CSV parsing in Java - working example

Question

I want to write a program for a school java project to parse some CSV I do not know  I do know the datatype of each column - although I do not know the delimiter   The problem I do not even marginally know how to fix is to parse Date or even DateTime Columns  They can be in one of many formats   I found many libraries but have no clue which is the best for my needs  http   opencsv sourceforge net  http   www csvreader com java csv php http   supercsv sourceforge net  http   flatpack sourceforge net   The problem is I am a total java beginner  I am afraid non of those libraries can do what I need or I can t convince them to do it   I bet there are a lot of people here who have code sample that could get me started in no time for what I need    automatically split in Columns  delimiter unknown  Columntypes are known  cast to Columntype  should cope with       etc   convert dates to Java Date or Calendar Objects   It would be nice to get as many code samples as possible by email   Thanks a lot  AS

User · Answer

You might want to have a look at this specification for CSV. Bear in mind that there is no official recognized specification.

If you do not now the delimiter it will not be possible to do this so you have to find out somehow. If you can do a manual inspection of the file you should quickly be able to see what it is and hard code it in your program. If the delimiter can vary your only hope is to be able to deduce if from the formatting of the known data. When Excel imports CSV files it lets the user choose the delimiter and this is a solution you could use as well.

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I would recommend that you start by pulling your task apart into it s component parts    Read string data from a CSV Convert string data to appropriate format   Once you do that  it should be fairly trivial to use one of the libraries you link to  which most certainly will handle task  1    Then iterate through the returned values  and cast convert each String value to the value you want   If the question is how to convert strings to different objects  it s going to depend on what format you are starting with  and what format you want to wind up with   DateFormat parse    for example  will parse dates from strings   See SimpleDateFormat for quickly constructing a DateFormat for a certain string representation  Integer parseInt   will prase integers from strings   Currency  you ll have to decide how you want to capture it   If you want to just capture as a float  then Float parseFloat   will do the trick  just use String replace   to remove all   and commas before you parse it    Or you can parse into a BigDecimal  so you don t have rounding problems    There may be a better class for currency handling  I don t do much of that  so am not familiar with that area of the JDK

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I agree with  Brian Clapper   I have used SuperCSV as a parser though I ve had mixed results   I enjoy the versatility of it  but there are some situations within my own csv files for which I have not been able to reconcile  yet    I have faith in this product and would recommend it overall--I m just missing something simple  no doubt  that I m doing in my own implementation   SuperCSV can parse the columns into various formats  do edits on the columns  etc   It s worth taking a look-see   It has examples as well  and easy to follow   The one only limitation I m having is catching an  empty  column and parsing it into an Integer or maybe a blank  etc   I m getting null-pointer errors  but javadocs suggest each cellProcessor checks for nulls first   So  I m blaming myself first  for now    -   Anyway  take a look at SuperCSV   http   supercsv sourceforge net

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At a minimum you are going to need to know the column delimiter

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You also have the Apache Commons CSV library  maybe it does what you need  See the guide  Updated to Release 1 1 in 2014-11   Also  for the foolproof edition  I think you ll need to code it yourself   through SimpleDateFormat you can choose your formats  and specify various types  if the Date isn t like any of your pre-thought types  it isn t a Date

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Basically you will need to read the file line by line   Then you will need to split each line by the delimiter  say a comma  CSV stands for comma-separated values   with  String   strArr line split         This will turn it into an array of strings which you can then manipulate  for example with  String name strArr 0   int yearOfBirth   Integer valueOf strArr 1    int monthOfBirth   Integer valueOf strArr 2    int dayOfBirth   Integer valueOf strArr 3    GregorianCalendar dob new GregorianCalendar yearOfBirth  monthOfBirth  dayOfBirth   Student student new Student name  dob     lets pretend you are creating instances of Student   You will need to do this for every line so wrap this code into a while loop   If you don t know the delimiter just open the file in a text editor

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There is a serious problem with using   String   strArr line split         in order to parse CSV files  and that is because there can be commas within the data values  and in that case you must quote them  and ignore commas between quotes   There is a very very simple way to parse this         returns a row of values as a list   returns null if you are past the end of the input stream    public static List lt String gt  parseLine Reader r  throws Exception       int ch   r read        while  ch      r               ignore linefeed chars wherever  particularly just before end of file         ch   r read              if  ch lt 0            return null            Vector lt String gt  store   new Vector lt String gt         StringBuffer curVal   new StringBuffer        boolean inquotes   false      boolean started   false      while  ch gt  0            if  inquotes                started true              if  ch                            inquotes   false                            else                   curVal append  char ch                                   else               if  ch                            inquotes   true                  if  started                           if this is the second quote in a value  add a quote                        this is for the double quote in the middle of a value                     curVal append                                                    else if  ch                           store add curVal toString                     curVal   new StringBuffer                    started   false                            else if  ch      r                       ignore LF characters                           else if  ch      n                       end of a line  break out                 break                            else                   curVal append  char ch                                   ch   r read              store add curVal toString         return store      There are many advantages to this approach   Note that each character is touched EXACTLY once   There is no reading ahead  pushing back in the buffer  etc   No searching ahead to the end of the line  and then copying the line before parsing   This parser works purely from the stream  and creates each string value once   It works on header lines  and data lines  you just deal with the returned list appropriate to that   You give it a reader  so the underlying stream has been converted to characters using any encoding you choose   The stream can come from any source  a file  a HTTP post  an HTTP get  and you parse the stream directly   This is a static method  so there is no object to create and configure  and when this returns  there is no memory being held   You can find a full discussion of this code  and why this approach is preferred in my blog post on the subject   The Only Class You Need for CSV Files

User · Answer

Writing your own parser is fun  but likely you should have a look at Open CSV  It provides numerous ways of accessing the CSV and also allows to generate CSV  And it does handle escapes properly  As mentioned in another post  there is also a CSV-parsing lib in the Apache Commons  but that one isn t released yet

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My approach would not be to start by writing your own API  Life s too short  and there are more pressing problems to solve  In this situation  I typically    Find a library that appears to do what I want  If one doesn t exist  then implement it  If a library does exist  but I m not sure it ll be suitable for my needs  write a thin adapter API around it  so I can control how it s called  The adapter API expresses the API I need  and it maps those calls to the underlying API  If the library doesn t turn out to be suitable  I can swap another one in underneath the adapter API  whether it s another open source one or something I write myself  with a minimum of effort  without affecting the callers    Start with something someone has already written  Odds are  it ll do what you want  You can always write your own later  if necessary  OpenCSV is as good a starting point as any

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i had to use a csv parser about 5 years ago  seems there are at least two csv standards  http   en wikipedia org wiki Comma-separated values and what microsoft does in excel   i found this libaray which eats both  http   ostermiller org utils CSV html  but afaik  it has no way of inferring what data type the columns were

[java] CSV parsing in Java - working example..?

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