Ideal method to truncate a string with ellipsis
It seems like you might get more accurate geometry from the Java graphics context's FontMetrics.
Addendum: In approaching this problem, it may help to distinguish between the model and view. The model is a String, a finite sequence of UTF-16 code points, while the view is a series of glyphs, rendered in some font on some device.
In the particular case of Java, one can use SwingUtilities.layoutCompoundLabel() to effect the translation. The example below intercepts the layout call in BasicLabelUI to demonstrate the effect. It may be possible to use the utility method in other contexts, but the appropriate FontMetrics would have to be be determined empirically.
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.FontMetrics;
import java.awt.GridLayout;
import java.awt.Rectangle;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;
import javax.swing.BorderFactory;
import javax.swing.Icon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import javax.swing.border.LineBorder;
import javax.swing.plaf.basic.BasicLabelUI;
/** @see http://stackoverflow.com/questions/3597550 */
public class LayoutTest extends JPanel {
private static final String text =
"A damsel with a dulcimer in a vision once I saw.";
private final JLabel sizeLabel = new JLabel();
private final JLabel textLabel = new JLabel(text);
private final MyLabelUI myUI = new MyLabelUI();
public LayoutTest() {
super(new GridLayout(0, 1));
this.setBorder(BorderFactory.createCompoundBorder(
new LineBorder(Color.blue), new EmptyBorder(5, 5, 5, 5)));
textLabel.setUI(myUI);
textLabel.setFont(new Font("Serif", Font.ITALIC, 24));
this.add(sizeLabel);
this.add(textLabel);
this.addComponentListener(new ComponentAdapter() {
@Override
public void componentResized(ComponentEvent e) {
sizeLabel.setText(
"Before: " + myUI.before + " after: " + myUI.after);
}
});
}
private static class MyLabelUI extends BasicLabelUI {
int before, after;
@Override
protected String layoutCL(
JLabel label, FontMetrics fontMetrics, String text, Icon icon,
Rectangle viewR, Rectangle iconR, Rectangle textR) {
before = text.length();
String s = super.layoutCL(
label, fontMetrics, text, icon, viewR, iconR, textR);
after = s.length();
System.out.println(s);
return s;
}
}
private void display() {
JFrame f = new JFrame("LayoutTest");
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
f.add(this);
f.pack();
f.setLocationRelativeTo(null);
f.setVisible(true);
}
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
@Override
public void run() {
new LayoutTest().display();
}
});
}
}
I'm shocked no one mentioned Commons Lang StringUtils#abbreviate().
Update: yes it doesn't take the slim characters into account but I don't agree with that considering everyone has different screens and fonts setup and a large portion of the people that land here on this page are probably looking for a maintained library like the above.
If you're talking about a web site - ie outputting HTML/JS/CSS, you can throw away all these solutions because there is a pure CSS solution.
text-overflow:ellipsis;
It's not quite as simple as just adding that style to your CSS, because it interracts with other CSS; eg it requires that the element has overflow:hidden; and if you want your text on a single line, white-space:nowrap; is good too.
I have a stylesheet that looks like this:
.myelement {
word-wrap:normal;
white-space:nowrap;
overflow:hidden;
-o-text-overflow:ellipsis;
text-overflow:ellipsis;
width: 120px;
}
You can even have a "read more" button that simply runs a javascript function to change the styles, and bingo, the box will re-size and the full text will be visible. (in my case though, I tend to use the html title attribute for the full text, unless it's likely to get very long)
Hope that helps. It's a much simpler solution that trying to mess calculate the text size and truncate it, and all that. (of course, if you're writing a non-web-based app, you may still need to do that)
There is one down-side to this solution: Firefox doesn't support the ellipsis style. Annoying, but I don't think critical -- It does still truncate the text correctly, as that is dealt with by by overflow:hidden, it just doesn't display the ellipsis. It does work in all the other browsers (including IE, all the way back to IE5.5!), so it's a bit annoying that Firefox doesn't do it yet. Hopefully a new version of Firefox will solve this issue soon.
[EDIT]
People are still voting on this answer, so I should edit it to note that Firefox does now support the ellipsis style. The feature was added in Firefox 7. If you're using an earlier version (FF3.6 and FF4 still have some users) then you're out of luck, but most FF users are now okay. There's a lot more detail about this here: text-overflow:ellipsis in Firefox 4? (and FF5)
I like the idea of letting "thin" characters count as half a character. Simple and a good approximation.
The main issue with most ellipsizings however, are (imho) that they chop of words in the middle. Here is a solution taking word-boundaries into account (but does not dive into pixel-math and the Swing-API).
private final static String NON_THIN = "[^iIl1\\.,']";
private static int textWidth(String str) {
return (int) (str.length() - str.replaceAll(NON_THIN, "").length() / 2);
}
public static String ellipsize(String text, int max) {
if (textWidth(text) <= max)
return text;
// Start by chopping off at the word before max
// This is an over-approximation due to thin-characters...
int end = text.lastIndexOf(' ', max - 3);
// Just one long word. Chop it off.
if (end == -1)
return text.substring(0, max-3) + "...";
// Step forward as long as textWidth allows.
int newEnd = end;
do {
end = newEnd;
newEnd = text.indexOf(' ', end + 1);
// No more spaces.
if (newEnd == -1)
newEnd = text.length();
} while (textWidth(text.substring(0, newEnd) + "...") < max);
return text.substring(0, end) + "...";
}
A test of the algorithm looks like this:
