转自：https://www.cnblogs.com/jun1019/p/11521145.html

假如我有一个订单相关的统计接口，需要返回3样数据：今日订单数、今日交易额、总交易额。

一般的我们的做法是串行调用3个函数，把调用返回的结果返回给调用者，这3次调用时串行执行的，如果每个调用耗时1秒的话，3次调用总耗时就是3秒。

这种做法效率非常低，因为3次调用之间无所谓先后顺序，所以采用并行执行效率会更好。比如使用线程池ExecutorService实现异步调用。

其实Java8提供了一个非常牛逼的CompletableFuture类，也可以实现异步化：

import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Service;

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.TimeUnit;

@Slf4j
@Service
public class OrderService {

    /**
     * 今日订单数
     *
     * @return
     */
    public CompletableFuture<String> todayOrderCount() {
        return CompletableFuture.supplyAsync(() -> this.getTodayOrderCount());
    }

    public CompletableFuture<String> todayTurnover() {
        return CompletableFuture.supplyAsync(() -> this.getTodayTurnover());
    }

    public CompletableFuture<String> totalTurnover() {
        return CompletableFuture.supplyAsync(() -> this.getTotalTurnover());
    }

    private String getTodayOrderCount() {
        System.out.println(">>>>>>> 查询今日订单数:" + Thread.currentThread().getName());
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return "50";
    }

    /**
     * 今日交易额
     *
     * @return
     */
    private String getTodayTurnover() {
        System.out.println(">>>>>>> 查询今日交易额:" + Thread.currentThread().getName());
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return "200";
    }

    /**
     * 总交易额
     *
     * @return
     */
    private String getTotalTurnover() {
        System.out.println(">>>>>>> 查询总交易额:" + Thread.currentThread().getName());
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return "800";
    }
}

import com.alibaba.fastjson.JSONObject;
import com.example.sb.service.test.impl.OrderService;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.concurrent.CompletableFuture;

@Slf4j
@RestController
@RequestMapping("/order")
public class OrderController {

    @Autowired
    private OrderService orderService;

    @GetMapping("/report")
    public JSONObject report() {
        long start = System.currentTimeMillis();
        JSONObject json = orderReport();
        System.out.println("耗时:" + (System.currentTimeMillis() - start));
        return json;
    }

    private JSONObject orderReport() {
        CompletableFuture<String> todayOrderCountFuture = orderService.todayOrderCount();
        CompletableFuture<String> todayTurnoverFuture = orderService.todayTurnover();
        CompletableFuture<String> totalTurnoverFuture = orderService.totalTurnover();

        JSONObject json = new JSONObject();

        todayOrderCountFuture.whenComplete((v, t) -> {
            json.put("todayOrderCountFuture", v);
        });
        todayTurnoverFuture.whenComplete((v, t) -> {
            json.put("todayTurnoverFuture", v);
        });
        totalTurnoverFuture.whenComplete((v, t) -> {
            json.put("totalTurnoverFuture", v);
        });

        CompletableFuture.allOf(todayOrderCountFuture, todayTurnoverFuture, totalTurnoverFuture)
                .thenRun(() -> System.out.println("完成！！！！"))
                .join();
        return json;
    }
}

浏览器访问：http://localhost:8080/order/report 执行结果截图如下：

因为每个OrderService的调用模拟都是耗时1秒，3个调用并行执行，最终耗时自然也是1秒。