关于ThreadLocal对request和response的用法说明

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{
 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(FilterConfigfilterConfig)throwsServletException{
 
 }
}

3.InterceptorContext实体

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.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(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);
}

补充知识：利用ThreadLocal管理request和session以及用户信息，实现 Use anywhere

1.我们有时需要获取request或session中的数据的时候，首先需要获取request和session对象，这个通常是在Controller的时候当做入参获取，这样方法的入参会显得很长很臃肿的感觉。这就是的出发点，接下来就展示一下是如何实现的。

2.首先我们写个一个拦截器：WebContextFilter

package com.office.common.filter;
import java.io.IOException;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.web.filter.OncePerRequestFilter;
import com.office.common.context.WebContextHolder;
 
/**
 * webcontent信息加载到TheadLocal中
 * @author Neo
 * @date 2017年10月20日11:38:45
 */
public class WebContextFilter extends OncePerRequestFilter {
 
	public WebContextFilter() {
	}
 
	protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
			throws ServletException, IOException {
		if (request == null || response == null) {
			return;
		} else {
			WebContextHolder.setRequest(request);
			WebContextHolder.setResponse(response);
			filterChain.doFilter(request, response);
			return;
		}
	}
}

3.然后我们将写好的拦截器配置到web.xml中：

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0" xmlns="http://java.sun.com/xml/ns/javaee"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
	http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
	
	<display-name>Archetype Created Web Application</display-name>
 
	<context-param>
		<param-name>contextConfigLocation</param-name>
		<param-value></param-value>
	</context-param>
 
	<filter>
		<filter-name>encodingFilter</filter-name>
		<filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
		<init-param>
			<param-name>encoding</param-name>
			<param-value>UTF-8</param-value>
		</init-param>
		<init-param>
			<param-name>forceEncoding</param-name>
			<param-value>true</param-value>
		</init-param>
	</filter>
	<filter-mapping>
		<filter-name>encodingFilter</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>
	
	<!-- ******************************************************************* -->
	<!-- *************** webcontent信息加载到TheadLocal中 ******************** -->
	<!-- ******************************************************************* -->
	<filter>
		<filter-name>webContentFilter</filter-name>
		<filter-class>com.office.common.filter.WebContextFilter</filter-class>
	</filter>
	<filter-mapping>
		<filter-name>webContentFilter</filter-name>
		<url-pattern>/*</url-pattern><!-- /* -->
	</filter-mapping>
	<listener>
		<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
	</listener>
	
 
	<servlet>
		<servlet-name>springMVC</servlet-name>
		<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
		<init-param>
			<param-name>contextConfigLocation</param-name>
			<param-value>classpath*:applicationContext.xml</param-value>
		</init-param>
		<load-on-startup>1</load-on-startup>
	</servlet>
	<servlet-mapping>
		<servlet-name>springMVC</servlet-name>
		<url-pattern>/</url-pattern>
	</servlet-mapping>
</web-app>

4.编写一个同一个管理操作工具类：WebContextHolder

package com.office.common.context;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import com.office.common.dto.UserDTO;
 
/**
 * 上下文
 * @author Neo
 * @date 2017年10月20日11:42:57
 */
@SuppressWarnings({ "rawtypes", "unchecked" })
public class WebContextHolder {
 
	public WebContextHolder() {
	}
 
	public static String getRequestIp() {
		if (getRequest() == null)
			return null;
		HttpServletRequest request = getRequest();
		String ip = request.getHeader("X-Forwarded-For");
		if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
			if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip))
				ip = request.getHeader("Proxy-Client-IP");
			if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip))
				ip = request.getHeader("WL-Proxy-Client-IP");
			if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip))
				ip = request.getHeader("HTTP_CLIENT_IP");
			if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip))
				ip = request.getHeader("HTTP_X_FORWARDED_FOR");
			if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip))
				ip = request.getRemoteAddr();
		} else if (ip.length() > 15) {
			String ips[] = ip.split(",");
			int index = 0;
			do {
				if (index >= ips.length)
					break;
				String strIp = ips[index];
				if (!"unknown".equalsIgnoreCase(strIp)) {
					ip = strIp;
					break;
				}
				index++;
			} while (true);
		}
		return ip;
	}
 
	public static HttpServletRequest getRequest() {
		if (requestLocal == null)
			return null;
		else
			return (HttpServletRequest) requestLocal.get();
	}
 
	public static String getContextPath() {
		if (getRequest() == null)
			return null;
		else
			return (new StringBuilder()).append(getRequest().getContextPath()).append("/").toString();
	}
 
	public static String getCurrRequestURI() {
		if (getRequest() == null)
			return null;
		else
			return (new StringBuilder()).append(getRequest().getRequestURI().replace(getRequest().getContextPath(), ""))
					.append("/").toString();
	}
 
	public static HttpServletResponse getResponse() {
		if (responseLocal == null)
			return null;
		else
			return (HttpServletResponse) responseLocal.get();
	}
 
	public static HttpSession getSession() {
		if (requestLocal == null)
			return null;
		if (requestLocal.get() == null)
			return null;
		else
			return ((HttpServletRequest) requestLocal.get()).getSession();
	}
 
	public static UserDTO getLoginUserSession(Class loginUserClass) {
		if (getSession() == null)
			return null;
		Object obj = getSession().getAttribute(CURRENT_USER);
		if (obj == null)
			return null;
		else
			return (UserDTO) obj;
	}
 
	public static UserDTO getLoginUserSession() {
		return getLoginUserSession(UserDTO.class);
	}
 
	public static void createLoginUserSession(UserDTO loginUser) {
		if (loginUser != null)
			getSession().setAttribute(CURRENT_USER, loginUser);
	}
 
	public static void destroyLoginUserSession() {
		if (getLoginUserSession() != null) {
			getSession().removeAttribute(CURRENT_USER);
			getSession().invalidate();
		}
	}
 
	public static void setRequest(HttpServletRequest request) {
		if (requestLocal == null)
			requestLocal = new ThreadLocal();
		requestLocal.set(request);
	}
 
	public static void setResponse(HttpServletResponse response) {
		if (responseLocal == null)
			responseLocal = new ThreadLocal();
		responseLocal.set(response);
	}
	
 /**
  * 获取项目请求的根目录
  * 
  * @return eg:http://localhost:8080/projectName
  */
	public static String getProjectRequestRootPath() {
		HttpServletRequest request = WebContextHolder.getRequest();
		StringBuffer sb = new StringBuffer();
		sb.append(request.getScheme()).
		 append("://").
		 append(request.getServerName()).
		 append(":").
		 append(request.getServerPort()).
		 append(request.getContextPath()).
		 append("/");
		return sb.toString();
	}
 
	private static ThreadLocal requestLocal;
	private static ThreadLocal responseLocal;
	public static String CURRENT_USER = "CURRENT_USER";
 
}

5.使用展示：

//我们可以在任何地方使用这种方法取值

WebContextHolder.getRequest().getParameter("id");

以上这篇关于ThreadLocal对request和response的用法说明就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持猪先飞。