字符串替换

请实现一个函数，将一个字符串中的每个空格替换成“%20”。例如，当字符串为We Are Happy Coder.则经过替换之后的字符串为We%20Are%20Happy%20Coder

public class ReplaceSpace {
    public static void main(String[] args) {
        String str = "We Are Happy Coder.";
        System.out.println(replaceSpace(str, " ", "%20"));
        System.out.println(replaceSpace2(str));
    }

    /**
     * 调用api实现内容替换
     *
     * @param str
     * @return
     */
    private static String replaceSpace2(String str) {
        return str.replaceAll("\s", "%20");
    }

    /**
     * 替换内容
     *
     * @param str         原始的句子
     * @param replaceStr  被替换的内容
     * @param replacement 替换的内容
     * @return
     */
    private static String replaceSpace(String str, String replaceStr, String replacement) {
        int length = str.length();
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < length; i++) {
            char b = str.charAt(i);
            if (String.valueOf(b).equals(replaceStr)) {
                sb.append(replacement);
            } else {
                sb.append(b);
            }
        }
        return sb.toString();
    }

}