复杂的Java对象到CSV

Question

我正在尝试从相当复杂的Java对象生成CSV文件.该对象是具有一些属性的会话,以及具有某些属性的字符串和消息列表以及具有某些属性的注释列表.

会话类如下;

public class Session {

    private Long id;

    private Date startDate;

    private Date endDate;

    private List<Message> messages;

    private List<String> participants;

    public TweetSession() {
    }  

    public TweetSession(Date startDate, List<Message> messages, List<String>     participants) {
        this.startDate = startDate;
        this.messages = messages;
        this.participants = participants;
    }

    public Long getId() {
        return id;
    }

    public Date getStartDate() {
        return startDate;
    }

    public void setStartDate(Date startDate) {
        this.startDate = startDate;
    }

    public Date getEndDate() {
        return endDate;
    }

    public void setEndDate(Date endDate) {
        this.endDate = endDate;
    }

    public List<Message> getMessages() {
        return messages;
    }

    public void setMessage(List<Message> messages) {
        this.message = message;
    }

    public List<String> getParticipants() {
        return participants;
    }

    public void setParticipants(List<String> participants) {
        this.participants = participants;
    }
}

消息类如下;

public class Message {

    private Long id;

    private Session session;

    private Date date;

    private String participant;

    private String content;

    private List<Comment> comments;

    public Message() {
    }

    public Message(String participant, Session session, Date date, String content) {
        this.participant = participant;
        this.session = session;
        this.content = content;
        this.date = date;
        this.comments = new ArrayList<>();
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getParticipant() {
        return participant;
    }

    public void setParticipant(String participant) {
        this.participant = participant;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }

    public List<Comment> getComments() {
        return comments;
    }

    public void setComments(List<Comment> comments) {
        this.comments = comments;
    }

    public void addComment(Comment comment) {
        this.comments.add(comment);
    }

    public Date getDate() {
        return date;
    }

    public void setDate(Date date) {
        this.date = date;
    }

    public TweetSession getSession() {
        return session;
    }

    public void setSession(TweetSession session) {
        this.session = session;
    }
}

而评论课;

public class Comment {

    private Long id;

    private Message message;

    private String participant;

    private String message;

    private Date date;

    public Comment() {
    }

    public Comment(String participant, Message message, String content, Date date) {
        this.participant = participant;
        this.content = content;
        this.message = message;
        this.date = date;
    }

    public String getParticipant() {
        return participant;
    }

    public void setParticipant(String participant) {
        this.participant = participant;
    }

    public Message getMessage() {
        return message;
    }

    public void setMessage(Message message) {
        this.message = message;
    }

    public Date getDate() {
        return date;
    }

    public void setDate(Date date) {
        this.date = date;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }
}   

我想知道是否可以将其映射到CSV文件.当我将会话对象转换为JSON格式并将该JSON转换为在线生成器中的CSV时,我得到了正确的输出,所以我认为它必须是可能的.我只是不知道如何.我试过像这样使用net.sf.supercsv库;

public void generateCSV(Session session, HttpServletResponse response) throws IOException {
    String csvFileName = "session.csv";
    response.setContentType("text/csv");

    String headerKey = "Content-Disposition";
    String headerValue = String.format("attachment; filename=\"%s\"",
            csvFileName);
    response.setHeader(headerKey, headerValue);

    ICsvBeanWriter csvWriter = new CsvBeanWriter(response.getWriter(),
            CsvPreference.STANDARD_PREFERENCE);

    // Generate header for the CSV
    Field fields[] = session.getClass().getDeclaredFields();
    String[] header = new String[fields.length];
    for (int i = 0; i < fields.length; i++) {
        header[i] = fields[i].getName();
    }

    csvWriter.writeHeader(header);

    // Generate CSV content from data
    csvWriter.write(session, header);

    csvWriter.close();
}

但这当然不会产生预期的结果.

谁能指出我正确的方向？

提前致谢,

尼尔斯

编辑:

这是一个JSON格式的示例会话:

{
    "id": 22,
    "startDate": 1447368081000,
    "endDate": null,
    "messages": [
        {
            "id": 10,
            "date": 1447368159000,
            "participant": "1",
            "content": "This is a message",
            "comments": []
        },
        {
            "id": 11,
            "date": 1447368168000,
            "participant": "1",
            "content": "This is also a message",
            "comments": []
        },
        {
            "id": 12,
            "date": 1447368179000,
            "participant": "1",
            "content": "This is another message",
            "comments": [
                {
                    "id": 10,
                    "participant": "1",
                    "message": "This is a comment",
                    "date": 1447368227000
                },
                {
                    "id": 11,
                    "participant": "1",
                    "message": "This is also a comment",
                    "date": 1447368234000
                }
            ]
        }
    ],
    "participants": [
        "1",
        "23"
    ]
}

当我将其转换为CSV时,我会得到这样的结果:

实际上,开始考虑(单个)CSV可能不是解决此问题的最佳方法.

Answer 1

您拥有的数据中包含许多1:n依赖项,并不适合单个 CSV文件.

我用过或看过的方法用于此:

• 一个"混合" CSV与Session自己的数据,即id,startDate,endDate在第一列和消息和参与者然后两列打印为JSON

  "123", "2015-11-17", "2015-11-18", "[{id: 345, date: ...}, {id: 789, date: ...}]", "[...]"
  

  (注意你需要使用一个好的CSV库来逃避包含的值,或"s)

• 多个CSV文件 - 模仿您为您的结构建模关系数据库,即

  • sessions.csv含有id,startDate,endDate
  • messages.csv含id,session_id,date,...
  • ...

  然后将它们压缩为单个文件下载

• 请求您的用户提供更精确的规范 - 找出他们打算对数据做什么,然后以一种格式让他们对数据进行"查看",以便他们轻松阅读 - 就像数据库查看和创建报告是为了向用户提供面向任务的数据视图.