问题背景

项目开发会用到异步线程去处理一些事情，这个时候使用注解 @Async 非常的简单方便

@Async测试用例

新建一个 springboot 工程，复制一下pom文件的依赖

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.6.2</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>AsyncTest</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>AsyncTest</name>
    <description>AsyncTest</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <!--scope>test</scope-->
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>compile</scope>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

可以看到我把 <scope>test</scope> 注释掉了，因为我是在 main.java 文件夹下使用 @SpringTest ，如果不注释掉，那么就不能使用该注解，只能在 test 文件夹下使用，所以 scope 指的就是一个使用的范围
我添加了 junit 依赖，因为测试类的 @Test 注解必须使用这个类

添加 @EnableAsync 注解在启动类上面

package com.yg.asynctest;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.scheduling.annotation.EnableAsync;

@EnableAsync
@SpringBootApplication
public class AsyncTestApplication {
    public static void main(String[] args) {
        SpringApplication.run(AsyncTestApplication.class, args);
    }
}

创建异步和同步的方法类

package com.yg.asynctest;

import org.springframework.scheduling.annotation.Async;
import org.springframework.scheduling.annotation.AsyncResult;
import org.springframework.stereotype.Component;
import java.util.concurrent.Future;

@Component
public class Method {
    public int syncMethod() {
        System.out.println("SyncMethod thread: "+Thread.currentThread().getName());
        return 1;
    }
    @Async
    public Future<Integer> asyncMethod() throws InterruptedException {
        System.out.println("AsyncMethod thread: "+Thread.currentThread().getName());
        // 异步线程延时 5s 返回结果
        Thread.sleep(5000);
        return new AsyncResult<>(2);
    }
}

异步方法延时了5s，查看异步调用方法的效果

创建测试类

package com.yg.asynctest;


import lombok.extern.slf4j.Slf4j;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;

@Slf4j
@RunWith(SpringRunner.class)
@SpringBootTest
public class AsyncTest {
    @Autowired
    Method method;

    @Test
    public void test() throws ExecutionException, InterruptedException {
        log.info("Sync is {}", method.syncMethod());
        Future<Integer> future = method.asyncMethod();
        log.info("Async is {}", future.get());
    }
}

如果导入 @Test 注解的包错了，会出现如下错误

import org.junit.jupiter.api.Test; // 错误包

java.lang.Exception: No runnable methods

	at org.junit.runners.BlockJUnit4ClassRunner.validateInstanceMethods(BlockJUnit4ClassRunner.java:191)
	at org.junit.runners.BlockJUnit4ClassRunner.collectInitializationErrors(BlockJUnit4ClassRunner.java:128)
	at org.junit.runners.ParentRunner.validate(ParentRunner.java:416)
	at org.junit.runners.ParentRunner.<init>(ParentRunner.java:84)
	at org.junit.runners.BlockJUnit4ClassRunner.<init>(BlockJUnit4ClassRunner.java:65)
	at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.<init>(SpringJUnit4ClassRunner.java:137)
	at org.springframework.test.context.junit4.SpringRunner.<init>(SpringRunner.java:49)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

使用正确的 @Test 包

import org.junit.Test;

运行 test() 方法，查看日志打印

SyncMethod thread: main
2021-12-24 11:41:40.400  INFO 70184 --- [main] com.yg.asynctest.AsyncTest: Sync is 1
AsyncMethod thread: task-1
2021-12-24 11:41:45.456  INFO 70184 --- [main] com.yg.asynctest.AsyncTest: Async is 2