解析XML——简单直接的来。_JAVA_编程开发_程序员俱乐部

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================== 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();
??? }
}

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