使用XML 就应该简单点_西西软件资讯

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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
*/
publicclass 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
*/
publicboolean match(String path, Attributes attributes) {
if (xmlPath.equals(path) ==false) {
returnfalse;
}

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

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

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

public String getXmlPath() {
return xmlPath;
}

publicvoid 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
*/
publicvoid setExpectedAttr(String expectedAttr) {
this.expectedAttr = expectedAttr;
}

/**
* hash code can be cached if all properties are not be be changed.
*/
@Override
publicint hashCode() {
finalint 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
publicboolean equals(Object obj) {
if (this== obj)
returntrue;
if (obj ==null)
returnfalse;
if (getClass() != obj.getClass())
returnfalse;
XMLSearchUnit other = (XMLSearchUnit) obj;
if (attributeMatchValidation ==null) {
if (other.attributeMatchValidation !=null)
returnfalse;
} elseif (!attributeMatchValidation
.equals(other.attributeMatchValidation))
returnfalse;
if (expectedAttr ==null) {
if (other.expectedAttr !=null)
returnfalse;
} elseif (!expectedAttr.equals(other.expectedAttr))
returnfalse;
if (xmlPath ==null) {
if (other.xmlPath !=null)
returnfalse;
} elseif (!xmlPath.equals(other.xmlPath))
returnfalse;
returntrue;
}

}

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
*/

publicclass DoubanSearchParser extends DefaultHandler {

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

publicstaticfinal XMLSearchUnit DETAILS_CONTENT_PATH =new XMLSearchUnit(
"/entry/summary");

publicstaticfinal XMLSearchUnit DETAILS_TITLE_PATH =new XMLSearchUnit(
"/entry/title");

publicstaticfinal XMLSearchUnit DETAILS_CHINESE_NAME_PATH =new XMLSearchUnit(
"/entry/db:attribute");

publicstaticfinal XMLSearchUnit DETAILS_RATINGE_PATH =new XMLSearchUnit(
"/entry/gd:rating");

publicstaticfinal XMLSearchUnit DETAILS_RATINGE_RATER_COUNT_PATH =new XMLSearchUnit(
"/entry/gd:rating");

publicstaticfinal 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.
privateint count =0;

private StringBuilder path =new StringBuilder();

privatestaticfinal 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;
}

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

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

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