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Java parsing, better way to use tokenizer?

Posted on 2007-11-23
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Last Modified: 2008-09-20
I'm trying to parse a csv file (probably made in excel, or access).

Each field is separated by a "," (comma) but some fields are empty, so I'm not getting the data correctly.

Below is what I'm doing now. Is there a better way to parse?


This line works fine:
23, something, aTitle, something, Smith

This line gives me wrong values:

21,,anotherTitle,,Jones

Both come from the same table with 4 fields.

Thanks.
//...			
String line = in.readLine();
while(line!=null)
{
	StringTokenizer st = new StringTokenizer(line,",");
	int fieldCount=0;
			
	while(st.hasMoreTokens())
	{
		String nextFieldData = st.nextToken();
		++fieldCount;
				
					
		switch(fieldCount)
		{
			case 1: 
			String ID = (nextFieldData);
			break;
						
			case 3: 
			String Title  = (nextFieldData);
			break;
 
			case 5: 
			String Name  = (nextFieldData);
			break;
		}
//...

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Question by:polkadot
10 Comments
 
LVL 26

Expert Comment

by:ksivananth
ID: 20339104
there are lot of issues which you have to take care if you do it that ways...

instead try some readily available parsers,

http://opencsv.sourceforge.net/
http://www.csvreader.com/
0
 

Author Comment

by:polkadot
ID: 20339344
csvreader works great, but its a bit bulky, I just wanted some ideas in just parsing it simply ... any other ideas
0
 
LVL 27

Expert Comment

by:mrcoffee365
ID: 20339554
Then you can't use StringTokenizer, you have to write your own parser.  Read the line character by character, check to see if there's a comma, and parse accordingly.
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LVL 86

Expert Comment

by:CEHJ
ID: 20339614
http://ostermiller.org/utils/CSV.html

I would not use home-brewed parsing. If it were that simple, there would not be any need for classes such as these
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LVL 26

Expert Comment

by:ksivananth
ID: 20339620
>>StringTokenizer st = new StringTokenizer(line,",");

to

StringTokenizer st = new StringTokenizer( line,",", true );

and discard the odd( which is the comma ) tokens in the traversing process...
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LVL 92

Expert Comment

by:objects
ID: 20340802
you can find a lightweight csv parser here:

http://mindprod.com/zips/csv24.zip
0
 
LVL 16

Accepted Solution

by:
gnoon earned 2000 total points
ID: 20344564
I've surveyed the source code of ST. If delemeters are successive (having blank field(s)), they will be group as a delemeter. For example

data: 1,,3,   will become   1,3,   (ST acts with ,, as ,)
return: {1,3,}

ST is not appropriate to parse CSV file.
If you will use JRE 1.4+, use String.split() instead    String[] fields = line.split(",").
If you will use JRE 1.3-, write your own function to parse the line (never use StringTokenizer) and returns array of fields.
0
 
LVL 16

Expert Comment

by:gnoon
ID: 20344587
public String[] parse(String s, char delim)
{
    StringBuffer b = new StringBuffer();
    ArrayList a = new ArrayList();
    char c;
    for(int i=0; i<s.length(); i++)
    {
        c = s.charAt(i);
        if(c == delim)
        {
            a.add(b);
            b = new StringBuffer();
        }
        else b.append(c);
    }
    String[] r = new String[a.size()];
    for(int i=0; i<r.length; i++)
        r[i] = (String) a.get(i);
    return r;
}
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