线程封闭
线程封闭一般通过以下三个方法：
Ad-hoc线程封闭：程序控制实现，最糟糕，忽略
堆栈封闭：局部变量，无并发问题
-
ThreadLocal线程封闭：特别好的封闭方法
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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
/**
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*
* @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
*/
@Slf4j
public 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
*/
@Slf4j
public 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
*/
@SpringBootApplication
public 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http://localhost:8080/threadLocal/test，控制台输出如下：
