一文带你了解Java8 Stream流处理中的收集器技巧

List<String> names = peopleStream.map(Person::getName)
                                 .collect(Collectors.toList());

Long collect = studentList.stream().collect(Collectors.counting());

Optional<Student> optional = studentList.stream().collect(Collectors.maxBy(Comparator.comparing(Student::getAge));)
if (optional.isPresent()){
    Student student = optional.get();
    System.out.println(student);
}

Integer collect  = peopleStream.collect(Collectors.summingLnt(Person::getAge));
int sum = peopleStream.mapToInt(Person::getAge).sum();

Double collect  = peopleStream.collect(Collectors.averagingLnt(Person::getAge));

Person collect  = peopleStream.collect(Collectors.joining());

Map<Integer,List<Student>> map = peopleStream.collect(Collectors.groupingBy(Person::getAge));

package com.jdk8.features.stream.collector;
import com.jdk8.features.lambda.Student;
import java.util.ArrayList;
import java.util.EnumSet;
import java.util.List;
import java.util.Set;
import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;
public class MyCollector implements Collector<Student, List<Student>,List<Student>> {
  @Override
  public Supplier<List<Student>> supplier() {
    return ArrayList::new;
  }
  @Override
  public BiConsumer<List<Student>, Student> accumulator() {
    return ((studentList, student) -> {
      if (student.getIsPass()){
        studentList.add(student);
      }
    });
  }
  @Override
  public BinaryOperator<List<Student>> combiner() {
    return null;
  }
  @Override
  public Function<List<Student>, List<Student>> finisher() {
    return Function.identity();
  }
  @Override
  public Set<Characteristics> characteristics() {
    return EnumSet.of(Characteristics.IDENTITY_FINISH,Characteristics.UNORDERED);
  }
}

import com.jdk8.features.lambda.Student;
import java.util.ArrayList;
import java.util.List;
public class MyCollectorDemo {
  public static void main(String[] args) {
    List<Student> studentList = new ArrayList<>();
    studentList.add(new Student(1,"张三",18,19));
    studentList.add(new Student(2,"李四",19,18));
    studentList.add(new Student(3,"王五",20,21));
    studentList.add(new Student(4,"赵六",21,80));
    List<Student> list = studentList.stream().collect(new MyCollector());
    System.out.println(list);
  }
}