【Android】SAX解析之错误纠正！！

在讲这次错误之前，先看一下下面这段代码。 【◆以下解析方法是错误的×】

import java.util.ArrayList;import java.util.List;import org.xml.sax.Attributes;import org.xml.sax.SAXException;import org.xml.sax.helpers.DefaultHandler;import android.util.Log;public class XmlHandler extends DefaultHandler{private final String TAG = this.getClass().getSimpleName();/**XML文件中标签定义*/private final String TAG_Article = "Article";private final String TAG_ArticleID = "ArticleID";private final String TAG_Title = "Title";private final String TAG_Date = "Date";private final String TAG_SmallPictures = "SmallPictures";private final String TAG_LargePictures = "LargePictures";private final String TAG_Category = "Category";private static final String TAG_HeadNote = "HeadNote";private static final String TAG_SubTitle = "SubTitle";private static final String TAG_Source = "Source";//当前正在解析的TAGprivate String currentName;//单个文章private News news = null;//文章列表private List<News>  newsList = null;//解析开始时间private long start_time;private boolean flag = false;@Overridepublic void characters(char[] ch, int start, int length)throws SAXException {super.characters(ch, start, length);if(!flag) {return;}// 取值String value = new String(ch, start, length);Log.d(TAG, "Element: " + currentName  + " Element Value: " + value);if(value != null) {if(TAG_ArticleID.equals(currentName)) {news.setArticleId(value);} else if(TAG_Title.equals(currentName)) {news.setTitle(value);} else if(TAG_Date.equals(currentName)) {news.setDate(value);} else if(TAG_Category.equals(currentName)) {news.setCategory(value);} else if(TAG_SmallPictures.equals(currentName)) {news.setSmallPicture(value);} else if(TAG_LargePictures.equals(currentName)) {news.setLargePicture(value);} else if(TAG_HeadNote.equals(currentName)) {news.setHeadNote(value);} else if(TAG_SubTitle.equals(currentName)) {news.setSubTitle(value);} else if(TAG_Source.equals(currentName)) {news.setSource(value);}}}@Overridepublic void startDocument() throws SAXException {super.startDocument();start_time = System.currentTimeMillis();newsList = new ArrayList<News>();}@Overridepublic void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {super.startElement(uri, localName, qName, attributes);this.currentName = localName;flag = true;if(TAG_Article.equals(localName)) {news = new News();}}@Overridepublic void endElement(String uri, String localName, String qName)throws SAXException {super.endElement(uri, localName, qName);flag = false;if(TAG_Article.equals(localName)) {newsList.add(news);}}@Overridepublic void endDocument() throws SAXException {super.endDocument();long end = System.currentTimeMillis();Log.d(TAG, "Parse List's Xml Cost: " + (end - start_time) + " !!");}}

Baidu 或者 Google 一下 “Android Sax 解析” ，给出的Sample无一例外都是如此。坑爹啊... 甚至连有些书籍中都是这么写的，比如《Android开发入门与实践》。（本书亲自确认过，其他书情况不详）

没错，一般情况下，这么写是可以的，而且在大多数情况下解析出来也是正确的。但是就是偶尔会出错，这个时候通常你都莫不着头脑，怎么回事? 数据没错啊，解析部分代码貌似也没问题.. 真是奇了怪了。其实问题都出在上面那段代码上！！

大家都认为 SAX 解析过程大致如下：

startDocument -> startElement ->characters ->endElement ->endDocument

没错，就是这样，startElement 读取起始标签，endElement 读取结束标签，characters 呢？当然是读取其值，这没错，但是大家都天真的以为characters 只执行一次，并且一次就读取了全部内容。错就错在这！

其实characters 是很有可能会执行多次的，当遇到内容中有回车，\t等等内容时，它很有可能就执行多次。有的人可能会说，那我没有这些是不是就只执行一次了？看下我实测结果：

【Android】SAX解析之错误纠正！！

测试用XML如下：

可以很明显的看到，在解析 <ArticleID>1000553</ArticleID> 这一段时，characters执行了两次，将内容"1000553"分两次读取.. 用上面那种方式的最终结果就是ArticleID = 00553 了。那如果你的应用需要根据这个id 进一步获取内容岂不是死翘翘了？（比如这边根据id获取新闻详细内容）

好了，废话不多说了，看下正确的写法！ 【★以下解析方法才是正确的 √ 】

import java.util.ArrayList;import java.util.List;import org.xml.sax.Attributes;import org.xml.sax.SAXException;import org.xml.sax.helpers.DefaultHandler;import android.util.Log;public class XmlHandler extends DefaultHandler{private final String TAG = this.getClass().getSimpleName();/**XML文件中标签定义*/private final String TAG_Article = "Article";private final String TAG_ArticleID = "ArticleID";private final String TAG_Title = "Title";private final String TAG_Date = "Date";private final String TAG_SmallPictures = "SmallPictures";private final String TAG_LargePictures = "LargePictures";private final String TAG_Category = "Category";private static final String TAG_HeadNote = "HeadNote";private static final String TAG_SubTitle = "SubTitle";private static final String TAG_Source = "Source";//单个文章private News news = null;//文章列表private List<News>  newsList = null;//解析开始时间private long start_time;//(1)private StringBuilder sb = new StringBuilder();@Overridepublic void characters(char[] ch, int start, int length)throws SAXException {super.characters(ch, start, length);//(2)不管在startElement到endElement的过程中，执行了多少次characters， 都会将内容添加到StringBuilder中，不会丢失内容sb.append(ch, start, length);}@Overridepublic void startDocument() throws SAXException {super.startDocument();start_time = System.currentTimeMillis();newsList = new ArrayList<News>();}@Overridepublic void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {super.startElement(uri, localName, qName, attributes);//(3) 开始收集新的标签的数据时，先清空历史数据sb.setLength(0);if(TAG_Article.equals(localName)) {news = new News();}}@Overridepublic void endElement(String uri, String localName, String qName)throws SAXException {super.endElement(uri, localName, qName);//(4)原来在characters中取值，现改在此取值String value = sb.toString();if(TAG_ArticleID.equals(localName)) {news.setArticleId(value);} else if(TAG_Title.equals(localName)) {news.setTitle(value);} else if(TAG_Date.equals(localName)) {news.setDate(value);} else if(TAG_Category.equals(localName)) {news.setCategory(value);} else if(TAG_SmallPictures.equals(localName)) {news.setSmallPicture(value);} else if(TAG_LargePictures.equals(localName)) {news.setLargePicture(value);} else if(TAG_HeadNote.equals(localName)) {news.setHeadNote(value);} else if(TAG_SubTitle.equals(localName)) {news.setSubTitle(value);} else if(TAG_Source.equals(localName)) {news.setSource(value);}if(TAG_Article.equals(localName)) {newsList.add(news);}}@Overridepublic void endDocument() throws SAXException {super.endDocument();long end = System.currentTimeMillis();Log.d(TAG, "Parse List's Xml Cost: " + (end - start_time) + " !!");}}

归纳为三点：

1.startElement的时候，new StringBuilder(); 或者sb.setLength(0); (我建议后者)
2.characters的时候，sb.append(ch, start, length);
3.endElement的时候，sb.toString(); 此时StringBuilder中的内容才是解析的结果

通过这种方法就不会再有数据离奇丢失的情况了(同时也不需要像错误方法那样再设个currentTag之类的了，逻辑繁杂了，还出错)！

希望大家可以尽早看到这篇文章，不要继续被吭了！！！

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