字符串替换

    public static String replace(String s, String s1, String s2)
    {
        if(s == null || s1 == null || s2 == null)
            throw new NullPointerException("Null parameter");
        int i = s.indexOf(s1);
        if(i < 0)
            return s;
        int j = s1.length();
        int k = 0;
        StringBuffer stringbuffer = new StringBuffer(s.length() * 2);
        for(; i >= 0; i = s.indexOf(s1, k))
        {
            stringbuffer.append(s.substring(k, i));
            stringbuffer.append(s2);
            k = i + j;
        }

        stringbuffer.append(s.substring(k));
        return stringbuffer.toString();
    }

    public static String replaceFileSeparator(String s)
    {
        s = replace(s, "//", File.separator);
        s = replace(s, "/", File.separator);
        return s;
    }