Java自定義過濾器和攔截器實現ThreadLocal執行緒封閉

2022-08-05 14:00:05

執行緒封閉

執行緒封閉一般通過以下三個方法：

Ad-hoc執行緒封閉：程式控制實現，最糟糕，忽略
堆疊封閉：區域性變數，無並行問題
ThreadLocal執行緒封閉：特別好的封閉方法

方法2是最常用的，變數定義在介面內，本文主要講解方法三，SpringBoot專案通過自定義過濾器和攔截器實現ThreadLocal執行緒封閉。實現Filter介面自定義過濾器和繼承HandlerInterceptorAdapter自定義攔截器。

ThreadLocal執行緒封閉實現步驟

封裝ThredLocal的方法

/**
 * <p>自定義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();
    }

}

自定義過濾器

自定義定義攔截器繼承Filter介面，實現ThredLocal.add()方法

/**
 * <p>自定義過濾器</p>
 *
 * @Author zjq
 * @Date 2021/12/7
 */
@Slf4j
public class HttpFilter implements Filter {

    /**
     * 為Filter初始化 提供支援
     *
     * @param filterConfig
     * @throws ServletException
     */
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {

    }

    /**
     * 攔截到要執行的請求時，doFilter就會執行。這裡我們可以寫對請求和響應的預處理。
     * FilterChain把請求和響應傳遞給下一個 Filter處理
     *
     * @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強轉成httpServlet
        HttpServletRequest httpServletRequest = (HttpServletRequest) servletRequest;
        Long threadId = Thread.currentThread().getId();
        log.info("do filter,threadId:{} servletPath:{}", threadId, httpServletRequest.getServletPath());
        //把當前執行緒id放入requestHolder
        RequestHolder.set(threadId);
        //放行
        filterChain.doFilter(httpServletRequest, servletResponse);
    }

    /**
     * Filter 範例銷燬前的準備工作
     */
    @Override
    public void destroy() {

    }
}

自定義攔截器

自定義攔截器線上程使用完畢後移除ThredLocal中內容，避免記憶體溢位

/**
 * <p>自定義攔截器</p>
 *
 * @Author zjq
 * @Date 2021/12/7
 */
@Slf4j
public class HttpInterceptor extends HandlerInterceptorAdapter {

    /**
     * 攔截處理程式的執行。在 HandlerMapping 確定合適的處理程式物件之後，在 HandlerAdapter 呼叫處理程式之前呼叫。
     * @param request
     * @param response
     * @param handler
     * @return
     * @throws Exception
     */
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        log.info("preHandle執行。。。");
        return true;
    }

    /**
     * 請求處理完成後（渲染檢視後）的回撥。將在處理程式執行的任何結果上呼叫，從而允許進行適當的資源清理。
     * @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執行。。。");
        return;
    }
}

Application類啟動類中設定自定義過濾器和攔截器

/**
 * 
 * @author zjq
 */
@SpringBootApplication
public class Application extends WebMvcConfigurationSupport {

    public static void main(String[] args) {
        SpringApplication.run(ConcurrencyApplication.class, args);
    }

    /**
     * 自定義過濾器
     * @return
     */
    @Bean
    public FilterRegistrationBean filterRegistrationBean(){
        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
        filterRegistrationBean.setFilter(new HttpFilter());
        //設定自定義過濾器攔截的url
        filterRegistrationBean.addUrlPatterns("/threadLocal/*");
        return filterRegistrationBean;
    }

    /**
     * 定義自定義攔截器原先需要繼承WebMvcConfigurerAdapter
     * SpringBoot2.0後WebMvcConfigurerAdapter被定義成過時了，推薦使用繼承WebMvcConfigurationSupport
     * @param registry
     */
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new HttpInterceptor()).addPathPatterns("/**");
    }
}

定義呼叫介面

/**
 * ThreadLocal測試controller
 * @author zjq
 */
@Controller
@RequestMapping("/threadLocal")
public class ThreadLocalController {

    @RequestMapping("/test")
    @ResponseBody
    public Long test() {
        return RequestHolder.get();
    }
}