Java Matcher: How to match multiple lines with one regex

Question

My method takes a file, and tries to extract the text between the header ###Title### and closing ###---###. I need it to extract multiple lines and put each line into an array. But since readAllLines() converts all lines into an array, I don't know how to compare and match it.

public static ArrayList<String> getData(File f, String title) throws IOException {
    ArrayList<String> input = (ArrayList<String>) Files.readAllLines(f.toPath(), StandardCharsets.US_ASCII);
    ArrayList<String> output = new ArrayList<String>();

    //String? readLines = somehow make it possible to match
    System.out.println("Checking entry.");

    Pattern p = Pattern.compile("###" + title + "###(.*)###---###", Pattern.DOTALL);
    Matcher m = p.matcher(readLines);
    if (m.matches()) {
        m.matches();
        String matched = m.group(1);
        System.out.println("Contents: " + matched);
        String[] array = matched.split("\n");
        ArrayList<String> array2 = new ArrayList<String>();
        for (String j:array) {
            array2.add(j);
        }
        output = array2;
    } else {
        System.out.println("No matches.");
    }
    return output;
}

Here is my file, and I'm 100% sure that the compiler is reading the correct one.

###Test File###
Entry 1
Entry 2
Data 1
Data 2
Test 1
Test 2
###---###

The output says "No matches." instead of the entries.

@PM77-1 How do I make it so it matches instead of returning a "No matches." method? — Brandon Nguyen
– Brandon Nguyen, Commented Dec 23, 2013 at 2:40

Brandon Nguyen · Accepted Answer · 2013-12-23 02:50:41Z

4

You don't need regex for that. It's enough to loop through the array and compare items line by line, taking those between the start and end tags.

ArrayList<String> input = (ArrayList<String>) Files.readAllLines(f.toPath(), StandardCharsets.US_ASCII);
ArrayList<String> output = new ArrayList<String>();

boolean matched = false;
for (String line : input) {
    if (line.equals("###---###") && matched) matched = false; //needed parentheses
    if (matched) output.add(line);
    if (line.equals("###Test File###") && !matched) matched = true;
}

edited Dec 23, 2013 at 2:50

Brandon Nguyen

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answered Dec 23, 2013 at 2:42

Szymon

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1 Comment

Keerthivasan Over a year ago

Now, i can understand it. when header is matched, adding the next line. when the footer is matched, you are making matched as false. This will add only the lines in between them. cool :) I have rep +1

Keerthivasan · Accepted Answer · 2013-12-23 02:46:40Z

1

As per your comment, if they are going to be in the same way as posted, then i don't think regex is needed for this requirement. You can read line by line and do a contains of '###'

public static void main(String args[])
  {
  ArrayList<String> dataList = new ArrayList<String>();
  try{
  // Open the file that is the first 
  // command line parameter
  FileInputStream fstream = new FileInputStream("textfile.txt");
  // Get the object of DataInputStream
  DataInputStream in = new DataInputStream(fstream);
  BufferedReader br = new BufferedReader(new InputStreamReader(in));
  String strLine;
  //Read File Line By Line
  while ((strLine = br.readLine()) != null)   {
  // this line will skip the header and footer with '###'
  if(!strLine.contains("###");
   dataList.add(strLine);
  }
  //Close the input stream
  in.close();
    }catch (Exception e){//Catch exception if any
  System.err.println("Error: " + e.getMessage());
  }
  }
//Now dataList has all the data between ###Test File### and ###---###
}

You can also change the contains method parameter according to your requirement to ignore lines!

answered Dec 23, 2013 at 2:46

Keerthivasan

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3 Comments

Szymon Over a year ago

This will also match lines before the start tag and after the end tag.

Szymon Over a year ago

Maybe. But the text of the question suggested a broader usage.

Alan Moore Over a year ago

Why are you using a DataInputStream? You can construct the InputStreamReader directly from the FileInputStream; the DataInputStream adds nothing of value.

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