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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亿速云。
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