package com.artisan.example.threadLocal;
import lombok.extern.slf4j.Slf4j;
/**
 * 通常情况下都要具备三个方法  add  get  remove 
 * 特别是remove，否则容易造成内存泄漏
 * @author yangshangwei
 *
 */
@Slf4j
public class RequestHolder {
  private final static ThreadLocal<ArtisanUser>  USER_HOLDER = new ThreadLocal<ArtisanUser>();
  public static void addCurrentUser(ArtisanUser artisanUser) {
    //  将当前线程作为key, artisanUser作为value 存入ThreadLocal类的ThreadLocalMap中
    USER_HOLDER.set(artisanUser);
    log.info("将artisanUser:{} 写入到ThreadLocal",artisanUser.toString());
  }
  public static ArtisanUser getCurrentUser() {
    //  通过当前线程这个key ,获取存放在当前线程的ThreadLocalMap变量中的value
    ArtisanUser artisanUser = USER_HOLDER.get();
    log.info("从ThreadLocal中获取artisanUser:{}",artisanUser.toString());
    return artisanUser;
  }
  public static void removeCurrentUser() {
    log.info("从ThreadLocal中移除artisanUser:{}", getCurrentUser());
    //  通过当前线程这个key获取当前线程的ThreadLocalMap，从中移除value
    USER_HOLDER.remove();
  }
}

package com.artisan.interceptors;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.checkerframework.checker.index.qual.LengthOf;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;
import com.artisan.example.threadLocal.ArtisanUser;
import com.artisan.example.threadLocal.RequestHolder;
import lombok.extern.slf4j.Slf4j;
/**
 * 实现 Handlerlnterceptor接口,覆盖其对应的方法即完成了拦截器的开发
 * 
 * @author yangshangwei
 *
 */
@Slf4j
public class MyInterceptor implements HandlerInterceptor {
  /**
   * preHandle在执行Controller之前执行 
   * 返回true：继续执行处理器逻辑，包含Controller的功能 
   * 返回false：中断请求
   * 
   * 处理器执行前方法
   */
  @Override
  public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
      throws Exception {
    log.info("MyInterceptor-处理器执行前方法preHandle，返回true则不拦截后续的处理");
    // 模拟user存在session中
    ArtisanUser user = new ArtisanUser();
    user.setName("artisan");
    user.setAge(20);
    request.getSession().setAttribute("user", user);
    // 将用户信息添加到ThreadLocal中
    RequestHolder.addCurrentUser((ArtisanUser)request.getSession().getAttribute("user"));
    return true;
  }
  /**
   * postHandle在请求执行完之后渲染ModelAndView返回之前执行
   * 
   * 处理器处理后方法
   */
  @Override
  public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
      ModelAndView modelAndView) throws Exception {
  }
  /**
   * afterCompletion在整个请求执行完毕后执行,无论是否发生异常都会执行
   * 
   * 处理器完成后方法
   * 
   * 
   * 在这个方法中移除当前用户
   */
  @Override
  public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
      throws Exception {
    log.info("MyInterceptor-处理器完成后方法afterCompletion");
    RequestHolder.removeCurrentUser();
  }
}

package com.artisan.config;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
import com.artisan.interceptors.MyInterceptor;
/**
 * 实现 WebMvcConfigurer 接 口， 最后覆盖其addInterceptors方法进行注册拦截器
 * @author yangshangwei
 *
 */
// 标注为配置类
@Configuration 
public class WebConfig implements WebMvcConfigurer {
  @Override
  public void addInterceptors(InterceptorRegistry registry) {
    //  注册拦截器到 Spring MVC 机制， 然后 它会返 回 一个拦截器注册
    InterceptorRegistration regist =  registry.addInterceptor(new MyInterceptor());
    // 指定拦截匹配模式，限制拦截器拦截请求
    regist.addPathPatterns("/artisan/threadLocal/*");
  }
}

package com.artisan.controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import com.artisan.example.threadLocal.ArtisanUser;
import com.artisan.example.threadLocal.RequestHolder;
@RestController
@RequestMapping("/artisan/threadLocal")
public class ThreadLocalTestController {
  @GetMapping("/getCurrentUser")
  public ArtisanUser getCurrentUser() {
    return RequestHolder.getCurrentUser();
  }
}