JAVA8之stream流式处理-蒲公英云

1.筛选与切片（各个操作可以一起使用，对同一个流进行处理）

说明

测试代码：

package test.java8.stream;

import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;

/**

筛选与切片
@author linaibo
@version 1.0
Create by 2022/8/7 19:45
*/

public class Test1 {

public static  void  main(String[] args){
    List<student> list = new ArrayList<student>();
    list.add(new student(1,"张三"));
    list.add(new student(1,"张三"));
    list.add(new student(3,"王五"));
    list.add(new student(3,"王五"));
    list.add(new student(5,"小七"));
    //filter
    List<student> list1 = list.stream().filter(s->(s.getId()>1)).filter(e->(e.getName().equals("王五"))).collect(Collectors.toList());
    list1.stream().forEach((s) ->{
        System.out.print(s.getId());
        System.out.println(s.getName());
    });
    System.out.println("filter11111111");
    //limit
    List<student> collect = list.stream().limit(2).collect(Collectors.toList());
    collect.forEach(item->{
        System.out.print(item.getId());
        System.out.println(item.getName());
    });
    System.out.println("limit11111111");
    //skip
    List<student> collect1 = list.stream().skip(3).collect(Collectors.toList());
    collect1.forEach(item->{
        System.out.print(item.getId());
        System.out.println(item.getName());
    });
    System.out.println("skip11111111");
    //distinct
    List<student> collect2 = list.stream().distinct().collect(Collectors.toList());
    collect2.forEach(item->{
        System.out.print(item.getId());
        System.out.println(item.getName());
    });
}
public static class student {
    private int id;
    private String name;
    public student(int id, String name) {
        this.id = id;
        this.name = name;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof student)) return false;
        student student = (student) o;
        return id == student.id && Objects.equals(name, student.name);
    }
    @Override
    public int hashCode() {
        return Objects.hash(id, name);
    }
}

}

测试结果

3王五
3王五
filter11111111
1张三
1张三
limit11111111
3王五
5小七
skip11111111
1张三
3王五
5小七

2.映射

测试代码

package test.java8.stream;

import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;

/**

映射
@author linaibo
@version 1.0
Create by 2022/10/15 15:15
*/

public class Test2 {

public static void main(String[] args) {
    List<Student> list = new ArrayList<Student>();
    list.add(new Student(1,"张三"));
    list.add(new Student(1,"张三"));
    list.add(new Student(3,"王五"));
    list.add(new Student(3,"王五"));
    list.add(new Student(5,"小七"));
    //map
    List<Integer> collect = list.stream().map(Student::getId).collect(Collectors.toList());
    collect.forEach(System.out::print);
    System.out.println("    map111111");
    //flatmap
    List<String> list2 = Arrays.asList("aaa","bbb","ccc");
    List<Object> collect1 = list2.stream().flatMap(Test2::filterCharter).collect(Collectors.toList());
    collect1.forEach(System.out::print);
    System.out.println("    flatMap111  11");
}
public static Stream<Character> filterCharter(String str){
    List<Character> list = new ArrayList<>();
    for(Character ch : str.toCharArray()){
        list.add(ch);
    }
    return list.stream();
}
public static class Student {
    private int id;
    private String name;
    public Student(int id, String name) {
        this.id = id;
        this.name = name;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
}

}

测试结果

11335 map111111
aaabbbccc flatMap11111

List collect = goodsRecordList.stream().map((goodsRecordTemp) -> {

        GoodsRecordVO goodsRecordVO = new GoodsRecordVO();
        BeanUtils.copyProperties(goodsRecordTemp, goodsRecordVO);
        goodsRecordVO.setCustomerName(codeToNameMap.get(goodsRecordTemp.getCustomerCode()));
        return goodsRecordVO;
    }).collect(Collectors.toList());

map的用法也可以对进行两个bean之间的映射编辑处理，返回一个bean的集合，上述操作也可以使用for循环处理。

3.排序

内容

souted()—自然排序（Comparable）

自然排序的对象必须实现compareble，按照compareto方法进行排序

sorted（Comparator com）—定制排序（Comparator）

比如student对象没有自然排序方式，只能用定制排序，根据对象中的某些项目进行定制排序

测试代码

package test.java8.stream;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Objects;
import java.util.stream.Collectors;
import java.util.stream.Stream;

/**

@author linaibo
@version 1.0
Create by 2022/10/16 10:05
*/

public class Test3 {

public static void main(String[] args) {
    List<String> list1 = Arrays.asList("aaa", "eee", "ccc", "ddd");
    List<String> collect1 = list1.stream().sorted().collect(Collectors.toList());
    collect1.forEach(System.out::println);
    System.out.println("自然排序111111");
    List<Student> list = new ArrayList<Student>();
    list.add(new Student(1, 18, "张三"));
    list.add(new Student(5, 19, "张三"));
    list.add(new Student(9, 20, "王五"));
    list.add(new Student(8, 14, "王五"));
    list.add(new Student(1, 16, "小七"));
    List<Student> collect2 = list.stream()
            .sorted((e1, e2) -> {
                if (e1.getId() == e2.getId()) {
                    return -(e1.getAge() - e2.getAge());
                } else {
                    return -(e1.getId() - e2.getId());
                }
            })
            .collect(Collectors.toList());
    collect2.forEach(item -> {
        System.out.print(item.getId());
        System.out.print(item.getAge());
        System.out.println(item.getName());
    });
    System.out.println("定制排序111111");
}

    public static class Student {
        private int id;
        private int age;
        private String name;
        public Student(int id, int age, String name) {
            this.id = id;
            this.age = age;
            this.name = name;
        }
        public int getId() {
            return id;
        }
        public void setId(int id) {
            this.id = id;
        }
        public int getAge() {
            return age;
        }
        public void setAge(int age) {
            this.age = age;
        }
        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (!(o instanceof Student)) return false;
            Student student = (Student) o;
            return id == student.id && age == student.age && Objects.equals(name, student.name);
        }
        @Override
        public int hashCode() {
            return Objects.hash(id, age, name);
        }
    }
}

测试结果

aaa
ccc
ddd
eee
自然排序111111
920王五
814王五
519张三
118张三
116小七
定制排序111111

4.查找与匹配

allMatch—检查是否匹配所有元素

anyMatch—检查是否至少匹配一个元素

noneMatch—检查是否没有匹配所有元素

findFirst—返回第一个元素

findAny—返回当前流中的任意元素

count—返回流中元素的总个数

max—返回流中的最大值

min—返回流中的最小值

package test.java8.stream;
import java.util.*;
/**
 * @author linaibo
 * @version 1.0
 * Create by 2022/10/16 10:46
 */
public class Test4 {
    public static void main(String[] args) {
        List<Student> list = new ArrayList<Student>();
        list.add(new Student(1, 18, "张三"));
        list.add(new Student(5, 19, "张三"));
        list.add(new Student(9, 20, "王五"));
        list.add(new Student(8, 14, "王五"));
        list.add(new Student(1, 16, "小七"));
        //allMatch
        boolean allMatch = list.stream().allMatch(s -> s.getAge() == 18);
        System.out.println(allMatch);
        System.out.println("allMatch");
        //anyMatch
        boolean anyMatch = list.stream().anyMatch(s -> s.getAge() == 18);
        System.out.println(anyMatch);
        System.out.println("anyMatch");
        //noneMatch
        boolean noneMatch = list.stream().noneMatch(s -> s.getAge() == 18);
        System.out.println(noneMatch);
        System.out.println("noneMatch");
        //findFirst
        Optional<Student> first = list.stream().findFirst();
        Student student = first.get();
        System.out.print(student.getId());
        System.out.print(student.getAge());
        System.out.print(student.getName());
        System.out.println("findFirst");
        //findAny
        Optional<Student> any = list.stream().findAny();
        Student student1 = any.get();
        System.out.print(student1.getId());
        System.out.print(student1.getAge());
        System.out.print(student1.getName());
        System.out.println("findAny");
        //count
        long count = list.stream().count();
        System.out.println(count);
        System.out.println("count");
        //max
        Optional<Student> max = list.stream().max(Comparator.comparingInt(Student::getAge));
        Student student2 = max.get();
        System.out.print(student2.getId());
        System.out.print(student2.getAge());
        System.out.print(student2.getName());
        System.out.println("max");
        //min
        Optional<Student> min = list.stream().min(Comparator.comparingInt(Student::getAge));
        Student student3 = min.get();
        System.out.print(student3.getId());
        System.out.print(student3.getAge());
        System.out.print(student3.getName());
        System.out.println("min");
    }
    public static class Student {
        private int id;
        private int age;
        private String name;
        public Student(int id, int age, String name) {
            this.id = id;
            this.age = age;
            this.name = name;
        }
        public int getId() {
            return id;
        }
        public void setId(int id) {
            this.id = id;
        }
        public int getAge() {
            return age;
        }
        public void setAge(int age) {
            this.age = age;
        }
        public String getName() {
            return name;
        }
        public void setName(String name) {
            this.name = name;
        }
        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (!(o instanceof Student)) return false;
            Student student = (Student) o;
            return id == student.id && age == student.age && Objects.equals(name, student.name);
        }
        @Override
        public int hashCode() {
            return Objects.hash(id, age, name);
        }
    }
}

测试结果

false
allMatch
true
anyMatch
false
noneMatch
118张三findFirst
118张三findAny
5
count
920王五max
814王五min

5.归约

reduce—将流中元素反复结合起来，最后得到一个值

测试代码

package test.java8.stream;

import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.Optional;

/**

@author linaibo
@version 1.0
Create by 2022/10/16 11:09
*/

public class Test5 {

public static void main(String[] args) {
    List<Student> list = new ArrayList<Student>();
    list.add(new Student(1, 18, "张三"));
    list.add(new Student(5, 19, "张三"));
    list.add(new Student(9, 20, "王五"));
    list.add(new Student(8, 14, "王五"));
    list.add(new Student(1, 16, "小七"));
    //reduce
    Integer reduce = list.stream().map(Student::getAge).reduce(0, (x, y) -> x + y);
    System.out.println(reduce);
    System.out.println("reduce");
    //reduce
    Optional<Integer> reduce1 = list.stream().map(Student::getAge).reduce((x, y) -> x + y);
    System.out.println(reduce1.get());
    System.out.println("reduce");
}
public static class Student {
    private int id;
    private int age;
    private String name;
    public Student(int id, int age, String name) {
        this.id = id;
        this.age = age;
        this.name = name;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Student)) return false;
        Student student = (Student) o;
        return id == student.id && age == student.age && Objects.equals(name, student.name);
    }
    @Override
    public int hashCode() {
        return Objects.hash(id, age, name);
    }
}

}

测试结果

87
reduce
87
reduce

6.归集

测试代码

package test.java8.stream;

import java.util.*;
import java.util.function.BinaryOperator;
import java.util.stream.Collector;
import java.util.stream.Collectors;

/**

@author linaibo
@version 1.0
Create by 2022/10/16 11:09
*/

public class Test6 {

public static void main(String[] args) {
    List<Student> list = new ArrayList<Student>();
    list.add(new Student(1, 18, "张三"));
    list.add(new Student(5, 19, "张三"));
    list.add(new Student(9, 20, "王五"));
    list.add(new Student(8, 14, "王五"));
    list.add(new Student(1, 16, "小七"));
    //toList
    List<Student> collect = list.stream().filter(s -> s.getAge() == 18).collect(Collectors.toList());
    collect.forEach(item->{
        System.out.print(item.getId());
        System.out.print(item.getAge());
        System.out.println(item.getName());
    });
    System.out.println("toList");
    //toSet
    Set<Student> collect1 = list.stream().filter(s -> s.getAge() == 19).collect(Collectors.toSet());
    collect1.forEach(item->{
        System.out.print(item.getId());
        System.out.print(item.getName());
        System.out.println(item.getAge());
    });
    System.out.println("toSet");
    //toMap
    Map<Integer, String> collect2 = list.stream().filter(s -> s.getAge() > 15).collect(Collectors.toMap(Student::getId, Student::getName,(v1,v2)->v1));
    collect2.forEach((k,v)->{
        System.out.print(k);
        System.out.println(v);
    });
    System.out.println("toMap1");
    Map<Integer, Student> collect3 = list.stream().filter(s -> s.getAge() > 15).collect(Collectors.toMap(Student::getId, s -> s,(v1,v2)->v2));
    collect3.forEach((k,v)->{
        System.out.print(k);
        System.out.println(v.getName());
    });
    System.out.println("toMap2");
    //count
    Long collect5 = list.stream().filter(s -> s.getAge() > 18).collect(Collectors.counting());
    System.out.println(collect5);
    System.out.println("count");
    //summingInt
    Integer collect4 = list.stream().filter(s -> s.getAge() > 18).collect(Collectors.summingInt(Student::getAge));
    System.out.println(collect4);
    System.out.println("summingInt");
    //averagingInt
    Double collect7 = list.stream().filter(s -> s.getAge() > 18).collect(Collectors.averagingInt(Student::getAge));
    System.out.println(collect7);
    System.out.println("averagingInt");
    //groupingBy 可以多级分组
    Map<Integer, List<Student>> collect6 = list.stream().filter(s -> s.getAge() > 18).collect(Collectors.groupingBy(Student::getId));
    collect6.forEach((k,v)->{
        System.out.println(k);
        System.out.println(v.size());
    });
    System.out.println("groupingBy");
    //maxBy
    Optional<Student> collect8 = list.stream().collect(Collectors.maxBy(Comparator.comparingInt(Student::getAge)));
    Student student = collect8.get();
    System.out.print(student.getId());
    System.out.println(student.getName());
    System.out.println("maxBy");
    //minBy
    Optional<Student> collect9 = list.stream().collect(Collectors.minBy(Comparator.comparingInt(Student::getAge)));
    Student student2 = collect9.get();
    System.out.print(student2.getId());
    System.out.println(student2.getName());
    System.out.println("minBy");
    //partitioningBy
    Map<Boolean, List<Student>> collect10 = list.stream().collect(Collectors.partitioningBy(s -> s.getAge() > 18));
    collect10.forEach((k,v)->{
        System.out.println(k);
        System.out.println(v.size());
    });
    System.out.println("partitioningBy");
    //groupingBy AND reducing
    Map<Integer, Optional<Student>> collect11 = list.stream().collect(Collectors.groupingBy(Student::getId, Collectors.reducing(BinaryOperator.maxBy(Comparator.comparingInt(Student::getAge)))));
    collect11.forEach((k,v)->{
        System.out.println(k);
        System.out.println(v.get().getAge());
    });
    System.out.println("groupingBy AND reducing");
}
public static class Student {
    private int id;
    private int age;
    private String name;
    public Student(int id, int age, String name) {
        this.id = id;
        this.age = age;
        this.name = name;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Student)) return false;
        Student student = (Student) o;
        return id == student.id && age == student.age && Objects.equals(name, student.name);
    }
    @Override
    public int hashCode() {
        return Objects.hash(id, age, name);
    }
}

}

测试结果

118张三
toList
5张三19
toSet
1张三
5张三
9王五
toMap1
1小七
5张三
9王五
toMap2
2
count
39
summingInt
19.5
averagingInt
5
1
9
1
groupingBy
9王五
maxBy
8王五
minBy
false
3
true
2
partitioningBy
1
18
5
19
8
14
9
20
groupingBy AND reducing

分组求和

Map<String, Integer> materInfoMap = list
                .stream()
                .filter(item -> item.getMaterialCode() != null)
                .collect(groupingBy(Goods::getMaterialCode, reducing(0, Goods::getMaterialQty, Integer::sum)));
        materInfoMap.forEach((key,value)->{
            System.out.println(key + value);
        });