java 驼峰转下划线 下划线转驼峰

public class StringUtil {

    public static void main(String[] args) {
        System.out.println(toCamelCase("user_name"));
        System.out.println(toUnderlineCase("userName"));
    }

    /**
     * 下划线转驼峰
     * user_name  ---->  userName
     * userName   --->  userName
     *
     * @param underlineStr 带有下划线的字符串
     * @return 驼峰字符串
     */
    public static String toCamelCase(String underlineStr) {
        if (underlineStr == null) {
            return null;
        }
        // 分成数组
        char[] charArray = underlineStr.toCharArray();
        // 判断上次循环的字符是否是"_"
        boolean underlineBefore = false;
        StringBuffer buffer = new StringBuffer();
        for (int i = 0, l = charArray.length; i < l; i++) {
            // 判断当前字符是否是"_",如果跳出本次循环
            if (charArray[i] == 95) {
                underlineBefore = true;
            } else if (underlineBefore) {
                // 如果为true，代表上次的字符是"_",当前字符需要转成大写
                buffer.append(charArray[i] -= 32);
                underlineBefore = false;
            } else {
                // 不是"_"后的字符就直接追加
                buffer.append(charArray[i]);
            }
        }
        return buffer.toString();
    }

    /**
     * 驼峰转 下划线
     * userName  ---->  user_name
     * user_name  ---->  user_name
     *
     * @param camelCaseStr 驼峰字符串
     * @return 带下滑线的String
     */
    public static String toUnderlineCase(String camelCaseStr) {
        if (camelCaseStr == null) {
            return null;
        }
        // 将驼峰字符串转换成数组
        char[] charArray = camelCaseStr.toCharArray();
        StringBuffer buffer = new StringBuffer();
        //处理字符串
        for (int i = 0, l = charArray.length; i < l; i++) {
            if (charArray[i] >= 65 && charArray[i] <= 90) {
                buffer.append("_").append(charArray[i] += 32);
            } else {
                buffer.append(charArray[i]);
            }
        }
        return buffer.toString();
    }
}