BufferedReader: read multiple lines into a single string

Question

I'm reading numbers from a txt file using BufferedReader for analysis. The way I'm going about this now is- reading a line using .readline, splitting this string into an array of strings using .split

public InputFile () {
    fileIn = null;

    //stuff here

    fileIn = new FileReader((filename + ".txt"));
    buffIn = new BufferedReader(fileIn);


    return;
    //stuff here
}

---

public String ReadBigStringIn() {
    String line = null;

    try { line = buffIn.readLine(); }
    catch(IOException e){};

    return line;
}

---

public ProcessMain() {
    initComponents();
    String[] stringArray;
    String line;

    try {
        InputFile stringIn = new InputFile();
        line = stringIn.ReadBigStringIn();
        stringArray = line.split("[^0-9.+Ee-]+"); 
        // analysis etc.
    }
}

This works fine, but what if the txt file has multiple lines of text? Is there a way to output a single long string, or perhaps another way of doing it? Maybe use while(buffIn.readline != null) {}? Not sure how to implement this.

Ideas appreciated, thanks.

Answer 1

You are right, a loop would be needed here.

The usual idiom (using only plain Java) is something like this:

public String ReadBigStringIn(BufferedReader buffIn) throws IOException {
    StringBuilder everything = new StringBuilder();
    String line;
    while( (line = buffIn.readLine()) != null) {
       everything.append(line);
    }
    return everything.toString();
}

This removes the line breaks - if you want to retain them, don't use the readLine() method, but simply read into a char[] instead (and append this to your StringBuilder).

Please note that this loop will run until the stream ends (and will block if it doesn't end), so if you need a different condition to finish the loop, implement it in there.

Answer 2

I would strongly advice using library here but since Java 8 you can do this also using streams.

    try (InputStreamReader in = new InputStreamReader(System.in);
         BufferedReader buffer = new BufferedReader(in)) {
        final String fileAsText = buffer.lines().collect(Collectors.joining());
        System.out.println(fileAsText);
    } catch (Exception e) {
        e.printStackTrace();
    }

You can notice also that it is pretty effective as joining is using StringBuilder internally.