Why are there so many ways of getting a String[] from a comma-separated String in Java, and none of the basic ones really work (split(",") or StringTokenizer) ? I don't know, but this is my ultimate solution at the moment. Are there more cases to cover ?

SplitUtil.java

import java.util.regex.Pattern;

public class SplitUtil {
    private static final Pattern COMMA_DELIMITED_SPLIT = Pattern.compile("(\\s*,\\s*)+");
    private static final String[] EMPTY = new String[0];

    public static String[] commaDelimited(String s) {
        if (s == null) {
            return EMPTY;
        }
        s = s.trim();
        if (s.length() == 0) {
            return EMPTY;
        }
        return COMMA_DELIMITED_SPLIT.split(s, 0);
    }
}

SplitUtilTest.java

import org.junit.Test;
import static org.junit.Assert.assertArrayEquals;

public class SplitUtilTest {
    @Test
    public void commaDelimitedBasicTest() {
        assertArrayEquals(new String[]{"abc", "def"}, SplitUtil.commaDelimited("abc,def"));
    }

    @Test
    public void commaDelimitedRemovesWhiteSpaceAroundCommas() {
        assertArrayEquals(new String[]{"abc", "def"}, SplitUtil.commaDelimited(" abc ,   \tdef "));
    }

    @Test
    public void commaDelimitedCanDealWithSingleElement() {
        assertArrayEquals(new String[]{"abc"}, SplitUtil.commaDelimited("abc"));
        assertArrayEquals(new String[]{"abc"}, SplitUtil.commaDelimited("  abc "));
    }

    @Test
    public void commaDelimitedReturnsEmptyArrayForEmptyInput() {
        assertArrayEquals(new String[]{}, SplitUtil.commaDelimited(""));
    }

    @Test
    public void commaDelimitedReturnsEmptyArrayForNullInput() {
        assertArrayEquals(new String[]{}, SplitUtil.commaDelimited(null));
    }

    @Test
    public void commaDelimitedReturnsEmptyArrayForSpaceOnlyInput() {
        assertArrayEquals(new String[]{}, SplitUtil.commaDelimited("   "));
    }

    @Test
    public void commaDelimitedReturnsEmptyArrayForCommaOnlyInput() {
        assertArrayEquals(new String[]{}, SplitUtil.commaDelimited(","));
        assertArrayEquals(new String[]{}, SplitUtil.commaDelimited(" ,  "));
        assertArrayEquals(new String[]{}, SplitUtil.commaDelimited(",,"));
        assertArrayEquals(new String[]{}, SplitUtil.commaDelimited(" ,  ,"));
    }
}