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list.stream().map().collect(Collectors.toList())

时间：2022-11-08 23:26:11

javaapi 特性

stream只能被“消费”一次，一旦遍历过就会失效，就像容器的迭代器那样，想要再次遍历必须重新生成

map():用于映射每个元素到对应的结果。

filter():filter 方法用于通过设置的条件过滤出元素。

Collectors.toList() 用来结束Stream流

例如：

//userList User实体类对象集合

//User 实体类

//getId 实体类属性的get方法

List<int> ids= userList.stream().map(User::getId).collect(Collectors.toList())

//或者把数据放到map根据user.getId(条件) 循环在转换成list

List<int> ids= userList.stream().map(user->user.getId()).collect(Collectors.toList());

//过滤list集合中属性type为1的值并赋值给permissions集合在返回list集合 .collect(Collectors.toList()) 转换成list集合

List<Permission> permissions = list.stream().filter(l -> l.getType().equals(1))

.collect(Collectors.toList());

list转map

Map<String,Entity> statMap = statList.stream().collect(Collectors.toMap(Entity::getId, Entity -> Entity));

List<String> collect = roleResultList.stream().map(AcAppRole::getName).collect(Collectors.toList());

Map<Integer, String> map = new HashMap<>();

map.put(10, "apple");

map.put(20, "orange");

map.put(30, "banana");

map.put(40, "watermelon");

map.put(50, "dragonfruit");

System.out.println("\n1. Export Map Key to List...");

List<Integer> result = map.keySet().stream().collect(Collectors.toList());

result.forEach(System.out::println);

System.out.println("\n2. Export Map Value to List...");

List<String> result2 = map.values().stream().collect(Collectors.toList());

result2.forEach(System.out::println);

System.out.println("\n3. Export Map Value to List..., say no to banana");

List<String> result3 = map.keySet().stream().filter(x -> !"banana".equalsIgnoreCase(x)).collect(Collectors.toList());

result3.forEach(System.out::println);

List<String> resultValues = map.entrySet().stream().sorted(Map.Entry.<Integer, String>comparingByKey().reversed())

.peek(e -> resultSortedKey.add(e.getKey()))

.map(x -> x.getValue())

.filter(x -> !"banana".equalsIgnoreCase(x))

.collect(Collectors.toList());

public static void main(String args[]) {

SqlServerReader tester = new SqlServerReader();

tester.testCaseFormat();

}

private void testCaseFormat() {

System.out.println(CaseFormat.LOWER_HYPHEN.to(CaseFormat.LOWER_CAMEL, "test-data"));

System.out.println(CaseFormat.LOWER_UNDERSCORE.to(CaseFormat.LOWER_CAMEL, "test_data"));

System.out.println(CaseFormat.UPPER_UNDERSCORE.to(CaseFormat.UPPER_CAMEL, "test_data"));

System.out.println(CaseFormat.LOWER_CAMEL.to(CaseFormat.LOWER_UNDERSCORE, "testdata"));

System.out.println();

System.out.println(CaseFormat.LOWER_CAMEL.to(CaseFormat.LOWER_HYPHEN, "testData"));

}

list转逗号分隔的字符串CollectionUtil.join

List<SysRole> roleList = sysRoleService.list(roleWrapper);List<String> roleIdList = roleList.stream().map(SysRole::getId).collect(Collectors.toList());List<String> roleNames = roleList.stream().map(SysRole::getRoleName).collect(Collectors.toList());sysUser.setUserRoleNames(CollectionUtil.join(roleNames, ","));

字符串转list

List<Long> shipIdList = Arrays.stream(shipIds.split(",")).map(Long::parseLong).collect(Collectors.toList());

list根据某个对象属性去重

// 根据name去重

List<Person> unique = persons.stream().collect(

Collectors.collectingAndThen(

Collectors.toCollection(() -> new TreeSet<>(paring(Person::getName))), ArrayList::new)

);

// 根据name,sex两个属性去重

List<Person> unique = persons.stream().collect(

Collectors. collectingAndThen(

Collectors.toCollection(() -> new TreeSet<>(paring(o -> o.getName() + ";" + o.getSex()))), ArrayList::new)