private static Pattern linePattern = Pattern.compile("_(\\w)");

/** 下划线转驼峰 */
public static String lineToHump(String str) {
    str = str.toLowerCase();
    Matcher matcher = linePattern.matcher(str);
    StringBuffer sb = new StringBuffer();
    while (matcher.find()) {
        matcher.appendReplacement(sb, matcher.group(1).toUpperCase());
    }
    matcher.appendTail(sb);
    return sb.toString();
}

/** 驼峰转下划线(简单写法，效率低于{@link #humpToLine2(String)}) */
public static String humpToLine(String str) {
    return str.replaceAll("[A-Z]", "_$0").toLowerCase();
}

private static Pattern humpPattern = Pattern.compile("[A-Z]");

/** 驼峰转下划线,效率比上面高 */
public static String humpToLine2(String str) {
    Matcher matcher = humpPattern.matcher(str);
    StringBuffer sb = new StringBuffer();
    while (matcher.find()) {
        matcher.appendReplacement(sb, "_" + matcher.group(0).toLowerCase());
    }
    matcher.appendTail(sb);
    return sb.toString();
}