Read CSV file column by column

Question

I want to read specific columns from a multi column csv file and print those columns in other csv file using Java  Any help please  Following is my code to print each token line by line  But I am looking to print only few columns out of the multi column csv   import java io BufferedReader  import java io FileReader  import java io FileWriter  import java util StringTokenizer   public class ParseCSV        public static void main String   args             try                          csv file containing data             String strFile    C   Users  rsaluja  CMS Evaluation  Drupal 12 08 27 csv                  create BufferedReader to read csv file             BufferedReader br   new BufferedReader  new FileReader strFile                String strLine                   StringTokenizer st   null              int lineNumber   0  tokenNumber   0                 read comma separated file line by line             while   strLine   br readLine       null                                lineNumber                       break comma separated line using                     st   new StringTokenizer strLine                         while st hasMoreTokens                                        display csv values                 tokenNumber                    System out println  Line       lineNumber                                      Token       tokenNumber                                      Token      st nextToken                                   System out println cols 4

User · Answer

We can use the core java stuff alone to read the CVS file column by column  Here is the sample code I have wrote for my requirement  I believe that it will help for some one    BufferedReader br   new BufferedReader new FileReader csvFile        String line   EMPTY      int lineNumber   0       int productURIIndex   -1      int marketURIIndex   -1      int ingredientURIIndex   -1      int companyURIIndex   -1          read comma separated file line by line     while   line   br readLine       null            lineNumber               use comma as line separator         String   splitStr   line split COMMA           int splittedStringLen   splitStr length              get the product title and uri column index by reading csv header            line         if  lineNumber    1                for  int i   0  i  lt  splittedStringLen  i                      if  splitStr i  equals PRODUCTURI TITLE                         productURIIndex   i                      System out println  product uri index     productURIIndex                                      if  splitStr i  equals MARKETURI TITLE                         marketURIIndex   i                      System out println  marketURIIndex     marketURIIndex                                      if  splitStr i  equals COMPANYURI TITLE                         companyURIIndex   i                      System out println  companyURIIndex     companyURIIndex                                      if  splitStr i  equals INGREDIENTURI TITLE                         ingredientURIIndex   i                      System out println  ingredientURIIndex     ingredientURIIndex                                             else               if  splitStr    null                    String conditionString   EMPTY                     avoiding arrayindexoutboundexception when the line                    contains only                               for  String s   splitStr                        conditionString   s                                    if   conditionString equals EMPTY                         if  productURIIndex    -1                            productCVSUriList add splitStr productURIIndex                                              if  companyURIIndex    -1                            companyCVSUriList add splitStr companyURIIndex                                              if  marketURIIndex    -1                            marketCVSUriList add splitStr marketURIIndex                                              if  ingredientURIIndex    -1                            ingredientCVSUriList add splitStr ingredientURIIndex

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Finds all files in folder and write that data to ArrayList row   Initialize  ArrayList lt ArrayList lt String gt  gt  row new ArrayList lt ArrayList lt String gt  gt     BufferedReader br null    For Accessing row  for ArrayList lt String gt  data row   data get col no      or row get 0  get 0     getting first row first col   Functions that reads all files from folders and concatenate them row   static void readData    String path  C   Users  Galaxy Computers  Desktop  Java project  Nasdaq     File files new File path   String   list files list     try           String sCurrentLine         char check         for String filename list            br   new BufferedReader new FileReader path filename            br readLine     If file contains uneccessary first line          while   sCurrentLine   br readLine       null                row add splitLine sCurrentLine                                         catch  IOException e            e printStackTrace                   try               if  br    null br close              catch  IOException ex                ex printStackTrace                         static ArrayList lt String gt  splitLine String line      String   ar line split          ArrayList lt String gt  d new ArrayList lt String gt        for String data ar       d add data            return d

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Reading a CSV file in very simple and common in Java  You actually don t require to load any extra third party library to do this for you  CSV  comma separated value  file is just a normal plain-text file  store data in column by column  and split it by a separator  e g comma         In order to read specific columns from the CSV file  there are several ways  Simplest of all is as below   Code to read CSV without any 3rd party library  BufferedReader br   new BufferedReader new FileReader csvFile    while   line   br readLine       null           use comma as separator     String   cols   line split cvsSplitBy       System out println  Coulmn 4      cols 4        Column 5     cols 5        If you notice  nothing special is performed here  It is just reading a text file  and spitting it by a separator            Consider an extract from legacy country CSV data at GeoLite Free Downloadable Databases   1 0 0 0   1 0 0 255   16777216   16777471   AU   Australia   1 0 1 0   1 0 3 255   16777472   16778239   CN   China   1 0 4 0   1 0 7 255   16778240   16779263   AU   Australia   1 0 8 0   1 0 15 255   16779264   16781311   CN   China   1 0 16 0   1 0 31 255   16781312   16785407   JP   Japan   1 0 32 0   1 0 63 255   16785408   16793599   CN   China   1 0 64 0   1 0 127 255   16793600   16809983   JP   Japan   1 0 128 0   1 0 255 255   16809984   16842751   TH   Thailand    Above code will output as below   Column 4   AU    Column 5  Australia  Column 4   CN    Column 5  China  Column 4   AU    Column 5  Australia  Column 4   CN    Column 5  China  Column 4   JP    Column 5  Japan  Column 4   CN    Column 5  China  Column 4   JP    Column 5  Japan  Column 4   TH    Column 5  Thailand    You can  in fact  put the columns in a Map and then get the values simply by using the key   Shishir

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I sugges to use the Apache Commons CSV https   commons apache org proper commons-csv   Here is one example       Path currentRelativePath   Paths get          String currentPath   currentRelativePath toAbsolutePath   toString        String csvFile   currentPath     pathInYourProject test csv        Reader in      Iterable lt CSVRecord gt  records   null      try               in   new FileReader csvFile           records   CSVFormat EXCEL withHeader   parse in      header will be ignored           catch  IOException e                e printStackTrace               for  CSVRecord record   records            String line               for   int i 0  i  lt  record size    i                          if   line                         line   line concat record get i                else                 line   line concat       record get i                      System out println  read line      line           It automaticly recognize   and   but not    maybe it can be configured       My example file is   col1 col2 col3 val1  val2  val3  val4  val5 val6 val7  val8    And output is   read line  val1 val2 val3 read line  val4 val5 read line  val6 val7  val8    Last line is considered like one value

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To read some specific column I did something like this   dpkcs csv content  FN LN EMAIL CC Name1 Lname1 email1 gmail com CC1 Nmae2 Lname2 email2r gmail com CC2   The function to read it   private void getEMailRecepientList                     List lt EmailRecepientData gt  emailList   null    Blank list of POJO class                 Scanner scanner   null                  BufferedReader reader   null                  try                       reader   new BufferedReader new FileReader  dpkcs csv                         Map lt String  Integer gt  mailHeader   new HashMap lt String  Integer gt                            read file line by line                     String line   null                      int index   0                      line   reader readLine                           Get header from 1st row of csv                     if  line    null                            StringTokenizer str   new StringTokenizer line                                int headerCount   str countTokens                            for  int i   0  i  lt  headerCount  i                                  String headerKey   str nextToken                                mailHeader put headerKey toUpperCase    new Integer i                                                                         emailList   new ArrayList lt EmailRecepientData gt                          while   line   reader readLine       null                           POJO class for getter and setters                         EmailRecepientData email   new EmailRecepientData                            scanner   new Scanner line                           scanner useDelimiter                             Use Specific key to get value what u want                         while  scanner hasNext                                  String data   scanner next                                if  index    mailHeader get  EMAIL                                    email setEmailId data                               else if  index    mailHeader get  FN                                    email setFirstName data                               else if  index    mailHeader get  LN                                    email setLastName data                               else if  index    mailHeader get  CC                                    email setCouponCode data                                index                                                      index   0                          emailList add email                                             reader close                      catch  Exception e                        StringWriter stack   new StringWriter                        e printStackTrace new PrintWriter stack                       finally                       scanner close                                       System out println  list--    emailList                    The POJO Class   public class EmailRecepientData       private String emailId      private String firstName      private String lastName      private String couponCode       public String getEmailId             return emailId             public void setEmailId String emailId            this emailId   emailId             public String getFirstName             return firstName             public void setFirstName String firstName            this firstName   firstName             public String getLastName             return lastName             public void setLastName String lastName            this lastName   lastName             public String getCouponCode             return couponCode             public void setCouponCode String couponCode            this couponCode   couponCode              Override     public String toString             return  Email Id     emailId      First Name     firstName                            Last Name     lastName      Coupon Code     couponCode

User · Answer

Well  how about this     This code calculates both row and column count in a csv file  Try this out         static int   getRowsColsNo         Scanner scanIn   null      int rows   0      int cols   0      String InputLine           try           scanIn   new Scanner new BufferedReader                  new FileReader  filename csv              scanIn useDelimiter               while  scanIn hasNextLine                  InputLine   scanIn nextLine                String   InArray   InputLine split                   rows                cols   InArray length                   catch  Exception e            System out println e             return new int     rows  cols

User · Answer

You should use the excellent OpenCSV for reading and writing CSV files   To adapt your example to use the library it would look like this   public class ParseCSV     public static void main String   args        try           csv file containing data       String strFile    C  Users rsaluja CMS Evaluation Drupal 12 08 27 csv         CSVReader reader   new CSVReader new FileReader strFile          String    nextLine        int lineNumber   0        while   nextLine   reader readNext       null            lineNumber            System out println  Line       lineNumber               nextLine   is an array of values from the line         System out println nextLine 4     etc

User · Answer

I am sorry  but none of these answers provide an optimal solution  If you use a library such as OpenCSV you will have to write a lot of code to handle special cases to extract information from specific columns   For example  if you have rows with less columns than what you re after  you ll have to write a lot of code to handle it  Using the OpenCSV example     CSVReader reader   new CSVReader new FileReader strFile      String    nextLine    while   nextLine   reader readNext       null             let s say you are interested in getting columns 20  30  and 40        String   outputRow   new String 3          if parsedRow length  lt  40               outputRow 2    null           else               outputRow 2    parsedRow 40                  if parsedRow length  lt  30               outputRow 1    null           else               outputRow 1    parsedRow 30                  if parsedRow length  lt  20               outputRow 0    null           else               outputRow 0    parsedRow 20                  This is a lot of code for a simple requirement  It gets worse if you are trying to get values of columns by name  You should use a more modern parser such as the one provided by uniVocity-parsers   To reliably and easily get the columns you want  simply write   CsvParserSettings settings   new CsvParserSettings    parserSettings selectIndexes 20  30  40   CsvParser parser   new CsvParser settings   List lt String   gt  allRows   parser parseAll new FileReader yourFile      Disclosure  I am the author of this library  It s open-source and free  Apache V2 0 license

[java] Read CSV file column by column

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