code: public static String getOauth2Url(String appId, String redirectUri) throws UnsupportedEncodingException {
  		return new StringBuffer().append("https://openauth.alipay.com/oauth2/appToAppAuth.htm?app_id=").append(appId)
  				.append("&redirect_uri=").append(URLEncoder.encode(redirectUri, "UTF-8")).toString();
  	}
docs: 应用授权URL拼装
  
  @param appId
  @param redirectUri
  @return 应用授权URL
  @throws {UnsupportedEncodingException}