Question

I have this kind of CSV file which I have to parse in Java.

2012-11-01 00,  1106,   2194.1971066908
2012-11-01 01,  760,    1271.8460526316
.
.
.
2012-11-30 21,  1353,   1464.0014781966
2012-11-30 22,  1810,   1338.8331491713
2012-11-30 23,  1537,   1222.7826935589
        
720 rows selected.      
        
Elapsed: 00:37:00.23

This is Java code I created in order to segregate each column and store it in a list.

public void extractFile(String fileName){
        try{
            BufferedReader bf = new BufferedReader(new FileReader(fileName));
            try {
                String readBuff = bf.readLine();
                
                while (readBuff!=null){
                    
                    Pattern checkData = Pattern.compile("[a-zA-Z]");
                    Matcher match = checkData.matcher(readBuff);
                    
                    if (match.find()){
                        readBuff = null;
                    }
                    
                    else if (!match.find()){
                        
                        String[] splitReadBuffByComma = new String[3];
                        splitReadBuffByComma = readBuff.split(",");
                        
                            for (int x=0; x<splitReadBuffByComma.length; x++){
                                
                                if (x==0){
                                    dHourList.add(splitReadBuffByComma[x]);
                                }
                                else if (x==1){
                                    throughputList.add(splitReadBuffByComma[x]);
                                }
                                else if (x==2){
                                    avgRespTimeList.add(splitReadBuffByComma[x]);
                                }
                            }
                    }
                    
                    readBuff = bf.readLine();
                }
            }
            finally{
                bf.close();
            }
        }
        catch(FileNotFoundException e){
            System.out.println("File not found dude: "+ e);
        }
        catch(IOException e){
            System.out.println("Error Exception dude: "+e);
        }
    }

The problem is that the regex I created is a bit faulty because it still includes the text "720 rows selected" and stores them in dHourList.
dHourList should only store the date column represented like this "2012-11-01 00…etc"
throughputList = "1106, 760 …etc"
avgResponseTime = "2194.192, 1271.846…etc"

What should be the correct reg expression for this?

Update

2012-11-30 21
2012-11-30 22
2012-11-30 23

720 rows selected.

Elapsed: 00:37:00.23

Size of date-hour: 724 size of throughput: 720 size of avg resp time: 720

I used this in checkData regex instead because if I use one slash \d compile will say invalid escape sequence

Pattern checkData = Pattern.compile("^(19|20)\\d\\d([-/.])(0[1-9]|1[012])\2(0[1-9]|[12][0-9]|3[01])\b.+$"); 

but its still showing 720 rows selected and another line which shouldn’t be there.

Update 2

Working code:

while (readBuff!=null){
                    
                    
                    Pattern checkData = Pattern.compile("^(19|20)\\d\\d([-/.])(0[1-9]|1[012])\\2(0[1-9]|[12][0-9]|3[01])\\b.+$");
                    
                    Matcher match = checkData.matcher(readBuff);
                    
                    if (!match.find()){
                        readBuff = null;
                    }
                    
                    else{
                        
                        String[] splitReadBuffByComma = new String[3];
                        splitReadBuffByComma = readBuff.split(",");
                        
                            for (int x=0; x<splitReadBuffByComma.length; x++){
                                
                                if (x==0){
                                    dHourList.add(splitReadBuffByComma[x]);
                                }
                                else if (x==1){
                                    throughputList.add(splitReadBuffByComma[x]);
                                }
                                else if (x==2){
                                    avgRespTimeList.add(splitReadBuffByComma[x]);
                                }
                            }
                    }
                    
                    readBuff = bf.readLine();
                }

I removed else if condition and changed it to else and used the regex suggested by Cylian
now I have the output

2012-11-30 21
2012-11-30 22
2012-11-30 23

Size of date-hour: 720 size of throughput: 720 size of avg resp time: 720

Thanks alot!

Answer 1

Try this [your code, but a bit modified]:

public void extractFile(String fileName){
        try{
            BufferedReader bf = new BufferedReader(new FileReader(fileName));
            try {
                String readBuff = bf.readLine();

                while (readBuff!=null){

                    Pattern checkData = Pattern.compile("^(19|20)\\d\\d([-/.])(0[1-9]|1[012])\\2(0[1-9]|[12][0-9]|3[01])\\b.+$");
                    Matcher match = checkData.matcher(readBuff);

                    if (!match.find()){
                        readBuff = null;
                    }

                    else if (match.find()){

                        String[] splitReadBuffByComma = new String[3];
                        splitReadBuffByComma = readBuff.split(",");

                            for (int x=0; x<splitReadBuffByComma.length; x++){

                                if (x==0){
                                    dHourList.add(splitReadBuffByComma[x]);
                                }
                                else if (x==1){
                                    throughputList.add(splitReadBuffByComma[x]);
                                }
                                else if (x==2){
                                    avgRespTimeList.add(splitReadBuffByComma[x]);
                                }
                            }
                    }

                    readBuff = bf.readLine();
                }
            }
            finally{
                bf.close();
            }
        }
        catch(FileNotFoundException e){
            System.out.println("File not found dude: "+ e);
        }
        catch(IOException e){
            System.out.println("Error Exception dude: "+e);
        }
    }

regex anatomy

# ^(19|20)\d\d([-/.])(0[1-9]|1[012])\2(0[1-9]|[12][0-9]|3[01])\b.+$
# 
# Options: ^ and $ match at line breaks
# 
# Assert position at the beginning of a line (at beginning of the string or after a line break character) «^»
# Match the regular expression below and capture its match into backreference number 1 «(19|20)»
#    Match either the regular expression below (attempting the next alternative only if this one fails) «19»
#       Match the characters “19” literally «19»
#    Or match regular expression number 2 below (the entire group fails if this one fails to match) «20»
#       Match the characters “20” literally «20»
# Match a single digit 0..9 «\d»
# Match a single digit 0..9 «\d»
# Match the regular expression below and capture its match into backreference number 2 «([-/.])»
#    Match a single character present in the list “-/.” «[-/.]»
# Match the regular expression below and capture its match into backreference number 3 «(0[1-9]|1[012])»
#    Match either the regular expression below (attempting the next alternative only if this one fails) «0[1-9]»
#       Match the character “0” literally «0»
#       Match a single character in the range between “1” and “9” «[1-9]»
#    Or match regular expression number 2 below (the entire group fails if this one fails to match) «1[012]»
#       Match the character “1” literally «1»
#       Match a single character present in the list “012” «[012]»
# Match the same text as most recently matched by capturing group number 2 «\2»
# Match the regular expression below and capture its match into backreference number 4 «(0[1-9]|[12][0-9]|3[01])»
#    Match either the regular expression below (attempting the next alternative only if this one fails) «0[1-9]»
#       Match the character “0” literally «0»
#       Match a single character in the range between “1” and “9” «[1-9]»
#    Or match regular expression number 2 below (attempting the next alternative only if this one fails) «[12][0-9]»
#       Match a single character present in the list “12” «[12]»
#       Match a single character in the range between “0” and “9” «[0-9]»
#    Or match regular expression number 3 below (the entire group fails if this one fails to match) «3[01]»
#       Match the character “3” literally «3»
#       Match a single character present in the list “01” «[01]»
# Assert position at a word boundary «\b»
# Match any single character that is not a line break character «.+»
#    Between one and unlimited times, as many times as possible, giving back as needed (greedy) «+»
# Assert position at the end of a line (at the end of the string or before a line break character) «$»

UPDATE

As long I understand, your input string contains many lines starts with a date but not contains commas in them. For this change the previous Pattern to this following:

^(19|20)\d\d([-/.])(0[1-9]|1[012])\2(0[1-9]|[12][0-9]|3[01])\s+\d+,[^,]+,[^,]+$

or escaped

^(19|20)\\d\\d([-/.])(0[1-9]|1[012])\\2(0[1-9]|[12][0-9]|3[01])\\s+\\d+,[^,]+,[^,]+$