Java-How to extend InputStream to read from a JTextField?

Question

Working on a project I got into running java applications through a small console-like window. Thanks to the wonderful community in here I managed to solve the problem with outputting the data from a proccess but my command-line applications running will constantly give errors as there is no input stream.

Based on the last helpful reply in that thread I suppose I shall approach similarly the JTextFieldInputStream extends InputStream implementation, but looking in the javadocs and throughout google and the internet for some class that does just that I really found nothing explaining how to do this.

So I am asking for some link, example, tutorial, sample code for it just like in the previous topic. Give me just a class that extends InputStream and can be extended to read from a JTextField when I press Enter and I will do the rest with implementing this and making it work! Thanks in advance!

Solution 1

How about this implementation

import java.io.IOException;
import java.io.InputStream;

import javax.swing.JTextField;


public class JTextFieldInputStream extends InputStream {
    byte[] contents;
    int pointer = 0;

    public JTextFieldInputStream(final JTextField text) {

        text.addKeyListener(new KeyAdapter() {
            @Override
            public void keyReleased(KeyEvent e) {
                if(e.getKeyChar()=='\n'){
                    contents = text.getText().getBytes();
                    pointer = 0;
                    text.setText("");
                }
                super.keyReleased(e);
            }
        });
    }

    @Override
    public int read() throws IOException {
        if(pointer >= contents.length) return -1;
        return this.contents[pointer++];
    }

}

to use this input stream, do the following

 InputStream in = new JTextFieldInputStream( someTextField );
 char c;
 while( (c = in.read()) != -1){
    //do whatever with c
 }

does it read only when I hit enter?

it reads when you call in.read() if the return value -1 it means end of the stream

(And will I be able to modify so that the Enter key empties the JTextField?)

you need to add an action listener and this functionality has nothing to do with the job of input stream

Solution 2

What I don't understand if why you need a JTextField that extends InputStream? Basically, what you are looking for is:

1. Add an ActionListener on the JTextField (ie, when use presses Enter, actionPerformed will be invoked)
2. You need to grab the text of the JTextField using getText()
3. You can then "transform" the String text to an InputStream with new ByteArrayInputStream(text.getBytes("UTF-8"));

Here is a small snippet that should get you the basic idea:

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.ByteArrayInputStream;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;

import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;

public class TestTextField {

    private void initUI() {
        JFrame frame = new JFrame(TestTextField.class.getSimpleName());
        frame.setLayout(new FlowLayout());
        final JTextField textfield = new JTextField(20);
        textfield.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                try {
                    String text = textfield.getText();
                    InputStream is = new ByteArrayInputStream(text.getBytes("UTF-8"));
                    // Here do something with your input stream (something non-blocking)
                    System.err.println(text);
                } catch (UnsupportedEncodingException e1) {
                    e1.printStackTrace();
                }

            }
        });
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(textfield);
        frame.setSize(300, 300);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                new TestTextField().initUI();
            }
        });
    }

}

Comments

[Guillaume Polet]

@Spiritios Havaing multiple ActionListener is not a problem. It is also possible that the ActionListener you have, is actually the same as the one I am mentionning in my answer. I am almost 99% sure that this is the way to go, so you are probably overlooking ;-).

[Angelos Chalaris]

Hmmm ok... But I am using Apache Commons PumpStreamHandler and basically I need an InputStream for it that will be passed to the constructor in order to be used by the subprocess I call so can this be done using Listeners really?? :O

[Guillaume Polet]

@Spiritios I added a sample code that should give you the basic idea on how to go. In the action listener, you can call your Apache commons pumpstreamhandler etc...