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();
}
}
