1.概述
本篇主要介绍lambda中常用的收集器，收集器的作用就是从数据流中生成需要的数据接口。
最常用的就是Collectors.toList()，只要将它传递给collect()函数，就能够使用它了。
在我们使用收集器的时候经常会用到“方法引用”这样的简写语法：
方法引用:ClassName::methodName
2.代码示例
按照收集器的作用分类
公共代码：
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Artist {
private String name;
private String age;
private boolean isMan;
List<Artist> artists = Lists.newArrayList();
Artist artist1 = new Artist("kido", "28", false);
Artist artist2 = new Artist("tom", "23", true);
Artist artist3 = new Artist("whale", "22", false);
Artist artist4 = new Artist("jack", "26", true);
artists.add(artist1);
artists.add(artist2);
artists.add(artist3);
artists.add(artist4);
// 1.方法引用:ClassName::methodName
List<String> list = artists.stream().map(Artist::getName).collect(Collectors.toList());
list.forEach(name -www.michenggw.com> System.out.println(name));
// 2.元素顺序,集合有序流就有序，集合无序流也无序，使用sorted()可以使得流变得有序
Set<Integer> numbers = new HashSet<>(Arrays.asList(4, 3, 2, 1, 6, 9, 8, 10));
numbers.stream().forEach(x -> System.out.println(x));
System.out.println("---------------------------");
List<Integer> numbersOrder = numbers.stream().sorted().collect(Collectors.toList());
numbersOrder.forEach(x -> System.out.println(x));
// 3.使用收集器, toList() toSet()等
Set<String> set = artists.stream().map(Artist::getName).collect(Collectors.toSet());
set.forEach(x ->yongshiyule178.com/ System.out.println(x));
Map<String, String> map = artists.stream(www.quwanyule157.com ).collect(Collectors.toMap(Artist::getName, Artist::getAge));
map.forEach((key, value) -> System.out.println(key + "<--->" + value));
// 4.转换成值, 找出年龄最大的
Optional<Artist> collect = artists.stream().collect(Collectors.maxBy(Comparator.comparing(item -> item.getAge())));
System.out.println(collect.get());
// 5.数据分块, Predicate对象为true和false
Map<Boolean, List<Artist>> map2 = artists.stream().collect(Collectors.partitioningBy(Artist::isMan));
map2.forEach((key, value) -> {System.out.println(key + "<--->" +value);});
// 6.数据分组，按照姓名分组
Map<String, List<Artist>> map3 = artists.stream().collect(Collectors.groupingBy(Artist::getAge));
map3.forEach((key, value) -> {System.out.println(key + "<--->" +value);});
// 7.字符串，将收集流中的数据生成字符串
String string = artists.stream().map(item www.mhylpt.com/ -> item.getName()).collect(Collectors.joining(", ", "[", "]"));
System.out.println(string);
// 8.组合收集器, 使用groupingBy先分组在计数
Map<Boolean, Long> map4 = artists.stream().collect(Collectors.groupingBy(Artist::isMan, Collectors.counting()));
map4.forEach((key, value) -> {System.out.println(key + "<--->" +value);});