Java单例模式示范

package com.ricoh.rapp.ezcx.iwbservice.util;

import java.util.ArrayList;
import java.util.List;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import com.alibaba.fastjson.JSONObject;
import com.ricoh.rapp.ezcx.iwbservice.model.IwbUsage;
import com.ricoh.rapp.ezcx.iwbservice.webservice.HttpsRequest;

public class UserLoginStatusUtil {
    private final Logger logger = LoggerFactory.getLogger(UserLoginStatusUtil.class);

    private static UserLoginStatusUtil userLoginInfo;

    private IwbUsage iwbUsage;

    private List<IwbUsage> iwbUsageList;

    public static UserLoginStatusUtil instance() {
        if (userLoginInfo == null) {
            synchronized (UserLoginStatusUtil.class) {
                if (userLoginInfo == null) {
                    userLoginInfo = new UserLoginStatusUtil();
                }
            }
        }
        return userLoginInfo;
    }

    public IwbUsage getIwbUsage() {
        return iwbUsage;
    }

    public void setIwbUsage(IwbUsage iwbUsage) {
        this.iwbUsage = iwbUsage;
    }

    public List<IwbUsage> getIwbUsageList() {
        if (iwbUsageList == null) {
            iwbUsageList = new ArrayList<IwbUsage>();
        }
        return iwbUsageList;
    }

    public void setIwbUsageList(List<IwbUsage> iwbUsageList) {
        this.iwbUsageList = iwbUsageList;
    }

    public JSONObject sendHttpsReq(String ip, JSONObject requestJson) {
        // String url = "https://172.25.73.163:50005/api/v2/system";
        String url = new StringBuilder("https://").append(ip).append(":").append(Constant.HttpsConstant.REQUEST_PORT)
                .append(Constant.HttpsConstant.REQUEST_SUF_URL).toString();

        HttpsRequest request = new HttpsRequest();
        logger.info("get login status url:" + url);
        JSONObject responseJson = request.httpsRequest(url, Constant.HttpsConstant.REQUEST_METHOD,
                requestJson.toString());
        logger.info("login status https responseJson :" + responseJson);
        return responseJson;
    }

}