CompletableFuture是java8提供的异步任务创建,回调,编排和异常处理.

创建异步任务

1. runAsync(Runnable runnable),创建一个没有返回值的异步任务,接受一个Runnable接口的实现类对象.

static CompletableFuture<Void> runAsync(Runnable runnable)

示例,异步读取指定文件

 public static void main(String[] args) throws ExecutionException, InterruptedException {
        ExecutorService executor = Executors.newFixedThreadPool(5);
        CommonUtil.printThreadLog("start");
 		CompletableFuture.runAsync(() -> {
            CommonUtil.printThreadLog("读取文件");
            String news = CommonUtil.readFile("news.txt");
            CommonUtil.printThreadLog(news);
            CommonUtil.printThreadLog("读取文件结束");

        },executor);
        //关闭线程池
        executor.shutdown();
        CommonUtil.printThreadLog("end");

2. supplyAsync(Supplier supplier),创建一个有返回值的异步任务

static <U> CompletableFuture<U> supplyAsync(Supplier<U> supplier)

示例

ExecutorService executor = Executors.newFixedThreadPool(5);
        CommonUtil.printThreadLog("start");
        CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> {
            CommonUtil.printThreadLog("读取文件");
            String news = CommonUtil.readFile("news.txt");
            CommonUtil.printThreadLog("读取文件结束");
            return news;
        },executor);

        CommonUtil.printThreadLog(future.get());
        //关闭线程池
        executor.shutdown();
        CommonUtil.printThreadLog("end");

示例中使用到的CommonUtil

public class CommonUtil {

    /**
     * 读取指定路径的文件
     * @param pathFile
     * @return
     */
    public static String readFile(String pathFile){
        try {
            pathFile = "D:\\study\\zlm_platform\\src\\main\\resources\\"+pathFile;
            return Files.readString(Paths.get(pathFile));
        } catch (IOException e) {
            e.printStackTrace();
            return "";
        }
    }

    /**
     * 休眠指定毫秒数
     * @param millis
     */
    public static void sleepMillis(long millis){
        try {
            TimeUnit.MILLISECONDS.sleep(millis);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    /**
     * 休眠指定秒数
     * @param seconds
     */
    public static void sleepSecond(int seconds){
        try {
            TimeUnit.SECONDS.sleep(seconds);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    /**
     * 答应输出带线程信息的日志
     * @param message
     */
    public static void printThreadLog(String message){
        String result = new StringJoiner(" | ")
                .add(String.valueOf(System.currentTimeMillis()))
                .add(String.format("%2d",Thread.currentThread().getId()))
                .add(String.valueOf(Thread.currentThread().getName()))
                .add(message)
                .toString();
        System.out.println(result);
    }

}