Complex Java object to CSV

Question

I'm trying to generate a CSV file from a rather complex Java object. The object is a Session with some attributes and a list of Strings and Messages who in turn have some attributes and a list of Comments that have some attributes.

The session class is as follows;

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;
    }
}

The message class is as follows;

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;
    }
}

And the Comment class;

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;
    }
}   

I'm wondering if it is possible to map this to a CSV file. When I convert the session object to JSON format and convert that JSON to CSV in an online generator I get the proper output so I think it must be possible. I just don't really know how. I've tried using the net.sf.supercsv library like this;

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();
}

But this will of course not give the desired result.

Can anyone point me in the right direction?

Thanks in advance,

Niels

Edit:

This is a sample session in JSON format:

{
    "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"
    ]
}

When I convert this to CSV I get something like this:

Indeed starting to think (a single) CSV might not be the best approach to this problem.

Answer 1

The data you have has many 1:n dependencies in it and is not really fit for a single CSV file.

Approaches I've used or seen used for this:

• One "hybrid" CSV with Session's own data, i.e. id, startDate, endDate in first columns and then two columns for messages and participants printed as a JSON

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

  (notice you'll need to use a good CSV library that escapes the values containing , or "s)

• Multiple CSV files - modeled like you'd model a relational database for your structure, i.e.

  • sessions.csv containing id, startDate, endDate
  • messages.csv containing id, session_id, date, ...
  • ...

  then ZIP them for a single file download

• Ask your user for a more precise specification - work to find out what they intend to do with the data, then give them a "view" of the data in a format that will enable them to read them easily - just the way database views and reports are created to give users a task-oriented view of data.