java stream 常用操作

Optional对null值进行处理

Map collect = studentDTOS.stream().collect(Collectors
 .toMap(StudentDTO::getStudentId,
 studentDTO -> Optional.ofNullable(studentDTO.getStudentName())));
 
for(Map.Entry entry:collect.entrySet()){
 System.out.println(entry.getKey()+"="+entry.getValue().orElse(""));
}