How to read a file into string in java?

Question

I have read a file into a String. The file contains various names, one name per line. Now the problem is that I want those names in a String array.

For that I have written the following code:

String [] names = fileString.split("\n"); // fileString is the string representation of the file

But I am not getting the desired results and the array obtained after splitting the string is of length 1. It means that the "fileString" doesn't have "\n" character but the file has this "\n" character.

So How to get around this problem?

Answer 1

What about using Apache Commons (Commons IO and Commons Lang)?

String[] lines = StringUtils.split(FileUtils.readFileToString(new File("...")), '\n');

Answer 2

The problem is not with how you're splitting the string; that bit is correct.

You have to review how you are reading the file to the string. You need something like this:

private String readFileAsString(String filePath) throws IOException {
        StringBuffer fileData = new StringBuffer();
        BufferedReader reader = new BufferedReader(
                new FileReader(filePath));
        char[] buf = new char[1024];
        int numRead=0;
        while((numRead=reader.read(buf)) != -1){
            String readData = String.valueOf(buf, 0, numRead);
            fileData.append(readData);
        }
        reader.close();
        return fileData.toString();
    }

Answer 3

As suggested by Garrett Rowe and Stan James you can use java.util.Scanner:

try (Scanner s = new Scanner(file).useDelimiter("\\Z")) {
  String contents = s.next();
}

or

try (Scanner s = new Scanner(file).useDelimiter("\\n")) {
  while(s.hasNext()) {
    String line = s.next();
  }
}

This code does not have external dependencies.

WARNING: you should specify the charset encoding as the second parameter of the Scanner's constructor. In this example I am using the platform's default, but this is most certainly wrong.

Here is an example of how to use java.util.Scanner with correct resource and error handling:

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

class TestScanner {
  public static void main(String[] args)
    throws FileNotFoundException {
    File file = new File(args[0]);

    System.out.println(getFileContents(file));

    processFileLines(file, new LineProcessor() {
      @Override
      public void process(int lineNumber, String lineContents) {
        System.out.println(lineNumber + ": " + lineContents);
      }
    });
  }

  static String getFileContents(File file)
    throws FileNotFoundException {
    try (Scanner s = new Scanner(file).useDelimiter("\\Z")) {
      return s.next();
    }
  }

  static void processFileLines(File file, LineProcessor lineProcessor)
    throws FileNotFoundException {
    try (Scanner s = new Scanner(file).useDelimiter("\\n")) {
      for (int lineNumber = 1; s.hasNext(); ++lineNumber) {
        lineProcessor.process(lineNumber, s.next());
      }
    }
  }

  static interface LineProcessor {
    void process(int lineNumber, String lineContents);
  }
}

Answer 4

Particularly i love this one using the java.nio.file package also described here.

You can optionally include the Charset as a second argument in the String constructor.

 String content = new String(Files.readAllBytes(Paths.get("/path/to/file")));
 

Cool huhhh!

Answer 5

You could read your file into a List instead of a String and then convert to an array:

//Setup a BufferedReader here    
List<String> list = new ArrayList<String>();
String line = reader.readLine();
while (line != null) {
  list.add(line);
  line = reader.readLine();
}
String[] arr = list.toArray(new String[0]);

Answer 6

There is no built-in method in Java which can read an entire file. So you have the following options:

• Use a non-standard library method, such as Apache Commons, see the code example in romaintaz's answer.
• Loop around some read method (e.g. FileInputStream.read, which reads bytes, or FileReader.read, which reads chars; both read to a preallocated array). Both classes use system calls, so you'll have to speed them up with bufering (BufferedInputStream or BufferedReader) if you are reading just a small amount of data (say, less than 4096 bytes) at a time.
• Loop around BufferedReader.readLine. There has a fundamental problem that it discards the information whether there was a '\n' at the end of the file -- so e.g. it is unable to distinguish an empty file from a file containing just a newline.

I'd use this code:

// charsetName can be null to use the default charset.
public static String readFileAsString(String fileName, String charsetName)
    throws java.io.IOException {
  java.io.InputStream is = new java.io.FileInputStream(fileName);
  try {
    final int bufsize = 4096;
    int available = is.available();
    byte[] data = new byte[available < bufsize ? bufsize : available];
    int used = 0;
    while (true) {
      if (data.length - used < bufsize) {
        byte[] newData = new byte[data.length << 1];
        System.arraycopy(data, 0, newData, 0, used);
        data = newData;
      }
      int got = is.read(data, used, data.length - used);
      if (got <= 0) break;
      used += got;
    }
    return charsetName != null ? new String(data, 0, used, charsetName)
                               : new String(data, 0, used);
  } finally {
    is.close();
  }
}

The code above has the following advantages:

• It's correct: it reads the whole file, not discarding any byte.
• It lets you specify the character set (encoding) the file uses.
• It's fast (no matter how many newlines the file contains).
• It doesn't waste memory (no matter how many newlines the file contains).

Answer 7

FileReader fr=new FileReader(filename);
BufferedReader br=new BufferedReader(fr);
String strline;
String arr[]=new String[10];//10 is the no. of strings
while((strline=br.readLine())!=null)
{
arr[i++]=strline;
}

Answer 8

I always use this way:

String content = "";
String line;
BufferedReader reader = new BufferedReader(new FileReader(...));
while ((line = reader.readLine()) != null)
{
    content += "\n" + line;
}
// Cut of the first newline;
content = content.substring(1);
// Close the reader
reader.close();

Answer 9

The simplest solution for reading a text file line by line and putting the results into an array of strings without using third party libraries would be this:

ArrayList<String> names = new ArrayList<String>();
Scanner scanner = new Scanner(new File("names.txt"));
while(scanner.hasNextLine()) {
    names.add(scanner.nextLine());
}
scanner.close();
String[] namesArr = (String[]) names.toArray();

Answer 10

A simpler (without loops), but less correct way, is to read everything to a byte array:

FileInputStream is = new FileInputStream(file);
byte[] b = new byte[(int) file.length()];  
is.read(b, 0, (int) file.length());
String contents = new String(b);

Also note that this has serious performance issues.

Answer 11

If you have only InputStream, you can use InputStreamReader.

SmbFileInputStream in = new SmbFileInputStream("smb://host/dir/file.ext");
InputStreamReader r=new InputStreamReader(in);
char buf[] = new char[5000];
int count=r.read(buf);
String s=String.valueOf(buf, 0, count);

You can add cycle and StringBuffer if needed.

Answer 12

You can also use java.nio.file.Files to read an entire file into a String List then you can convert it to an array etc. Assuming a String variable named filePath, the following 2 lines will do that:

List<String> strList = Files.readAllLines(Paths.get(filePath), Charset.defaultCharset());
String[] strarray = strList.toArray(new String[0]);

Answer 13

You can try Cactoos:

import org.cactoos.io.TextOf;
import java.io.File;
new TextOf(new File("a.txt")).asString().split("\n")

Answer 14

Fixed Version of @Anoyz's answer:

import java.io.FileInputStream;
import java.io.File;

public class App {
public static void main(String[] args) throws Exception {

    File f = new File("file.txt");
    long fileSize = f.length();

    String file = "test.txt";

    FileInputStream is = new FileInputStream("file.txt");
    byte[] b = new byte[(int) f.length()];  
    is.read(b, 0, (int) f.length());
    String contents = new String(b);
}
}