ThreadLocal對request和response的使用

記得在一篇博文中看到描述threadLocal的一句話：

ThreadLocal除了適用於多線程保證每條線程都有自己的變量副本外，還適用於在線程上下文中共享某些變量值。

這兩種說法是有區別的。前者強調的是，使用ThreadLocal對副本做保護，避免同步、加鎖，降低效率；後者強調的是，某個變量線程上下文中，A處用到、B處用到、C處用到，先在入口處set一個值，後使用ThreadLocal的get方法直接在需要用到的地方拿這個值。

項目中，最近理由cookie存值，使用到了threadLocal這個字段，自己就想去研究下，原理這裏跟後者強調的一樣，上代碼：

1.web.xml裏邊配置過濾器，攔截請求，做處理

 

<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.賦值

public class InterceptorFilter implements Filter{
	publicvoiddestroy(){
		
	}
	publicvoiddoFilter(ServletRequestrequest,ServletResponseresponse,FilterChainchain)throwsIOException,ServletException{
		HttpServletRequesthttpRequest=(HttpServletRequest)request;
		HttpServletResponsehttpResponse=(HttpServletResponse)response;
		InterceptorContext.setRequest(httpRequest);
		InterceptorContext.setResponse(httpResponse);
		try{
			chain.doFilter(request,
			response);
		}finally{
			//不管有木有出現異常，finally塊中代碼都會執行;在這裏，相當於只服務於當前請求。
			InterceptorContext.removeRequest();
			InterceptorContext.removeResponse();
		}
	}
	public void init(FilterConfigfilterConfig)throwsServletException{
		
	}
}

 

3.InterceptorContext實體

public class InterceptorContext{
	private static ThreadLocal<httpservletrequest>  _request = newThreadLocal<httpservletrequest>();
	private static ThreadLocal<httpservletresponse> _response = newThreadLocal<httpservletresponse>();
	publicstaticvoidsetRequest(HttpServletRequestrequest){
		_request.set(request);
	}
	public static HttpServletRequestgetRequest(){
		HttpServletRequestrequest=_request.get();returnrequest;
	}
	public static void removeRequest(){
		_request.remove();
	}
	public static void setResponse(HttpServletResponseresponse){
		_response.set(response);
	}
	public static HttpServletResponsegetResponse(){
		HttpServletResponseresponse=_response.get();
		return response;
	}
	public static void removeResponse(){
		_response.remove();
	}
}

 

4.項目中的開始調用。（因爲這兩個方法調用的地方太多，每次都帶一個參數也比較繁瑣，所以採用這種方式，文章開頭總結過）

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