天气预报是非常有用的服务，如果能在网站上集成天气预报，能极大地方便用户查询.
    寻遍了国内所有的气象站点，没找见提供Web服务的，太小气了，只能去国外找。NOAA（www.weather.gov）提供一个Web服务，但是死活连不上服务器，估计被屏蔽了，其他提供全球天气预报的有www.weather.com和yahoo， 不过weather.com的服务太麻烦，还需要注册，相比之下，yahoo的天气服务既简单又快速，只需一个http请求，然后解析返回的XML即可获得天气预报。

以北京为例，在weather.yahoo.com查找北京的城市代码为CHXX0008，对应的URL为：

http://xml.weather.yahoo.com/forecastrss?u=c&p=CHXX0008

然后，通过SAX解析返回的XML：

URL url = new URL(" http://xml.weather.yahoo.com/forecastrss?u=c&p=CHXX0008 ");
InputStream input = url.openStream();
SAXParserFactory factory = SAXParserFactory.newInstance();
factory.setNamespaceAware(false);
SAXParser parser = factory.newSAXParser();
parser.parse(input, new YahooHandler());

自己定义一个YahooHandler来响应SAX事件：

import org.xml.sax.Attributes;import org.xml.sax.SAXException;import javax.xml.parsers.SAXParserFactory;import javax.xml.parsers.SAXParser;import org.xml.sax.helpers.DefaultHandler;import java.net.URL;import java.io.InputStream;import java.util.Date;import java.util.Locale;import java.text.SimpleDateFormat;/*** For more information, please visit: http://www.crackj2ee.com* Author: Liao Xuefeng*/public class YahooHandler extends DefaultHandler {public void startElement(String uri, String localName, 
                                  String qName, Attributes attributes) throws SAXException {       if("yweather:condition".equals(qName)) {           String s_date = attributes.getValue(3);           try {Date publish = 
    new SimpleDateFormat("EEE, dd MMM yyyy hh:mm a z", Locale.US).parse(s_date);               //System.out.println("Publish: " + publish.toString());           }           catch (Exception e) {               e.printStackTrace();               throw new SAXException("Cannot parse date: " + s_date);           }       }       else if("yweather:forecast".equals(qName)) {           String s_date = attributes.getValue(1);           Date date = null;           try {           date = new SimpleDateFormat("dd MMM yyyy", Locale.US).parse(s_date);           }           catch (Exception e) {               e.printStackTrace();               throw new SAXException("Cannot parse date: " + s_date);           }           int low = Integer.parseInt(attributes.getValue(2));           int high = Integer.parseInt(attributes.getValue(3));           String text = attributes.getValue(4);           int code = Integer.parseInt(attributes.getValue(5));System.out.println("Weather: "+ text + ", low=" + low + ", high=" + high);       }       super.startElement(uri, localName, qName, attributes);   }   public static void main(String args[]){    try{URL url = new URL("http://xml.weather.yahoo.com/forecastrss?u=c&p=CHXX0008");     InputStream input = url.openStream();     SAXParserFactory factory = SAXParserFactory.newInstance();     factory.setNamespaceAware(false);     SAXParser parser = factory.newSAXParser();     parser.parse(input, new YahooHandler());   }catch(Exception e){       System.out.println(e.toString());   }  }}

运行结果：C:\java>java    YahooHandler
Weather: Mostly Cloudy, low=17, high=28
Weather: AM Clouds/PM Sun, low=16, high=26

 Yahoo会返回当天和第二天的Weather预报

OVER