oss文字水印报错（Input is not base64 decoding）

String str = "已学习英语第3节课《6月份课堂测试-英语V2-1111》 进行水印操作报错

String lessonNumBase64 = new BASE64Encoder().encode(str.getBytes(Charset.forName("utf8"))); String lessonNumBase64Str = lessonNumBase64.replace('+', '-'); lessonNumBase64Str = lessonNumBase64Str.replace('/', ''); lessonNumBase64Str = lessonNumBase64Str.replaceAll("=", ""); String waterMarkLessonNum = "/watermark,size_26,text" + lessonNumBase64Str + ",color_5E5E5E,t_100,g_nw,x_269,y_599";