Java CSV Reader module. Drop into any project and use. Supports Excel compatible CSV (multi-line columns, etc).

CSV.java

package sample;

import java.io.InputStream;
import java.io.PushbackInputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.BufferedReader;

import java.util.List;
import java.util.ArrayList;

/*
 * Copyright 2017 Jay Sridhar
 * 
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 * 
 * The above copyright notice and this permission notice shall be
 * included in all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 * 
 * @Author Jay Sridhar
 */
public class CSV
{
  static final private int NUMMARK = 10;
  static final private char COMMA = ',';
  static final private char DQUOTE = '"';
  static final private char CRETURN = '\r';
  static final private char LFEED = '\n';
  static final private char SQUOTE = '\'';
  static final private char COMMENT = '#';

  /**
   * Should we ignore multiple carriage-return/newline characters
   * at the end of the record?
   */
  private boolean stripMultipleNewlines;

  /**
   * What should be used as the separator character?
   */
  private char separator;
  private ArrayList<String> fields;
  private boolean eofSeen;
  private Reader in;

  static public Reader stripBom(InputStream in)
    throws java.io.IOException,
           java.io.UnsupportedEncodingException
  {
    PushbackInputStream pin = new PushbackInputStream(in, 3);
    byte[] b = new byte[3];
    int len = pin.read(b, 0, b.length);
    if ( (b[0] & 0xFF) == 0xEF && len == 3 ) {
      if ( (b[1] & 0xFF) == 0xBB && 
           (b[2] & 0xFF) == 0xBF ) {
        return new InputStreamReader(pin, "UTF-8");
      } else {
        pin.unread(b, 0, len);
      }
    }
    else if ( len >= 2 ) {
      if ( (b[0] & 0xFF) == 0xFE &&
           (b[1] & 0xFF) == 0xFF ) {
        return new InputStreamReader(pin, "UTF-16BE");
      } else if ( (b[0] & 0xFF) == 0xFF &&
                  (b[1] & 0xFF) == 0xFE ) {
        return new InputStreamReader(pin, "UTF-16LE");
      } else {
        pin.unread(b, 0, len);
      }
    } else if ( len > 0 ) {
      pin.unread(b, 0, len);
    }
    return new InputStreamReader(pin, "UTF-8");
  }

  public CSV(boolean stripMultipleNewlines,
             char separator,
             Reader input)
  {
    this.stripMultipleNewlines = stripMultipleNewlines;
    this.separator = separator;
    this.fields = new ArrayList<String>();
    this.eofSeen = false;
    this.in = new BufferedReader(input);
  }

  public CSV(boolean stripMultipleNewlines,
             char separator,
             InputStream input)
    throws java.io.IOException,
           java.io.UnsupportedEncodingException
  {
    this.stripMultipleNewlines = stripMultipleNewlines;
    this.separator = separator;
    this.fields = new ArrayList<String>();
    this.eofSeen = false;
    this.in = new BufferedReader(stripBom(input));
  }

  public boolean hasNext() throws java.io.IOException
  {
    if ( eofSeen ) return false;
    fields.clear();
    eofSeen = split( in, fields );
    if ( eofSeen ) return ! fields.isEmpty();
    else return true;
  }

  public List<String> next()
  {
    return fields;
  }

  // Returns true if EOF seen.
  static private boolean discardLinefeed(Reader in,
                                         boolean stripMultiple)
    throws java.io.IOException
  {
    if ( stripMultiple ) {
      in.mark(NUMMARK);
      int value = in.read();
      while ( value != -1 ) {
        char c = (char)value;
        if ( c != CRETURN && c != LFEED ) {
          in.reset();
          return false;
        } else {
          in.mark(NUMMARK);
          value = in.read();
        }
      }
      return true;
    } else {
      in.mark(NUMMARK);
      int value = in.read();
      if ( value == -1 ) return true;
      else if ( (char)value != LFEED ) in.reset();
      return false;
    }
  }

  private boolean skipComment(Reader in)
    throws java.io.IOException
  {
    /* Discard line. */
    int value;
    while ( (value = in.read()) != -1 ) {
      char c = (char)value;
      if ( c == CRETURN )
        return discardLinefeed( in, stripMultipleNewlines );
    }
    return true;
  }

  // Returns true when EOF has been seen.
  private boolean split(Reader in,ArrayList<String> fields)
    throws java.io.IOException
  {
    StringBuilder sbuf = new StringBuilder();
    int value;
    while ( (value = in.read()) != -1 ) {
      char c = (char)value;
      switch(c) {
      case CRETURN:
        if ( sbuf.length() > 0 ) {
          fields.add( sbuf.toString() );
          sbuf.delete( 0, sbuf.length() );
        }
        return discardLinefeed( in, stripMultipleNewlines );

      case LFEED:
        if ( sbuf.length() > 0 ) {
          fields.add( sbuf.toString() );
          sbuf.delete( 0, sbuf.length() );
        }
        if ( stripMultipleNewlines )
          return discardLinefeed( in, stripMultipleNewlines );
        else return false;

      case DQUOTE:
        {
          // Processing double-quoted string ..
          while ( (value = in.read()) != -1 ) {
            c = (char)value;
            if ( c == DQUOTE ) {
              // Saw another double-quote. Check if
              // another char can be read.
              in.mark(NUMMARK);
              if ( (value = in.read()) == -1 ) {
                // Nope, found EOF; means End of
                // field, End of record and End of
                // File
                if ( sbuf.length() > 0 ) {
                  fields.add( sbuf.toString() );
                  sbuf.delete( 0, sbuf.length() );
                }
                return true;
              } else if ( (c = (char)value) == DQUOTE ) {
                // Found a second double-quote
                // character. Means the double-quote
                // is included.
                sbuf.append( DQUOTE );
              } else if ( c == CRETURN ) {
                // Found End of line. Means End of
                // field, and End of record.
                if ( sbuf.length() > 0 ) {
                  fields.add( sbuf.toString() );
                  sbuf.delete( 0, sbuf.length() );
                }
                // Read and discard a line-feed if we
                // can indeed do so.
                return discardLinefeed( in,
                                        stripMultipleNewlines );
              } else if ( c == LFEED ) {
                // Found end of line. Means End of
                // field, and End of record.
                if ( sbuf.length() > 0 ) {
                  fields.add( sbuf.toString() );
                  sbuf.delete( 0, sbuf.length() );
                }
                // No need to check further. At this
                // point, we have not yet hit EOF, so
                // we return false.
                if ( stripMultipleNewlines )
                  return discardLinefeed( in, stripMultipleNewlines );
                else return false; 
              } else {
                // Not one of EOF, double-quote,
                // newline or line-feed. Means end of
                // double-quote processing. Does NOT
                // mean end-of-field or end-of-record.
                // System.err.println("EOR on '" + c +
                // "'");
                in.reset();
                break;
              }
            } else {
              // Not a double-quote, so no special meaning.
              sbuf.append( c );
            }
          }
          // Hit EOF, and did not see the terminating double-quote.
          if ( value == -1 ) {
            // We ignore this error, and just add whatever
            // left as the next field.
            if ( sbuf.length() > 0 ) {
              fields.add( sbuf.toString() );
              sbuf.delete( 0, sbuf.length() );
            }
            return true;
          }
        }
        break;

      default:
        if ( c == separator ) {
          fields.add( sbuf.toString() );
          sbuf.delete(0, sbuf.length());
        } else {
          /* A comment line is a line starting with '#' with
           * optional whitespace at the start. */
          if ( c == COMMENT && fields.isEmpty() &&
               sbuf.toString().trim().isEmpty() ) {
            boolean eof = skipComment(in);
            if ( eof ) return eof;
            else sbuf.delete(0, sbuf.length());
            /* Continue with next line if not eof. */
          } else sbuf.append(c);
        }
      }
    }
    if ( sbuf.length() > 0 ) {
      fields.add( sbuf.toString() );
      sbuf.delete( 0, sbuf.length() );
    }
    return true;
  }
}

lovely. wish it had a test harness. ;-)

Thank you. This is great.

Cool... it's great!

Great post, Cool that's professional!!, Awesome, made my day

do you have the maven dependency

It is assigning new fields array (headers) everytime with new line and not using the actual headers.

It is assigning new fields array (headers) everytime with new line and not using the actual headers.

Do you mind indicating where it is doing that?

Sure,

Here the fieldNames list is returning different name inside in the for loop, everytime while (csv.hasNext()) this gets called. It is not clear that how this csv.hasNext() is changing the final variable value of this class.

CSV csv = null;
        try {
            csv = new CSV(false, '\t', objectInputStream);
            if (!csv.hasNext()){
                return;
            }
            final List<String> fieldNames = new ArrayList<>(csv.next());
            List<Map<String, String>> list = new ArrayList<>();
            while (csv.hasNext()) {
                List<String> x = csv.next();
                Map<String, String> obj = new LinkedHashMap<>();
                for (int i = 0; i < fieldNames.size(); i++) {
                    obj.put(fieldNames.get(i), x.get(i));
                }
                list.add(obj);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }