测试类
import com.xd.pojo.Student;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;
import java.io.UnsupportedEncodingException;
import java.nio.charset.StandardCharsets;
import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.Stream;
@SpringBootTest
public class StreamTests {
List<Student> students = new ArrayList<>();
@BeforeEach
public void testInitUser() {
students.add(new Student(1, 19, "张三", "A", true));
students.add(new Student(1, 20, "张三", "A", true));
students.add(new Student(1, 18, "李四", "a", false));
students.add(new Student(1, 21, "王五", "B", true));
students.add(new Student(1, 20, "赵六", "b", false));
students.add(new Student(1, 20, "赵六", "F", false));
students.add(new Student(1, 20, "赵六", "F", false));
students.add(new Student(1, 21, "赵六", "F", false));
}
@Test
void testStreamOf() {
Stream.of(new Student(1, 21, "张三", "1", true), new Student(2, 21, "李四", "2", true)).
forEach(System.out::println);
}
@Test
void testFilter() {
students.stream().
filter(student -> student.getAge() > 20).
forEach(System.out::println);
}
@Test
void testToList(){
printStr("toList");
List<Student> collect = students.stream().
filter(student -> student.getAge() > 20).
collect(Collectors.toList());
collect.forEach(System.out::println);
printStr("toSet");
Set<Student> collect1 = students.stream().
filter(student -> student.getAge() > 20).
collect(Collectors.toSet());
collect1.forEach(System.out::println);
}
@Test
void testDistinct() {
printStr("distinct");
students.stream().
distinct().
forEach(System.out::println);
}
/**
* 一对一转换
* 一对多转换
*/
@Test
void testTrans(){
printStr("trans use map 一对一转换");
List<String> list = Arrays.asList("234", "100", "200", "305");
List<Integer> collect = list.stream().map(Integer::valueOf).collect(Collectors.toList());
collect.forEach(System.out::println);
printStr("map 对值进行处理");
list.stream().map(s -> Integer.parseInt(s) * 10).forEach(System.out::println);
printStr("flatMap 一对多转换");
List<String> strs = Arrays.asList(" hello world","Jia Gou Wu Dao ","a", "b");
List<String> collect1 = strs.stream().flatMap(s -> Arrays.stream(s.split(" "))).collect(Collectors.toList());
collect1.forEach(System.out::println);
Arrays.stream("hello world".split(" ")).forEach(System.out::println);
}
// 6.peek中间管道，对stream中的每个元素逐个遍历处理，
// 中间管道必须搭配终止管道一起使用，否则中间管道的操作不会执行。
@Test
void testPeek() {
printStr("peek");
List<String> list = Arrays.asList(" hello world","Jia Gou Wu Dao ","a", "b");
list.stream().peek(s -> System.out.println("before: " + s)).map(s -> s.toUpperCase()).peek(s -> System.out.println("after: " + s)).forEach(System.out::println);
printStr("peek 无终止 不执行");
list.stream().peek(s -> System.out.println("before: " + s));
}
// 7.List或者数组中的值拼接到一个字符串里并以逗号分隔开, Collectors.joining
@Test
void testJoining() {
printStr("join");
List<String> list = Arrays.asList(" hello world","Jia Gou Wu Dao ","a", "b");
String collect = list.stream().collect(Collectors.joining(","));
System.out.println(collect);
}
// 8.Collectors.averagingInt, 求集合均值
@Test
void testverage() {
printStr("average");
List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
Double average = list.stream().collect(Collectors.averagingInt(i -> i));
System.out.println(average);
}
// 9.统计信息， Collectors.summarizingInt
@Test
void testSummarizingInt() {
printStr("summarizingInt");
List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
IntSummaryStatistics summaryStatistics = list.stream().collect(Collectors.summarizingInt(i -> i));
System.out.println(summaryStatistics.getMax());
System.out.println(summaryStatistics.getMin());
System.out.println(summaryStatistics.getSum());
System.out.println(summaryStatistics.getAverage());
System.out.println(summaryStatistics);
}
// 10.Collectors.groupingBy
@Test
void testGroupingBy() {
printStr("groupingBy");
Map<String, List<Student>> collect = students.stream().collect(Collectors.groupingBy(Student::getSex));
collect.forEach((k, v) -> {
System.out.println(k + ":" + v);
});
}
// 11.sorted排序, 默认升序，可自定义排序规则。
@Test
void testSortBy() {
printStr("sortBy asc");
students.stream().sorted(Comparator.comparing(stu -> stu.getAge())).forEach(System.out::println);
printStr("sortBy2 desc");
students.stream().sorted(Comparator.comparing(Student::getAge).reversed()).collect(Collectors.toList()).forEach(System.out::println);
printStr("sortBy2 desc 换种方法");
students.stream()
.distinct()
.sorted( Comparator.comparing(Student::getAge, Comparator.reverseOrder())).forEach(System.out::println);
printStr("sortBy2 age sex 多级排序");
students.stream().sorted(Comparator.comparing(Student::getAge)
.thenComparing(Student::getSex, Comparator.reverseOrder()))
.forEach(System.out::println);
printStr("在sorted中自定义排序规则.");
students.stream()
.distinct()
.sorted((o1, o2) -> o2.getAge() - o1.getAge()).
forEach(System.out::println);
// 字典顺序排序
printStr("字典顺序.");
students.stream()
.distinct()
.sorted((o1, o2) -> {
try {
String str1 = new String(o1.getName().getBytes("GB2312"), StandardCharsets.ISO_8859_1);
String str2 = new String(o2.getName().getBytes("GB2312"), StandardCharsets.ISO_8859_1);
return str1.compareTo(str2);
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
}
return 0;
}).forEach(System.out::println);
}
void printStr(String str){
System.out.println();
System.out.println(str);
System.out.println(String.valueOf("=").repeat(str.length()));
}
}
模型
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Student {
private int id;
private int age;
private String name;
private String sex;
private boolean option;
}
