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 perline. 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

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 2

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 3

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 4

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

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

Answer 5

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).