通過之前三篇關(guān)于Spring Boot異步任務(wù)實現(xiàn)的博文，我們分別學(xué)會了用@Async創(chuàng)建異步任務(wù)、為異步任務(wù)配置線程池、使用多個線程池隔離不同的異步任務(wù)。今天這篇，我們繼續(xù)對上面的知識進行完善和優(yōu)化！

如果你已經(jīng)看過上面幾篇內(nèi)容并已經(jīng)掌握之后，一起來思考下面這個問題：

假設(shè)，線程池配置為核心線程數(shù)2、最大線程數(shù)2、緩沖隊列長度2。此時，有5個異步任務(wù)同時開始，會發(fā)生什么？

場景重現(xiàn)

我們先來把上面的假設(shè)用代碼實現(xiàn)一下：

第一步：創(chuàng)建Spring Boot應(yīng)用，根據(jù)上面的假設(shè)寫好線程池配置。

@EnableAsync
@SpringBootApplication
public class Chapter78Application {

    public static void main(String[] args) {
        SpringApplication.run(Chapter78Application.class, args);
    }

    @EnableAsync
    @Configuration
    class TaskPoolConfig {

        @Bean
        public Executor taskExecutor1() {
            ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
            executor.setCorePoolSize(2);
            executor.setMaxPoolSize(2);
            executor.setQueueCapacity(2);
            executor.setKeepAliveSeconds(60);
            executor.setThreadNamePrefix("executor-1-");
            return executor;
        }

    }

}

第二步：用@Async注解實現(xiàn)一個部分任務(wù)

@Slf4j
@Component
public class AsyncTasks {

    public static Random random = new Random();

    @Async("taskExecutor1")
    public CompletableFuture<String> doTaskOne(String taskNo) throws Exception {
        log.info("開始任務(wù)：{}", taskNo);
        long start = System.currentTimeMillis();
        Thread.sleep(random.nextInt(10000));
        long end = System.currentTimeMillis();
        log.info("完成任務(wù)：{}，耗時：{} 毫秒", taskNo, end - start);
        return CompletableFuture.completedFuture("任務(wù)完成");
    }

}

第三步：編寫測試用例

@Slf4j
@SpringBootTest
public class Chapter78ApplicationTests {

    @Autowired
    private AsyncTasks asyncTasks;

    @Test
    public void test2() throws Exception {
        // 線程池配置：core-2,max-2,queue=2，同時有5個任務(wù)，出現(xiàn)下面異常：
        // org.springframework.core.task.TaskRejectedException: Executor [java.util.concurrent.ThreadPoolExecutor@59901c4d[Running, pool size = 2,
        // active threads = 0, queued tasks = 2, completed tasks = 4]] did not accept task: java.util.concurrent.CompletableFuture$AsyncSupply@408e96d9

        long start = System.currentTimeMillis();

        // 線程池1
        CompletableFuture<String> task1 = asyncTasks.doTaskOne("1");
        CompletableFuture<String> task2 = asyncTasks.doTaskOne("2");
        CompletableFuture<String> task3 = asyncTasks.doTaskOne("3");
        CompletableFuture<String> task4 = asyncTasks.doTaskOne("4");
        CompletableFuture<String> task5 = asyncTasks.doTaskOne("5");

        // 一起執(zhí)行
        CompletableFuture.allOf(task1, task2, task3, task4, task5).join();

        long end = System.currentTimeMillis();

        log.info("任務(wù)全部完成，總耗時：" + (end - start) + "毫秒");
    }

}

執(zhí)行一下，可以類似下面這樣的日志信息：

2021-09-22 17:33:08.159  INFO 21119 --- [   executor-1-2] com.didispace.chapter78.AsyncTasks       : 開始任務(wù)：2
2021-09-22 17:33:08.159  INFO 21119 --- [   executor-1-1] com.didispace.chapter78.AsyncTasks       : 開始任務(wù)：1

org.springframework.core.task.TaskRejectedException: Executor [java.util.concurrent.ThreadPoolExecutor@3e1a3801[Running, pool size = 2, active threads = 2, queued tasks = 2, completed tasks = 0]] did not accept task: java.util.concurrent.CompletableFuture$AsyncSupply@64968732

 at org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor.execute(ThreadPoolTaskExecutor.java:324)
 at java.util.concurrent.CompletableFuture.asyncSupplyStage(CompletableFuture.java:1604)
 at java.util.concurrent.CompletableFuture.supplyAsync(CompletableFuture.java:1830)
 at org.springframework.aop.interceptor.AsyncExecutionAspectSupport.doSubmit(AsyncExecutionAspectSupport.java:274)
 at org.springframework.aop.interceptor.AsyncExecutionInterceptor.invoke(AsyncExecutionInterceptor.java:129)
 at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
 at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:750)
 at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:692)
 at com.didispace.chapter78.AsyncTasks$$EnhancerBySpringCGLIB$$c7e8d57b.doTaskOne(<generated>)
 at com.didispace.chapter78.Chapter78ApplicationTests.test2(Chapter78ApplicationTests.java:51)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
 at java.lang.reflect.Method.invoke(Method.java:498)
 at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:688)
 at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
 at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)
 at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:149)
 at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:140)
 at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:84)
 at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115)
 at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105)
 at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)
 at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)
 at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)
 at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)
 at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104)
 at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98)
 at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$6(TestMethodTestDescriptor.java:210)
 at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
 at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:206)
 at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:131)
 at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:65)
 at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
 at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
 at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
 at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
 at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
 at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
 at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
 at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
 at java.util.ArrayList.forEach(ArrayList.java:1255)
 at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
 at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143)
 at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
 at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
 at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
 at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
 at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
 at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
 at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
 at java.util.ArrayList.forEach(ArrayList.java:1255)
 at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
 at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143)
 at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
 at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
 at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
 at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
 at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
 at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
 at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
 at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32)
 at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
 at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51)
 at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:108)
 at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:88)
 at org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:54)
 at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:67)
 at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:52)
 at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:96)
 at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:75)
 at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:71)
 at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
 at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:235)
 at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:54)
Caused by: java.util.concurrent.RejectedExecutionException: Task java.util.concurrent.CompletableFuture$AsyncSupply@64968732 rejected from java.util.concurrent.ThreadPoolExecutor@3e1a3801[Running, pool size = 2, active threads = 2, queued tasks = 2, completed tasks = 0]
 at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:2063)
 at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:830)
 at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:1379)
 at org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor.execute(ThreadPoolTaskExecutor.java:321)
 ... 74 more

從異常信息org.springframework.core.task.TaskRejectedException: Executor [java.util.concurrent.ThreadPoolExecutor@3e1a3801[Running, pool size = 2, active threads = 2, queued tasks = 2, completed tasks = 0]] did not accept task: 中，可以很明確的知道，第5個任務(wù)因為超過了執(zhí)行線程+緩沖隊列長度，而被拒絕了。

所有，默認(rèn)情況下，線程池的拒絕策略是：當(dāng)線程池隊列滿了，會丟棄這個任務(wù)，并拋出異常。

配置拒絕策略

雖然線程池有默認(rèn)的拒絕策略，但實際開發(fā)過程中，有些業(yè)務(wù)場景，直接拒絕的策略往往并不適用，有時候我們可能會選擇舍棄最早開始執(zhí)行而未完成的任務(wù)、也可能會選擇舍棄剛開始執(zhí)行而未完成的任務(wù)等更貼近業(yè)務(wù)需要的策略。所以，為線程池配置其他拒絕策略或自定義拒絕策略是很常見的需求，那么這個要怎么實現(xiàn)呢？

下面就來具體說說今天的正題，如何為線程池配置拒絕策略、如何自定義拒絕策略。

看下面這段代碼的最后一行，setRejectedExecutionHandler方法就是為線程池設(shè)置拒絕策略的方法：

ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();

//...其他線程池配置

executor.setRejectedExecutionHandler(new ThreadPoolExecutor.AbortPolicy());

在ThreadPoolExecutor中提供了4種線程的策略可以供開發(fā)者直接使用，你只需要像下面這樣設(shè)置即可：

// AbortPolicy策略
executor.setRejectedExecutionHandler(new ThreadPoolExecutor.AbortPolicy());

// DiscardPolicy策略
executor.setRejectedExecutionHandler(new ThreadPoolExecutor.DiscardPolicy());

// DiscardOldestPolicy策略
executor.setRejectedExecutionHandler(new ThreadPoolExecutor.DiscardOldestPolicy());

// CallerRunsPolicy策略
executor.setRejectedExecutionHandler(new ThreadPoolExecutor.CallerRunsPolicy());

這四個策略對應(yīng)的含義分別是：

• AbortPolicy策略：默認(rèn)策略，如果線程池隊列滿了丟掉這個任務(wù)并且拋出RejectedExecutionException異常。
• DiscardPolicy策略：如果線程池隊列滿了，會直接丟掉這個任務(wù)并且不會有任何異常。
• DiscardOldestPolicy策略：如果隊列滿了，會將最早進入隊列的任務(wù)刪掉騰出空間，再嘗試加入隊列。
• CallerRunsPolicy策略：如果添加到線程池失敗，那么主線程會自己去執(zhí)行該任務(wù)，不會等待線程池中的線程去執(zhí)行。

而如果你要自定義一個拒絕策略，那么可以這樣寫：

executor.setRejectedExecutionHandler(new RejectedExecutionHandler() {
    @Override
    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
        // 拒絕策略的邏輯
    }
});

當(dāng)然如果你喜歡用Lamba表達(dá)式，也可以這樣寫：

executor.setRejectedExecutionHandler((r, executor1) -> {
    // 拒絕策略的邏輯
});

好了，今天的學(xué)習(xí)就到這里！

代碼示例

本文的完整工程可以查看下面?zhèn)}庫中2.x目錄下的chapter7-8工程：

• Github：https://github.com/dyc87112/SpringBoot-Learning/
• Gitee：https://gitee.com/didispace/SpringBoot-Learning/

到此這篇關(guān)于Spring Boot配置線程池拒絕策略，妥善處理好溢出的任務(wù)的文章就介紹到這了,更多相關(guān)Spring Boot配置線程池內(nèi)容請搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持腳本之家！