title: springBoot使用多线程
date: 2021-06-06 22:19:38
categories:
- springBoot
tags:
- springBoot
- 多线程
cover: https://coupon-image.oss-cn-shanghai.aliyuncs.com/image/blog/java.jpeg
description: springBoot多线程使用以及基础配置

线程配置类


package com.example.server.thread;
 
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.scheduling.annotation.EnableAsync;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
 
import java.util.concurrent.Executor;
 
@Configuration
@EnableAsync  // 启用异步任务
public class AsyncConfiguration {
 
    // 声明一个线程池(并指定线程池的名字)
    @Bean("nbpiTaskExecutor")
    public Executor asyncExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
 
        //核心线程数：线程池创建时候初始化的线程数
        executor.setCorePoolSize(5);
 
        //最大线程数：线程池最大的线程数，只有在缓冲队列满了之后才会申请超过核心线程数的线程
        executor.setMaxPoolSize(500);
 
        //允许线程的空闲时间60秒：当超过了核心线程出之外的线程在空闲时间到达之后会被销毁
        executor.setKeepAliveSeconds(60);
 
        //线程池名的前缀：设置好了之后可以方便我们定位处理任务所在的线程池
        executor.setThreadNamePrefix("DailyAsync-");
        executor.initialize();
        return executor;
    }
}

服务类

package com.example.server.thread;
 
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.scheduling.annotation.Async;
import org.springframework.stereotype.Service;
 
 
@Service
public class CustomMultiThreadingService {
 
    private static final Logger logger = LoggerFactory.getLogger(CustomMultiThreadingService.class);
 
    /*
    如何让异步调用的执行任务使用这个线程池中的资源来运行呢？方法非常简单，我们只需要在@Async注解中指定线程池名即可
     */
 
    @Async("nbpiTaskExecutor")
    public void executeAysncTask(Integer i) throws InterruptedException {
        logger.info("CustomMultiThreadingService ==> executeAysncTask1 method: 执行异步任务{} ", i);
        Thread.sleep(500L);
    }
 
}

控制类

package com.example.server.thread;
 
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
 
@RestController
@RequestMapping(value="/multithreading")
public class CustomMultiThreadingController {
 
    @Autowired
    private CustomMultiThreadingService customMultiThreadingService;
 
    @RequestMapping("/dotask")
    public String doTask() {
 
        try {
            for (int i=0;i<100000;i++){
                customMultiThreadingService.executeAysncTask(i);
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
 
        return "success";
    }
 
}

获取异步方法返回值

当异步方法有返回值时，如何获取异步方法执行的返回结果呢？这时需要异步调用的方法带有返回值CompletableFuture。
CompletableFuture是对Feature的增强，Feature只能处理简单的异步任务，而CompletableFuture可以将多个异步任务进行复杂的组合

@RestController
public class AsyncController {

    @Autowired
    private AsyncService asyncService;

    @SneakyThrows
    @ApiOperation("异步 有返回值")
    @GetMapping("/open/somethings")
    public String somethings() {
        CompletableFuture<String> createOrder = asyncService.doSomething1("create order");
        CompletableFuture<String> reduceAccount = asyncService.doSomething2("reduce account");
        CompletableFuture<String> saveLog = asyncService.doSomething3("save log");

        // 等待所有任务都执行完
        CompletableFuture.allOf(createOrder, reduceAccount, saveLog).join();
        // 获取每个任务的返回结果
        String result = createOrder.get() + reduceAccount.get() + saveLog.get();
        return result;
    }
}


@Slf4j
@Service
public class AsyncService {

    @Async("doSomethingExecutor")
    public CompletableFuture<String> doSomething1(String message) throws InterruptedException {
        log.info("do something1: {}", message);
        Thread.sleep(1000);
        return CompletableFuture.completedFuture("do something1: " + message);
    }

    @Async("doSomethingExecutor")
    public CompletableFuture<String> doSomething2(String message) throws InterruptedException {
        log.info("do something2: {}", message);
        Thread.sleep(1000);
        return CompletableFuture.completedFuture("; do something2: " + message);
    }

    @Async("doSomethingExecutor")
    public CompletableFuture<String> doSomething3(String message) throws InterruptedException {
        log.info("do something3: {}", message);
        Thread.sleep(1000);
        return CompletableFuture.completedFuture("; do something3: " + message);
    }
}

注意事项

@Async注解会在以下几个场景失效，也就是说明明使用了@Async注解，但就没有走多线程。

    异步方法使用static关键词修饰；
    异步类不是一个Spring容器的bean（一般使用注解@Component和@Service，并且能被Spring扫描到）；
    SpringBoot应用中没有添加@EnableAsync注解；
    在同一个类中，一个方法调用另外一个有@Async注解的方法，注解不会生效。原因是@Async注解的方法，是在代理类中执行的。
需要注意的是： 异步方法使用注解@Async的返回值只能为void或者Future及其子类，当返回结果为其他类型时，方法还是会异步执行，但是返回值都是null，