前言

在使用框架日常開發中需要在controller中進行一些非同步操作減少請求時間，但是發現在使用@Anysc註解後會出現Request對象無法獲取的情況，本文就此情況給出完整的解決方案

原因分析

• @Anysc註解會開啟一個新的線程，主線程的Request和子線程是不共用的，所以獲取為null
• 在使用springboot的自定帶的線程共用後，代碼如下，Request不為null，但是偶發的其中body/head/urlparam內容出現獲取不到的情況，是因為非同步任務在未執行完畢的情況下，主線程已經返回，拷貝共用的Request對象數據被清空

ServletRequestAttributes servletRequestAttributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
//設置子線程共用
RequestContextHolder.setRequestAttributes(servletRequestAttributes, true);
HttpServletRequest request = servletRequestAttributes.getRequest();

解決方案

前置條件

• 啟動類添加@EnableAsync註解

• 標記@Async的非同步方法不能和調用者在同一個class中

pom配置

        <!-- 阿裡線程共用 -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>transmittable-thread-local</artifactId>
            <version>2.11.0</version>
        </dependency>

requrest共用

通過TransmittableThreadLocal對象進行線程對象共用

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();
    }
}

註：系統中所有Request獲取需要統一從CommonUtil指定來源，例如token鑒權等

自定義request過濾器

通過自定義過濾器對Request的內容進行備份保存，主線程結束時Request清除結束不會影響到子線程的相應參數的獲取，也適用於增加攔截器/過濾器後body參數無法重覆獲取的問題。需要註意的是對header參數處理時key要忽略大小寫

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);
        }
        //獲取請求中的流如何，將取出來的字元串，再次轉換成流，然後把它放入到新request對象中。
        // 在chain.doFiler方法中傳遞新的request對象
        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);
    }
}

自定義任務執行器

用於攔截非同步任務執行，在任務執前統一進行Request共用操作，且可以定義多個，不影響原有的非同步任務代碼

public class CustomTaskDecorator implements TaskDecorator {
    @Override
    public Runnable decorate(Runnable runnable) {
        ServletRequestAttributes requestAttributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
        HttpServletRequest request = requestAttributes.getRequest();
        System.out.println("非同步任務共用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 屬性的配置
        executor.setTaskDecorator(new CustomTaskDecorator());
        executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());
        executor.initialize();
        return executor;
    }
}

調用示例

給@Anysc註解指定進行共用攔截的任務執行器即可

    @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("開始執行executeAsync");
        Thread.sleep(3000);
        System.out.println("結束執行executeAsync");
    }
}