Split and Join function for strings such as CSV, TSV

StringUtils.java

public class StringUtilsTest {
    @Test
    public void testSplit() {
        assertThat(StringUtils.split(null, ',', '"'), is(Collections.EMPTY_LIST));
        assertThat(StringUtils.split("", ',', '"'), is(Collections.<String>singletonList(null)));
        assertThat(StringUtils.split("\"\"", ',', '"'), is(Collections.singletonList("")));
        assertThat(StringUtils.split("\"\",,\"\"", ',', '"'), is(Arrays.asList("", null, "")));
        assertThat(StringUtils.split("a,b,c", ',', '"'), is(Arrays.asList("a", "b", "c")));
        assertThat(StringUtils.split("a\"b,c", ',', '"'), is(Arrays.asList("a\"b", "c")));
        assertThat(StringUtils.split("\"a\"\"b\",c", ',', '"'), is(Arrays.asList("a\"b", "c")));
        assertThat(StringUtils.split("\"a,b\",c", ',', '"'), is(Arrays.asList("a,b", "c")));
    }

    @Test
    public void testJoin() {
        assertThat(StringUtils.join(null, ',', '"'), is(nullValue()));
        assertThat(StringUtils.join(Collections.<String>emptyList(), ',', '"'), is(nullValue()));
        assertThat(StringUtils.join(Collections.<String>singletonList(null), ',', '"'), is(""));
        assertThat(StringUtils.join(Collections.singletonList(""), ',', '"'), is("\"\""));
        assertThat(StringUtils.join(Arrays.asList("", null, ""), ',', '"'), is("\"\",,\"\""));
        assertThat(StringUtils.join(Arrays.asList("a", "b", "c"), ',', '"'), is("a,b,c"));
        assertThat(StringUtils.join(Arrays.asList("a\"b", "c"), ',', '"'), is("\"a\"\"b\",c"));
        assertThat(StringUtils.join(Arrays.asList("a,b", "c"), ',', '"'), is("\"a,b\",c"));
    }
}

public class StringUtils {
    public static List<String> split(String src, char delim, char bracket) {
        ArrayList<String> result = new ArrayList<>();
        if (src == null) {
            return result;
        }
        StringBuilder sb = new StringBuilder();
        int mode = 0;

        for (int i = 0; i <= src.length(); i++) {
            char ch = (i < src.length()) ? src.charAt(i) : delim;
            switch (mode) {
                case 0:
                    if (ch == delim) {
                        if (sb.length() == 0) {
                            result.add(null);
                        } else {
                            result.add(sb.toString());
                        }
                        sb.delete(0, sb.length());
                    } else if (ch == bracket) {
                        mode = 1;
                    } else {
                        sb.append(ch);
                        mode = 3;
                    }
                    break;
                case 1:
                    if (ch == delim) {
                        sb.append(ch);
                    } else if (ch == bracket) {
                        mode = 2;
                    } else {
                        sb.append(ch);
                    }
                    break;
                case 2:
                    if (ch == delim) {
                        result.add(sb.toString());
                        sb.delete(0, sb.length());
                        mode = 0;
                    } else if (ch == bracket) {
                        sb.append(ch);
                        mode = 1;
                    } else {
                        // Error case
                        sb.append(delim);
                        sb.append(ch);
                        mode = 1;
                    }
                    break;
                case 3:
                    if (ch == delim) {
                        result.add(sb.toString());
                        sb.delete(0, sb.length());
                        mode = 0;
                    } else if (ch == bracket) {
                        sb.append(ch);
                    } else {
                        sb.append(ch);
                    }
                    break;
                default:
                    throw new RuntimeException("ERROR");
            }
        }
        return result;
    }

    public static String join(List<String> src, char delim, char bracket) {
        if (src == null || src.size() == 0) {
            return null;
        }
        String bracketStr = "" + bracket;
        String bracketStr2 = "" + bracket + bracket;
        StringBuilder sb = new StringBuilder();
        boolean first = true;
        for (String s : src) {
            if (first) {
                first = false;
            } else {
                sb.append(delim);
            }
            if (s == null) {
                // none
            } else if (s.length() == 0) {
                sb.append(bracket);
                sb.append(bracket);
            } else if (s.indexOf(delim) != -1 || s.indexOf(bracket) != -1) {
                sb.append(bracket);
                sb.append(s.replace(bracketStr, bracketStr2));
                sb.append(bracket);
            } else {
                sb.append(s);
            }
        }
        return sb.toString();
    }
}