对List数据进行分组输出Map

设置的方法：

               //查询出来的所有学生
  List allStudents = null ;
  Map> map = new HashMap>();

  
  for(Student student : allStudents)
  {
   if(map.containsKey(student.getGroupNo()))
   {
    List students = map.get(student.getGroupNo());
    students.add(student);
   }
   else
   {
    List students = new ArrayList();
    students.add(student);
    map.put(student.getGroupNo(), students);
   }
  }

Student类：

public class Student
{
 private String groupNo;
 private String name;
 public String getGroupNo()
 {
  return groupNo;
 }
 public void setGroupNo(String groupNo)
 {
  this.groupNo = groupNo;
 }
 public String getName()
 {
  return name;
 }
 public void setName(String name)
 {
  this.name = name;
 }
 
}