在程序里处理简单的Email

package common;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class GetEmail {

 public static int MAXEMAILLEN = 256;
 
 /**
  * 从指定的字符串中提取Email
  *
  */
 public static String parse(String content) {
  String email = null;
  if (content==null || content.length()<1) {
   return email;
  }
  //找出含有@
  int beginPos;
  int i;
  String token = "@";
  String preHalf="";
  String sufHalf = "";
  
  beginPos = content.indexOf(token);
  if (beginPos>-1) {
   //前项扫描
   String s = null;
   i= beginPos;
   while(i>0) {
    s = content.substring(i-1,i);
    if (isLetter(s))
     preHalf = s+preHalf;
    else
     break;
    i--;
   }
   //后项扫描
   i= beginPos+1;
   while( i<content.length()) {
    s = content.substring(i,i+1);
    if (isLetter(s))
     sufHalf =  sufHalf +s;
    else
     break;
    i++;  
   }
   //判断合法性
   email = preHalf + "@" + sufHalf;
   if (email.length()>MAXEMAILLEN) {
    return null;
   }
  }
  return email;
 }
 /**
  * 判断是不是合法Email
  *
  */
 public static String isEmail(String email) {
  try {
   
   if (email==null || email.length()<1) {
    return null;
   }
   String check = "^([0-9a-zA-Z]+[_.0-9a-zA-Z-]+)@([a-zA-Z0-9-]+[.])+([a-zA-Z]{2,3})$";
   Pattern regex = Pattern.compile(check);
   Matcher matcher = regex.matcher(email);
   boolean isMatched = matcher.matches();
   if(isMatched) {
    return email;
   } else {
    return null;
   }
  } catch (RuntimeException e) {
   return null;
  }
 }
 /**
  * 判断是不是合法字符
  *
  */
 public static boolean isLetter(String c) {
  boolean result = false;
  
  if (c==null || c.length()<0)
   return false;
  //a-z 
  if (c.compareToIgnoreCase("a")>=0 && c.compareToIgnoreCase("z")<=0)
   return true;
  //0-9
  if (c.compareToIgnoreCase("0")>=0 && c.compareToIgnoreCase("9")<=0)
   return true;
  //. - _
  if (c.equals(".") || c.equals("-") || c.equals("_") )
   return true;

  return result; 
 } 
}