1 Future接口

1.1 FutureTask相关接口关系

1.2 Future接口的优缺点

1.2.1 优点

结合线程池，可以提升程序的运算效率。

1.2.2 缺点

（1） get方法阻塞

（2）isDone通常会轮询


我们还想需要：
(1) 缺少完成时的回调通知。
(2) 多个任务前后依赖可以组合处理。
（3）选择计算速度最快的那个线程。

2 Complatable Future

2.1 CompletionStage

2.2 使用案例

2.2.1 runAsync

2.2.2 supplyAsync

package org.example.completablefuturetest;import java.util.concurrent.*;public class CompletableFutureUseDemo {public static void main(String[] args) {ExecutorService threadPool = Executors.newFixedThreadPool(3);try {CompletableFuture.supplyAsync(() -> {System.out.println(Thread.currentThread().getName() + "-------come in.");int result = ThreadLocalRandom.current().nextInt(10);try {TimeUnit.SECONDS.sleep(2);} catch (InterruptedException e) {throw new RuntimeException(e);}System.out.println("---------2s之后出结果---" + result);if (result > 2) {throw new RuntimeException("sk, throw a run time exception.");}return result;}, threadPool).whenComplete((value, exception) -> {if (exception == null) {System.out.println("-------计算完成，更新系统value：---" + value);}}).exceptionally(exception -> {System.out.println("sk, will handle a ex.");exception.printStackTrace();return null;});System.out.println(Thread.currentThread().getName() + "线程先去忙其他任务");} catch (Exception exception) {exception.printStackTrace();} finally {threadPool.shutdown();}}
}

2.2.3 join和get的区别

就是抛出的异常不一样。 join不需要使用方显示地捕获异常。

public class CompletableFutureMallDemo {public static void main(String[] args) {CompletableFuture cf = CompletableFuture.supplyAsync(new Supplier<String>() {@Overridepublic String get() {return "sk, 1234";}});System.out.println(cf.join());}
}

2.2.4 CF simple project使用案例

package org.example.cfmall;import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;import java.util.Arrays;
import java.util.List;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ThreadLocalRandom;
import java.util.concurrent.TimeUnit;
import java.util.function.Supplier;
import java.util.stream.Collectors;public class CompletableFutureMallDemo {static List<NetMall> list = Arrays.asList(new NetMall("jingdong"),new NetMall("dangdang"),new NetMall("taobao"));public static List<String> getPrice(List<NetMall> list, String productName) {// return getPriceStepByStep(list, productName);return getPriceAsync(list, productName);}private static List<String> getPriceAsync(List<NetMall> list, String productName) {return list.stream().map(netMall -> CompletableFuture.supplyAsync(new Supplier<String>() {@Overridepublic String get() {return String.format(productName + "in %s price is %.2f",netMall.getNetMallName(), netMall.calcPrice(productName));}})).collect(Collectors.toList()).stream().map(cf -> cf.join()).collect(Collectors.toList());}private static List<String> getPriceStepByStep(List<NetMall> list, String productName) {return list.stream().map(netMall -> String.format(productName + "in %s price is %.2f",netMall.getNetMallName(), netMall.calcPrice(productName))).collect(Collectors.toList());}public static void main(String[] args) {long startTime = System.currentTimeMillis();List<String> priceList = getPrice(list, "mysql");for (String price : priceList) {System.out.println(price);}long endTime = System.currentTimeMillis();System.out.println("------costTime: " + (endTime - startTime) + " ms");}
}@AllArgsConstructor
@NoArgsConstructor
@Data
class NetMall {private String netMallName;public double calcPrice(String productName) {try {TimeUnit.SECONDS.sleep(1);} catch (InterruptedException e) {e.printStackTrace();}return ThreadLocalRandom.current().nextDouble() * 2 + productName.charAt(0);}
}

2.2.5 CF 常用API

2.2.5.1 获取结果和主动触发计算

2.2.5.2 对计算结果进行处理

2.2.5.3 对计算结果进行消费

带Async后缀和不带后缀的api的区别

2.2.5.4 对计算速度进行选用