多平台统一管理软件接口,如何实现多平台统一管理软件接口
289
2022-06-06
上次老师跟大家分享了 cookie、session和token,今天给大家分享一下Java 8中的Stream API。
Stream简介
1、Java 8引入了全新的Stream API。这里的Stream和I/O流不同,它更像具有Iterable的集合类,但行为和集合类又有所不同。
2、stream是对集合对象功能的增强,它专注于对集合对象进行各种非常便利、高效的聚合操作,或者大批量数据操作。
3、只要给出需要对其包含的元素执行什么操作,比如 “过滤掉长度大于 10 的字符串”、“获取每个字符串的首字母”等,Stream 会隐式地在内部进行遍历,做出相应的数据转换。
为什么要使用Stream
1、函数式编程带来的好处尤为明显。这种代码更多地表达了业务逻辑的意图,而不是它的实现机制。易读的代码也易于维护、更可靠、更不容易出错。
2、高端
实例数据源
public class Data { private static List<PersonModel> list = null; static { PersonModel wu = new PersonModel("wu qi", 18, "男"); PersonModel zhang = new PersonModel("zhang san", 19, "男"); PersonModel wang = new PersonModel("wang si", 20, "女"); PersonModel zhao = new PersonModel("zhao wu", 20, "男"); PersonModel chen = new PersonModel("chen liu", 21, "男"); list = Arrays.asList(wu, zhang, wang, zhao, chen); } public static List<PersonModel> getData() { return list; } }
Filter
/** * 过滤所有的男性 */ public static void fiterSex(){ List<PersonModel> data = Data.getData(); //old List<PersonModel> temp=new ArrayList<>(); for (PersonModel person:data) { if ("男".equals(person.getSex())){ temp.add(person); } } System.out.println(temp); //new List<PersonModel> collect = data .stream() .filter(person -> "男".equals(person.getSex())) .collect(toList()); System.out.println(collect); } /** * 过滤所有的男性 并且小于20岁 */ public static void fiterSexAndAge(){ List<PersonModel> data = Data.getData(); //old List<PersonModel> temp=new ArrayList<>(); for (PersonModel person:data) { if ("男".equals(person.getSex())&&person.getAge()<20){ temp.add(person); } } //new 1 List<PersonModel> collect = data .stream() .filter(person -> { if ("男".equals(person.getSex())&&person.getAge()<20){ return true; } return false; }) .collect(toList()); //new 2 List<PersonModel> collect1 = data .stream() .filter(person -> ("男".equals(person.getSex())&&person.getAge()<20)) .collect(toList()); }
Map
/** * 取出所有的用户名字 */ public static void getUserNameList(){ List<PersonModel> data = Data.getData(); //old List<String> list=new ArrayList<>(); for (PersonModel persion:data) { list.add(persion.getName()); } System.out.println(list); //new 1 List<String> collect = data.stream().map(person -> person.getName()).collect(toList()); System.out.println(collect); //new 2 List<String> collect1 = data.stream().map(PersonModel::getName).collect(toList()); System.out.println(collect1); //new 3 List<String> collect2 = data.stream().map(person -> { System.out.println(person.getName()); return person.getName(); }).collect(toList()); }
FlatMap
public static void flatMapString() { List<PersonModel> data = Data.getData(); //返回类型不一样 List<String> collect = data.stream() .flatMap(person -> Arrays.stream(person.getName().split(" "))).collect(toList()); List<Stream<String>> collect1 = data.stream() .map(person -> Arrays.stream(person.getName().split(" "))).collect(toList()); //用map实现 List<String> collect2 = data.stream() .map(person -> person.getName().split(" ")) .flatMap(Arrays::stream).collect(toList()); //另一种方式 List<String> collect3 = data.stream() .map(person -> person.getName().split(" ")) .flatMap(str -> Arrays.asList(str).stream()).collect(toList()); }
Reduce
public static void reduceTest(){ //累加,初始化值是 10 Integer reduce = Stream.of(1, 2, 3, 4) .reduce(10, (count, item) ->{ System.out.println("count:"+count); System.out.println("item:"+item); return count + item; } ); System.out.println(reduce); Integer reduce1 = Stream.of(1, 2, 3, 4) .reduce(0, (x, y) -> x + y); System.out.println(reduce1); String reduce2 = Stream.of("1", "2", "3") .reduce("0", (x, y) -> (x + "," + y)); System.out.println(reduce2); }
Collect
/** * toList */ public static void toListTest(){ List<PersonModel> data = Data.getData(); List<String> collect = data.stream() .map(PersonModel::getName) .collect(Collectors.toList()); } /** * toSet */ public static void toSetTest(){ List<PersonModel> data = Data.getData(); Set<String> collect = data.stream() .map(PersonModel::getName) .collect(Collectors.toSet()); } /** * toMap */ public static void toMapTest(){ List<PersonModel> data = Data.getData(); Map<String, Integer> collect = data.stream() .collect( Collectors.toMap(PersonModel::getName, PersonModel::getAge) ); data.stream() .collect(Collectors.toMap(per->per.getName(), value->{ return value+"1"; })); } /** * 指定类型 */ public static void toTreeSetTest(){ List<PersonModel> data = Data.getData(); TreeSet<PersonModel> collect = data.stream() .collect(Collectors.toCollection(TreeSet::new)); System.out.println(collect); } /** * 分组 */ public static void toGroupTest(){ List<PersonModel> data = Data.getData(); Map<Boolean, List<PersonModel>> collect = data.stream() .collect(Collectors.groupingBy(per -> "男".equals(per.getSex()))); System.out.println(collect); } /** * 分隔 */ public static void toJoiningTest(){ List<PersonModel> data = Data.getData(); String collect = data.stream() .map(personModel -> personModel.getName()) .collect(Collectors.joining(",", "{", "}")); System.out.println(collect); } /** * 自定义 */ public static void reduce(){ List<String> collect = Stream.of("1", "2", "3").collect( Collectors.reducing(new ArrayList<String>(), x -> Arrays.asList(x), (y, z) -> { y.addAll(z); return y; })); System.out.println(collect); }
Optional
public static void main(String[] args) { PersonModel personModel=new PersonModel(); //对象为空则打出 - Optional<Object> o = Optional.of(personModel); System.out.println(o.isPresent()?o.get():"-"); //名称为空则打出 - Optional<String> name = Optional.ofNullable(personModel.getName()); System.out.println(name.isPresent()?name.get():"-"); //如果不为空,则打出xxx Optional.ofNullable("test").ifPresent(na->{ System.out.println(na+"ifPresent"); }); //如果空,则返回指定字符串 System.out.println(Optional.ofNullable(null).orElse("-")); System.out.println(Optional.ofNullable("1").orElse("-")); //如果空,则返回 指定方法,或者代码 System.out.println(Optional.ofNullable(null).orElseGet(()->{ return "hahah"; })); System.out.println(Optional.ofNullable("1").orElseGet(()->{ return "hahah"; })); //如果空,则可以抛出异常 System.out.println(Optional.ofNullable("1").orElseThrow(()->{ throw new RuntimeException("ss"); })); // Objects.requireNonNull(null,"is null"); //利用 Optional 进行多级判断 EarthModel earthModel1 = new EarthModel(); //old if (earthModel1!=null){ if (earthModel1.getTea()!=null){ //... } } //new Optional.ofNullable(earthModel1) .map(EarthModel::getTea) .map(TeaModel::getType) .isPresent(); // Optional<EarthModel> earthModel = Optional.ofNullable(new EarthModel()); // Optional<List<PersonModel>> personModels = earthModel.map(EarthModel::getPersonModels); // Optional<Stream<String>> stringStream = personModels.map(per -> per.stream().map(PersonModel::getName)); //判断对象中的list Optional.ofNullable(new EarthModel()) .map(EarthModel::getPersonModels) .map(pers->pers .stream() .map(PersonModel::getName) .collect(toList())) .ifPresent(per-> System.out.println(per)); List<PersonModel> models=Data.getData(); Optional.ofNullable(models) .map(per -> per .stream() .map(PersonModel::getName) .collect(toList())) .ifPresent(per-> System.out.println(per)); }
并发
//根据数字的大小,有不同的结果 private static int size=10000000; public static void main(String[] args) { System.out.println("-----------List-----------"); testList(); System.out.println("-----------Set-----------"); testSet(); } /** * 测试list */ public static void testList(){ List<Integer> list = new ArrayList<>(size); for (Integer i = 0; i < size; i++) { list.add(new Integer(i)); } List<Integer> temp1 = new ArrayList<>(size); //老的 long start=System.currentTimeMillis(); for (Integer i: list) { temp1.add(i); } System.out.println(+System.currentTimeMillis()-start); //同步 long start1=System.currentTimeMillis(); list.stream().collect(Collectors.toList()); System.out.println(System.currentTimeMillis()-start1); //并发 long start2=System.currentTimeMillis(); list.parallelStream().collect(Collectors.toList()); System.out.println(System.currentTimeMillis()-start2); } /** * 测试set */ public static void testSet(){ List<Integer> list = new ArrayList<>(size); for (Integer i = 0; i < size; i++) { list.add(new Integer(i)); } Set<Integer> temp1 = new HashSet<>(size); //老的 long start=System.currentTimeMillis(); for (Integer i: list) { temp1.add(i); } System.out.println(+System.currentTimeMillis()-start); //同步 long start1=System.currentTimeMillis(); list.stream().collect(Collectors.toSet()); System.out.println(System.currentTimeMillis()-start1); //并发 long start2=System.currentTimeMillis(); list.parallelStream().collect(Collectors.toSet()); System.out.println(System.currentTimeMillis()-start2); }
调试
private static void peekTest() { List<PersonModel> data = Data.getData(); //peek打印出遍历的每个per data.stream().map(per->per.getName()).peek(p->{ System.out.println(p); }).collect(toList()); }
版权声明:本文内容由网络用户投稿,版权归原作者所有,本站不拥有其著作权,亦不承担相应法律责任。如果您发现本站中有涉嫌抄袭或描述失实的内容,请联系我们jiasou666@gmail.com 处理,核实后本网站将在24小时内删除侵权内容。
发表评论
暂时没有评论,来抢沙发吧~