(关于java执行正则的问题)看看这段代码怎么老报错

[size=large][color=green]问题代码在红色部分
问题：执行代码报错：

Exception in thread "main" java.lang.IllegalStateException: No match found ???[/color][/size]

public String getUrlStr(String urlPathStr){
String setStr = "";
StringBuffer sb = new StringBuffer();
try {
URL readsource = new URL(urlPathStr);
BufferedReader in = new BufferedReader(new InputStreamReader(readsource.openStream(),"utf-8"));

        while ((setStr = in.readLine()) != null) {
            sb.append(setStr+"\r\n");

        }
        in.close();

    } catch (MalformedURLException e) {
        // TODO 自动生成 catch 块
        e.printStackTrace();
    } catch (IOException e) {
        // TODO 自动生成 catch 块
        e.printStackTrace();
    }
    return sb.toString();//返指定Url的抓取的内容
}

[color=red]public static String getByFlagStr(String isStr){

    Pattern p = Pattern.compile("<a.*?天气.*?℃.*?</a>");
    Matcher m  = p.matcher(isStr);
    m.matches();
    if(m.find()){//启动开始匹配
        m.group();
    }
    return m.group();
}[/color]

public static void main(String[] args) {
   System.out.println(new GetUrlStr().getByFlagStr(new GetUrlStr().getUrlStr("http://3g.sina.com.cn/?vt=3&pos=103")));

}