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解析XML (很给力)

XML是一种简单的数据存储语言,使用一系列简单的标记描述数据,而这些标记可以用方便的方式建立,虽然XML占用的空间比二进制数据要占用更多的空间,但XML极其简单易于掌握和使用。本文解析XML,分享给大家!

==================作者有话================

xml确实有点复杂,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。

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.H ashMap;
import java.util.Map;

import org.xml.sax.Attributes;

/**
*
* Represent a search task. Tar get 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 sk ipped.
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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