Pattern p = Pattern.compile("a*b");
 Matcher m = p.matcher("aaaaab");
 boolean b = m.matches();

public static void getDemo()
{
  String str = "da jia zhu yi le,ming tian bu fang jia,xie xie!";
  //想要获取由3个字母组成的单词。
  //刚才的功能返回的都是一个结果，只有split返回的是数组，但是它是把规则作为分隔符，不会获取符合规则的内容。
  //这时我们要用到一些正则对象。
  String reg = "\\b[a-z]{3}\\b";
  Pattern p = Pattern.compile(reg);
  Matcher m = p.matcher(str);
  while(m.find())
  {
    System.out.println(m.start()+"...."+m.end());
    System.out.println("sub:"+str.substring(m.start(),m.end()));
    System.out.println(m.group());
  }
//   System.out.println(m.find());//将规则对字符串进行匹配查找。
//   System.out.println(m.find());//将规则对字符串进行匹配查找。
//   System.out.println(m.group());//在使用group方法之前，必须要先找，找到了才可以取。
}

public static void checkMail()
{
  String mail = "abc123@sina.com.cn";
  mail = "1@1.1";
  String reg = "[a-zA-Z_0-9]+@[a-zA-Z0-9]+(\\.[a-zA-Z]+)+";
  reg = "\\w+@\\w+(\\.\\w+)+";//简化的规则。笼统的匹配。
  boolean b = mail.matches(reg);
  System.out.println(mail+":"+b);
}

class GetMailList 
{
public static void main(String[] args) throws Exception
{
  String reg = "\\w+@[a-zA-Z]+(\\.[a-zA-Z]+)+";
  getMailsByWeb(reg);
}
public static void getMailsByWeb(String regex)throws Exception
{
  URL url = new URL("http://localhost:8080/myweb/mail.html");
  URLConnection conn = url.openConnection();
  BufferedReader bufIn = new BufferedReader(new InputStreamReader(conn.getInputStream()));
  String line = null;
  Pattern p = Pattern.compile(regex);   
  while((line=bufIn.readLine())!=null)
  {
    //System.out.println(line);
    Matcher m = p.matcher(line);
    while(m.find())
    {
      System.out.println(m.group());
    }
  }
  bufIn.close();
}
public static void getMails(String regex)throws Exception
{
  BufferedReader bufr = 
    new BufferedReader(new FileReader("mail.txt"));
  String line = null;
  Pattern p = Pattern.compile(regex);   
  while((line=bufr.readLine())!=null)
  {
    //System.out.println(line);
    Matcher m = p.matcher(line);
    while(m.find())
    {
      System.out.println(m.group());
    }
  }
  bufr.close();
}
}