場景：在Web專案中，有一些物件是經常用到的，如Session中的使用者、HttpServletRequest等，當然可以通過Spring依賴注入，但是依賴注入不方便的時候，可以通過ThreadLocal儲存每一個請求所用到的資料。

• Filter解析Session獲得使用者和HttpServletRequest

package com.yjy.filter;

import com.yjy.common.RequestHolder;
import com.yjy.model.SysUser;
import lombok.extern.slf4j.Slf4j;

import
 
 javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@Slf4j
public class LoginFilter implements Filter {

    public void init(FilterConfig filterConfig) throws ServletException {

    }

    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws
 
 IOException, ServletException {
        HttpServletRequest req = (HttpServletRequest) servletRequest;
        HttpServletResponse resp = (HttpServletResponse) servletResponse;

        SysUser sysUser = (SysUser) req.getSession().getAttribute("user");
        if (sysUser == null) {
            String path = "/signIn.jsp"
 
;
            resp.sendRedirect(path);
            return;
        }
        RequestHolder.add(sysUser);
        RequestHolder.add(req);
        filterChain.doFilter(servletRequest, servletResponse);
        return;
    }

    public void destroy() {

    }
}

• RequestHolder利用ThreadLocal儲存和獲取物件

package com.yjy.common;

import com.yjy.model.SysUser;

import javax.servlet.http.HttpServletRequest;

public class RequestHolder {

    private static final ThreadLocal<SysUser> userHolder = new ThreadLocal<SysUser>();

    private static final ThreadLocal<HttpServletRequest> requestHolder = new ThreadLocal<HttpServletRequest>();

    public static void add(SysUser sysUser) {
        userHolder.set(sysUser);
    }

    public static void add(HttpServletRequest request) {
        requestHolder.set(request);
    }

    public static SysUser getCurrentUser() {
        return userHolder.get();
    }

    public static HttpServletRequest getCurrentRequest() {
        return requestHolder.get();
    }

    public static void remove() {
        userHolder.remove();
        requestHolder.remove();
    }
}

• 獲取物件

SysUser sysUser = RequestHolder.getCurrentUser();

HttpServletRequest request = RequestHolder.getCurrentRequest();