CompletableFuture、ForEach、DateTime、LocalDateTime

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异步API

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。

runAsync() 异步无参返回

@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

@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)

@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)

@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

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

@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

@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

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

forEach对Map的循环

@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";
}

时间类

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

DateTimeFormatter

/**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转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

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

/**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**/
@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**/
@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);
}