It has recently come to my attention that Java text components use line feed characters (LF, \n, 0x0A) to represent and interpret line breaks internally. This came as quite a surprise to me and puts my assumption, that using System.getProperty('line.separator') everywhere is a good practice, under a question mark.
It would appear that whenever you are dealing with a text component you should be very careful when using the mentioned property, since if you use JTextComponent.setText(String) you might end up with a component that contains invisible newlines (CRs for example). This might not seem that important, unless the content of the text component can be saved to a file. If you save and open the text to a file using the methods that are provided by all text components, your hidden newlines suddenly materialize in the component upon the file being re-opened. The reason for that seems to be that JTextComponent.read(...) method does the normalization.
So why doesn't JTextComponent.setText(String) normalize line endings? Or any other method that allows text to be modified within a text component for that matter? Is using System.getProperty('line.separator') a good practice when dealing with text components? Is it a good practice at all?
Some code to put this question into perspective:
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.Reader;
import java.io.UnsupportedEncodingException;
import java.io.Writer;
import javax.swing.AbstractAction;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;
public class TextAreaTest extends JFrame {
private JTextArea jtaInput;
private JScrollPane jscpInput;
private JButton jbSaveAndReopen;
public TextAreaTest() {
super();
setDefaultCloseOperation(EXIT_ON_CLOSE);
setTitle("Text Area Test");
GridBagLayout layout = new GridBagLayout();
setLayout(layout);
jtaInput = new JTextArea();
jtaInput.setText("Some text followed by a windows newline\r\n"
+ "and some more text.");
jscpInput = new JScrollPane(jtaInput);
GridBagConstraints constraints = new GridBagConstraints();
constraints.gridx = 0; constraints.gridy = 0;
constraints.gridwidth = 2;
constraints.weightx = 1.0; constraints.weighty = 1.0;
constraints.fill = GridBagConstraints.BOTH;
add(jscpInput, constraints);
jbSaveAndReopen = new JButton(new SaveAndReopenAction());
constraints = new GridBagConstraints();
constraints.gridx = 1; constraints.gridy = 1;
constraints.anchor = GridBagConstraints.EAST;
constraints.insets = new Insets(5, 0, 2, 2);
add(jbSaveAndReopen, constraints);
pack();
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
TextAreaTest tat = new TextAreaTest();
tat.setVisible(true);
}
});
}
private class SaveAndReopenAction extends AbstractAction {
private File file = new File("text-area-test.txt");
public SaveAndReopenAction() {
super("Save and Re-open");
}
private void saveToFile()
throws UnsupportedEncodingException, FileNotFoundException,
IOException {
Writer writer = null;
try {
writer = new OutputStreamWriter(
new FileOutputStream(file), "UTF-8");
TextAreaTest.this.jtaInput.write(writer);
} finally {
if (writer != null) {
try {
writer.close();
} catch (IOException ex) {
}
}
}
}
private void openFile()
throws UnsupportedEncodingException, IOException {
Reader reader = null;
try {
reader = new InputStreamReader(
new FileInputStream(file), "UTF-8");
TextAreaTest.this.jtaInput.read(reader, file);
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException ex) {
}
}
}
}
public void actionPerformed(ActionEvent e) {
Throwable exc = null;
try {
saveToFile();
openFile();
} catch (UnsupportedEncodingException ex) {
exc = ex;
} catch (FileNotFoundException ex) {
exc = ex;
} catch (IOException ex) {
exc = ex;
}
if (exc != null) {
JOptionPane.showConfirmDialog(
TextAreaTest.this, exc.getMessage(), "An error occured",
JOptionPane.DEFAULT_OPTION, JOptionPane.ERROR_MESSAGE);
}
}
}
}
An example of what this program saves on my windows machine after adding a new line of text (why the single CR? o_O):
Edit01
I ran/debugged this from within Netbeans IDE, which uses JDK1.7u15 64bit (C:\Program Files\Java\jdk1.7.0_15) on Windows 7.