Reading specific column of file line by line in Java exception

Question

I have this code below.What i'm trying to do is read a text file which every line has Strings separated by tabs.For example (name \t country \t id \t content) where \t is the tab.Then i want to print only the 2nd column of each line.I'm trying split the whole line to tokens but it works fine only for the 1st line of the file and then it throws ArrayIndexOutOfBoundsException. Also it works perfect when i try to print only the 1st column (tokens[0]) but not for tokens[1] which I need.So what am I need to do to get the 2nd columns of each line?

public static void main(String[] args) throws FileNotFoundException, IOException
{
    FileInputStream fis=new FileInputStream("a.txt");
    BufferedReader br = new BufferedReader(new InputStreamReader(dis)) ;
    String line;
    while ((line = br.readLine()) != null) 
    {
        String[] tokens=line.split("\\t");
        System.out.println(tokens[1]);  

    }
    fis.close();
}

If the input is valid, your code should be fine. Check the input file. — erickson, Feb 17 '16 at 19:45
You should not escape \ character, Try this: line.split("\t") — andrucz, Feb 17 '16 at 19:48
If the input is not valid,can i make it work somehow if i split the tokens with spaces? like String[] tokens=line.split("\\s") ? — Jack21, Feb 17 '16 at 19:49
Arrays are zero-indexed. You grab something in the second position of the array, not the "first". I recommend splitting on `"\\s+"` and using an if-statement before accessing the array — OneCricketeer, Feb 17 '16 at 19:50
@andrucz Because split takes a regex, using the the escape or a literal tab works the same. — erickson, Feb 17 '16 at 19:56
You'll have to define better requirements. Are you saying that tokens are separated by spaces, not tabs? Or that tokens can be separated by spaces or tabs? Or maybe it's just tabs, and it's okay to skip lines that don't have a value in every column. How do you want it to work? — erickson, Feb 17 '16 at 20:00
I just wrote:if(tokens.length>1) above the System.out.println and it worked. — Jack21, Feb 17 '16 at 20:05
Okay, so you should have said that you want to skip invalid lines in your question. — erickson, Feb 17 '16 at 20:11
i didnt thought that there were invalid lines in the file thats why i didnt mention it — Jack21, Feb 17 '16 at 20:13

score 1 · Answer 1 · edited May 23 '17 at 12:31

1

If the line looks for example like this

asdf\t\t\t

Then you have a problem. You should use

String[] tokens=line.split("\\t", -1);

See Java: String split(): I want it to include the empty strings at the end

edited May 23 '17 at 12:31

Community

1
1

answered Feb 17 '16 at 19:46

radoh

4,554
5
30
45

score 0 · Accepted Answer · answered Feb 17 '16 at 19:45

0

if no tab exists in the line you get the exception.

you should check if tokens.length()>1 before accessing the second element.

answered Feb 17 '16 at 19:45

Jens

67,715
15
98
113

This worked!!! I just put an if state above the print.Thank you very much for you help – Jack21 Feb 17 '16 at 20:02

Bax · Answer 3 · 2016-02-17T20:44:42.533

0

Java 8 :

    try (Stream<String> stream = Files.lines(Paths.get("a.txt"))) {
        stream.map(line -> line.split("\\t"))
                .filter(tokens -> tokens.length > 1)
                .forEach(tokens -> System.out.println(tokens[1]));
    } catch (IOException e) {
        e.printStackTrace();
    }

edited Feb 17 '16 at 20:44

answered Feb 17 '16 at 19:53

Bax

4,260
5
43
65

1

This doesn't print the desired column, it prints any columns. – erickson Feb 17 '16 at 20:18

Reading specific column of file line by line in Java exception

3 Answers3