How to convert array of key codes to text in java

Question

I have a java program that sends some data over the network. I also capture all the keys pressed on the client and send them to the server therefore server maintains a buffer containing all the keys pressed on the client.

I need to create a file containing the final text produced by client. Take the following sequence as an example:

press j
press h
press BACKSPACE
press H
press e
press l
press HOME
press DEL
press END
press l
press o

Processing this sequence produces:

Hello

This is a simple example but notice that it can contain arrow keys as well.

Processing this buffer can be error prone and time consuming. I'd appreciate it if anyone could introduce a library that does these things or shows a simple way for doing it.

EDIT: I changed my question to ask a specific question instead of looking for a library.

I don't want to create a console parser and no need for history or tab completion. So my question is different from readline-like library in java.

Thanks.

Answer 1

sounds like you're building a key logger. I guess this is the reason why 2 people down voted you already. Funny that I'm writing my master's degree thesis about this kind of stuff at the moment :P https://github.com/kamiljano/CloudDoorThesis My POC doesn't do any key logging though, just allows you to remotely download files from a remote device.

Anyway, judging from your input you're communicating with the server over a TCP socket. Don't! Firewall will never let you through. Stick to something more common, like HTTP. Then you can have an endpoint like http://server.com/keys and send a JSON requsts to it like

{
  "strokes": [
     "a", "b", "c", "backspace"
  ]
}

Don't upload your stuff every time the user presses a button -> that generates a lot of stress on the network. So you will generate an HTTP PUT request every 20 key strokes, or every 1 minute. Make sure that the request is done by the key logger in a separate thread, or the user will notice that it takes 0.5-2 seconds for the character to appear on the screen. Don't store the keys in the memory of the application -> you will run out of memory as soon as 10 users write a new post on Facebook. Instead store every change in a database. At that point you first write a small piece of code like

String result = "";
for (String key : strokes) {
   if ("backspace".equals(key) && result.size() > 0) {
     result = result.substring(0, result.size() - 2);
   } else if ("del".equals(key) && result.size() > 0) {
     result = result.subscring(1, result.size() - 1);
   } else {
     result += key;
   }
}
updateDatabaseEntry(userId, result);

Answer 2

so there are no libraries for what you want to do. I would suggest implementing your own class that collects all the changes and builds a string one key stroke at a time. As a kickstarter for you I wrote the following class (although it obviously needs to be extended with the logic for additional keys that you want to be able to process)

public class KeyBuffer {

  private static final String SIMPLE_CHARACTERS = "abcdefghijklmopqrstuvqxyz;?!#$%^&&*()_+";//TODO: extend with all characters that the users can enter

  private String buffer = "";
  private int position = 0;

  private String[] splitAtCurrentPosition() {
    return new String[]{
      buffer.substring(0, position),
      buffer.substring(position, buffer.length() == position ? position : buffer.length())
    };
  }

  private void addCharacter(String character) {
    String[] parts = splitAtCurrentPosition();
    buffer = parts[0].substring(0, parts[0].length()) + character + parts[1];
    position++;
  }

  public void add(String key) {
    if (SIMPLE_CHARACTERS.contains(key)) {
      addCharacter(key);
      return;
    }
    if ("backspace".equals(key) && buffer.length() > 0) {
      String[] parts = splitAtCurrentPosition();
      buffer = parts[0].substring(0, parts[0].length() - 1) + parts[1];
      position --;
    } else if ("arrow_left".equals(key)) {
      if (position > 0) {
        position --;
      }
    } else {
      throw new UnsupportedOperationException("The key " + key + " is not supported");
    }

    //TODO: add logic for all remaining special keys
  }

  @Override
  public String toString() {
    return buffer;
  }
}

Quickly tested with the following junit tests:

public class KeyBufferTest {

  @Test
  public void addSimpleCharacter() {
    KeyBuffer buffer = new KeyBuffer();
    buffer.add("a");
    buffer.add("b");
    buffer.add("c");

    assertEquals("abc", buffer.toString());
  }

  @Test
  public void addUsingArrows() {
    KeyBuffer buffer = new KeyBuffer();
    buffer.add("a");
    buffer.add("b");
    buffer.add("arrow_left");
    buffer.add("c");

    assertEquals("acb", buffer.toString());
  }

  @Test
  public void addBackspace() {
    KeyBuffer buffer = new KeyBuffer();
    buffer.add("a");
    buffer.add("b");
    buffer.add("arrow_left");
    buffer.add("backspace");
    buffer.add("c");

    assertEquals("cb", buffer.toString());
  }

}