java stream的常用方法

han_hanker2026-05-10 15:20

Arrays.stream

java 复制代码

String[] names = {"Alice", "Bob", "Charlie"};
Stream<String> stream = Arrays.stream(names);

// 示例：转大写并收集
List<String> upperNames = Arrays.stream(names)
    .map(String::toUpperCase)
    .collect(Collectors.toList());
// 结果: ["ALICE", "BOB", "CHARLIE"]

java 复制代码

int[] numbers = {1, 2, 3, 4, 5};
IntStream intStream = Arrays.stream(numbers);

// 求和
int sum = Arrays.stream(numbers).sum(); // 15

// 过滤偶数
int[] evens = Arrays.stream(numbers)
    .filter(n -> n % 2 == 0)
    .toArray(); // [2, 4]

把数组变成List

下面的例子: 把String 类型先split用逗号切割成数组, 再左右去空格, 转型为Long类型

java 复制代码

List<Long> idList = Arrays.stream(ids.split(","))
                .map(String::trim)
                .map(Long::parseLong)
                .collect(Collectors.toList());

List.stream

java 复制代码

private UserVO convertToVO(User user) {
        UserVO vo = new UserVO();
        BeanUtils.copyProperties(user, vo);
}

java 复制代码

 List<User> userList = new ArrayList<>()
 userList.add(new User(1))
 userList.add(new User(2))
 List<UserVO> voList = userList.stream()
 				.filter(Objects::nonNull)   
                .map(this::convertToVO)
                .collect(Collectors.toList());