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一、異步執(zhí)行

實(shí)現(xiàn)方式二種：

1. 使用異步注解@aysnc、啟動類：添加@EnableAsync注解

2. JDK 8本身有一個非常好用的Future類——CompletableFuture

@AllArgsConstructor
public?class?AskThread?implements?Runnable{
????private?CompletableFuture re = null;

????public?void?run()?{
????????int?myRe = 0;
????????try?{
????????????myRe = re.get() * re.get();
????????} catch?(Exception e) {
????????????e.printStackTrace();
????????}
????????System.out.println(myRe);
????}

????public?static?void?main(String[] args)?throws?InterruptedException {
????????final?CompletableFuture future = new?CompletableFuture<>();
????????new?Thread(new?AskThread(future)).start();
????????//模擬長時間的計(jì)算過程
????????Thread.sleep(1000);
????????//告知完成結(jié)果
????????future.complete(60);
????}
}

在該示例中，啟動一個線程，此時AskThread對象還沒有拿到它需要的數(shù)據(jù)，執(zhí)行到 myRe = re.get() * re.get()會阻塞。我們用休眠1秒來模擬一個長時間的計(jì)算過程，并將計(jì)算結(jié)果告訴future執(zhí)行結(jié)果，AskThread線程將會繼續(xù)執(zhí)行。如果您正在學(xué)習(xí)Spring Boot，那么推薦一個連載多年還在繼續(xù)更新的免費(fèi)教程：http://blog.didispace.com/spring-boot-learning-2x/

public?class?Calc?{
????public?static?Integer calc(Integer para)?{
????????try?{
????????????//模擬一個長時間的執(zhí)行
????????????Thread.sleep(1000);
????????} catch?(InterruptedException e) {
????????????e.printStackTrace();
????????}
????????return?para * para;
????}

????public?static?void?main(String[] args)?throws?ExecutionException, InterruptedException {
????????final?CompletableFuture future = CompletableFuture.supplyAsync(() -> calc(50))
????????????????.thenApply((i) -> Integer.toString(i))
????????????????.thenApply((str) -> "\""?+ str + "\"")
????????????????.thenAccept(System.out::println);
????????future.get();
????}
}

CompletableFuture.supplyAsync方法構(gòu)造一個CompletableFuture實(shí)例，在supplyAsync()方法中，它會在一個新線程中，執(zhí)行傳入的參數(shù)。在這里它會執(zhí)行calc()方法，這個方法可能是比較慢的，但這并不影響CompletableFuture實(shí)例的構(gòu)造速度，supplyAsync()會立即返回。

而返回的CompletableFuture實(shí)例就可以作為這次調(diào)用的契約，在將來任何場合，用于獲得最終的計(jì)算結(jié)果。最近整理了一份最新的面試資料，里面收錄了2021年各個大廠的面試題，打算跳槽的小伙伴不要錯過，點(diǎn)擊領(lǐng)取吧！

supplyAsync用于提供返回值的情況，CompletableFuture還有一個不需要返回值的異步調(diào)用方法runAsync(Runnable runnable),一般我們在優(yōu)化Controller時，使用這個方法比較多。這兩個方法如果在不指定線程池的情況下，都是在ForkJoinPool.common線程池中執(zhí)行，而這個線程池中的所有線程都是Daemon（守護(hù)）線程，所以，當(dāng)主線程結(jié)束時，這些線程無論執(zhí)行完畢都會退出系統(tǒng)。

核心代碼：

CompletableFuture.runAsync(()?->
???this.afterBetProcessor(betRequest,betDetailResult,appUser,id)
);

異步調(diào)用使用Callable來實(shí)現(xiàn)

@RestController??
public?class?HelloController { 
??
????private?static?final Logger logger = LoggerFactory.getLogger(HelloController.class); 
??????
????@Autowired??
????private?HelloService hello; 
??
????@GetMapping("/helloworld") 
????public?String?helloWorldController() { 
????????return?hello.sayHello(); 
????} 
??
????/** 
?????* 異步調(diào)用restful 
?????* 當(dāng)controller返回值是Callable的時候，springmvc就會啟動一個線程將Callable交給TaskExecutor去處理 
?????* 然后DispatcherServlet還有所有的spring攔截器都退出主線程，然后把response保持打開的狀態(tài) 
?????* 當(dāng)Callable執(zhí)行結(jié)束之后，springmvc就會重新啟動分配一個request請求，然后DispatcherServlet就重新 
?????* 調(diào)用和處理Callable異步執(zhí)行的返回結(jié)果， 然后返回視圖 
?????* 
?????* @return 
?????*/??
????@GetMapping("/hello") 
????public?Callable<String> helloController() { 
????????logger.info(Thread.currentThread().getName() + " 進(jìn)入helloController方法"); 
????????Callable<String> callable = new?Callable<String>() { 
??
????????????@Override??
????????????public?String?call() throws Exception { 
????????????????logger.info(Thread.currentThread().getName() + " 進(jìn)入call方法"); 
????????????????String?say = hello.sayHello(); 
????????????????logger.info(Thread.currentThread().getName() + " 從helloService方法返回"); 
????????????????return?say; 
????????????} 
????????}; 
????????logger.info(Thread.currentThread().getName() + " 從helloController方法返回"); 
????????return?callable; 
????} 
}

異步調(diào)用的方式 WebAsyncTask

@RestController??
public?class?HelloController { 
??
????private?static?final Logger logger = LoggerFactory.getLogger(HelloController.class); 
??????
????@Autowired??
????private?HelloService hello; 
??
????????/** 
?????* 帶超時時間的異步請求 通過WebAsyncTask自定義客戶端超時間 
?????* 
?????* @return 
?????*/??
????@GetMapping("/world") 
????public?WebAsyncTask<String> worldController() { 
????????logger.info(Thread.currentThread().getName() + " 進(jìn)入helloController方法"); 
??
????????// 3s鐘沒返回，則認(rèn)為超時 
????????WebAsyncTask<String> webAsyncTask = new?WebAsyncTask<>(3000, new?Callable<String>() { 
??
????????????@Override??
????????????public?String?call() throws Exception { 
????????????????logger.info(Thread.currentThread().getName() + " 進(jìn)入call方法"); 
????????????????String?say = hello.sayHello(); 
????????????????logger.info(Thread.currentThread().getName() + " 從helloService方法返回"); 
????????????????return?say; 
????????????} 
????????}); 
????????logger.info(Thread.currentThread().getName() + " 從helloController方法返回"); 
??
????????webAsyncTask.onCompletion(new?Runnable() { 
??
????????????@Override??
????????????public?void?run() { 
????????????????logger.info(Thread.currentThread().getName() + " 執(zhí)行完畢"); 
????????????} 
????????}); 
??
????????webAsyncTask.onTimeout(new?Callable<String>() { 
??
????????????@Override??
????????????public?String?call() throws Exception { 
????????????????logger.info(Thread.currentThread().getName() + " onTimeout"); 
????????????????// 超時的時候，直接拋異常，讓外層統(tǒng)一處理超時異常 
????????????????throw?new?TimeoutException("調(diào)用超時"); 
????????????} 
????????}); 
????????return?webAsyncTask; 
????} 
??
????/** 
?????* 異步調(diào)用，異常處理，詳細(xì)的處理流程見MyExceptionHandler類 
?????* 
?????* @return 
?????*/??
????@GetMapping("/exception") 
????public?WebAsyncTask<String> exceptionController() { 
????????logger.info(Thread.currentThread().getName() + " 進(jìn)入helloController方法"); 
????????Callable<String> callable = new?Callable<String>() { 
??
????????????@Override??
????????????public?String?call() throws Exception { 
????????????????logger.info(Thread.currentThread().getName() + " 進(jìn)入call方法"); 
????????????????throw?new?TimeoutException("調(diào)用超時!"); 
????????????} 
????????}; 
????????logger.info(Thread.currentThread().getName() + " 從helloController方法返回"); 
????????return?new?WebAsyncTask<>(20000, callable); 
????} 
??
}

二、增加內(nèi)嵌Tomcat的最大連接數(shù)

@Configuration
public?class?TomcatConfig?{
????@Bean
????public?ConfigurableServletWebServerFactory webServerFactory()?{
????????TomcatServletWebServerFactory tomcatFactory = new?TomcatServletWebServerFactory();
????????tomcatFactory.addConnectorCustomizers(new?MyTomcatConnectorCustomizer());
????????tomcatFactory.setPort(8005);
????????tomcatFactory.setContextPath("/api-g");
????????return?tomcatFactory;
????}
????class?MyTomcatConnectorCustomizer?implements?TomcatConnectorCustomizer?{
????????public?void?customize(Connector connector)?{
????????????Http11NioProtocol protocol = (Http11NioProtocol) connector.getProtocolHandler();
????????????//設(shè)置最大連接數(shù) 
????????????protocol.setMaxConnections(20000);
????????????//設(shè)置最大線程數(shù) 
????????????protocol.setMaxThreads(2000);
????????????protocol.setConnectionTimeout(30000);
????????}
????}

}

三、使用@ComponentScan()定位掃包比@SpringBootApplication掃包更快

四、默認(rèn)tomcat容器改為Undertow（Jboss下的服務(wù)器，Tomcat吞吐量5000，Undertow吞吐量8000）

<exclusions>
??<exclusion>
?????<groupId>org.springframework.bootgroupId>
?????<artifactId>spring-boot-starter-tomcatartifactId>
??exclusion>
exclusions>

改為:

<dependency>
??<groupId>org.springframework.bootgroupId>
??<artifactId>spring-boot-starter-undertowartifactId>
dependency>

五、使用 BufferedWriter 進(jìn)行緩沖

六、Deferred方式實(shí)現(xiàn)異步調(diào)用

@RestController
public?class?AsyncDeferredController?{
????private?final?Logger logger = LoggerFactory.getLogger(this.getClass());
????private?final?LongTimeTask taskService;
????
????@Autowired
????public?AsyncDeferredController(LongTimeTask taskService)?{
????????this.taskService = taskService;
????}
????
????@GetMapping("/deferred")
????public?DeferredResult executeSlowTask()?{
????????logger.info(Thread.currentThread().getName() + "進(jìn)入executeSlowTask方法");
????????DeferredResult deferredResult = new?DeferredResult<>();
????????// 調(diào)用長時間執(zhí)行任務(wù)
????????taskService.execute(deferredResult);
????????// 當(dāng)長時間任務(wù)中使用deferred.setResult("world");這個方法時，會從長時間任務(wù)中返回，繼續(xù)controller里面的流程
????????logger.info(Thread.currentThread().getName() + "從executeSlowTask方法返回");
????????// 超時的回調(diào)方法
????????deferredResult.onTimeout(new?Runnable(){
??
???@Override
???public?void?run()?{
????logger.info(Thread.currentThread().getName() + " onTimeout");
????// 返回超時信息
????deferredResult.setErrorResult("time out!");
???}
??});
????????
????????// 處理完成的回調(diào)方法，無論是超時還是處理成功，都會進(jìn)入這個回調(diào)方法
????????deferredResult.onCompletion(new?Runnable(){
??
???@Override
???public?void?run()?{
????logger.info(Thread.currentThread().getName() + " onCompletion");
???}
??});
????????
????????return?deferredResult;
????}
}

七、異步調(diào)用可以使用AsyncHandlerInterceptor進(jìn)行攔截

@Component
public?class?MyAsyncHandlerInterceptor?implements?AsyncHandlerInterceptor?{
?
?private?static?final?Logger logger = LoggerFactory.getLogger(MyAsyncHandlerInterceptor.class);
?
?@Override
?public?boolean?preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
???throws?Exception {
??return?true;
?}
?
?@Override
?public?void?postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
???ModelAndView modelAndView)?throws?Exception {
// HandlerMethod handlerMethod = (HandlerMethod) handler;
??logger.info(Thread.currentThread().getName()+ "服務(wù)調(diào)用完成，返回結(jié)果給客戶端");
?}
?
?@Override
?public?void?afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
???throws?Exception {
??if(null?!= ex){
???System.out.println("發(fā)生異常:"+ex.getMessage());
??}
?}
?
?@Override
?public?void?afterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response, Object handler)
???throws?Exception {
??
??// 攔截之后，重新寫回?cái)?shù)據(jù)，將原來的hello world換成如下字符串
??String resp = "my name is chhliu!";
??response.setContentLength(resp.length());
??response.getOutputStream().write(resp.getBytes());
??
??logger.info(Thread.currentThread().getName() + " 進(jìn)入afterConcurrentHandlingStarted方法");
?}
?
}

參考

https://my.oschina.net/u/3768341/blog/3001731
https://blog.csdn.net/liuchuanhong1/article/details/78744138

來源：https://xhcom.blog.csdn.net/article/details/88046026

在央企當(dāng)程序員是一種怎樣的體驗(yàn)?

CTO 說了，不懂 @Autowired 和 @Resource 區(qū)別的人可以領(lǐng)盒飯了

國家出手，開始整治互聯(lián)網(wǎng)加班了

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7 種提升 Spring Boot 吞吐量神技！

二、增加內(nèi)嵌Tomcat的最大連接數(shù)

三、使用@ComponentScan()定位掃包比@SpringBootApplication掃包更快

四、默認(rèn)tomcat容器改為Undertow（Jboss下的服務(wù)器，Tomcat吞吐量5000，Undertow吞吐量8000）

五、使用 BufferedWriter 進(jìn)行緩沖

六、Deferred方式實(shí)現(xiàn)異步調(diào)用

七、異步調(diào)用可以使用AsyncHandlerInterceptor進(jìn)行攔截

參考

7 種提升 Spring Boot 吞吐量神技！

三、使用@ComponentScan()定位掃包比@SpringBootApplication掃包更快

四、默認(rèn)tomcat容器改為Undertow（Jboss下的服務(wù)器，Tomcat吞吐量5000，Undertow吞吐量8000）

五、使用 BufferedWriter 進(jìn)行緩沖

六、Deferred方式實(shí)現(xiàn)異步調(diào)用

七、異步調(diào)用可以使用AsyncHandlerInterceptor進(jìn)行攔截