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Android 使用Pull方法解析XML文件的方法

 更新時(shí)間：2013年05月22日 12:04:43   作者：  
本篇文章是對(duì)Android中使用Pull方法解析XML文件的方法進(jìn)行了詳細(xì)的分析介紹，需要的朋友參考下
Pull解析方法給應(yīng)用程序完全的控制文檔該怎么樣被解析。Android中對(duì)Pull方法提供了支持的API，主要是
復(fù)制代碼 代碼如下:

org.xmlpull.v1.XmlPullParser;
org.xmlpull.v1.XmlPullParserFactory;

二個(gè)類，其中主要使用的是XmlPullParser，XmlPullParserFactory是一個(gè)工廠，用于構(gòu)建XmlPullParser對(duì)象。
應(yīng)用程序通過(guò)調(diào)用XmlPullParser.next()等方法來(lái)產(chǎn)生Event，然后再處理Event?？梢钥吹剿cPush方法的不同，Push方法是由Parser自己主動(dòng)產(chǎn)生Event，回調(diào)給應(yīng)用程序。而Pull方法是主動(dòng)的調(diào)用Parser的方法才能產(chǎn)生事件。
假如XML中的語(yǔ)句是這樣的："<author country="United States">James Elliott</author>"，author是TAG，country是ATTRIBUTE，"James Elliott"是TEXT。
要想解析文檔先要構(gòu)建一個(gè)XmlPullParser對(duì)象
復(fù)制代碼 代碼如下:

final XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
factory.setNamespaceAware(true);
final XmlPullParser parser = factory.newPullParser();

Pull解析是一個(gè)遍歷文檔的過(guò)程，每次調(diào)用next()，nextTag(), nextToken()和nextText()都會(huì)向前推進(jìn)文檔，并使Parser停留在某些事件上面，但是不能倒退。
然后把文檔設(shè)置給Parser
復(fù)制代碼 代碼如下:

parser.setInput(new StringReader("<author country=\"United States\">James Elliott</author>");

這時(shí)，文檔剛被初始化，所以它應(yīng)該位于文檔的開(kāi)始，事件應(yīng)該是START_DOCUMENT，可以通過(guò)XmlPullParser.getEventType()來(lái)獲取。然后調(diào)用next()會(huì)產(chǎn)生
START_TAG，這個(gè)事件告訴應(yīng)用程序一個(gè)標(biāo)簽已經(jīng)開(kāi)始了，調(diào)用getName()會(huì)返回"author";再next()會(huì)產(chǎn)生
TEXT事件，調(diào)用getText()會(huì)返回"James Elliott"，再next()，會(huì)產(chǎn)生
END_TAG，這個(gè)告訴你一個(gè)標(biāo)簽已經(jīng)處理完了，再next()，會(huì)產(chǎn)生
END_DOCUMENT，它告訴你整個(gè)文檔已經(jīng)處理完成了。
除了next()外，nextToken()也可以使用，只不過(guò)它會(huì)返回更加詳細(xì)的事件，比如 COMMENT, CDSECT, DOCDECL, ENTITY等等非常詳細(xì)的信息。如果程序得到比較底層的信息，可以用nextToken()來(lái)驅(qū)動(dòng)并處理詳細(xì)的事件。需要注意一點(diǎn)的是TEXT事件是有可能返回空白的White Spaces比如換行符或空格等。
另外有二個(gè)非常實(shí)用的方法nextTag()和nextText()
nextTag()--首先它會(huì)忽略White Spaces，如果可以確定下一個(gè)是START_TAG或END_TAG，就可以調(diào)用nextTag()直接跳過(guò)去。通常它有二個(gè)用處：當(dāng)START_TAG時(shí)，如果能確定這個(gè)TAG含有子TAG，那么就可以調(diào)用nextTag()產(chǎn)生子標(biāo)簽的START_TAG事件；當(dāng)END_TAG時(shí)，如果確定不是文檔結(jié)尾，就可以調(diào)用nextTag()產(chǎn)生下一個(gè)標(biāo)簽的START_TAG。在這二種情況下如果用next()會(huì)有TEXT事件，但返回的是換行符或空白符。
nextText()--它只能在START_TAG時(shí)調(diào)用。當(dāng)下一個(gè)元素是TEXT時(shí)，TEXT的內(nèi)容會(huì)返回；當(dāng)下一個(gè)元素是END_TAG時(shí)，也就是說(shuō)這個(gè)標(biāo)簽的內(nèi)容為空，那么空字串返回；這個(gè)方法返回后，Parser會(huì)停在END_TAG上。比如：
復(fù)制代碼 代碼如下:

<author>James Elliott</author>
<author></author>
<author/>

當(dāng)START_TAG時(shí)，調(diào)用nextText()，依次返回：
"James Elliott"
""(empty)
""(empty)
這個(gè)方法在處理沒(méi)有子標(biāo)簽的標(biāo)簽時(shí)很有用。比如：
復(fù)制代碼 代碼如下:

<title>What Is Hibernate</title>
<author>James Elliott</author>
<category>Web</category>

就可以用以下代碼來(lái)處理：
復(fù)制代碼 代碼如下:

        while (eventType != XmlPullParser.END_TAG) {
            switch (eventType) {
            case XmlPullParser.START_TAG:
                tag = parser.getName();
                final String content = parser.nextText();
                Log.e(TAG, tag + ": [" + content + "]");
                eventType = parser.nextTag();
                break;
            default:
                break;
            }
        }

這就要比用next()來(lái)處理方便多了，可讀性也大大的加強(qiáng)了。
最后附上一個(gè)解析XML的實(shí)例Android程序
復(fù)制代碼 代碼如下:

import java.io.IOException;
import java.io.InputStream;
import org.xmlpull.v1.XmlPullParser;
import org.xmlpull.v1.XmlPullParserException;
import org.xmlpull.v1.XmlPullParserFactory;
import android.util.Log;
public class RssPullParser extends RssParser {
    private final String TAG = FeedSettings.GLOBAL_TAG;

    private InputStream mInputStream;

    public RssPullParser(InputStream is) {
        mInputStream = is;
    }

    public void parse() throws ReaderBaseException, XmlPullParserException, IOException {
        if (mInputStream == null) {
            throw new ReaderBaseException("no input source, did you initialize this class correctly?");
        }
        final XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
        factory.setNamespaceAware(true);
        final XmlPullParser parser = factory.newPullParser();

        parser.setInput(mInputStream);
        int eventType = parser.getEventType();
        if (eventType != XmlPullParser.START_DOCUMENT) {
            throw new ReaderBaseException("Not starting with 'start_document'");
        }
        eventType = parseRss(parser);
        if (eventType != XmlPullParser.END_DOCUMENT) {
            throw new ReaderBaseException("not ending with 'end_document', do you finish parsing?");
        }
        if (mInputStream != null) {
            mInputStream.close();
        } else {
            Log.e(TAG, "inputstream is null, XmlPullParser closed it??");
        }
    }

    /**
     * Parsing the Xml document. Current type must be Start_Document.
     * After calling this, Parser is positioned at END_DOCUMENT.
     * @param parser
     * @return event end_document
     * @throws XmlPullParserException
     * @throws ReaderBaseException
     * @throws IOException
     */
    private int parseRss(XmlPullParser parser) throws XmlPullParserException, ReaderBaseException, IOException {
        int eventType = parser.getEventType();
        if (eventType != XmlPullParser.START_DOCUMENT) {
            throw new ReaderBaseException("not starting with 'start_document', is this a new document?");
        }
        Log.e(TAG, "starting document, are you aware of that!");
        eventType = parser.next();
        while (eventType != XmlPullParser.END_DOCUMENT) {
            switch (eventType) {
            case XmlPullParser.START_TAG: {
                Log.e(TAG, "start tag: '" + parser.getName() + "'");
                final String tagName = parser.getName();
                if (tagName.equals(RssFeed.TAG_RSS)) {
                    Log.e(TAG, "starting an RSS feed <<");
                    final int attrSize = parser.getAttributeCount();
                    for (int i = 0; i < attrSize; i++) {
                        Log.e(TAG, "attr '" + parser.getAttributeName(i) + "=" + parser.getAttributeValue(i) + "'");
                    }
                } else if (tagName.equals(RssFeed.TAG_CHANNEL)) {
                    Log.e(TAG, "\tstarting an Channel <<");
                    parseChannel(parser);
                }
                break;
            }
            case XmlPullParser.END_TAG: {
                Log.e(TAG, "end tag: '" + parser.getName() + "'");
                final String tagName = parser.getName();
                if (tagName.equals(RssFeed.TAG_RSS)) {
                    Log.e(TAG, ">> edning an RSS feed");
                } else if (tagName.equals(RssFeed.TAG_CHANNEL)) {
                    Log.e(TAG, "\t>> ending an Channel");    
                }
                break;
            }
            default:
                break;
            }
            eventType = parser.next();
        }
        Log.e(TAG, "end of document, it is over");
        return parser.getEventType();
    }

    /**
     * Parse a channel. MUST be start tag of an channel, otherwise exception thrown.
     * Param XmlPullParser
     * After calling this function, parser is positioned at END_TAG of Channel.
     * return end tag of a channel
     * @throws XmlPullParserException
     * @throws ReaderBaseException
     * @throws IOException
     */
    private int parseChannel(XmlPullParser parser) throws XmlPullParserException, ReaderBaseException, IOException {
        int eventType = parser.getEventType();
        String tagName = parser.getName();
        if (eventType != XmlPullParser.START_TAG || !RssFeed.TAG_CHANNEL.equals(tagName)) {
            throw new ReaderBaseException("not start with 'start tag', is this a start of a channel?");
        }
        Log.e(TAG, "\tstarting " + tagName);
        eventType = parser.nextTag();
        while (eventType != XmlPullParser.END_TAG) {
            switch (eventType) {
            case XmlPullParser.START_TAG: {
                final String tag = parser.getName();
                if (tag.equals(RssFeed.TAG_IMAGE)) {
                    parseImage(parser);
                } else if (tag.equals(RssFeed.TAG_ITEM)) {
                    parseItem(parser);
                } else {
                    final String content = parser.nextText();
                    Log.e(TAG, tag + ": [" + content + "]");
                }
                // now it SHOULD be at END_TAG, ensure it
                if (parser.getEventType() != XmlPullParser.END_TAG) {
                    throw new ReaderBaseException("not ending with 'end tag', did you finish parsing sub item?");
                }
                eventType = parser.nextTag();
                break;
            }
            default:
                break;
            }
        }
        Log.e(TAG, "\tending " + parser.getName());
        return parser.getEventType();
    }

    /**
     * Parse image in a channel.
     * Precondition: position must be at START_TAG and tag MUST be 'image'
     * Postcondition: position is END_TAG of '/image'
     * @throws IOException
     * @throws XmlPullParserException
     * @throws ReaderBaseException
     */
    private int parseImage(XmlPullParser parser) throws XmlPullParserException, IOException, ReaderBaseException {
        int eventType = parser.getEventType();
        String tag = parser.getName();
        if (eventType != XmlPullParser.START_TAG || !RssFeed.TAG_IMAGE.equals(tag)) {
            throw new ReaderBaseException("not start with 'start tag', is this a start of an image?");
        }
        Log.e(TAG, "\t\tstarting image " + tag);
        eventType = parser.nextTag();
        while (eventType != XmlPullParser.END_TAG) {
            switch (eventType) {
            case XmlPullParser.START_TAG:
                tag = parser.getName();
                Log.e(TAG, tag + ": [" + parser.nextText() + "]");
                // now it SHOULD be at END_TAG, ensure it
                if (parser.getEventType() != XmlPullParser.END_TAG) {
                    throw new ReaderBaseException("not ending with 'end tag', did you finish parsing sub item?");
                }
                eventType = parser.nextTag();
                break;
            default:
                break;
            }
        }
        Log.e(TAG, "\t\tending image " + parser.getName());
        return parser.getEventType();
    }

    /**
     * Parse an item in a channel.
     * Precondition: position must be at START_TAG and tag MUST be 'item'
     * Postcondition: position is END_TAG of '/item'
     * @throws IOException
     * @throws XmlPullParserException
     * @throws ReaderBaseException
     */
    private int parseItem(XmlPullParser parser) throws XmlPullParserException, IOException, ReaderBaseException {
        int eventType = parser.getEventType();
        String tag = parser.getName();
        if (eventType != XmlPullParser.START_TAG || !RssFeed.TAG_ITEM.equals(tag)) {
            throw new ReaderBaseException("not start with 'start tag', is this a start of an item?");
        }
        Log.e(TAG, "\t\tstarting " + tag);
        eventType = parser.nextTag();
        while (eventType != XmlPullParser.END_TAG) {
            switch (eventType) {
            case XmlPullParser.START_TAG:
                tag = parser.getName();
                final String content = parser.nextText();
                Log.e(TAG, tag + ": [" + content + "]");
                // now it SHOULD be at END_TAG, ensure it
                if (parser.getEventType() != XmlPullParser.END_TAG) {
                    throw new ReaderBaseException("not ending with 'end tag', did you finish parsing sub item?");
                }
                eventType = parser.nextTag();
                break;
            default:
                break;
            }
        }
        Log.e(TAG, "\t\tending " + parser.getName());
        return parser.getEventType();
    }
}

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