Remove all blank spaces and empty lines

Question

How to remove all blank spaces and empty lines from a txt File using Java SE?

Input:

qwe
    qweqwe
  qwe



qwe

Output:

qwe
qweqwe
qwe
qwe

Thanks!

I was going to respond, but I also need to see whether this is homework first. — Shlublu, Aug 25 '11 at 12:54
Not homework. Can't think of the most efficient way to read a really really large text file and remove ALL spaces and empty lines. — Shumon Saha, Aug 25 '11 at 12:57

score 14 · Accepted Answer · edited Nov 25 '13 at 23:56

How about something like this:

FileReader fr = new FileReader("infile.txt"); 
BufferedReader br = new BufferedReader(fr); 
FileWriter fw = new FileWriter("outfile.txt"); 
String line;

while((line = br.readLine()) != null)
{ 
    line = line.trim(); // remove leading and trailing whitespace
    if (!line.equals("")) // don't write out blank lines
    {
        fw.write(line, 0, line.length());
    }
} 
fr.close();
fw.close();

Note - not tested, may not be perfect syntax but gives you an idea/approach to follow.

See the following JavaDocs for reference purposes: http://download.oracle.com/javase/7/docs/api/java/io/FileReader.html http://download.oracle.com/javase/7/docs/api/java/io/FileWriter.html

This will remove all the newlines in the file. – Peter Lawrey May 09 '14 at 12:39 — Peter Lawrey, May 09 '14 at 12:39

score 4 · Answer 2 · edited Nov 26 '13 at 00:02

4

Have a look at trim() function

http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/String.html#trim()

Also, some code would be helpful...

edited Nov 26 '13 at 00:02

Afshin Moazami

2,092
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answered Aug 25 '11 at 12:52

Trefex

2,290
16
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1

That the only valid solution which is already emdedded in the String object. There is absolutely no need to do anything else. This should be set as the answer – Omri Oct 11 '15 at 12:14
2

`Returns a copy of the string, with leading and trailing whitespace omitted.` It does not remove whitespace within the text file, only leading & trailing. This is not what the OP asked for. OP wants to remove all spaces and tabs. – Kevin Van Ryckegem Mar 05 '16 at 02:44

score 3 · Answer 3 · answered Aug 25 '11 at 13:28

...
Scanner scanner = new Scanner(new File("infile.txt"));
PrintStream out = new PrintStream(new File("outfile.txt"));
while(scanner.hasNextLine()){
    String line = scanner.nextLine();
    line = line.trim();
    if(line.length() > 0)
        out.println(line);
}
...

Vasilis Chatzikyriakos · Answer 4 · 2020-11-08T14:40:09.720

This my first time answering to a question in this site so please be understandable, after a lot of searching I have found this that works for me.

FileReader fr = new FileReader("Input_Code.txt"); 
BufferedReader br = new BufferedReader(fr); 
FileWriter fw = new FileWriter("output_Code.txt"); 
String line;

while((line = br.readLine()) != null)
{ 
     line = line.trim(); // remove leading and trailing whitespace
            line=line.replaceAll("\\s+", " ").trim().concat("\n");
            if (!line.equals("")) // don't write out blank lines
    {
        fw.write(line, 0, line.length());
    }
            
         
} 
fr.close();
fw.close();

Please correct the typos while answering a question. – nilakantha singh deo Nov 08 '20 at 14:28 — nilakantha singh deo, Nov 08 '20 at 14:28

score 0 · Answer 5 · answered Nov 22 '13 at 10:53

Remove spaces for each line and do not consider empty and null lines:

String line =  buffer.readLine();

while (line != null) {
    line = removeSpaces(line);        
    //ignore empty lines
    if (line.isEmpty()) return;

      ....code....


    line =  buffer.readLine();
} 




public String removeSpaces (String arg)
{
    Pattern whitespace = Pattern.compile("\\s");
    Matcher matcher = whitespace.matcher(arg);
    String result = "";
    if (matcher.find()) {
        result = matcher.replaceAll("");
    }
    return result;
}

score 0 · Answer 6 · answered Mar 09 '17 at 11:21

Used to remove empty lines in same the file.

public static void RemoveEmptyLines(String FilePath) throws IOException
{
    File inputFile = new File(FilePath);
    BufferedReader reader = new BufferedReader(new FileReader(inputFile));
    String inputFileReader;
    ArrayList <String> DataArray = new ArrayList<String>();
    while((inputFileReader=reader.readLine())!=null)
    {
        if(inputFileReader.length()==0)
        {
            continue;
        }
        DataArray.add(inputFileReader);
    }
    reader.close();

    BufferedWriter bw = new BufferedWriter(new FileWriter(FilePath));
    for(int i=0;i<DataArray.size();i++)
    {
        bw.write(DataArray.get(i));
        bw.newLine();
        bw.flush();
    }
    bw.close();
}

score 0 · Answer 7 · answered Oct 14 '17 at 11:55

package com.home.interview;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class RemoveInReadFile {

    public static void main(String[] args) {

        try {
            Scanner scanner = new Scanner(new File("Readme.txt"));


            while(scanner.hasNext())
            {
                String line = scanner.next();

                String lineAfterTrim = line.trim();
                System.out.print(lineAfterTrim);
            }


        } 

        catch (FileNotFoundException e) {

            e.printStackTrace();
        }

    }

}

In this program, I have removed all the white spaces and read everything from the file I read in a single line. — Nagarjun BN, Oct 14 '17 at 11:57

score 0 · Answer 8 · answered May 06 '21 at 14:11

I think you just want a regex expression:

        txt= txt.replaceAll("\\n\\s*\\n", "\n");  //remove empty lines
        txt= txt.replaceAll("\\s*", "");  //remove whitespaces

As for reading/writing files, there are plenty of other resources to find out how to do that.

Remove all blank spaces and empty lines

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