ThreadLocal对request和response的使用

记得在一篇博文中看到描述threadLocal的一句话：

ThreadLocal除了适用于多线程保证每条线程都有自己的变量副本外，还适用于在线程上下文中共享某些变量值。

这两种说法是有区别的。前者强调的是，使用ThreadLocal对副本做保护，避免同步、加锁，降低效率；后者强调的是，某个变量线程上下文中，A处用到、B处用到、C处用到，先在入口处set一个值，后使用ThreadLocal的get方法直接在需要用到的地方拿这个值。

项目中，最近理由cookie存值，使用到了threadLocal这个字段，自己就想去研究下，原理这里跟后者强调的一样，上代码：

1.web.xml里边配置过滤器，拦截请求，做处理

<filter> <filter-name>InterceptorFilter</filter-name> <filter-class>com.fx.anniversary.core.filter.InterceptorFilter</filter-class> </filter> <filter-mapping> <filter-name>InterceptorFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping>

2.赋值

public class InterceptorFilter implements Filter {public void destroy() {}public void doFilter(ServletRequest request, ServletResponse response,FilterChain chain) throws IOException, ServletException {HttpServletRequest httpRequest = (HttpServletRequest)request;HttpServletResponse httpResponse = (HttpServletResponse)response;InterceptorContext.setRequest(httpRequest);InterceptorContext.setResponse(httpResponse);try{chain.doFilter(request, response);}finally{ //不管有木有出现异常，finally块中代码都会执行;在这里，相当于只服务于当前请求。InterceptorContext.removeRequest();InterceptorContext.removeResponse();}}public void init(FilterConfig filterConfig) throws ServletException {}}

3.InterceptorContext实体

public class InterceptorContext {private static ThreadLocal<httpservletrequest> _request = new ThreadLocal<httpservletrequest>();private static ThreadLocal<httpservletresponse> _response = new ThreadLocal<httpservletresponse>();public static void setRequest(HttpServletRequest request) {_request.set(request);}public static HttpServletRequest getRequest() {HttpServletRequest request = _request.get();return request;}public static void removeRequest() {_request.remove();}public static void setResponse(HttpServletResponse response) {_response.set(response);}public static HttpServletResponse getResponse() {HttpServletResponse response = _response.get();return response;}public static void removeResponse() {_response.remove();}}</httpservletresponse></httpservletresponse></httpservletrequest></httpservletrequest>

4.项目中的开始调用。（因为这两个方法调用的地方太多，每次都带一个参数也比较繁琐，所以采用这种方式，文章开头总结过）

public String getAttribute(String key) {HttpServletRequest request = InterceptorContext.getRequest();Cookie[] cookies = request.getCookies();if(cookies != null){for(Cookie cookie : cookies){if(cookie.getName().equals(key)){return cookie.getValue();}}}return "";}@Overridepublic void setAttribute(String key,String value){HttpServletResponse response = InterceptorContext.getResponse();Cookie cookie = new Cookie(key,value);response.addCookie(cookie);}