SpringBoot项目打包成jar后获取classpath下文件失败的解决

ResourceUtils.getFile("classpath:");

ClassPathResource resource = new ClassPathResource("\\static\\pattern\\test.txt");    // static/pattern下的 test.txt文件
InputStream in = resource.getInputStream();  //获取文件输入流

package com.example.jekins.controller;
import org.springframework.core.io.ClassPathResource;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URLEncoder;
@RestController
public class DownloadController {
    @GetMapping("/download/pattern")
    public void downloadPattern(HttpServletRequest request, HttpServletResponse response){
        System.out.println("开始下载文件.....");
        ClassPathResource resource = new ClassPathResource("\\static\\pattern\\test.txt");
        try {
        	//获取文件输入流
            InputStream in = resource.getInputStream();
            //下载文件
            downFile("test文件.txt",request,response,in);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    /**
     * 下载文件
     * @param fileName 下载文件名称
     * @param response 响应
     * @throws IOException 异常
     */
    public static void downFile(String fileName,HttpServletRequest request,
                                HttpServletResponse response,InputStream in) throws IOException {
        //输出流自动关闭，java1.7新特性
        try(OutputStream os = response.getOutputStream()) {
            fileName = URLEncoder.encode(fileName, "UTF-8");
            response.reset();
            response.setHeader("Content-Disposition", "attachment; filename=" + fileName);
            response.setContentType("application/octet-stream; charset=UTF-8");
            byte[] b = new byte[in.available()];
            in.read(b);
            os.write(b);
            os.flush();
        } catch (Exception e) {
            System.out.println("fileName=" + fileName);
            e.printStackTrace();
        } finally {
            if (in != null) {
                in.close();
            }
        }
    }
}