java使用多线程并行处理逻辑后合并处理结果（Async注解方式）

1. 需求描述

业务逻辑中需要使用多线程去分别执行不同的方法，然后将所有方法的返回结果进行合并，即并行调用若干方法，然后将若干方法各自的返回结果做下一步处理，比如：
sync1()执行需要1s
sync2()执行需要2s
sync3()执行需要3s
那么代码将这3个方法并行执行后，结果应该>=3s，实际肯定超过3s

2. 使用@Async注解实现

2.1. 开启异步调用

项目启动类加上@EnableAsync注解
业务逻辑类或具体方法加上@Async注解

2.2. 编写异步的Service业务逻辑类

package xxx;

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

import java.util.concurrent.Future;

@Service
@Async
public class AsyncService {

    public Future<String> sync1() throws InterruptedException {
        Thread.sleep(1000);
        return new AsyncResult<>("sync1");
    }
    public Future<String> sync2() throws InterruptedException {
        Thread.sleep(2000);
        return new AsyncResult<>("sync2");
    }
    public Future<String> sync3() throws InterruptedException {
        Thread.sleep(3000);
        return new AsyncResult<>("sync3");
    }
}

2.3. 测试结果

package xxx;

import lombok.SneakyThrows;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.scheduling.annotation.Async;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.*;
import java.util.stream.Collectors;

@SpringBootTest
public class AsyncTest {

    @Autowired
    private AsyncService asyncService;

    @SneakyThrows
    @Test
    void test4(){
        long start = System.currentTimeMillis();
        Future<String> r1 = asyncService.sync1();
        Future<String> r2 = asyncService.sync2();
        Future<String> r3 = asyncService.sync3();
        String rr1 = r1.get();
        String rr2 = r2.get();
        String rr3 = r3.get();
        long end = System.currentTimeMillis();
        System.out.println("耗时："+(end-start));
        System.out.println("r1="+rr1);
        System.out.println("r2="+rr2);
        System.out.println("r3="+rr3);
    }
}

并行执行完3个方法后，每个方法的返回值需要.get()才能获取到，切记。