java 8 stream包

List<Student> targetStudentList =
people.getStudents().stream()
.filter(Student -> student.getId().equals(studentId))
.collect(Collectors.toList()); //筛选符合条件的数据并返回List

List<Long> studentIdList = 
people.getStudents().stream()
.map(Student::getId)
.collect(Collectors.toList());//筛选List中每条数据的特定数据，并返回这个数据的List

https://www.ibm.com/developerworks/cn/java/j-lo-java8streamapi/