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怎么在Spring-MVC中對Servlet異步進(jìn)行處理?很多新手對此不是很清楚,為了幫助大家解決這個難題,下面小編將為大家詳細(xì)講解,有這方面需求的人可以來學(xué)習(xí)下,希望你能有所收獲。
Servlet3.0對異步請求的支持
在Servlet3.0規(guī)范中使用異步處理請求非常簡單,只需要在請求處理過程中調(diào)用request的startAsync返回AsyncContext。
什么是AsyncContext在異步請求中充當(dāng)著非常重要的角色,可以稱為異步請求上下文也可以稱為異步請求容器。類似于ServletContext.我們多次調(diào)用startAsync都是返回的同一個AsyncContext。代碼如下:
public interface AsyncContext { String ASYNC_REQUEST_URI = "javax.servlet.async.request_uri"; String ASYNC_CONTEXT_PATH = "javax.servlet.async.context_path"; String ASYNC_PATH_INFO = "javax.servlet.async.path_info"; String ASYNC_SERVLET_PATH = "javax.servlet.async.servlet_path"; String ASYNC_QUERY_STRING = "javax.servlet.async.query_string"; ServletRequest getRequest(); ServletResponse getResponse(); boolean hasOriginalRequestAndResponse(); void dispatch(); void dispatch(String var1); void dispatch(ServletContext var1, String var2); void complete(); void start(Runnable var1); void addListener(AsyncListener var1); void addListener(AsyncListener var1, ServletRequest var2, ServletResponse var3); <T extends AsyncListener> T createListener(Class<T> var1) throws ServletException; void setTimeout(long var1); long getTimeout(); }
getResponse() 用于獲取response。dispatch用于分發(fā)新地址。complete用于通知容器已經(jīng)處理完了,start方法用于啟動實際處理線程,addListener用于添加監(jiān)聽器;setTimeout方法用于修改超時時間。
@WebServlet( name = “WorkServlet”, urlPatterns = “/work”, asyncSupported = true ) public class WorkServlet extends HttpServlet { private static final long serialVersionUID =1L; @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { this.doPost(req, resp); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //設(shè)置ContentType,關(guān)閉緩存 resp.setContentType("text/plain;charset=UTF-8"); resp.setHeader("Cache-Control","private"); resp.setHeader("Pragma","no-cache"); final PrintWriter writer= resp.getWriter(); writer.println("老師檢查作業(yè)了"); writer.flush(); List<String> zuoyes=new ArrayList<String>(); for (int i = 0; i < 10; i++) { zuoyes.add("zuoye"+i);; } final AsyncContext ac=req.startAsync();//開啟異步請求 doZuoye(ac,zuoyes); writer.println("老師布置作業(yè)"); writer.flush(); } private void doZuoye(final AsyncContext ac, final List<String> zuoyes) { ac.setTimeout(1*60*60*1000L); ac.start(new Runnable() { @Override public void run() { //通過response獲得字符輸出流 try { PrintWriter writer=ac.getResponse().getWriter(); for (String zuoye:zuoyes) { writer.println("\""+zuoye+"\"請求處理中"); Thread.sleep(1*1000L); writer.flush(); } ac.complete(); } catch (Exception e) { e.printStackTrace(); } } }); }
在上面的程序是我們最基本的異步請求,不過不夠完善。老師是需要思考宏觀問題,所以在寫完作業(yè)之后需要給老師匯報哪些題難,哪些題目有問題或者自己的這次經(jīng)驗總結(jié),不過這些事不應(yīng)該由做作業(yè)的學(xué)生來做,應(yīng)該由專門的學(xué)習(xí)匯報員來統(tǒng)計分析。所以就有了監(jiān)聽器。
public class TeacherListener implements AsyncListener { final SimpleDateFormat formatter=new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); @Override public void onComplete(AsyncEvent event) throws IOException { System.out.println("在"+formatter.format(new Date())+"工作處理完成"); } @Override public void onTimeout(AsyncEvent event) throws IOException { System.out.println("在"+formatter.format(new Date())+"工作超時"); } @Override public void onError(AsyncEvent event) throws IOException { System.out.println("在"+formatter.format(new Date())+"工作處理錯誤"); } @Override public void onStartAsync(AsyncEvent event) throws IOException { System.out.println("在"+formatter.format(new Date())+"工作處理開始"); } }
所有代碼具體參照github地址
https://github.com/lzggsimida123/ServletAsync
補充:SpringMVC對Servlet3異步請求的支持
SpringMVC對Servlet3異步請求的支持有兩種方式,分別是通過處理器方法返回Callable和DeferredResult。
按照Servlet3的規(guī)范,支持異步請求時需要配置對應(yīng)的Servlet和Filter支持異步請求,為了使SpringMVC支持異步請求的處理,需要在定義DispatcherServlet時配置其支持異步請求,在DispatcherServlet之前定義的Filter也需要配置支持異步請求。
<servlet> <servlet-name>springmvc</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <init-param> <param-name>contextConfigLocation</param-name> <param-value>/WEB-INF/applicationContext-mvc.xml</param-value> </init-param> <load-on-startup>1</load-on-startup> <!-- 啟用異步支持 --> <async-supported>true</async-supported> </servlet> <servlet-mapping> <servlet-name>springmvc</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping>
當(dāng)處理器的返回方法是Callable類型時會默認(rèn)發(fā)起異步請求,并使用一個TaskExecutor來調(diào)用返回的Callable,之后的處理就跟正常的SpringMVC請求是一樣的。Callable的返回結(jié)果也跟正常請求SpringMVC的一樣,可以返回Model、ModelAndView、String、Object等,也可以結(jié)合@ResponseBody使用,具體可以參考CallableMethodReturnValueHandler的handleReturnValue()。
@RequestMapping("/callable") public Callable<String> forCallable(Model model) throws Exception { return () -> { TimeUnit.SECONDS.sleep(1);//睡眠1秒,模仿某些業(yè)務(wù)操作 model.addAttribute("a", "aaaaaaa"); return "async_request_callable"; }; }
如果需要針對于單個Callable請求指定超時時間,我們可以把Callable用一個WebAsyncTask包裹起來。然后還可以指定超時回調(diào)和正常處理完成的回調(diào)。
@RequestMapping("/callable/timeout") public WebAsyncTask<String> forCallableWithTimeout(Model model) throws Exception { long timeout = 5 * 1000L; WebAsyncTask<String> asyncTask = new WebAsyncTask<>(timeout, () -> { TimeUnit.MILLISECONDS.sleep(timeout + 10); model.addAttribute("a", "aaaaaaa"); return "async_request_callable"; }); asyncTask.onTimeout(() -> { System.out.println("響應(yīng)超時回調(diào)"); return "async_request_callable_timeout"; }); asyncTask.onCompletion(() -> { System.out.println("響應(yīng)callable調(diào)用完成的回調(diào)"); }); return asyncTask; }
使用DeferredResult的返回結(jié)果的編程通常是在處理器方法中創(chuàng)建一個DeferredResult實例,把它保存起來后再進(jìn)行返回,比如保存到一個隊列中,然后在另外的一個線程中會從這個隊列中拿到相應(yīng)的DeferredResult對象進(jìn)行相應(yīng)的業(yè)務(wù)處理后會往DeferredResult中設(shè)置對應(yīng)的返回值。返回了DeferredResult后SpringMVC將創(chuàng)建一個DeferredResultHandler用于監(jiān)聽DeferredResult,一旦DeferredResult中設(shè)置了返回值后,DeferredResultHandler就將對返回值進(jìn)行處理。DeferredResult的處理過程見DeferredResultMethodReturnValueHandler的handleReturnValue()。
@RequestMapping("/deferredresult") public DeferredResult<String> forDeferredResult() throws Exception { DeferredResult<String> result = new DeferredResult<>(); new Thread(() -> { try { TimeUnit.SECONDS.sleep(2); } catch (InterruptedException e) { e.printStackTrace(); } result.setResult("async_request_deferredresult"); }).start(); return result; }
對于DeferredResult也是可以單獨指定超時時間和超時后的回調(diào)的,它的超時時間可以直接通過構(gòu)造函數(shù)傳遞,單位是毫秒。
@RequestMapping("/deferredresult/timeout") public DeferredResult<String> forDeferredResultWithTimeout() throws Exception { DeferredResult<String> result = new DeferredResult<>(10 * 1000); new Thread(() -> { try { TimeUnit.SECONDS.sleep(31); } catch (InterruptedException e) { e.printStackTrace(); } result.setResult("async_request_deferredresult"); }).start(); result.onTimeout(() -> { System.out.println("響應(yīng)超時回調(diào)函數(shù)"); }); result.onCompletion(() -> { System.out.println("響應(yīng)完成的回調(diào)函數(shù)"); }); return result; }
可以通過<mvc:annotation-driven/>的子元素<mvc:async-support/>來定義處理異步請求默認(rèn)的超時時間和需要使用的TaskExecutor。如果不指定默認(rèn)超時時間則默認(rèn)會使用容器的異步請求超時時間,如果不指定需要使用的TaskExecutor,則默認(rèn)會使用一個SimpleAsyncTaskExecutor。在下面的配置中我們就配置了默認(rèn)的超時時間是15秒,且處理異步請求的TaskExecutor是bean容器中名為asyncTaskExecutor的TaskExecutor。
<mvc:annotation-driven> <mvc:async-support default-timeout="15000" task-executor="asyncTaskExecutor"/> </mvc:annotation-driven>
返回Callable類型的請求可以通過實現(xiàn)CallableProcessingInterceptor接口自定義一個攔截器來攔截,也可以通過繼承CallableProcessingInterceptorAdapter抽象類來定義攔截器,這樣就只需要選擇自己感興趣的方法進(jìn)行實現(xiàn)。CallableProcessingInterceptor接口定義如下:
public interface CallableProcessingInterceptor { static final Object RESULT_NONE = new Object(); static final Object RESPONSE_HANDLED = new Object(); /** * Invoked <em>before</em> the start of concurrent handling in the original * thread in which the {@code Callable} is submitted for concurrent handling. * * <p> * This is useful for capturing the state of the current thread just prior to * invoking the {@link Callable}. Once the state is captured, it can then be * transferred to the new {@link Thread} in * {@link #preProcess(NativeWebRequest, Callable)}. Capturing the state of * Spring Security's SecurityContextHolder and migrating it to the new Thread * is a concrete example of where this is useful. * </p> * * @param request the current request * @param task the task for the current async request * @throws Exception in case of errors */ <T> void beforeConcurrentHandling(NativeWebRequest request, Callable<T> task) throws Exception; /** * Invoked <em>after</em> the start of concurrent handling in the async * thread in which the {@code Callable} is executed and <em>before</em> the * actual invocation of the {@code Callable}. * * @param request the current request * @param task the task for the current async request * @throws Exception in case of errors */ <T> void preProcess(NativeWebRequest request, Callable<T> task) throws Exception; /** * Invoked <em>after</em> the {@code Callable} has produced a result in the * async thread in which the {@code Callable} is executed. This method may * be invoked later than {@code afterTimeout} or {@code afterCompletion} * depending on when the {@code Callable} finishes processing. * * @param request the current request * @param task the task for the current async request * @param concurrentResult the result of concurrent processing, which could * be a {@link Throwable} if the {@code Callable} raised an exception * @throws Exception in case of errors */ <T> void postProcess(NativeWebRequest request, Callable<T> task, Object concurrentResult) throws Exception; /** * Invoked from a container thread when the async request times out before * the {@code Callable} task completes. Implementations may return a value, * including an {@link Exception}, to use instead of the value the * {@link Callable} did not return in time. * * @param request the current request * @param task the task for the current async request * @return a concurrent result value; if the value is anything other than * {@link #RESULT_NONE} or {@link #RESPONSE_HANDLED}, concurrent processing * is resumed and subsequent interceptors are not invoked * @throws Exception in case of errors */ <T> Object handleTimeout(NativeWebRequest request, Callable<T> task) throws Exception; /** * Invoked from a container thread when async processing completes for any * reason including timeout or network error. * * @param request the current request * @param task the task for the current async request * @throws Exception in case of errors */ <T> void afterCompletion(NativeWebRequest request, Callable<T> task) throws Exception; }
它的配置是通過<mvc:callable-interceptors/>配置的。
<mvc:annotation-driven> <mvc:async-support default-timeout="15000" task-executor="asyncTaskExecutor"> <mvc:callable-interceptors> <bean class="YourCallableProcessingInterceptor"/> </mvc:callable-interceptors> </mvc:async-support> </mvc:annotation-driven>
返回DeferredResult的也可以進(jìn)行攔截,這需要我們實現(xiàn)DeferredResultProcessingInterceptor接口或者繼承自DeferredResultProcessingInterceptorAdapter。DeferredResultProcessingInterceptor接口定義如下:
public interface DeferredResultProcessingInterceptor { /** * Invoked immediately before the start of concurrent handling, in the same * thread that started it. This method may be used to capture state just prior * to the start of concurrent processing with the given {@code DeferredResult}. * * @param request the current request * @param deferredResult the DeferredResult for the current request * @throws Exception in case of errors */ <T> void beforeConcurrentHandling(NativeWebRequest request, DeferredResult<T> deferredResult) throws Exception; /** * Invoked immediately after the start of concurrent handling, in the same * thread that started it. This method may be used to detect the start of * concurrent processing with the given {@code DeferredResult}. * * <p>The {@code DeferredResult} may have already been set, for example at * the time of its creation or by another thread. * * @param request the current request * @param deferredResult the DeferredResult for the current request * @throws Exception in case of errors */ <T> void preProcess(NativeWebRequest request, DeferredResult<T> deferredResult) throws Exception; /** * Invoked after a {@code DeferredResult} has been set, via * {@link DeferredResult#setResult(Object)} or * {@link DeferredResult#setErrorResult(Object)}, and is also ready to * handle the concurrent result. * * <p>This method may also be invoked after a timeout when the * {@code DeferredResult} was created with a constructor accepting a default * timeout result. * * @param request the current request * @param deferredResult the DeferredResult for the current request * @param concurrentResult the result to which the {@code DeferredResult} * @throws Exception in case of errors */ <T> void postProcess(NativeWebRequest request, DeferredResult<T> deferredResult, Object concurrentResult) throws Exception; /** * Invoked from a container thread when an async request times out before * the {@code DeferredResult} has been set. Implementations may invoke * {@link DeferredResult#setResult(Object) setResult} or * {@link DeferredResult#setErrorResult(Object) setErrorResult} to resume processing. * * @param request the current request * @param deferredResult the DeferredResult for the current request; if the * {@code DeferredResult} is set, then concurrent processing is resumed and * subsequent interceptors are not invoked * @return {@code true} if processing should continue, or {@code false} if * other interceptors should not be invoked * @throws Exception in case of errors */ <T> boolean handleTimeout(NativeWebRequest request, DeferredResult<T> deferredResult) throws Exception; /** * Invoked from a container thread when an async request completed for any * reason including timeout and network error. This method is useful for * detecting that a {@code DeferredResult} instance is no longer usable. * * @param request the current request * @param deferredResult the DeferredResult for the current request * @throws Exception in case of errors */ <T> void afterCompletion(NativeWebRequest request, DeferredResult<T> deferredResult) throws Exception; }
自定義的DeferredResultProcessingInterceptor是通過<mvc:deferred-result-interceptors>配置的。
<mvc:annotation-driven> <mvc:async-support default-timeout="15000" task-executor="asyncTaskExecutor"> <mvc:deferred-result-interceptors> <bean class="YourDeferredResultProcessingInterceptor"/> </mvc:deferred-result-interceptors> </mvc:async-support> </mvc:annotation-driven>
當(dāng)發(fā)起異步請求時,SpringMVC傳統(tǒng)的HandlerInterceptor的postHandle()和afterCompletion()不會執(zhí)行,但是等異步請求結(jié)束后它們還是會執(zhí)行的。如果需要在異步處理完成之后做一些事情,也可以選擇實現(xiàn)AsyncHandlerInterceptor接口的afterConcurrentHandlingStarted(),AsyncHandlerInterceptor接口繼承了HandlerInterceptor。
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