一、数据访问层

MessageMapper.java

@Mapper
public interface MessageMapper {
    // ...
    // 新增消息
    int insertMessage(Message message);

    // 修改消息的状态
    int updateStatus(List<Integer> ids, int status);

}

message-mapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.nowcoder.community.dao.MessageMapper">
    <!-- ... -->

    <insert id="insertMessage" parameterType="Message" keyProperty="id">
        insert into message(<include refid="insertFields"></include>)
        values(#{fromId},#{toId},#{conversationId},#{content},#{status},#{createTime})
    </insert>

    <update id="updateStatus">
        update message set status = #{status}
        where id in
        <foreach collection="ids" item="id" open="(" separator="," close=")">
            #{id}
        </foreach>
    </update>

</mapper>

二、业务层

MessageService.java

@Service
public class MessageService {

    @Autowired
    private MessageMapper messageMapper;

    @Autowired
    private SensitiveFilter sensitiveFilter;

    // ...

    public int addMessage(Message message) {
        message.setContent(HtmlUtils.htmlEscape(message.getContent()));
        message.setContent(sensitiveFilter.filter(message.getContent()));
        return messageMapper.insertMessage(message);
    }

    public int readMessage(List<Integer> ids) {
        return messageMapper.updateStatus(ids, 1);
    }

}

三、表现层

MessageController.java

@Controller
public class MessageController {
    // ...
    @RequestMapping(path = "/letter/send", method = RequestMethod.POST)
    @ResponseBody
    public String sendLetter(String toName, String content) {
        User target = userService.findUserByName(toName);
        if (target == null) {
            return CommunityUtil.getJSONString(1, "目标用户不存在!");
        }

        Message message = new Message();
        message.setFromId(hostHolder.getUser().getId());
        message.setToId(target.getId());
        if (message.getFromId() < message.getToId()) {
            message.setConversationId(message.getFromId() + "_" + message.getToId());
        } else {
            message.setConversationId(message.getToId() + "_" + message.getFromId());
        }
        message.setContent(content);
        message.setCreateTime(new Date());
        messageService.addMessage(message);

        return CommunityUtil.getJSONString(0);
    }
}

页面处理（略）