Question

I need to trim a String in java so that:

The quick brown fox jumps over the laz dog.

becomes

The quick brown…

In the example above, I’m trimming to 12 characters. If I just use substring I would get:

The quick br…

I already have a method for doing this using substring, but I wanted to know what is the fastest (most efficient) way to do this because a page may have many trim operations.

The only way I can think off is to split the string on spaces and put it back together until its length passes the given length. Is there an other way? Perhaps a more efficient way in which I can use the same method to do a “soft” trim where I preserve the last word (as shown in the example above) and a hard trim which is pretty much a substring.

Thanks,

Answer 1

Below is a method I use to trim long strings in my webapps.
The “soft” boolean as you put it, if set to true will preserve the last word.
This is the most concise way of doing it that I could come up with that uses a StringBuffer which is a lot more efficient than recreating a string which is immutable.

public static String trimString(String string, int length, boolean soft) {
    if(string == null || string.trim().isEmpty()){
        return string;
    }

    StringBuffer sb = new StringBuffer(string);
    int actualLength = length - 3;
    if(sb.length() > actualLength){
        // -3 because we add 3 dots at the end. Returned string length has to be length including the dots.
        if(!soft)
            return escapeHtml(sb.insert(actualLength, "...").substring(0, actualLength+3));
        else {
            int endIndex = sb.indexOf(" ",actualLength);
            return escapeHtml(sb.insert(endIndex,"...").substring(0, endIndex+3));
        }
    }
    return string;
}

Update

I’ve changed the code so that the ... is appended in the StringBuffer, this is to prevent needless creations of String implicitly which is slow and wasteful.

Note: escapeHtml is a static import from apache commons:

import static org.apache.commons.lang.StringEscapeUtils.escapeHtml;

You can remove it and the code should work the same.