BufferedReader.readLine() waits for input from console

Question

I am trying to read lines of text from the console. The number of lines is not known in advance. The BufferedReader.readLine() method reads a line but after the last line it waits for input from the console. What should be done in order to avoid this?

Please see the code snippet below:

    public static String[] getLinesFromConsole() {
    String strLine = "";
    try {
        // Get the object of DataInputStream
        InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader br = new BufferedReader(isr);
        String line = "";
        while ((line = br.readLine()) != null)
            strLine += line + "~"; //edited

        isr.close();
    } catch (IOException ioe) {
        ioe.printStackTrace();
    }
    return strLine.split("~");
}

My guess is that the code never exits the while loop. And correctly so. An idea would be that when you read something specific, like "exit", you could break. — dkateros, Jan 29 '13 at 10:53
Shouldn't that be `while ((line = br.readLine()) != null) strLine += **line** + "~";`? — OldCurmudgeon, Jan 29 '13 at 10:54
you should use some condition to exit the while loop, for example having the user type exit — B11, Jan 29 '13 at 10:55
You appear to be skipping every second line, which I suspect is not correct and you are waiting for the end of the input stream which is difficult for most console users to type. ;) — Peter Lawrey, Jan 29 '13 at 10:55
I try your code when you invoke readline second time while ((line = br.readLine()) != null) strLine += //here br.readLine() + "~"; console start to wait another character; you should use line variable OldCurmudgeon suggest this solution. And you can determine a exit command. — erhun, Jan 29 '13 at 11:13
Corrected the skipping line part. It was a typo. strLine += **line** + "~"; — ambar, Jan 29 '13 at 12:57
Is it possible to to end the readLine() execution without having an exit string? — ambar, Jan 29 '13 at 13:00
This is duplicate question. See this: http://stackoverflow.com/questions/5506778/java-read-from-console-until-getting-a-blank-line — araut, Sep 19 '14 at 22:53

score 4 · Answer 1 · edited Jan 29 '13 at 10:59

4

The below code might fix, replace text exit with your requirement specific string

  public static String[] getLinesFromConsole() {
    String strLine = "";
    try {
        // Get the object of DataInputStream
        InputStreamReader isr = new InputStreamReader(System.in);
        BufferedReader br = new BufferedReader(isr);
        String line = "";
        while ((line = br.readLine()) != null && !line.equals("exit") )
            strLine += br.readLine() + "~";

        isr.close();
    } catch (IOException ioe) {
        ioe.printStackTrace();
    }
    return strLine.split("~");
}

edited Jan 29 '13 at 10:59

Aaron Digulla

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answered Jan 29 '13 at 10:57

TheWhiteRabbit

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Is it possible to to end the readLine execution without having an exit string? – ambar Jan 29 '13 at 12:55
to rerminate the text input process , you need some 'text' to indicate quit or exit. – TheWhiteRabbit Jan 29 '13 at 13:00

score 1 · Answer 2 · edited Jun 20 '20 at 09:12

When reading from the console, you need to define a "terminating" input since the console (unlike a file) doesn't ever "end" (it continues to run even after your program terminates).

There are several solutions to your problem:

Put the input in a file and use IO redirection: java ... < input-file

The shell will hook up your process with the input file and you will get an EOF.
Type the EOF-character for your console. On Linux and Mac, it's Ctrl+D, on Windows, it's Ctrl+Z + Enter
Stop when you read an empty line. That way, the user can simply type Enter.

PS: there is a bug in your code. If you call readLine() twice, it will skip every second line.

BufferedReader.readLine() waits for input from console

2 Answers2

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