解析XML——简单直接的来。

 

================== 闲扯的话================

对于现在越来越轻量级，越来越讲究速度和接近用户的应用来说，xml 确实有点复杂了。解析起来不仅耗内存，而且很复杂。这就好像花了几千块钱买了个MS Office ，但是80% 的feature 都用不着，还白白的耗着CPU 和内存。

个人觉得，设置文件用XML 其实挺好，因为设置文件一般并不太大，而且要求可读性强，还有很多乱七八糟的需求，可以利用XML 的力量。昨天搞chrome 的设置，发现chrome 的设置文件也是使用的json ，读起来也是轻松愉快。

前阵子做了个程序，需要解析豆瓣API 调用返回的XML 。真想说一句。。。豆瓣你别用XML 了。。。至少，提供个json 版的API 调用吧。

（以上谨代表个人观点）

=================== 正文=================

解析豆瓣返回的xml ，实在是不想用DOM 这个重量级的玩意。DOM 这个玩意，说它强大好还是说它官僚好呢。我倾向于使用SAXP 解析。但是现在面 临的一个问题是，我需要根据xml 节点的名字和属性值（一个或者多个）来决定当前的值是不是我想要的。这就麻烦一点点。第一反应是考虑xpath 。后来觉 得不如自己做一个得了，权当是按需定制一个轻量级的xpath 。

首先定义XMLSearchUnit 类，这个类的实例用来描述一个需要在XML 中搜索的值，值可以是xml 节点的值，或者是节点的属性。

package com.deepnighttwo.resourceresolver.douban.resolver.utils;

import java.util.HashMap;
import java.util.Map;

import org.xml.sax.Attributes;

/**
  *
  * Represent a search task. Target could be value of a node or attribute of the
  * node.
  *
  * @author mzang
  */
public class XMLSearchUnit {

    // attribute values to be matched during search
    private Map<String, String> attributeMatchValidation = new HashMap<String, String>();

    // if target is an attribute, then set this member to be the attribute name.
    // if it is null or empty, then means the target is node value.
    private String expectedAttr;

     // xml path, format is: /node_name/node_name/...
    private String xmlPath;

    public XMLSearchUnit(String xmlPath) {
        this .xmlPath = xmlPath;
    }

    /**
     * if current node meets the search conditions or not. Meets means the path
     * is correct and the attribute value is matched.
     *
     * @param path
     * @param attributes
     * @return
     */
    public boolean match(String path, Attributes attributes) {
        if (xmlPath.equals(path) == false ) {
            return false ;
        }

        for (String key : attributeMatchValidation.keySet()) {
            String exp = attributeMatchValidation.get(key);
            String compare = attributes.getValue(key);
            if (exp.equalsIgnoreCase(compare) == false ) {
                 return false ;
            }
        }
        return true ;
    }

    public Map<String, String> getAttributeMatchValidation() {
        return attributeMatchValidation;
    }

    public void addAttributeValidation(String key, String value) {
         attributeMatchValidation.put(key, value);
    }

    public String getXmlPath() {
        return xmlPath;
    }

    public void setAttributeMatchValidation(
            Map<String, String> attributeMatchValidation) {
        this .attributeMatchValidation = attributeMatchValidation;
    }

    public String getExpectedAttr() {
        return expectedAttr;
    }

    /**
     * if target is node value, then set expectedAttr to null. if target is an
     * attribute value, set it to be the attribute name.
     *
     * @param expectedAttr
     */
    public void setExpectedAttr(String expectedAttr) {
        this .expectedAttr = expectedAttr;
    }

    /**
     * hash code can be cached if all properties are not be be changed.
     */
    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime
                * result
                + ((attributeMatchValidation == null ) ? 0
                        : attributeMatchValidation.hashCode());
        result = prime * result
                + ((expectedAttr == null ) ? 0 : expectedAttr.hashCode());
        result = prime * result + ((xmlPath == null ) ? 0 : xmlPath.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if ( this == obj)
            return true ;
        if (obj == null )
            return false ;
        if (getClass() != obj.getClass())
            return false ;
        XMLSearchUnit other = (XMLSearchUnit) obj;
        if (attributeMatchValidation == null ) {
            if (other.attributeMatchValidation != null )
                return false ;
        } else if (!attributeMatchValidation
                .equals(other.attributeMatchValidation))
            return false ;
        if (expectedAttr == null ) {
            if (other.expectedAttr != null )
                return false ;
        } else if (!expectedAttr.equals(other.expectedAttr))
            return false ;
        if (xmlPath == null ) {
            if (other.xmlPath != null )
                return false ;
        } else if (!xmlPath.equals(other.xmlPath))
            return false ;
        return true ;
    }

}

这个类比较简单。就是用一个hashmap 保待匹配的attribut 键值对，用一个字符串表示期待的attribute name ，用一个字符串表示期待的node path 。

然后就是如何在SAXP 里用到这个类的实例去搜索了。

package com.deepnighttwo.resourceresolver.douban.resolver.utils;

import java.io.InputStream;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

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;

/**
  *
  * SAXP parser working with XMLSearchUnit.
  *
  * @author mzang
  */

public class DoubanSearchParser extends DefaultHandler {

    // create and initial search units
    public static final XMLSearchUnit DETAILS_LINK_API_PATH = new XMLSearchUnit(
            "/feed/entry/id");

    public static final XMLSearchUnit DETAILS_CONTENT_PATH = new XMLSearchUnit(
            "/entry/summary");

    public static final XMLSearchUnit DETAILS_TITLE_PATH = new XMLSearchUnit(
            "/entry/title");

    public static final XMLSearchUnit DETAILS_CHINESE_NAME_PATH = new XMLSearchUnit(
            "/entry/db:attribute");

    public static final XMLSearchUnit DETAILS_RATINGE_PATH = new XMLSearchUnit(
            "/entry/gd:rating");

    public static final XMLSearchUnit DETAILS_RATINGE_RATER_COUNT_PATH = new XMLSearchUnit(
             "/entry/gd:rating");

    public static final XMLSearchUnit DETAILS_LINK_URL_PATH = new XMLSearchUnit(
            "/feed/entry/link");

    static {
        DETAILS_LINK_URL_PATH.addAttributeValidation("rel", "alternate");
        DETAILS_LINK_URL_PATH.setExpectedAttr("href");

        DETAILS_CHINESE_NAME_PATH.addAttributeValidation("lang", "zh_CN");
        DETAILS_CHINESE_NAME_PATH.addAttributeValidation("name", "aka");

        DETAILS_RATINGE_PATH.setExpectedAttr("average");

         DETAILS_RATINGE_RATER_COUNT_PATH.setExpectedAttr("numRaters");

    }

    // a map to store the XMLSearchUnit and value
    private Map<XMLSearchUnit, String> results = new HashMap<XMLSearchUnit, String>();

    // a counter of search unit. if it is 0, then all search unit finds a match
    // value and the result of the XML will be skipped.
    private int count = 0;

    private StringBuilder path = new StringBuilder();

    private static final String pathSeparater = "/";

    private XMLSearchUnit[] searchUnits;

    List<XMLSearchUnit> foundItems = new ArrayList<XMLSearchUnit>();

    /**
     * constructor, accept XML input stream, 0 or more search unit instances.
     *
     * @param input
     * @param expectedPath
     * @return
     */
     public Map<XMLSearchUnit, String> parseResults(InputStream input,
            XMLSearchUnit... expectedPath) {
        for (XMLSearchUnit search : expectedPath) {
            results.put(search, null );
        }

        searchUnits = expectedPath;

         count = expectedPath.length;

        XMLReader xmlReader = null ;
        try {
            SAXParserFactory spfactory = SAXParserFactory.newInstance();
            spfactory.setValidating( false );
            SAXParser saxParser = spfactory.newSAXParser();
            xmlReader = saxParser.getXMLReader();
            xmlReader.setContentHandler( this );
            xmlReader.parse( new InputSource(input));
        } catch (Exception e) {
            System.err.println(e);
            System.exit(1);
         }
        return results;
    }

    private void addToPath(String addPath) {
        path.append(pathSeparater).append(addPath.toLowerCase());
    }

    private void popPath() {
        int index = path.lastIndexOf(pathSeparater);
        // String removedPath = path.substring(index);
        path.delete(index, path.length());
    }

    @Override
    public void startElement(String uri, String localName, String qName,
            Attributes attributes) throws SAXException {
        foundItems.clear();
         if (count == 0) {
            return ;
        }

        // update path
        addToPath(qName);

        List<XMLSearchUnit> foundAttrItems = null ;

        // check if current node matches search units. if it is a node value
        // search, then store it in a member variable named foundItems because
        // the value of the node is known only when reaches the end of the
        // node.but for attribute search, it value is known here. So then are
        // put in a local variable list named foundAttrItems.
        for (XMLSearchUnit unit : searchUnits) {
            if (unit.match(path.toString(), attributes) == true ) {

                if (unit.getExpectedAttr() == null ) {
                    foundItems.add(unit);
                } else {
                     if (foundAttrItems == null ) {
                        foundAttrItems = new ArrayList<XMLSearchUnit>();
                    }
                    foundAttrItems.add(unit);
                }
            }
        }
        // if no attribute match, return.
        if (foundAttrItems == null ) {
            return ;
        }

        // fill search unit value using attribute value. update count.
        for (XMLSearchUnit attrUnit : foundAttrItems) {
            String attrValue = attributes.getValue(attrUnit.getExpectedAttr());
            if (results.get(attrUnit) == null ) {
                count--;
            }
            results.put(attrUnit, attrValue);
            count--;
        }
    }

    /**
     * if current node matches, the the node value is useful, store it.
     */
    @Override
    public void characters( char [] ch, int start, int length)
            throws SAXException {
        if (count == 0) {
            return ;
        }
        if (foundItems.size() == 0) {
             return ;
        }

        for (XMLSearchUnit unit : foundItems) {
            String content = new String(ch, start, length);
            if (results.get(unit) == null ) {
                count--;
            }
            results.put(unit, content);
         }
    }

    @Override
    public void endElement(String uri, String localName, String qName)
            throws SAXException {
        foundItems.clear();
        if (count == 0) {
            return ;
        }
        popPath();
    }
}