一个CompletableFuture的例子

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这是一个查询多个商店相同商品价格的例子，我会使用CompletableFuture的基础方法：

1.CompletableFuture.supplyAsync() : 异步获取方法返回值。

2.CompletableFuture.thenApply():将异步获取的返回值作为参数处理。

3.CompletableFuture.thenCompose():将上一个异步方法的返回值作为第二个异步方法的参数。

示例代码：

package ShopCompletableFuture;import org.apache.commons.lang3.RandomUtils;import java.util.Arrays;import java.util.List;import java.util.concurrent.*;import java.util.stream.Collectors;/** * Created by ibm on 2017/5/3. */public class ShopExercise {    public static void main(String[] args) {        long st = System.nanoTime();        ShopExercise shopExercise = new ShopExercise();        shopExercise.getPrices("xiaozhen");        long et = System.nanoTime();        System.out.println("耗时： " + (et -st)/1000_1000 + "ms");    }    /**     * 配置一个线程池的执行器，其中线程的数量等于查询的个数，然后设置为守护线程（不会阻止程序退出）     * 为什么使用线程池：因为开启的线程过多，返回会造成查询缓慢     */    final Executor executor = Executors.newFixedThreadPool(10, (Runnable r) -> {        Thread t = new Thread(r);        t.setDaemon(true);        return t;    });    /**     * 查询某个商品在每个商店的价格     */    public List<Double> getPrices(String product){        //初始化商店列表        List<String> shops = Arrays.asList("A_SHOP","B_SHOP","C_SHOP","D_SHOP","E_SHOP");        //并行查询 + 异步请求        List<CompletableFuture<Double>> futures = shops                .parallelStream()                .map(s -> CompletableFuture.supplyAsync(() -> getPrice(product,s),executor))                .map(future -> future.thenApply(Quote::parse))                .map(future -> future.thenCompose(quote ->                    CompletableFuture.supplyAsync(() -> DiscountService.apply(quote),executor)                ))                .collect(Collectors.toList());        return futures.stream().map(CompletableFuture::join).collect(Collectors.toList());        //=====下面的方式：在同一个stream中进行两次map操作：查询会顺序执行，因为流水线操作是顺序执行同步的====        //return shops.parallelStream().map(s -> CompletableFuture.supplyAsync(() -> {        //    StringBuilder result = new StringBuilder(s);        //    result.append(" : " + getPrice(product));        //    return result.toString();        //}))        //.map(CompletableFuture::join)        //.collect(Collectors.toList());    }    /**     * 同步获取价格     */    public String getPrice(String product,String shopName){        double price = calculatePrice(product);        Discount discount = Discount.CLOD;        String result = String.format("\n%s:%s:%s:%s:%s",shopName,product,price + "",discount.value + "",discount.desc);        System.out.println(result);        return result;    }    /**     * 计算价格：耗时查询 + 随机价格     * @param product 商品名称     * @return 随机价格     */    private double calculatePrice(String product){        delay();        return RandomUtils.nextDouble(10,100);    }    /**     * 制造耗时查询     */    private void delay(){        try {            Thread.sleep(2000l);        } catch (InterruptedException e) {            e.printStackTrace();        }    }    /**     * 折扣     */    enum Discount{        NONE(1,"没优惠"),        SILVER(0.7f,"七折"),        CLOD(0.5f,"五折"),        DIAMOND(0.3f,"三折");        double value;        String desc;         Discount(double value,String desc){            this.value = value;            this.desc = desc;        }    }//=============================================================    /**     * 异步获取价格     */    public Future<Double> getPriceAsync(String product){        CompletableFuture<Double> futurePrice = new CompletableFuture<>();        //在另一个线程中计算价格，当计算完成过后，将price赋值给future对象        new Thread(() -> {            try{                double price = calculatePrice(product);                futurePrice.complete(price);            }catch (Exception e){                //如果有异常，抛出去避免主线永久程阻塞                futurePrice.completeExceptionally(e);            }        }).start();        //使用supplyAsync工厂方法,两种方式完全等效        //CompletableFuture<Double> futurePrice2 = CompletableFuture.supplyAsync(() -> calculatePrice(product));        return futurePrice;    }}
package ShopCompletableFuture;/** * Created by ibm on 2017/5/8. */public class DiscountService {    public static double apply(Quote quote) {        try {            Thread.sleep(1000);        } catch (InterruptedException e) {            e.printStackTrace();        }        String sout = String.format("\n【折后 ：%s:%s:%s:%s:%s",quote.shopName,quote.product,quote.price * quote.discountValue,quote.discountValue + "",quote.discountDesc);        System.out.println(sout);        return quote.price * quote.discountValue;    }}

package ShopCompletableFuture;/** * Created by ibm on 2017/5/8. */public  class Quote{    String shopName;    String product;    double price;    double discountValue;    String discountDesc;    static Quote parse(String s){        String[] split = s.split(":");        Quote quote = new Quote();        quote.shopName = split[0];        quote.product = split[1];        quote.price = Double.valueOf(split[2]);        quote.discountValue = Double.valueOf(split[3]);        quote.discountDesc = split[4];        return quote;    }}

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