java8 异步api、循环、日期

java8 异步api、循环、日期

转载请注明出处：https://www.cnblogs.com/funnyzpc/p/10801470.html

异步api

对于多任务耗时的业务场景，一般我们会用到线程异步处理,在以前我们用 Thread 或者 Runnable 来实现异步，这是oracle官方做法，不过缺点很明显

• 对于复杂业务场景需要配置线程池
• 代码繁杂，对于新手容易造成不必要的bug
• 如果涉及到线程锁或线程通讯就棘手了

现在，java8为我们提供了CompletableFuture类，可以完全解决以上问题。

主要方法有:

• runAsync() 异步无参返回
  • 样例:

    @Test
    public void asyncThread()throws Exception{
        CompletableFuture async1 = CompletableFuture.runAsync(()->{
            try {
                Thread.sleep(1000);
                System.out.println(Thread.currentThread().getName());
                System.out.println("none return Async");
            }catch (Exception e){
                e.printStackTrace();
            }
        });
        // 调用get()将等待异步逻辑处理完成
        async1.get();
    }

• supplyAsync() 异步有参返回
  • 样例:

    @Test
    public void asyncThread2()throws Exception{
        CompletableFuture<String> async2 = CompletableFuture.supplyAsync(()->{
            return "hello";
        });
        String result = async2.get();
        // String result2 = async2.get(5L, TimeUnit.SECONDS);
        System.out.println(result);
    }

• allOf() 多个异步处理(针对有参返回)
  • 样例：

    @Test
    public void asyncThread3()throws Exception{
        CompletableFuture<String> a = CompletableFuture.supplyAsync(() -> "hello");
        CompletableFuture<String> b = CompletableFuture.supplyAsync(() -> "youth");
        CompletableFuture<String> c = CompletableFuture.supplyAsync(() -> "!");

        CompletableFuture all = CompletableFuture.allOf(a,b,c);
        all.get();

        String result = Stream.of(a, b,c)
                .map(CompletableFuture::join)
                .collect(Collectors.joining(" "));

        System.out.println(result);
    }

• anyOf() 多个异步随机处理(针对有参返回)
  • 样例

    @Test
    public void asyncThread4()throws Exception{
        CompletableFuture<String> a = CompletableFuture.supplyAsync(() ->{
                    try{
                        Thread.sleep(20);
                        return "hello";
                    }catch (Exception e){
                        e.printStackTrace();
                        return "none~";
                    }
                });
        CompletableFuture<String> b = CompletableFuture.supplyAsync(() -> "youth");
        CompletableFuture<String> c = CompletableFuture.supplyAsync(() -> "!");

        CompletableFuture<Object> any = CompletableFuture.anyOf(a,b,c);
        String result = (String)any.get();

        System.out.println(result);
    }

循环ForEach

java8 在原有for或iterator循环下又提供了 forEach 的方法，不过与for循环不同的是 forEach 循环是建立在stream之上的,而且比for或iterator方便的是，他可以循环Map对象，

如果您尝试配合filter处理就更赞了~

• forEach对List的循环样例

    @Test
    public void listForeach(){
        List<String> lst = new ArrayList<String>(5){{
            add("A");
            add("B");
            add("H");
            add("O");
            add("M");
        }};
        lst.forEach(System.out::println);
        lst.forEach((item)-> System.out.println(item.concat("_")));
    }

• forEach对数组的循环 样例

    @Test
    public void arrForeach(){
        String[] strArr = new String[]{"A","B","C","D"};

        Arrays.stream(strArr).forEach(System.out::println);
    }

• forEach对int范围的循环 样例

    @Test
    public void numericForeach(){
        IntStream.range(0,10).forEach(System.out::println);
    }

• forEach对Map的循环 样例:

       @Test
    public void mapForeach(){
        Map<String,Object> mps = new HashMap<String,Object>(5){{
            put("a",1);
            put("b",true);
            put("c",23.44F);
            put("d","hello");
            put("e",11L);
        }};
        mps.forEach((k,v)-> System.out.println(k.concat(":").concat(String.valueOf(v))));
        String str = "hello";
    }

新的时间类(LocalDate、LocalDateTime)

java8 之前我们处理时间 大多会涉及到这几个类Date、SimpleDateFormat、Calendar ，这种处理方式复杂、存在线程隐患、国际化困难、日期加减等处理麻烦等等。

现在有了 LocalDate、LocalDateTime、DateTimeFormatter 生活就变得简单了~

• 格式化及区域定义

    /**设置格式化模板**/
     private static final DateTimeFormatter DATE_TIME_FORMATTER = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss.SSSS");
    /**设置日期时区常量**/
    public static final ZoneId CHINA_ZONE_ID = ZoneId.systemDefault();

• Date格式化为DateTime

    /**Date格式化为DateTime**/
    @Test
    public void dateToDateTime(){
        Date date = new Date();
        LocalDateTime dateTime = date.toInstant().atZone(CHINA_ZONE_ID).toLocalDateTime();
        System.out.println(dateTime);
    }

• LocalDate/LocalDateTime转Date

    /**LocalDate/LocalDateTime转Date**/
        @Test
    public void toDate(){
        // LocalDate
        LocalDate localDate = LocalDate.now();
        Date d1 = Date.from(localDate.atStartOfDay(CHINA_ZONE_ID).toInstant());
        System.out.println(d1);

        // LocalDateTime
        LocalDateTime localDateTime = LocalDateTime.now();
        Date d2 = Date.from(localDateTime.atZone(CHINA_ZONE_ID).toInstant());
        System.out.println(d2);

    }

• 日期格式化

     /**日期格式化**/
    @Test
    public void formatDate(){
        System.out.println(LocalDateTime.now().format(DATE_TIME_FORMATTER));
    }

• 日期加减

    /**日期加减**/
    @Test
    public void plusDay(){
        LocalDateTime dateTime = LocalDateTime.now(CHINA_ZONE_ID);
        //天
        dateTime=dateTime.plusDays(1);
        //时
        dateTime=dateTime.plusHours(-1);
        //分钟
        dateTime=dateTime.plusMinutes(30);
        System.out.println(dateTime.format(DATE_TIME_FORMATTER));
    }

• 日期时间间隔

        /**日期时间间隔**/
    @Test
    public void betweenDay(){
        // LocalDateTime
        LocalDateTime startDate = LocalDateTime.of(2019,07,01,12,12,22);
        LocalDateTime endDate = LocalDateTime.of(2019,07,03,12,12,22);
        Long withSecond =  endDate.atZone(CHINA_ZONE_ID).toEpochSecond() - startDate.atZone(CHINA_ZONE_ID).toEpochSecond();
        System.out.println(withSecond/60/60/24);

        // LocalDate
        LocalDate startDate2 = LocalDate.of(2019,07,01);
        LocalDate endDate2 = LocalDate.of(2019,07,03);
        Long withSecond2 =  endDate2.toEpochDay() - startDate2.toEpochDay();
        System.out.println(withSecond2);
    }

• 第一天and最后一天

    /**第一天and最后一天**/
    @Test
    public void theLastDay(){
        // 当月第一天
        LocalDateTime dateTime = LocalDateTime.of(2019,07,03,12,12,22);
        dateTime = dateTime.with(TemporalAdjusters.firstDayOfMonth());
        System.out.println(dateTime);
        // 当月最后一天
        dateTime = dateTime.with(TemporalAdjusters.lastDayOfMonth());
        System.out.println(dateTime);

        //当月的第几天
        dateTime = LocalDateTime.now();
        int dayOfMonth = dateTime.getDayOfMonth();
        System.out.println(dayOfMonth);
        // 当前周的第几天
        int dayOfWeek = dateTime.getDayOfWeek().getValue();
        System.out.println(dayOfWeek);
    }

OK，本次分享就到这里，如有谬误恳请指正~