JAVA8十大新特性详解（精编）转载：https://www.jianshu.com/p/0bf8fe0f153b
List<String> stringCollection = new ArrayList<>();
stringCollection.add("ddd2");
stringCollection.add("aaa2");
stringCollection.add("bbb1");
stringCollection.add("aaa1");
stringCollection.add("bbb3");
stringCollection.add("ccc");
stringCollection.add("bbb2");
stringCollection.add("ddd1");
//截取列表中以a开头的字符串
stringCollection
.stream()
.filter((s) -> s.startsWith("a"))
.forEach(System.out::println);
// "aaa2", "aaa1"
//截取列表中以a开头的字符串并排序
stringCollection
.stream()
.sorted()
.filter((s) -> s.startsWith("a"))
.forEach(System.out::println);
// "aaa1", "aaa2"
System.out.println(stringCollection);
// ddd2, aaa2, bbb1, aaa1, bbb3, ccc, bbb2, ddd1
//将列表中每个字符串的字母变大写，并与a做比较排序
stringCollection
.stream()
.map(String::toUpperCase)
.sorted((a, b) -> b.compareTo(a))
.forEach(System.out::println);
// "DDD2", "DDD1", "CCC", "BBB3", "BBB2", "AAA2", "AAA1"
//判断列表中任意一个字符串是否以a开头
boolean anyStartsWithA =
stringCollection
.stream()
.anyMatch((s) -> s.startsWith("a"));
System.out.println(anyStartsWithA); // true
//判断列表中所有的字符串是否以a开头
boolean allStartsWithA =
stringCollection
.stream()
.allMatch((s) -> s.startsWith("a"));
System.out.println(allStartsWithA); // false
//判断列表中所有的字符串是否没有以z开头
boolean noneStartsWithZ =
stringCollection
.stream()
.noneMatch((s) -> s.startsWith("z"));
System.out.println(noneStartsWithZ); // true
//截取列表中以b开头的字符串并统计这些字符串的个数
long startsWithB =
stringCollection
.stream()
.filter((s) -> s.startsWith("b"))
.count();
System.out.println(startsWithB); // 3
//将列表中每个字符串以#号隔开
Optional<String> reduced =
stringCollection
.stream()
.sorted()
.reduce((s1, s2) -> s1 + "#" + s2);
reduced.ifPresent(System.out::println);
// "aaa1#aaa2#bbb1#bbb2#bbb3#ccc#ddd1#ddd2"
int max = 1000000;
List<String> values = new ArrayList<>(max);
for (int i = 0; i < max; i++) {
UUID uuid = UUID.randomUUID();
values.add(uuid.toString());
}
//串行排序 单线程
long t0 = System.nanoTime();
long count = values.stream().sorted().count();
System.out.println(count);
long t1 = System.nanoTime();
long millis = TimeUnit.NANOSECONDS.toMillis(t1 - t0);
System.out.println(String.format("sequential sort took: %d ms", millis));
//并行排序 多线程
t0 = System.nanoTime();
count = values.parallelStream().sorted().count();
System.out.println(count);
t1 = System.nanoTime();
millis = TimeUnit.NANOSECONDS.toMillis(t1 - t0);
System.out.println(String.format("parallel sort took: %d ms", millis));
//遍历map中的k-v对
Map<Integer, String> map = new HashMap<>();
for (int i = 0; i < 10; i++) {
map.putIfAbsent(i, "val" + i);
}
map.forEach((id, val) -> System.out.println(val));
//map的其他函数
map.computeIfPresent(3, (num, val) -> val + num);
map.get(3); // val33
map.computeIfPresent(9, (num, val) -> null);
map.containsKey(9); // false
map.computeIfAbsent(23, num -> "val" + num);
map.containsKey(23); // true
map.computeIfAbsent(3, num -> "bam");
map.get(3); // val33
//删除map中 key=3 value=val3 的键值对
map.remove(3, "val3");
map.get(3); // val33
//删除map中 key=3 value=val33 的键值对
map.remove(3, "val33");
map.get(3); // null
//尝试根据key获取map中的value，若没有则返回not found
map.getOrDefault(42, "not found"); // not found
//map合并
map.merge(9, "val9", (value, newValue) -> value.concat(newValue));
map.get(9); // val9
map.merge(9, "concat", (value, newValue) -> value.concat(newValue));
map.get(9); // val9concat
//更多详细参照：https://www.jianshu.com/p/0bf8fe0f153b
常用流转换示例
package com.xrosstools.xdecision.sample;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;
/**
* @author xushunjie
* @date 2021/12/7 14:11
*/
public class test4 {
public static void main(String[] args) throws Exception {
List<Person> personList = new ArrayList<>();
Person person1 = new Person();
person1.setId(1);
person1.setName("小明");
person1.setAge(25);
Person person2 = new Person();
person2.setId(2);
person2.setName("小张");
person2.setAge(26);
Person person3 = new Person();
person3.setId(3);
person3.setName("小李");
person3.setAge(26);
personList.add(person1);
personList.add(person2);
personList.add(person3);
List<Integer> personIdList = personList.stream().map(Person::getId).collect(Collectors.toList());
System.out.println(personIdList);
// [1, 2, 3]
personIdList = personList.stream().map(Person::getId).filter(id -> id >1).collect(Collectors.toList());
System.out.println(personIdList);
// [2, 3]
List<String> personNameList = personList.stream().map(Person::getName).collect(Collectors.toList());
String names = personNameList.stream().collect(Collectors.joining(","));
System.out.println(names);
// 小明,小张,小李
Map<Integer, String> map = personList.stream().collect(Collectors
.toMap(Person::getId, Person::getName));
System.out.println(map);
// {1=小明, 2=小张, 3=小李}
Map<Integer, Person> personMap = personList.stream().collect(Collectors
.toMap(Person::getId, Function.identity()));
System.out.println(personMap);
// {1=Person{id=1, name='小明', age=25}, 2=Person{id=2, name='小张', age=26}, 3=Person{id=3, name='小李', age=26}}
Map<Integer, List<Person>> stringListMap =
personList.stream().collect(Collectors.groupingBy(Person::getAge));
System.out.println(stringListMap);
// {25=[Person{id=1, name='小明', age=25}], 26=[Person{id=2, name='小张', age=26}, Person{id=3, name='小李', age=26}]}
List<Person> nonMatch = personList.stream().filter(person -> personList.stream().map(Person::getAge).noneMatch(age -> person.getAge() == 26)).collect(Collectors.toList());
System.out.println(nonMatch);
// [Person{id=1, name='小明', age=25}]
List<Person> anyMatch = personList.stream().filter(person -> personList.stream().map(Person::getAge).anyMatch(age -> person.getAge() == 26)).collect(Collectors.toList());
System.out.println(anyMatch);
// [Person{id=2, name='小张', age=26}, Person{id=3, name='小李', age=26}]
}
}
class Person {
private int id;
private String name;
private int age;
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;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "Person{" +
"id=" + id +
", name='" + name + '\'' +
", age=" + age +
'}';
}
}// 综合应用 // pojos 全部数据 (带id) // updatePojoList 需要更新的数据 (带id) // deletePojoList 需要删除的数据 (带id) // 从pojos中剔除updatePojoList中的数据，剩下的数据为需要删除的数据deletePojoList List<Pojo> deletePojoList = pojos.stream().filter(Pojo -> updatePojoList.stream().map(Pojo::getId).noneMatch(pojoId -> Objects.equals(Pojo.getId(), pojoId))).collect(Collectors.toList());
java steam对象根据属性值排序 正序 倒序
参考：https://blog.csdn.net/qq_15058425/article/details/107019176
public class SortTest {
public static void main(String[] args) {
User user1=new User("1111",20);
User user2=new User("2222",19);
User user3=new User("3333",21);
List<User> list=new ArrayList<>();
list.add(user1);
list.add(user2);
list.add(user3);
list = list.stream().sorted(Comparator.comparing(User::getAge)).collect(Collectors.toList());
System.out.println("根据年龄顺序：==="+list);
list = list.stream().sorted(Comparator.comparing(User::getAge,Comparator.reverseOrder())).collect(Collectors.toList());
System.out.println("根据年龄倒序：==="+list);
}
}
排序判空并倒序
generalNurseCountOut.sort(Comparator.comparing(PerformanceAppraisalRespDTO::getNurseLevel, Comparator.nullsFirst(String::compareTo)).reversed());
java steam对象根据属性值去重
List<User> distinctList = list.stream()
.collect(Collectors.collectingAndThen(
Collectors.toMap(User::getUserCode, Function.identity(), (existing, replacement) -> existing),
map -> new ArrayList<>(map.values())
));
stream操作嵌套列表
List<Long> scheduleIdList = userShowDetailRespDTOList.stream()
.filter(u -> ListUtils.isNotEmpty(u.getDateDetailList()))
.map(ScheduleUserShowDetailRespDTO::getDateDetailList)
.flatMap(Collection::stream)
.filter(d -> ListUtils.isNotEmpty(d.getScheduleList()))
.map(ScheduleUserDateDetailRespDTO::getScheduleList)
.flatMap(Collection::stream)
.map(ScheduleUserDetailRespDTO::getScheduleId)
.distinct().collect(toList());java stream groupingBy分组后再进行列表排序
Map<String, List<ScheduleUserDetailDO>> scheduleUserDetailMap = scheduleUserDetailDOList.stream().collect(groupingBy(ScheduleUserDetailDO::getUserId,
collectingAndThen(toList(), t -> t.stream().sorted(
Comparator.comparing(ScheduleUserDetailDO::getCreateTime)
.thenComparing(ScheduleUserDetailDO::getSortVal)
).collect(toList()))));java stream groupingBy分组后不改变列表顺序
Map<String, List<QCIndexDataRespDTO>> groupMap = qcIndexDataRespDTOList.stream()
.collect(Collectors.groupingBy(s -> s.getUnitId() + "|" + s.getQcIndexDictId() + "|" + s.getQcIndexTargetValue() + "|" + s.getQcIndexLevel(), LinkedHashMap::new, Collectors.toList()));
java stream 动态指定多个字段排序
int sortIndex = 0;
Comparator<ReportTableBody> comparator = null;
for (String orderExpr : globalOrderList) {
String columnId = orderExpr.split("-")[0];
String order = orderExpr.split("-")[1];
if (OrderByEnum.DESC.name().equals(order)) {
if (sortIndex == 0) {
comparator = Comparator.comparing(reportTableBody ->
reportTableBody.getColumnValueList().stream().filter(reportTableColumnValue -> StringUtil.equals(columnId, reportTableColumnValue.getColumnId()))
.findFirst().get().getValue(), Comparator.reverseOrder());
} else {
comparator = comparator.thenComparing(reportTableBody ->
reportTableBody.getColumnValueList().stream().filter(reportTableColumnValue -> StringUtil.equals(columnId, reportTableColumnValue.getColumnId()))
.findFirst().get().getValue(), Comparator.reverseOrder());
}
} else {
if (sortIndex == 0) {
comparator = Comparator.comparing(reportTableBody ->
reportTableBody.getColumnValueList().stream().filter(reportTableColumnValue -> StringUtil.equals(columnId, reportTableColumnValue.getColumnId()))
.findFirst().get().getValue());
} else {
comparator = comparator.thenComparing(reportTableBody ->
reportTableBody.getColumnValueList().stream().filter(reportTableColumnValue -> StringUtil.equals(columnId, reportTableColumnValue.getColumnId()))
.findFirst().get().getValue());
}
}
sortIndex++;
}
if (comparator != null) {
reportTableBodyList = reportTableBodyList.stream().sorted(comparator).collect(Collectors.toList());
}
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