session与cookie

session与cookie

cookie

会话数据保存再客户端，不能跨浏览器。

• 服务端给客户端设置cookie

  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
      //自定义cookie
      Cookie cookie = new Cookie("username", "123456");
      //cookie发送给客户端
      resp.addCookie(cookie);
  }

  浏览器请求的响应头中会带有设置cookie的信息

  

• 服务端获取客户端的cookie（同一浏览器）

  protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
      Cookie[] cookies = req.getCookies();
      if (cookies != null) {
          String username = "";
          for (int i = 0; i < cookies.length; i++) {
              if ("username".equals(cookies[i].getName())) {
                  username = cookies[i].getValue();
                  break;
              }
          }
          resp.getWriter().write("the value of username in cookie is " + username);
      } else {
          resp.getWriter().write("the cookie is null");
      }
  }

  浏览器的请求头中会带有cookie信息

  

• 设置cookie有效时长

  默认关闭浏览器后cookie失效。

  //设置cookie时长 为负数时浏览器关闭就失效，正数以秒为单位
  cookie.setMaxAge(60*3);

cookie的局限

• cookie只能存字符串类型，不能保存对象
• 只能存非中文
• 1个cookie的容量不超过4kb

session

会话数据保存再服务器端，内存中，客户端与服务端之间通讯使用sessionid。

自定义session

Cache：

public class Cache {
    
    @MetaData(name = "键", desc = "")
    private String key;
    @MetaData(name = "值", desc = "")
    private Object value;
    @MetaData(name = "有效期", desc = "")
    private Long timeout;
}

CacheManager：

public class CacheManager {

    private Map<String, Cache> cacheMap = new HashMap<>();

    public synchronized void put(String key, Object value, Long timeout) {
        Cache cache = new Cache();
        cache.setKey(key);
        cache.setValue(value);
        if (timeout != null) {
            cache.setTimeout(System.currentTimeMillis() + timeout);
        }
        cacheMap.put(key, cache);
    }

    public synchronized void put(String key, Object value) {
        put(key, value, null);
    }

    public synchronized Object get(String key) {
        if (cacheMap.containsKey(key)) {
            return cacheMap.get(key).getValue();
        }
        return null;
    }

    public synchronized void remove(String key) {
        if (cacheMap.containsKey(key)) {
            cacheMap.remove(key);
        }
    }
	
    //检查并移除超期缓存
    public synchronized void checkValidityData() {
        for (Map.Entry<String, Cache> entry : cacheMap.entrySet()) {
            Cache cache = entry.getValue();
            if (cache == null) {
                continue;
            }
            Long timeout = cache.getTimeout();
            Long now = System.currentTimeMillis();
            if (now > timeout) {
                remove(entry.getKey());
            }
        }
    }
}

TokenUtil：

public class TokenUtil {

    public static String getToken() {
        return UUID.randomUUID().toString();
    }
}

SessionUtil：

public class SessionUtil {

    private static final CacheManager cacheManager = new CacheManager();

    public static String setAtttibute(Object value) {
        String sessionId = TokenUtil.getToken();
        cacheManager.put(sessionId, value);
        return sessionId;
    }

    public static Object getAtttibute(String key) {
        return cacheManager.get(key);
    }

}