java随记

观察者模式:从任意数据结构生成XML解析器产生SAX事件

在j2ee1.4标准教材里看到一个很有趣的例子,从任意数据结构生成XML解析器产生SAX事件.数据结构可以是文本文件,PDF格式文档等.关键是自己解析这些数据源.另外一个有意思的地方是观察者模式的应用.所以就粗糙的改了一下并完整到可以测试运行.观察者模式简略UML图:

具体实现 被观察者对象ParseXMLSubject类:
package test;

import java.io.*;
import org.xml.sax.helpers.AttributesImpl;
import org.xml.sax.*;

public class ParseXMLSubject implements XMLReader {
    ContentHandler handler;

    String nsu = "";
    Attributes atts = new AttributesImpl();
    String rootElement = "addressbook";
    String indent = "\n    ";

    public ParseXMLSubject(){

    }

    public ContentHandler getContentHandler() {
        return handler;
    }

    public void parse(InputSource input) throws IOException, SAXException {
        try {
            // Get an efficient reader for the file
            java.io.Reader r = input.getCharacterStream();
            BufferedReader br = new BufferedReader(r);

            // Read the file and display it's contents.
            String line = br.readLine();

            while (null != (line = br.readLine())) {
                if (line.startsWith("email:")) {
                    break;
                }
            }

            if (handler == null) {
                throw new SAXException("No content handler");
            }

            // Note:
            // We're ignoring setDocumentLocator(), as well
            handler.startDocument();
            handler.startElement(nsu, rootElement, rootElement, atts);

            output("email",  line);
            line = br.readLine();
            output("html", line);
            line = br.readLine();
            output("firstname",  line);
            line = br.readLine();
            output("lastname", line);
            line = br.readLine();
            output("work",  line);
            line = br.readLine();
            output("home", line);
            line = br.readLine();
            output("fax",  line);
            line = br.readLine();
            output("pager", line);
            line = br.readLine();
            output("cell",  line);
            handler.ignorableWhitespace("\n".toCharArray(), 0, // start index
                                        1 // length
                    );
            handler.endElement(nsu, rootElement, rootElement);
            handler.endDocument();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void parse(String systemId) throws IOException, SAXException {
    }

    public DTDHandler getDTDHandler() {
        return null;
    }

    public EntityResolver getEntityResolver() {
        return null;
    }

    public ErrorHandler getErrorHandler() {
        return null;
    }

    public boolean getFeature(String name) throws SAXNotRecognizedException,
            SAXNotSupportedException {
        return false;
    }

    public Object getProperty(String name) throws SAXNotRecognizedException,
            SAXNotSupportedException {
        return null;
    }

    public void setContentHandler(ContentHandler handler) {
        this.handler = handler;
    }

    public void setDTDHandler(DTDHandler handler) {
    }

    public void setEntityResolver(EntityResolver resolver) {
    }

    public void setErrorHandler(ErrorHandler handler) {
    }

    public void setFeature(String name, boolean value) throws
            SAXNotRecognizedException, SAXNotSupportedException {
    }

    public void setProperty(String name, Object value) throws
            SAXNotRecognizedException, SAXNotSupportedException {
    }

    void output(String name, String line) throws SAXException {
        int tmp = name.length();
        int startIndex=tmp+1;
        int textLength = line.length() - startIndex;
        String characters = line.substring(startIndex,line.length()-1);
        handler.ignorableWhitespace(indent.toCharArray(), 0, // start index
                                    indent.length());
        handler.startElement(nsu, name, name /*"qName"*/, atts);

        handler.characters(characters.toCharArray(), startIndex, textLength);
        handler.endElement(nsu, name, name);
    }

}

具体观察者对象: ConcreateObserver类
package test;

import org.xml.sax.helpers.DefaultHandler;
import org.xml.sax.*;
public class ConcreateObserver extends DefaultHandler {
    public ConcreateObserver() {
    }

    public void startElement(String uri,
                         String localName,
                         String qName,
                         Attributes attributes)
                  throws SAXException{
              System.out.println("startElement: "+localName);
          }
          public void characters(char[] ch,
                                 int start,
                                 int length)
                throws SAXException{
            System.out.println("characters: ");
            System.out.print(ch);
            System.out.println();
        }
}

测试类:TestMain
package test;
import java.io.*;
import org.xml.sax.InputSource;
public class TestMain {
    public TestMain() {
    }

    public static void main(String[] args) throws Exception {
        TestMain testmain = new TestMain();
        FileReader in = new FileReader(new File("d:\\AddressBookReaderLog01.txt"));

        ConcreateObserver observer=new ConcreateObserver();
        ParseXMLSubject parse = new ParseXMLSubject();
        parse.setContentHandler(observer);

        parse.parse(new InputSource(in));
    }
}

测试文本文档:AddressBookReaderLog01.txt

AddressBookReader01 ../samples/PersonalAddressBook.ldif
nickname: Fred
email: fred@barneys.house
html: TRUE
firstname: Fred
lastname: Flintstone
work: 999-Quarry
home: 999-BedrockLane
fax: 888-Squawk
pager: 777-pager
cell: 555-cell

另外一个也比较也有意思的地方就是具体观察者类从DefaultHandler 继承,该类是缺省适配器模式的应用.
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posted on 2006-08-07 09:16 傻 瓜 阅读(1565) 评论(0)  编辑  收藏 所属分类: jaxp xml