JAVA8之stream流式处理

傷城~ 2024-04-03 12:49 263阅读 0赞

#### 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

![06e6b583862a4336a863e4ecd79130d3.jpeg][]

*  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 ####

![c65d23b82ab0424aa2cc70df333c9417.jpeg][]

*  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<GoodsRecordVO> 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

![2f7bfe7db86f4cda82d027221648afd0.jpeg][]

*  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);
            });

[06e6b583862a4336a863e4ecd79130d3.jpeg]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/03/8e60e5358e524139911b1dc4bbca146a.jpeg
[c65d23b82ab0424aa2cc70df333c9417.jpeg]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/03/6c3dc6d8d7d94ebfbf5ffe485a3b88da.jpeg
[2f7bfe7db86f4cda82d027221648afd0.jpeg]: https://image.dandelioncloud.cn/pgy_files/images/2024/04/03/7a229eb86fa74e2680eff92eaaae1118.jpeg