Android - 使用 SAXParser 的通用 XML 解析器

Question

我需要编写一个可以在整个 Android 应用程序中重用的 XML 解析类，据我所知，SAXParser 对于移动应用程序来说是最好的。我正在使用本指南：

http://www.jondev.net/articles/Android_XML_SAX_Parser_Example

我希望解析的文档类型是来自 Blogger GData API 的提要 - 示例是：

<?xml version='1.0' encoding='UTF-8'?>
<?xml-stylesheet href="http://www.blogger.com/styles/atom.css" type="text/css"?>
<feed xmlns='http://www.w3.org/2005/Atom' xmlns:openSearch='http://a9.com/-/spec/opensearch/1.1/' xmlns:gd='http://schemas.google.com/g/2005' gd:etag='W/&quot;CUIGRnc4fyp7ImA9Wx9SEEg.&quot;'>
    <id>tag:blogger.com,1999:user-464300745974.blogs</id>
    <updated>2010-11-29T17:58:47.937Z</updated>
    <title>Tim's Blogs</title>
    <link rel='http://schemas.google.com/g/2005#feed' type='application/atom+xml' href='http://www.blogger.com/feeds/blogid/blogs'/>
    <link rel='self' type='application/atom+xml' href='http://www.blogger.com/feeds/blogid/blogs'/>
    <link rel='alternate' type='text/html' href='http://www.blogger.com/profile/blogid'/>
    <author>
        <name>Tim</name>
        <uri>http://www.blogger.com/profile/blogid</uri>
        <email>[email protected]</email>
    </author>
    <generator version='7.00' uri='http://www.blogger.com'>Blogger</generator>
    <openSearch:totalResults>2</openSearch:totalResults>
    <openSearch:startIndex>1</openSearch:startIndex>
    <openSearch:itemsPerPage>25</openSearch:itemsPerPage>
    <entry gd:etag='W/&quot;DUIBQHg-cCp7ImA9Wx9TF0s.&quot;'>
        <id>tag:blogger.com,1999:user-464300745974.blog-blogid</id>
        <published>2010-06-22T10:59:38.603-07:00</published>
        <updated>2010-11-26T02:32:31.658-08:00</updated>
        <title>Application Testing Blog</title>
        <summary type='html'>This blog is for testing the Android application.</summary>
        <link rel='self' type='application/atom+xml' href='http://www.blogger.com/feeds/blogid/blogs/blogid'/>
        <link rel='alternate' type='text/html' href='http://devrum.blogspot.com/'/>
        <link rel='http://schemas.google.com/g/2005#feed' type='application/atom+xml' href='http://devrum.blogspot.com/feeds/posts/default'/>
        <link rel='http://schemas.google.com/g/2005#post' type='application/atom+xml' href='http://www.blogger.com/feeds/blogid/posts/default'/>
        <link rel='http://schemas.google.com/blogger/2008#template' type='application/atom+xml' href='http://www.blogger.com/feeds/blogid/template'/>
        <link rel='http://schemas.google.com/blogger/2008#settings' type='application/atom+xml' href='http://www.blogger.com/feeds/blogid/settings'/>
        <author>
            <name>Tim</name>
            <uri>http://www.blogger.com/profile/blogid</uri>
            <email>[email protected]</email>
        </author>
    </entry>
    <entry gd:etag='W/&quot;C08HRXo4eSp7ImA9Wx9TE0o.&quot;'>
        <id>tag:blogger.com,1999:user-464300745974.blog-515600026106499737</id>
        <published>2010-06-22T10:59:00.328-07:00</published>
        <updated>2010-11-21T12:37:14.431-08:00</updated>
        <title>Development Blog</title>
        <summary type='html'>etc</summary>
        <link rel='self' type='application/atom+xml' href='http://www.blogger.com/feeds/blogid/blogs/515600026106499737'/>
        <link rel='alternate' type='text/html' href='http://rumdev.blogspot.com/'/>
        <link rel='http://schemas.google.com/g/2005#feed' type='application/atom+xml' href='http://rumdev.blogspot.com/feeds/posts/default'/>
        <link rel='http://schemas.google.com/g/2005#post' type='application/atom+xml' href='http://www.blogger.com/feeds/515600026106499737/posts/default'/>
        <link rel='http://schemas.google.com/blogger/2008#template' type='application/atom+xml' href='http://www.blogger.com/feeds/515600026106499737/template'/>
        <link rel='http://schemas.google.com/blogger/2008#settings' type='application/atom+xml' href='http://www.blogger.com/feeds/515600026106499737/settings'/>
        <author>
            <name>Tim</name>
            <uri>http://www.blogger.com/etc</uri>
            <email>[email protected]</email>
        </author>
    </entry>
</feed>

我需要从上述提要中解析博客 ID 和帖子 ID。从我在 SAX 上找到的任何示例来看，它们根本不是通用的。我想写一个可重用的，您有任何示例如何相应地修改 SAXParser 吗？

Answer 1

SAX 解析器是事件驱动的解析器。您为每个类型的 XML 节点（开始元素、结束元素、属性、文本等）编写一个处理程序，然后解析器迭代 XML 文档，并将 SAX 事件发送给您（= 处理程序中的方法被调用）。

在您的特定情况下，您正在寻找两个节点序列：

所以您必须在处理程序中存储一些状态信息以了解您所在的位置。这是代码（我自己没有尝试过，你必须调试它）：

public class DataHandler extends DefaultHandler {

    private Feed feed;
    private Entry currentEntry;
    private boolean isId = false;

    public Feed getFeed() {
        return feed;
    }

    @Override
    public void startElement(String namespaceURI, String localName, String qName, Attributes atts) throws SAXException {
        if (localName.equals("feed")) {
            feed = new Feed();
        } else if (localName.equals("entry")) {
            currentEntry = new Entry();
        } else if (localName.equals("id")) {
            isId = true;
        }
    }

    @Override
    public void endElement(String namespaceURI, String localName, String qName) throws SAXException {
        if (localName.equals("feed")) {
            // </feed> - do nothing, it's the end
        } else if (localName.equals("entry")) {
            // </entry> - save current entry and reset variable
            feed.entries.add(currentEntry);
            currentEntry = null;
        } else if (localName.equals("id")) {
             isId = false;
        }
    }

    @Override
    public void characters(char ch[], int start, int length) {
        if(!isId) return;

        String chars = new String(ch, start, length);
        chars = chars.trim();

        if (currentEntry != null) {
            currentEntry.id = chars;
        } else {
            feed.id = chars;
        }
    }

    private class Feed {
        public String id;
        public List<Entry> entries = new ArrayList<Entry>();
    }

    private class Entry {
        public String id;
    }
}

Answer 2

尝试按照以下方式进行操作：

public class XmlParser extends DefaultHandler{
    private static final int        STATE_FEED      = 0;
    private static final int        STATE_ID        = 1;
    private static int          sDepth          = 0;
    private static int          sCurrentState   = 0;
    private String              mTheString;
public XmlParser(){}

@Override
public void startDocument() throws SAXException{}

@Override
public void endDocument() throws SAXException{}

@Override
public void startElement(String namespaceURI, String localName, String qName, Attributes atts) throws SAXException{
    mTheString = "";
    sDepth++;
    if (qName.equals("feed")){
        sCurrentState = STATE_FEED;
        return;
    }
    if (qName.equals("id")){
                    sCurrentState = STATE_ID;
            return;
    }
    sCurrentState = 0;
}

@Override
public void endElement(String namespaceURI, String localName, String qName) throws SAXException{
    sDepth--;
        switch (sCurrentState){
            case STATE_FEED:
                                   //Do something with the feed
                sCurrentState = 0;
                mTheString = "";
                break;
            case STATE_ID:
                // Save the ID or do whatever
                sCurrentState = 0;
                mTheString = "";
                break;
            default:
                //Do nothing
                mTheString = "";
                return;
        }
        mTheString = "";
}

@Override
public void characters(char ch[], int start, int length){
      mTheString = mTheString + new String(ch, start, length);
}

}

您可以使用如下方式访问自定义 SAXParser：

InputStream stream = //whatever your stream is (the document)
XmlParser handler = new XmlParser(); // your custom parser
XMLReader xmlreader = XMLReaderFactory.createXMLReader();
xmlreader.setContentHandler(handler); 
xmlreader.parse(new InputSource(stream));
   // Then you can create a method in the handler, like getResults to return the list of elements or something here.

因此，您将自定义解析器传递到 Xml Reader 中，并从源中获取结果。在 Xml 解析期间，处理程序从“起始文档”开始，然后迭代 xml 中的元素（在开头调用 startElement，在开头调用 endElement）。在这两者之间调用字符方法 - 拾取字符（然后您可以在 endElement 中执行任何您想要的操作）。解析器在调用 endDocument 时完成，因此您可以根据需要在元素或整个文档的开头和结尾处进行设置和拆除。

希望这会有所帮助，并且接近您想要做的事情。