Java1.8中的Collections类的功能增强很多，你可以直接调用串行的Collections.stream()或并行的Collections.parallelStream()来对List，Set中的数据进行处理与操作（不支持Map）。

1：stream是什么？

java.util.Stream是一个接口,是1.8引入。它表示了某原子的序列，可以对原子进行各种操作，Stream可以是中间操作，也可以做为最重操作。作为中间操作时返回流对象本身，作为最重操作时返回某种类型的值。作为中间操作时可以在这个流上多次调用操作方法。

2：lambda表达式

其实lambda表达式实质上是个匿名函数，它由三部分组成：参数列表，箭头（->），以及一个表达式或语句块。来看一个示例：

public void sum(int a, int b){return a+b;
}

转为 lambda表达式为

(int a, int b) -> a + b;

还可以这样写，因为java会根据上下文推断出参数类型

(a, b) -> {return a + b;}

或

(a, b) -> a + b;

3：具体示例

package cn.huiyunche.driver.controller;import java.util.ArrayList;
import java.util.List;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
import java.util.stream.Collectors;import org.apache.commons.collections.CollectionUtils;public class Lambda {private static List<String> lambdaList = new ArrayList<>();private static String string = "string";private static String integer = "integer";public Lambda() {initData(string);}public static void initData(String flag) {if (CollectionUtils.isNotEmpty(lambdaList)) {lambdaList.clear();}if (string.equals(flag)) {lambdaList.add("Ulrica");lambdaList.add("Quella");lambdaList.add("Cecilia");lambdaList.add("Claudia");lambdaList.add("Desdemona");lambdaList.add("Indira");} else {lambdaList.add("1");lambdaList.add("2");lambdaList.add("2");lambdaList.add("3");lambdaList.add("3");lambdaList.add("4");lambdaList.add("4");lambdaList.add("4");lambdaList.add("5");lambdaList.add("5");lambdaList.add("5");lambdaList.add("6");lambdaList.add("6");}}// 这种方式就不多讲了，以前旧版本比较常见的做法public static void runThreadUseInnerClass() {new Thread(new Runnable() {@Overridepublic void run() {System.out.println("内部类实现的线程");}}).start();}// 新版本写法public static void thred() {new Thread(() -> System.out.println("内部类实现的线程")).start();}// 遍历listpublic static void ergodicList() {initData(string);System.out.println("=================遍历list开始==========>>>>>>>>>>>");lambdaList.forEach((value) -> System.out.println("value = " + value));System.out.println("<<<<<<<<<<<======遍历list结束=====================");}// 正序排序listpublic static void asc() {initData(integer);System.out.println("=================正序排序list开始==========>>>>>>>>>>>");lambdaList.stream().sorted().forEach((value) -> System.out.println("value = " + value));System.out.println("=================正序排序list结束==========>>>>>>>>>>>");}// 倒序排序listpublic static void desc() {initData(integer);System.out.println("=================倒序排序list开始==========>>>>>>>>>>>");lambdaList.stream().sorted((a, b) -> b.compareTo(a)).forEach((value) -> System.out.println("value = " + value));System.out.println("=================倒序排序list结束==========>>>>>>>>>>>");}// 过滤public static void filter(String val) {initData(string);System.out.println("=================过滤开始==========>>>>>>>>>>>");lambdaList.stream().filter((value) -> value.toLowerCase().contains(val.toLowerCase())).forEach((value) -> System.out.println("value = " + value));System.out.println("=================过滤结束==========>>>>>>>>>>>");}// map使用public static void map() {initData(string);System.out.println("=================map使用开始==========>>>>>>>>>>>");//lambdaList.stream().map((value) -> value.toUpperCase()).forEach((value) -> System.out.println("value = " + value));lambdaList.stream().map(String::toUpperCase).forEach((value) -> System.out.println("value = " + value));System.out.println("=================map使用结束==========>>>>>>>>>>>");}//parallelStream (并行) 和 stream（串行）public static void stream() {System.out.println("=================parallelStream (并行) 和 stream（串行）开始==========>>>>>>>>>>>");int max = 1000000;long t0, t1, count, millis;List<String> list = new ArrayList<>(max);for (int i = 0; i < max; i++) {UUID uuid = UUID.randomUUID();list.add(uuid.toString());}// 串行t0 = System.nanoTime();count = list.stream().sorted().count();System.out.println("count = " + count);t1 = System.nanoTime();millis = TimeUnit.NANOSECONDS.toMillis(t1 - t0);System.out.println(String.format("串行排序耗时: %d ms", millis));System.out.println("===========================");long t00, t11, count0, millis0;List<String> list0 = new ArrayList<>(max);for (int i = 0; i < max; i++) {UUID uuid = UUID.randomUUID();list0.add(uuid.toString());}// 串行t00 = System.nanoTime();count0 = list0.stream().sorted().count();System.out.println("count0 = " + count0);t11 = System.nanoTime();millis0 = TimeUnit.NANOSECONDS.toMillis(t11 - t00);System.out.println(String.format("并行排序耗时: %d ms", millis0));System.out.println("===========================");long millis00;millis00 = TimeUnit.NANOSECONDS.toMillis((t1 - t0) - (t11 - t00));System.out.println(String.format("串行比并行排序多耗时: %d ms", millis00));System.out.println("=================parallelStream (并行) 和 stream（串行）结束==========>>>>>>>>>>>");}// noneMatchpublic static void noneMatch(String val) {System.out.println("=================noneMatch使用开始==========>>>>>>>>>>>");initData(string);boolean bool = lambdaList.stream().noneMatch((value) -> value.contains(val));System.out.println("contains bool = " + bool);bool = lambdaList.stream().noneMatch((value) -> value.endsWith(val));System.out.println("endsWith bool = " + bool);bool = lambdaList.stream().noneMatch((value) -> value.startsWith(val));System.out.println("startsWith bool = " + bool);System.out.println("=================noneMatch使用结束==========>>>>>>>>>>>");}// allMatchpublic static void allMatch(String val) {System.out.println("=================allMatch使用开始==========>>>>>>>>>>>");initData(string);boolean bool = lambdaList.stream().allMatch((value) -> value.startsWith(val));System.out.println("bool = " + bool);System.out.println("=================allMatch使用结束==========>>>>>>>>>>>");}// anyMatchpublic static void anyMatch(String val) {System.out.println("=================anyMatch使用开始==========>>>>>>>>>>>");initData(string);boolean bool = lambdaList.stream().anyMatch((value) -> value.matches(val));System.out.println("bool = " + bool);System.out.println("=================anyMatch使用结束==========>>>>>>>>>>>");}// collect(过滤数据，返回List)public static void collect(String val) {System.out.println("=================collect使用开始==========>>>>>>>>>>>");initData(string);List<String> lists = lambdaList.stream().filter((value) -> value.toLowerCase().contains(val.toLowerCase())).collect(Collectors.toList());System.out.println(String.format("lists.size: %d ", lists.size()));lists.forEach((value) -> System.out.println("value = " + value));System.out.println("=================collect使用结束==========>>>>>>>>>>>");}// reduce(拼接数据只返回一个结果集)public static void reduce() {System.out.println("=================reduce使用开始==========>>>>>>>>>>>");initData(string);lambdaList.stream().reduce((value1, value2) -> value1 + value2).ifPresent(System.out::println);System.out.println("=================reduce使用结束==========>>>>>>>>>>>");}// 统计大于2小于5public static void groupBysum() {System.out.println("=================统计大于2小于5使用开始==========>>>>>>>>>>>");initData(integer);lambdaList.parallelStream().map(Integer::new).filter(val -> val >= 2 && val <= 6).collect(Collectors.groupingBy(p -> new Integer(p), Collectors.summingInt(p -> p))).forEach((key, value) -> System.out.println("key = " + key + " value = " +value));System.out.println("=================统计大于2小于5使用结束==========>>>>>>>>>>>");}public static void main(String[] args) {thred();runThreadUseInnerClass();ergodicList();asc();desc();filter("c");map();stream();noneMatch("Claudia");allMatch("U");anyMatch("Claudia");collect("c");reduce();groupBysum();}}

输出结果

内部类实现的线程
内部类实现的线程
=================遍历list开始==========>>>>>>>>>>>
value = Ulrica
value = Quella
value = Cecilia
value = Claudia
value = Desdemona
value = Indira
<<<<<<<<<<<======遍历list结束=====================
=================正序排序list开始==========>>>>>>>>>>>
value = 1
value = 2
value = 3
value = 4
value = 4
value = 4
value = 5
value = 6
=================正序排序list结束==========>>>>>>>>>>>
=================倒序排序list开始==========>>>>>>>>>>>
value = 6
value = 6
value = 5
value = 4
value = 3
value = 2
value = 1
=================倒序排序list结束==========>>>>>>>>>>>
=================过滤开始==========>>>>>>>>>>>
value = Ulrica
value = Cecilia
value = Claudia
=================过滤结束==========>>>>>>>>>>>
=================map使用开始==========>>>>>>>>>>>
value = ULRICA
value = QUELLA
value = CECILIA
value = CLAUDIA
value = DESDEMONA
value = INDIRA
=================map使用结束==========>>>>>>>>>>>
=================parallelStream (并行) 和 stream（串行）开始==========>>>>>>>>>>>
count = 1000000
串行排序耗时: 826 ms
===========================
count0 = 1000000
并行排序耗时: 781 ms
===========================
串行比并行排序多耗时: 44 ms
=================parallelStream (并行) 和 stream（串行）结束==========>>>>>>>>>>>
=================noneMatch使用开始==========>>>>>>>>>>>
contains bool = false
endsWith bool = false
startsWith bool = false
=================noneMatch使用结束==========>>>>>>>>>>>
=================allMatch使用开始==========>>>>>>>>>>>
bool = false
=================allMatch使用结束==========>>>>>>>>>>>
=================anyMatch使用开始==========>>>>>>>>>>>
bool = true
=================anyMatch使用结束==========>>>>>>>>>>>
=================collect使用开始==========>>>>>>>>>>>
lists.size: 3
value = Ulrica
value = Cecilia
value = Claudia
=================collect使用结束==========>>>>>>>>>>>
=================reduce使用开始==========>>>>>>>>>>>
UlricaQuellaCeciliaClaudiaDesdemonaIndira
=================reduce使用结束==========>>>>>>>>>>>
=================统计大于2小于5使用开始==========>>>>>>>>>>>
key = 2 value = 4
key = 3 value = 6
key = 4 value = 12
key = 5 value = 15
key = 6 value = 12
=================统计大于2小于5使用结束==========>>>>>>>>>>>