前言

在使用框架日常开发中需要在controller中进行一些异步操作减少请求时间，但是发现在使用@Anysc注解后会出现Request对象无法获取的情况，本文就此情况给出完整的解决方案

原因分析

• @Anysc注解会开启一个新的线程，主线程的Request和子线程是不共享的，所以获取为null
• 在使用springboot的自定带的线程共享后，代码如下，Request不为null，但是偶发的其中body/head/urlparam内容出现获取不到的情况，是因为异步任务在未执行完毕的情况下，主线程已经返回，拷贝共享的Request对象数据被清空

ServletRequestAttributes servletRequestAttributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
//设置子线程共享
RequestContextHolder.setRequestAttributes(servletRequestAttributes, true);
HttpServletRequest request = servletRequestAttributes.getRequest();

解决方案

前置条件

• 启动类添加@EnableAsync注解

• 标记@Async的异步方法不能和调用者在同一个class中

pom配置

        <!-- 阿里线程共享 -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>transmittable-thread-local</artifactId>
            <version>2.11.0</version>
        </dependency>

requrest共享

通过TransmittableThreadLocal对象进行线程对象共享

public class CommonUtil {
    public static TransmittableThreadLocal<HttpServletRequest> requestTransmittableThreadLocal = new TransmittableThreadLocal<HttpServletRequest>();

    public static void shareRequest(HttpServletRequest request){
        requestTransmittableThreadLocal.set(request);
    }

    public static HttpServletRequest getRequest(){
        HttpServletRequest request = requestTransmittableThreadLocal.get();
        if(request!=null){
            return requestTransmittableThreadLocal.get();
        }else{
            ServletRequestAttributes requestAttributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
            if(requestAttributes!=null){
                return  requestAttributes.getRequest();
            }else{
                return  null;
            }
        }
    }

    public static void remove(){
        requestTransmittableThreadLocal.remove();
    }
}

注：系统中所有Request获取需要统一从CommonUtil指定来源，例如token鉴权等

自定义request过滤器

通过自定义过滤器对Request的内容进行备份保存，主线程结束时Request清除结束不会影响到子线程的相应参数的获取，也适用于增加拦截器/过滤器后body参数无法重复获取的问题。需要注意的是对header参数处理时key要忽略大小写

public class HttpServletRequestReplacedFilter implements Filter, Ordered {
    @Override
    public void destroy() {

    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
                         FilterChain chain) throws IOException, ServletException {
        ServletRequest requestWrapper = null;
        if (request instanceof HttpServletRequest) {
            requestWrapper = new RequestWrapper((HttpServletRequest) request);
        }
        //获取请求中的流如何，将取出来的字符串，再次转换成流，然后把它放入到新request对象中。
        // 在chain.doFiler方法中传递新的request对象
        if (requestWrapper == null) {
            chain.doFilter(request, response);
        } else {
            chain.doFilter(requestWrapper, response);
        }
    }

    @Override
    public void init(FilterConfig arg0) throws ServletException {

    }

    @Override
    public int getOrder() {
        return 10;
    }
}

public class RequestWrapper extends HttpServletRequestWrapper{

    private final byte[] body;
    private final HashMap<String,String> headMap;
    private final HashMap<String,String> requestParamMap;

    public RequestWrapper(HttpServletRequest request) throws IOException {
        super(request);
        body = CommonUtil.getBodyString(request).getBytes(Charset.forName("UTF-8"));

        headMap = new HashMap();
        Enumeration<String> headNameList = request.getHeaderNames();
        while (headNameList.hasMoreElements()){
            String key = headNameList.nextElement();
            headMap.put(key.toLowerCase(),request.getHeader(key));
        }

        requestParamMap = new HashMap<>();
        Enumeration<String> parameterNameList = request.getParameterNames();
        while (parameterNameList.hasMoreElements()){
            String key = parameterNameList.nextElement();
            requestParamMap.put(key,request.getParameter(key));
        }
    }

    @Override
    public BufferedReader getReader() throws IOException {
        return new BufferedReader(new InputStreamReader(getInputStream()));
    }

    @Override
    public ServletInputStream getInputStream() throws IOException {

        final ByteArrayInputStream bais = new ByteArrayInputStream(body);

        return new ServletInputStream() {

            @Override
            public int read() throws IOException {
                return bais.read();
            }

            @Override
            public boolean isFinished() {
                return false;
            }

            @Override
            public boolean isReady() {
                return false;
            }

            @Override
            public void setReadListener(ReadListener readListener) {

            }
        };
    }

    @Override
    public String getHeader(String name) {
        return headMap.get(name.toLowerCase());
    }

    @Override
    public String getParameter(String name) {
        return requestParamMap.get(name);
    }
}

自定义任务执行器

用于拦截异步任务执行，在任务执前统一进行Request共享操作，且可以定义多个，不影响原有的异步任务代码

public class CustomTaskDecorator implements TaskDecorator {
    @Override
    public Runnable decorate(Runnable runnable) {
        ServletRequestAttributes requestAttributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
        HttpServletRequest request = requestAttributes.getRequest();
        System.out.println("异步任务共享request");
        return () -> {
            try {
                CommonUtil.shareRequest(request);
                runnable.run();
            } finally {
                CommonUtil.remove();
            }
        };
    }
}

@Configuration
public class TaskExecutorConfig {

    @Bean()
    public Executor taskExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(10);
        executor.setMaxPoolSize(20);
        executor.setQueueCapacity(200);
        executor.setKeepAliveSeconds(60);
        executor.setThreadNamePrefix("taskExecutor-");
        executor.setAwaitTerminationSeconds(60);
        executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());
        executor.initialize();
        return executor;
    }

    @Bean("shareTaskExecutor")
    public Executor hpTaskExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(10);
        executor.setMaxPoolSize(20);
        executor.setQueueCapacity(200);
        executor.setKeepAliveSeconds(60);
        executor.setThreadNamePrefix("shareTaskExecutor-");
        executor.setWaitForTasksToCompleteOnShutdown(true);
        executor.setAwaitTerminationSeconds(60);
        // 增加 TaskDecorator 属性的配置
        executor.setTaskDecorator(new CustomTaskDecorator());
        executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());
        executor.initialize();
        return executor;
    }
}

调用示例

给@Anysc注解指定进行共享拦截的任务执行器即可

    @PostMapping("/testAsync")
    @ResponseBody
    public Object testAsync(@RequestBody Map<String, Object> params) throws Exception{
        Result result = Result.okResult();
        asyncUtil.executeAsync();
        return result;
    }

@Component
public class AsyncUtil {
    @Async("shareTaskExecutor")
    public void executeAsync () throws InterruptedException {
        System.out.println("开始执行executeAsync");
        Thread.sleep(3000);
        System.out.println("结束执行executeAsync");
    }
}