org.dom4j.io.XMLWriter;
import org.dom4j.xpath.DefaultXPath;

/**
 * xpath dom4j效率试验
 * @author corry sun
 */
public class TestXpath {

    /**
     * @param args
     */
    public static void main(String[] args) {
        //String xpath1="/broadcast/contentList/item[@sendId=\"99\" and @receiveId=\"100\" and @resId=\"200\"]";
        //String xpath1="/broadcast/item[@sendId=\"99\" and @receiveId=\"100\" and @resId=\"200\"]";
        //String xpath1="//item[@sendId=\"99\" and @receiveId=\"100\" and @resId=\"200\"]";
        String xpath1="/broadcast/contentList/item";
        
        //String xpath1="/broadcast/contentList/item[@sendId=\"20742\" and @receiveId=\"4413033\"]";
        //String xpath1="//item[@sendId=\"20742\" and @receiveId=\"4413033\" and @resId=\"0\"]";
        testTime("E:"+ File.separator+ "opt/broadcast.xml",xpath1);

        //String xpath2="//item[@sendId=\"99\" and @receiveId=\"100\" and @resId=\"200\"]";
        //testTime("E:"+ File.separator+ "opt/broadcast.xml",xpath2);
        
        
        /**
         * dom4j visitor遍历节点\
         */
        /*Date begin=new Date();
        Document doc=readXML("E:"+ File.separator+ "opt/broadcast.xml");
        Element root=doc.getRootElement();
        root.accept(new MyVisitor());
        Date end=new Date();
        long time=end.getTime()-begin.getTime();
        System.out.println("执行使用时间为:"+time+"ms");*/
        
        /**
         * 删除节点,需要大量的时间
         */
        
        /*String deleteXPath="//broadcast/contentList/item[position()<6]";
        Document doc=readXML("E:"+ File.separator+ "opt/broadcast.xml");
        if(deleteNodes(doc,deleteXPath)){
            System.out.println("delete nodes success");
            
        }else{
            System.out.println("delete nodes false");
        }*/
        
        /**
         * xpath二次查找效率和xpath直接查找差不多
         */
        /*String fileName="E:"+ File.separator+ "opt/broadcast.xml";
        String path1="/broadcast";
        //String path2="./item[@sendId=\"99\" and @receiveId=\"100\" and @resId=\"200\"]";
        String path2="./contentList/item";
        xpathTwice(fileName,path1,path2);*/
    }
    
    /**
     * 测试xpath程序运行时间
     * @param fileName
     * @param xpath
     */
    public static void testTime(String fileName,String xpath){
        Date begin=new Date();
        
        Document doc=readXML(fileName);
        
        Iterator iter=getChildren(doc,xpath).iterator();
        while(iter.hasNext()){
            Element ele=(Element)iter.next();
            System.out.println(ele.asXML());
        }
        
        Date end=new Date();
        long time=end.getTime()-begin.getTime();
        System.out.println(xpath+",执行使用时间为:"+time+"ms");
    }
    
    /**
     * 把xpath路径为两次查找
     *
     */
    public static void xpathTwice(String fileName,String path1,String path2){
        Date begin=new Date();
        
        Document doc=readXML(fileName);
        Node node=getChild(doc,path1);
        System.out.println(node.getName());
        Iterator iter=getChildren(node,path2).iterator();
        while(iter.hasNext()){
            Element ele=(Element)iter.next();
            System.out.println(ele.asXML());
        }
        
        Date end=new Date();
        long time=end.getTime()-begin.getTime();
        System.out.println(path1+path2+",执行使用时间为:"+time+"ms");
    }
    
    /**
     * 使用dom4j的DeafaultXPath查出节点的List
     * @param fileName
     * @return
     */
    public static Document readXML(String fileName){
        Document doc = file2Document(fileName);
        return doc;
    }
    
    public static List getChildren(Object ele, String childPath) {
        if (ele == null || childPath == null)
            return null;
        XPath path = new DefaultXPath(childPath);
        return path.selectNodes(ele);
    }

    /**
     * 使用dom4j的DeafaultXPath查出某个单一节点
     * @param element
     * @param childPath
     * @return
     */
    public static Node getChild(Object element, String childPath) {
        if (element == null || childPath == null)
            return null;
        XPath path = new DefaultXPath(childPath);
        return path.selectSingleNode(element);
    }
    
    /**
     * 
     * @param doc
     * @param childPath
     * @return
     */
    public static boolean deleteNodes(Document doc,String childPath){
        if (doc == null || childPath == null)
            return false;
        Iterator iter=getChildren(doc,childPath).iterator();
        while(iter.hasNext()){
            Element ele=(Element)iter.next();
            Element parent=ele.getParent();
            parent.remove(ele);
        }
        write(doc);
        return true;
    }
    
    /**
     * 写入xml文件
     * @param doc
     */
    public static void write(Document doc){
        XMLWriter writer=null;
        OutputFormat format=OutputFormat.createPrettyPrint();
        format.setEncoding("UTF-8");
        try {
            writer=new XMLWriter(new FileWriter("E:"+ File.separator+ "opt/broadcast.xml"),format);
            writer.write(doc);
        } catch (IOException e) {
            e.printStackTrace();
        }finally{
            try {
                writer.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    
    /**
     * 删除节点
     * @param filePath
     * @return
     */
    public static Document file2Document(String filePath) {
        Document doc = null;
        FileInputStream fis = null;
        try {
            SAXReader saxReader = new SAXReader();
            saxReader.setEncoding("UTF-8");
            File f = new File(filePath);
            if (f.exists()) {
                fis = new FileInputStream(f);
                doc = saxReader.read(fis);
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            try {
                fis.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return doc;
    }
}

package com.corry.test;

import org.dom4j.Attribute;
import org.dom4j.Element;
import org.dom4j.VisitorSupport;

public class MyVisitor extends VisitorSupport {
    public void visit(Element element) {

        System.out.println("element:"+element.getName());

    }

    public void visit(Attribute attr) {

        System.out.println("attribute:"+attr.getName());

    }

} 

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