Q：一般登录环境中，集群中需要处理session同步问题。
A：Tomcat的session共享有节点上限问题，因此无法解决session共享问题。
A： 留一台session服务器，使用redis存储，统一管理session。√
分布式：拆分工程
集群：同一套代码

SSO是一种使用单点登录的解决方案。其实就是另外搭建一台服务器用于单点登录，没什么特别的。
以下是示例：

Controller

@Controller
public class LoginController {

    @Autowired
    private LoginService loginService;
    
    @Value("${TOKEN_KEY}")
    private String TOKEN_KEY;
    
    @RequestMapping("/page/login")
    public String showLogin(String redirect, Model model) {
        model.addAttribute("redirect", redirect);
        return "login";
    }
    
    @RequestMapping(value="/user/login", method=RequestMethod.POST)
    @ResponseBody
    public E3Result login(String username, String password,
            HttpServletRequest request, HttpServletResponse response) {
        E3Result e3Result = loginService.userLogin(username, password);
        //判断是否登录成功
        if(e3Result.getStatus() == 200) {
            String token = e3Result.getData().toString();
            //如果登录成功需要把token写入cookie
            CookieUtils.setCookie(request, response, TOKEN_KEY, token);
        }
        //返回结果
        return e3Result;
    }
}

@Controller
public class TokenController {
//需要权限，Ajax请求
    @Autowired
    private TokenService tokenService;
    @RequestMapping(value="/user/token/{token}")
    @ResponseBody
    public Object getUserByToken(@PathVariable String token, String callback) {
        E3Result result = tokenService.getUserByToken(token);
        //响应结果之前，判断是否为jsonp请求
        if (StringUtils.isNotBlank(callback)) {
            //把结果封装成一个js语句响应
            MappingJacksonValue mappingJacksonValue = new MappingJacksonValue(result);
            mappingJacksonValue.setJsonpFunction(callback);
            return mappingJacksonValue;
        }
        return result;
    }
}

ServiceImpl

@Service
public class LoginServiceImpl implements LoginService {

    @Autowired
    private TbUserMapper userMapper;
    @Autowired
    private JedisClient jedisClient;
    @Value("${SESSION_EXPIRE}")
    private Integer SESSION_EXPIRE;
    
    @Override
    public E3Result userLogin(String username, String password) {
        // 1、判断用户和密码是否正确
        //根据用户名查询用户信息
        TbUserExample example = new TbUserExample();
        Criteria criteria = example.createCriteria();
        criteria.andUsernameEqualTo(username);
        //执行查询
        List<TbUser> list = userMapper.selectByExample(example);
        if (list == null || list.size() == 0) {
            //返回登录失败
            return E3Result.build(400, "用户名或密码错误");
        }
        //取用户信息
        TbUser user = list.get(0);
        //判断密码是否正确
        if (!DigestUtils.md5DigestAsHex(password.getBytes()).equals(user.getPassword())) {
            // 2、如果不正确，返回登录失败
            return E3Result.build(400, "用户名或密码错误");
        }
        // 3、如果正确生成token。
        String token = UUID.randomUUID().toString();
        // 4、把用户信息写入redis，key：token value：用户信息
        user.setPassword(null);
        jedisClient.set("SESSION:" + token, JsonUtils.objectToJson(user));
        // 5、设置Session的过期时间
        jedisClient.expire("SESSION:" + token, SESSION_EXPIRE);
        // 6、把token返回
         
        return E3Result.ok(token);
    }

}

CookieUtils

/**
 * 
 * Cookie 工具类
 *
 */
public final class CookieUtils {

    /**
     * 得到Cookie的值, 不编码
     * 
     * @param request
     * @param cookieName
     * @return
     */
    public static String getCookieValue(HttpServletRequest request, String cookieName) {
        return getCookieValue(request, cookieName, false);
    }

    /**
     * 得到Cookie的值,
     * 
     * @param request
     * @param cookieName
     * @return
     */
    public static String getCookieValue(HttpServletRequest request, String cookieName, boolean isDecoder) {
        Cookie[] cookieList = request.getCookies();
        if (cookieList == null || cookieName == null) {
            return null;
        }
        String retValue = null;
        try {
            for (int i = 0; i < cookieList.length; i++) {
                if (cookieList[i].getName().equals(cookieName)) {
                    if (isDecoder) {
                        retValue = URLDecoder.decode(cookieList[i].getValue(), "UTF-8");
                    } else {
                        retValue = cookieList[i].getValue();
                    }
                    break;
                }
            }
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        return retValue;
    }

    /**
     * 得到Cookie的值,
     * 
     * @param request
     * @param cookieName
     * @return
     */
    public static String getCookieValue(HttpServletRequest request, String cookieName, String encodeString) {
        Cookie[] cookieList = request.getCookies();
        if (cookieList == null || cookieName == null) {
            return null;
        }
        String retValue = null;
        try {
            for (int i = 0; i < cookieList.length; i++) {
                if (cookieList[i].getName().equals(cookieName)) {
                    retValue = URLDecoder.decode(cookieList[i].getValue(), encodeString);
                    break;
                }
            }
        } catch (UnsupportedEncodingException e) {
             e.printStackTrace();
        }
        return retValue;
    }

    /**
     * 设置Cookie的值 不设置生效时间默认浏览器关闭即失效,也不编码
     */
    public static void setCookie(HttpServletRequest request, HttpServletResponse response, String cookieName,
            String cookieValue) {
        setCookie(request, response, cookieName, cookieValue, -1);
    }

    /**
     * 设置Cookie的值 在指定时间内生效,但不编码
     */
    public static void setCookie(HttpServletRequest request, HttpServletResponse response, String cookieName,
            String cookieValue, int cookieMaxage) {
        setCookie(request, response, cookieName, cookieValue, cookieMaxage, false);
    }

    /**
     * 设置Cookie的值 不设置生效时间,但编码
     */
    public static void setCookie(HttpServletRequest request, HttpServletResponse response, String cookieName,
            String cookieValue, boolean isEncode) {
        setCookie(request, response, cookieName, cookieValue, -1, isEncode);
    }

    /**
     * 设置Cookie的值 在指定时间内生效, 编码参数
     */
    public static void setCookie(HttpServletRequest request, HttpServletResponse response, String cookieName,
            String cookieValue, int cookieMaxage, boolean isEncode) {
        doSetCookie(request, response, cookieName, cookieValue, cookieMaxage, isEncode);
    }

    /**
     * 设置Cookie的值 在指定时间内生效, 编码参数(指定编码)
     */
    public static void setCookie(HttpServletRequest request, HttpServletResponse response, String cookieName,
            String cookieValue, int cookieMaxage, String encodeString) {
        doSetCookie(request, response, cookieName, cookieValue, cookieMaxage, encodeString);
    }

    /**
     * 删除Cookie带cookie域名
     */
    public static void deleteCookie(HttpServletRequest request, HttpServletResponse response,
            String cookieName) {
        doSetCookie(request, response, cookieName, "", -1, false);
    }

    /**
     * 设置Cookie的值，并使其在指定时间内生效
     * 
     * @param cookieMaxage cookie生效的最大秒数
     */
    private static final void doSetCookie(HttpServletRequest request, HttpServletResponse response,
            String cookieName, String cookieValue, int cookieMaxage, boolean isEncode) {
        try {
            if (cookieValue == null) {
                cookieValue = "";
            } else if (isEncode) {
                cookieValue = URLEncoder.encode(cookieValue, "utf-8");
            }
            Cookie cookie = new Cookie(cookieName, cookieValue);
            if (cookieMaxage > 0)
                cookie.setMaxAge(cookieMaxage);
            if (null != request) {// 设置域名的cookie
                String domainName = getDomainName(request);
                System.out.println(domainName);
                if (!"localhost".equals(domainName)) {
                    cookie.setDomain(domainName);
                }
            }
            cookie.setPath("/");
            response.addCookie(cookie);
        } catch (Exception e) {
             e.printStackTrace();
        }
    }

    /**
     * 设置Cookie的值，并使其在指定时间内生效
     * 
     * @param cookieMaxage cookie生效的最大秒数
     */
    private static final void doSetCookie(HttpServletRequest request, HttpServletResponse response,
            String cookieName, String cookieValue, int cookieMaxage, String encodeString) {
        try {
            if (cookieValue == null) {
                cookieValue = "";
            } else {
                cookieValue = URLEncoder.encode(cookieValue, encodeString);
            }
            Cookie cookie = new Cookie(cookieName, cookieValue);
            if (cookieMaxage > 0)
                cookie.setMaxAge(cookieMaxage);
            if (null != request) {// 设置域名的cookie
                String domainName = getDomainName(request);
                System.out.println(domainName);
                if (!"localhost".equals(domainName)) {
                    cookie.setDomain(domainName);
                }
            }
            cookie.setPath("/");
            response.addCookie(cookie);
        } catch (Exception e) {
             e.printStackTrace();
        }
    }

    /**
     * 得到cookie的域名
     */
    private static final String getDomainName(HttpServletRequest request) {
        String domainName = null;

        String serverName = request.getRequestURL().toString();
        if (serverName == null || serverName.equals("")) {
            domainName = "";
        } else {
            serverName = serverName.toLowerCase();
            serverName = serverName.substring(7);
            final int end = serverName.indexOf("/");
            serverName = serverName.substring(0, end);
            final String[] domains = serverName.split("\\.");
            int len = domains.length;
            if (len > 3) {
                // www.xxx.com.cn
                domainName = "." + domains[len - 3] + "." + domains[len - 2] + "." + domains[len - 1];
            } else if (len <= 3 && len > 1) {
                // xxx.com or xxx.cn
                domainName = "." + domains[len - 2] + "." + domains[len - 1];
            } else {
                domainName = serverName;
            }
        }

        if (domainName != null && domainName.indexOf(":") > 0) {
            String[] ary = domainName.split("\\:");
            domainName = ary[0];
        }
        return domainName;
    }

}