如何保证access_token长期有效--微信公众平台开发

import javax.servlet.ServletContext;

import org.apache.log4j.Logger;
import org.springframework.web.context.ContextLoader;
import org.springframework.web.context.WebApplicationContext;

import com.alibaba.fastjson.JSONException;
import com.alibaba.fastjson.JSONObject;

public class TokenUtil {

private static final Logger logger = Logger.getLogger(MessageService.class);

public static String getAccessToken(String appId, String appSecret,String flag) {
WebApplicationContext webApplicationContext = ContextLoader.getCurrentWebApplicationContext();
ServletContext application = webApplicationContext.getServletContext();

if (application.getAttribute(flag) != null) {

WeixinAccessToken tempToken = (WeixinAccessToken) application.getAttribute(flag);

if (System.currentTimeMillis() < tempToken.getExpirationTime()) {
return tempToken.getAccessToken();
} else {
return getAccessTokenContent(appId, appSecret, application,flag);
}
}
return getAccessTokenContent(appId, appSecret, application,flag);

}

private static String getAccessTokenContent(String appId, String appSecret, ServletContext application,String flag) {
WeixinAccessToken accessTokenFromUrl = getAccessTokenFromUrl(appId, appSecret);
String accessToken = null;
if (accessTokenFromUrl != null) {
application.setAttribute(flag, accessTokenFromUrl);
accessToken = accessTokenFromUrl.getAccessToken();
logger.info("accessToken from url");
}
return accessToken;
}

public static WeixinAccessToken getAccessTokenFromUrl(String appId, String appSecret) {
String requestUrl = "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=APPID&secret=SECRET";

requestUrl = requestUrl.replace("APPID", appId);
requestUrl = requestUrl.replace("SECRET", appSecret);

JSONObject jsonObject = CommonUtil.httpsRequest(requestUrl, "GET", null);
WeixinAccessToken tokenModel = null;
if (null != jsonObject) {
try {
String access_token = jsonObject.getString("access_token");
int expires_in = jsonObject.getIntValue("expires_in");
tokenModel = new WeixinAccessToken(access_token, System.currentTimeMillis() + expires_in*1000);
} catch (JSONException e) {
logger.info("获取token失败 errcode:" + jsonObject.getIntValue("errcode") + ",errmsg:"
+ jsonObject.getString("errmsg"));
}
}
return tokenModel;
}
}

public class WeixinAccessToken {
private String accessToken;
private long expirationTime;

public WeixinAccessToken(){

}

public WeixinAccessToken(String accessToken,long expirationTime){
this.accessToken=accessToken;
this.expirationTime=expirationTime;
}

public String getAccessToken() {
return accessToken;
}
public void setAccessToken(String accessToken) {
this.accessToken = accessToken;
}
public long getExpirationTime() {
return expirationTime;
}
public void setExpirationTime(long expirationTime) {
this.expirationTime = expirationTime;
}

}