class path resource [api.pdf] cannot be opened because it does not exist

public void downloadApiDoc(HttpServletResponse response) {
        ClassPathResource classPathResource = new ClassPathResource("api.pdf");
        try (InputStream inputStream = classPathResource.getInputStream()){
            //得到文件大小
            int size =inputStream.available();
            byte[] data =new byte[size];
            //读数据
            inputStream.read(data);
            inputStream.close();
            response.reset();
            //设置返回的文件类型
            response.setContentType("application/pdf");
            response.setHeader("Content-disposition", "inline; filename=Api_Doc.pdf");
            response.setContentLength(size);
            OutputStream os = response.getOutputStream();
            os.write(data);
        } catch (IOException e) {
            e.printStackTrace();
            log.info("download api doc");
        }
    }