自定义过滤器和拦截器实现ThreadLocal线程封闭

线程封闭

线程封闭一般通过以下三个方法：

1. Ad-hoc线程封闭：程序控制实现，最糟糕，忽略
2. 堆栈封闭：局部变量，无并发问题
3. ThreadLocal线程封闭：特别好的封闭方法

方法2是最常用的，变量定义在接口内，本文主要讲解方法三，SpringBoot项目通过自定义过滤器和拦截器实现ThreadLocal线程封闭。实现Filter接口自定义过滤器和继承HandlerInterceptorAdapter自定义拦截器。

ThreadLocal线程封闭实现步骤

封装ThredLocal的方法

/** * <p>自定义RequestHolder</p></p> * * @Author zjq * @Date 2021/12 */public class RequestHolder {    private final static ThreadLocal<Long> requestHolder = new ThreadLocal<>();    public static void set(Long id) {        requestHolder.set(id);    }    public static Long get() {        return requestHolder.get();    }    public static void remove() {        requestHolder.remove();    }}

自定义过滤器

自定义定义拦截器继承Filter接口，实现ThredLocal.add()方法

/** * <p>自定义过滤器</p> * * @Author zjq * @Date 2021/12/7 */@Slf4jpublic class HttpFilter implements Filter {    /** * 为Filter初始化 提供支持 * * @param filterConfig * @throws ServletException */    @Override    public void init(FilterConfig filterConfig) throws ServletException {    }    /** * 拦截到要执行的请求时，doFilter就会执行。这里我们可以写对请求和响应的预处理。 * FilterChain把请求和响应传递给下一个 Filter处理 * * @param servletRequest * @param servletResponse * @param filterChain * @throws IOException * @throws ServletException */    @Override    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {        //把普通servlet强转成httpServlet        HttpServletRequest httpServletRequest = (HttpServletRequest) servletRequest;        Long threadId = Thread.currentThread().getId();        log.info("do filter,threadId:{} servletPath:{}", threadId, httpServletRequest.getServletPath());        //把当前线程id放入requestHolder        RequestHolder.set(threadId);        //放行        filterChain.doFilter(httpServletRequest, servletResponse);    }    /** * Filter 实例销毁前的准备工作 */    @Override    public void destroy() {    }}

自定义拦截器

自定义拦截器在线程使用完毕后移除ThredLocal中内容，避免内存溢出

/** * <p>自定义拦截器</p> * * @Author zjq * @Date 2021/12/7 */@Slf4jpublic class HttpInterceptor extends HandlerInterceptorAdapter {    /** * 拦截处理程序的执行。在 HandlerMapping 确定合适的处理程序对象之后，在 HandlerAdapter 调用处理程序之前调用。 * @param request * @param response * @param handler * @return * @throws Exception */    @Override    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {        log.info("preHandle执行。。。");        return true;    }    /** * 请求处理完成后（渲染视图后）的回调。将在处理程序执行的任何结果上调用，从而允许进行适当的资源清理。 * @param request * @param response * @param handler * @param ex * @throws Exception */    @Override    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {        RequestHolder.remove();        log.info("afterCompletion执行。。。");        return;    }}

Application类启动类中配置自定义过滤器和拦截器

/** * * @author zjq */@SpringBootApplicationpublic class Application extends WebMvcConfigurationSupport {    public static void main(String[] args) {        SpringApplication.run(ConcurrencyApplication.class, args);    }    /** * 自定义过滤器 * @return */    @Bean    public FilterRegistrationBean filterRegistrationBean(){        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();        filterRegistrationBean.setFilter(new HttpFilter());        //设置自定义过滤器拦截的url        filterRegistrationBean.addUrlPatterns("/threadLocal/*");        return filterRegistrationBean;    }    /** * 定义自定义拦截器原先需要继承WebMvcConfigurerAdapter * SpringBoot2.0后WebMvcConfigurerAdapter被定义成过时了，推荐使用继承WebMvcConfigurationSupport * @param registry */    @Override    public void addInterceptors(InterceptorRegistry registry) {        registry.addInterceptor(new HttpInterceptor()).addPathPatterns("/**");    }}

定义调用接口

/** * ThreadLocal测试controller * @author zjq */@Controller@RequestMapping("/threadLocal")public class ThreadLocalController {    @RequestMapping("/test")    @ResponseBody    public Long test() {        return RequestHolder.get();    }}

请求访问验证

访问调用接口，控制台输出如下：