spring @Async异步方法使用及原理说明

异步类：

package com.example.spring.async;

import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Service;

import com.example.spring.MyLog;
/**
 * 将一个类声明为异步类，那么这个类对外暴露的方法全部成为异步方法。
 * 与异步方法的区别是这里的注解是加到类上，异步方法的注解是加到方法上。仅此而已
 * @DESC 
 * @author guchuang
 *
 */
@Async
@Service
public class AsyncClass {
    public AsyncClass() {
        MyLog.info("-------------------------init AsyncClass--------------------");
    }
    volatile int index = 0;
    public void foo() {
        MyLog.info("asyncclass foo, index:" + index);
    }
    public void foo(int i) {
        this.index = i;
        MyLog.info("asyncclass foo, index:" + i);
    }
    public void bar(int i) {
        this.index = i;
        MyLog.info("asyncclass bar, index:" + i);
    }
}

异步方法：

package com.example.spring.async;

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

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.scheduling.annotation.Async;
import org.springframework.scheduling.annotation.AsyncResult;
import org.springframework.stereotype.Service;
import org.springframework.web.context.WebApplicationContext;

import com.example.spring.MyLog;
/**
 *异步方法示例，关键点有三步：
 *  1.启动类增加注解 @EnableAsync
 *  2.当前类声明为服务 @Service
 *  3.方法上面添加注解 @Async
 *限制：
 *   默认类内的方法调用不会被aop拦截，也就是说同一个类内的方法调用，@Async不生效
 *解决办法：
 *  如果要使同一个类中的方法之间调用也被拦截，需要使用spring容器中的实例对象，而不是使用默认的this，因为通过bean实例的调用才会被spring的aop拦截
 *  本例使用方法： AsyncMethod asyncMethod = context.getBean(AsyncMethod.class);    然后使用这个引用调用本地的方法即可达到被拦截的目的
 *备注：
 *  这种方法只能拦截protected，default，public方法，private方法无法拦截。这个是spring aop的一个机制。
 *  
 * 默认情况下异步方法的调用使用的是SimpleAsyncTaskExecutor来执行异步方法调用，实际是每个方法都会起一个新的线程。
 * 大致运行过程：（以asyncMethod.bar1();为例）
 *  1.调用bar1()方法被aop拦截
 *  2.使用cglib获取要执行的方法和入参、当前实例（后续用于反射调用方法）。这些是运行一个方法的必要条件，可以封装成独立的方法来运行
 *  3.启动新的线程，调用上面封装的实际要调用的方法
 *  4.返回方法调用的结果
 *  前提是启动的时候被spring提前处理，将方法进行封装，加载流程：
 *    AsyncAnnotationBeanPostProcessor -> 
 * 如果要修改@Async异步方法底层调用：
 *  可以实现AsyncConfigurer接口，或者提供TaskExecutor实例（然后在@Async中指定这个实例），详见本例代码
 * 
 * 异步方法返回类型只能有两种：void和java.util.concurrent.Future
 *  当返回类型为void的时候，方法调用过程产生的异常不会抛到调用者层面，可以通过注册AsyncUncaughtExceptionHandler来捕获此类异常
 *  当返回类型为Future的时候，方法调用过程差生的异常会抛到调用者层面
 * 
 * @DESC 
 * @author guchuang
 *
 */
@Service
public class AsyncMethod {
    //@Autowired
    AsyncMethod asyncMethod;
    
    @Autowired
    WebApplicationContext context;
    
    /*@PostConstruct
    public void init() {
        this.asyncMethod = context.getBean(AsyncMethod.class);
    }*/
    @Async
    public void bar() {
        MyLog.info("sleep bar");
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    @Async
    private void bar1() {
        MyLog.info("private bar");
    }
    @Async
    public void bar2() {
        MyLog.info("public bar");
    }
    @Async
    protected void bar3() {
        MyLog.info("protected bar");
    }
    @Async
    void bar4() {
        MyLog.info("default bar");
    }

    @Async
    public void foo1() {
        MyLog.info("foo1");
        this.bar1();
        this.bar2();
        asyncMethod = context.getBean(AsyncMethod.class);
        asyncMethod.bar();      //异步
        asyncMethod.bar1();     //同步
        asyncMethod.bar2();     //异步
        asyncMethod.bar3();     //异步
        asyncMethod.bar4();     //异步
    }
    
    /**
     * 指定这个异步方法使用的底层执行器TaskExecutor
     * @param index
     */
    @Async("async1")
    public void foo2(int index) {
        MyLog.info("foo2 with index:" + index);
       }
    
    @Async
    public void foo3(int index, String threadName) {
        Thread.currentThread().setName(threadName);
        MyLog.info("foo3 with index:" + index);
    }
    
    @Async
    public void fooE() {
        throw new RuntimeException("无返回值异步方法抛出异常");
    }
    @Async
    public Future<String> futureE() {
        throw new RuntimeException("有返回值异步方法抛出异常");
    }
    
    /**
     * 带返回值的异步调用
     * @return
     */
    @Async
    public Future<String> futureTask1() {
        MyLog.info("start run future task1");
        MyLog.sleep(1000);
        return new AsyncResult<String>("future task1");
    }
    @Async
    public CompletableFuture<String> futureTask2 () {
        MyLog.info("Running task  thread: " + Thread.currentThread().getName());

        CompletableFuture<String> future = new CompletableFuture<String>() {
            @Override
            public String get () throws InterruptedException, ExecutionException {
                return " task result";
            }
        };
        return future;
    }
    /**
     * 指定使用的TaskExecutor，这个bean在config中已经配置
     * @param index
     * @param time
     */
    @Async("async2")
    public void asyncSleep(int index, int time) {
        try {
            Thread.sleep(time * 1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        MyLog.info("task:" + index + " end");
    }
    
    @Async("async3")
    public void asyncSleep3(int index, int time) {
        try {
            Thread.sleep(time * 1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        MyLog.info("task:" + index + " end");
    }
}

配置类：

package com.example.spring.async.config;

import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

import org.springframework.aop.interceptor.AsyncUncaughtExceptionHandler;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.task.TaskExecutor;
import org.springframework.scheduling.annotation.AsyncConfigurer;
import org.springframework.scheduling.concurrent.ConcurrentTaskExecutor;

import com.example.spring.MyLog;
import com.example.spring.MyThreadFactory;
import com.example.spring.async.RejectedPolicy;
/**
 * @Async异步方法线程池配置，默认不使用线程池，使用SimpleAsyncTaskExecutor（一个线程执行器，每个任务都会新建线程去执行）
 * 这里实现了接口AsyncConfigurer，并覆写了其内的方法，这样@Async默认的运行机制发生变化（使用了线程池，设置了线程运行过程的异常处理函数）
 * 备注：
 *   这里只是展示写法，要达到这个目的，可以不实现这个接口，具体见下面的方法
 * @DESC 
 * @author guchuang
 *
 */
@Configuration
@EnableAsync
public class AsyncConfig implements AsyncConfigurer {

    private static ExecutorService threadPool = new ThreadPoolExecutor(5, 5,
            60L, TimeUnit.MILLISECONDS,
            new LinkedBlockingQueue<>(3), new MyThreadFactory("common1"));
    
    private static ExecutorService threadPoolWithRejectDeal = new ThreadPoolExecutor(5, 5,
            60L, TimeUnit.MILLISECONDS,
            new LinkedBlockingQueue<>(3), new MyThreadFactory("common2"), new RejectedPolicy());
    
    /**
     * 这个实例声明的TaskExecutor会成为@Async方法运行的默认线程执行器
     * @Bean 使这个实例完全被spring接管
     */
    @Bean
    @Override
    public TaskExecutor getAsyncExecutor() {
        return new ConcurrentTaskExecutor(Executors.newFixedThreadPool(5,new MyThreadFactory("async")));
    }
    /**
     * 定义@Async方法默认的异常处理机制（只对void型异步返回方法有效，Future返回值类型的异常会抛给调用者）
     */
    @Override
    public AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {
        return (e, method, objects) -> MyLog.error("Method:" + method + ", exception:"+e.getMessage());
    }
    /**
     * 如果不覆写AsyncConfigurer的话，这个方法暴露bean会被当做@Async的默认线程池。
     * 注意必须是这个方法名（也就是bean name， 或者显示指定bean name @Qualifier("taskExecutor")），返回类型可以是Executor或者TaskExecutor
     * 如果没有配置的Executor，则默认使用SimpleAsyncTaskExecutor
     * 备注： 这种方式声明的bean，方法名就是bean name
     * @return
     */
    @Bean
    public Executor taskExecutor() {
        return new ConcurrentTaskExecutor(Executors.newFixedThreadPool(5,new MyThreadFactory("async0")));
    }
    /**
     * 定义其它的TaskExecutor，声明@Async方法的时候可以指定TaskExecutor，达到切换底层的目的
     * @return
     */
    @Bean
    public TaskExecutor async1() {
        return new ConcurrentTaskExecutor(Executors.newFixedThreadPool(2,new MyThreadFactory("async1")));
    }
    
    /**
     * 没有设置拒绝策略
     * @return
     */
    @Bean
    @Qualifier("async2")
    public TaskExecutor myAsyncExecutor2() {
        return new ConcurrentTaskExecutor(threadPool);
    }
    
    @Bean
    @Qualifier("async3")
    public TaskExecutor myAsyncExecutor3() {
        return new ConcurrentTaskExecutor(threadPoolWithRejectDeal);
    }
    
}

线程池相关类：

package com.example.spring;

import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicInteger;

public class MyThreadFactory implements ThreadFactory {
    private static final AtomicInteger poolNumber = new AtomicInteger(1);
    private final ThreadGroup group;
    private final AtomicInteger threadNumber = new AtomicInteger(1);
    private final String namePrefix;

    public MyThreadFactory(String name) {
        SecurityManager s = System.getSecurityManager();
        group = (s != null) ? s.getThreadGroup() :
                              Thread.currentThread().getThreadGroup();
        namePrefix = name + "-pool-" +
                      poolNumber.getAndIncrement() +
                     "-thread-";
    }

    public Thread newThread(Runnable r) {
        Thread t = new Thread(group, r,
                              namePrefix + threadNumber.getAndIncrement(),
                              0);
        if (t.isDaemon())
            t.setDaemon(false);
        if (t.getPriority() != Thread.NORM_PRIORITY)
            t.setPriority(Thread.NORM_PRIORITY);
        return t;
    }
}

package com.example.spring.async;

import java.util.concurrent.RejectedExecutionHandler;
import java.util.concurrent.ThreadPoolExecutor;

import com.example.spring.MyLog;
/**
 * 线程池满之后的处理策略类
 * @DESC 
 * @author guchuang
 *
 */
public class RejectedPolicy implements RejectedExecutionHandler {
    public RejectedPolicy() { }

    /**
     * 向线程池中添加线程被拒绝时会调用这个方法。一般拒绝是因为线程池满了
     *
     * @param r 被拒绝的任务
     * @param e 拒绝这个任务的线程池
     */
    @Override
    public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
        MyLog.info("one thread is rejected, i will deal it");
        if (!e.isShutdown()) {
            r.run();
        }
    }
}

测试类：

package com.example.spring.async;

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

import org.junit.AfterClass;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.Test;
import org.springframework.beans.factory.annotation.Autowired;

import com.example.spring.BaseDemoApplicationTest;
import com.example.spring.MyLog;
import com.example.spring.async.AsyncMethod;

public class AsyncMethodTest extends BaseDemoApplicationTest {

    @Autowired
    AsyncMethod asyncMethod;
    
    @BeforeClass
    public static void setUpBeforeClass() throws Exception {
    }
    @AfterClass
    public static void afterClass() throws Exception {
        MyLog.sleep(3000);
    }

    @Before
    public void setUp() throws Exception {
    }

    @Test
    public void test1() {
        asyncMethod.foo1();
        MyLog.info("just wait");
        MyLog.sleep(2000);
    }
    @Test
    public void test2() {
        for (int i = 0; i < 10; i++) {
            asyncMethod.foo2(i);
        }
    }
    @Test
    public void test3() {
        for (int i = 0; i < 10; i++) {
            asyncMethod.foo3(i, "gc-thread-"+i);
        }
    }

    @Test
    public void testE() {
        try {
            Future<String> result = asyncMethod.futureE();
            //这里调用get才会获得异常
            MyLog.info(result.get());
        } catch(Exception e) {
            //e.printStackTrace();
            MyLog.info("this is excepted Exception:" + e.getMessage());
        }
        
        asyncMethod.fooE();
        MyLog.info("end call e");
        //MyLog.sleep(1000);
    }
    
    @Test
    public void testFuture() throws InterruptedException, ExecutionException {
        MyLog.info("
-----------------start-----------------------");
        Future<String> result1 = asyncMethod.futureTask1();
        CompletableFuture<String> result2 = asyncMethod.futureTask2();
        MyLog.info("result1:" + result1.get());
        MyLog.info("result2:" + result2.get());
    }
    
    @Test
    public void testReject() {
        MyLog.info("
-----------------start testReject-----------------------");
        MyLog.info("start add task");
        //当超过线程词最大容量的时候，会抛出TaskRejectedException
        try {
            for (int i = 0; i < 10; i++) {
                asyncMethod.asyncSleep(i, 1);
            }
        } catch(RejectedExecutionException e) {
            MyLog.info("excepted exception:" + e.getMessage());
        }
        MyLog.info("finished add task");
        MyLog.sleep(100 * 1000);
    }
    
    @Test
    public void testRejectWithDeal() {
        MyLog.info("
-----------------start testRejectWithDeal-----------------------");
        MyLog.info("start add task");
        //当超过线程词最大容量的时候，会抛出TaskRejectedException
        try {
            for (int i = 0; i < 10; i++) {
                asyncMethod.asyncSleep3(i, 1);
            }
        } catch(RejectedExecutionException e) {
            MyLog.info("excepted exception:" + e.getMessage());
        }
        MyLog.info("finished add task");
        MyLog.sleep(100 * 1000);
    }
}

package com.example.spring.async;

import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.Test;
import org.springframework.beans.factory.annotation.Autowired;

import com.example.spring.BaseDemoApplicationTest;
import com.example.spring.MyLog;
import com.example.spring.async.AsyncClass;

public class AsyncClassTest extends BaseDemoApplicationTest {

    @Autowired
    AsyncClass asyncClass;
    
    @BeforeClass
    public static void setUpBeforeClass() throws Exception {
    }

    @Before
    public void setUp() throws Exception {
    }

    @Test
    public void test() {
        asyncClass.foo();
        asyncClass.foo(10);
        MyLog.sleep(100);
        asyncClass.foo();
    }

}