public  Map<String, List<Message>> groupList(List<Message> list){

        //定义一个map集合用于分组

        Map<String, List<Message>> mapList = new HashMap<String, List<Message>>();

        //遍历集合以message的 toId和fromId组合为键，以message为值保存到mapList中

        for (Iterator it = list.iterator(); it.hasNext();){

            //将循环读取的结果放入对象中

            Message message = (Message) it.next();

            //如果在这个map中包含有相同的键，这创建一个集合将其存起来

            if (mapList.containsKey(message.getToId()+"-"+message.getFromId()+"-")){

                List<Message> syn = mapList.get(message.getToId()+"-"+message.getFromId()+"-");

                syn.add(message);

            }else if(mapList.containsKey(message.getFromId()+"-"+message.getToId()+"-")){

                List<Message> syn = mapList.get(message.getFromId()+"-"+message.getToId()+"-");

                syn.add(message);

            } else {//如果没有包含相同的键，在创建一个集合保存数据

                List<Message> newList = new ArrayList<Message>();

                newList.add(message);

                mapList.put(message.getFromId()+"-"+message.getToId()+"-", newList);

            }

        }

        return mapList;

    }

public class Message {

    @Id

    @GeneratedValue(strategy = GenerationType.AUTO)

    @Column(name="ID",nullable = false)

    private Long id;//主键ID

    @Column(name="ToID",nullable = false)

    private Long toId;//接收方UserId

    @Column(name="FromId",nullable = false)

    private Long fromId;//发送方UserID

    @Column(name="Content",nullable = true)

    private String content;//消息内容

    @Column(name="Status",nullable = false)

    private String status;//状态：unread未读，read 已读

    @Column(name="AddTime",nullable = false)

    private Timestamp addTime;//添加时间

get/set……方法省略