Java 8 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); }