protected void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {

  response.setContentType("text/html;charset=utf-8");
  String signature=new String("signature");//微信加密签名
  String timestamp=new String("timestamp");//时间戳
  String nonce=new String("nonce");//随机数
  String echostr=new String("echostr");//随机字符串
  
  PrintWriter out=response.getWriter();
  //调用CheckUtil类
  if (CheckUtil.checkSignature(signature, timestamp, nonce)) {
   //效验成功返回一个随机字符串
   out.print(echostr);
   System.out.println("验证成功");
  }else {
   System.out.println("验证失败");
  }
  
  
 }

public class CheckUtil {
 //设置一个token的值
 private static final String token="weixin";
 //生成一个效验方法
 public static boolean checkSignature(String signature,String timestamp,String nonce){
  //排序
  String[] arr=new String[]{token,timestamp,nonce};
  Arrays.sort(arr);
  //生成字符串
  StringBuffer conter=new StringBuffer();
  for (int i = 0; i < arr.length; i++) {
   conter.append(arr[i]);
   //System.out.println(conter);
   //System.out.println(conter.append(arr));
  }
  System.out.println(conter);
  //sha1加密
  String temp=getSha1(conter.toString());
  System.out.println(temp);
  return temp.equals(signature);
 }
 
 private static String getSha1(String str) {
  if (str == null || str.length() == 0) {
   return null;
  }
  char hexDigits[] = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f','A', 'B', 'C', 'D', 'E', 'F'};
  MessageDigest mdTemp;
  try {
   mdTemp = MessageDigest.getInstance("SHA1");
   mdTemp.update(str.getBytes("UTF-8"));
   byte[] md = mdTemp.digest();
   int j = md.length;
   char buf[] = new char[j * 2];
   int k = 0;
   for (int i = 0; i < j; i++) {
    byte b0 = md[i];
    buf[k++] = hexDigits[b0 >>> 4 & 0xf];
    buf[k++] = hexDigits[b0 & 0xf];
   }
   return new String(buf);
  } catch (Exception e) {
   return null;
  }
 }
}