而不是使用 .filter ，您需要使用 .map .
为了使代码更简洁，可以替换 item -> item.getId() 方法参考： Item::getId .
这将是最终结果：

List<String> ids = details.stream()
        .map(Item::getId)
        .collect(Collectors.toList());

样品适合你，

Employee emp1 = new Employee(1,"Ally");
        Employee emp2 = new Employee(2,"Billy");
        ArrayList<Employee> employeeList = new ArrayList<>(Arrays.asList(emp1,emp2));

        List<Integer> collect = employeeList.stream()
                                            .map(Employee::getId)
                                            .collect(Collectors.toList());
        System.out.println("collect = " + collect);