cannot be resolved to absolute file path because it does not reside in the file system 问题解决

╰半橙微兮° 2024-03-31 16:16 12阅读 0赞

## 项目场景： ##

在Springboot中利用Resource来获取文件并在前端返回该文件, 本地测试正常, 打包到远程报错:  
`cannot be resolved to absolute file path because it does not reside in the file system`

--------------------

## 问题描述: ##

> 紧接上一个问题: [项目打包成 jar 后包无法读取src/main/resources下文件][jar _src_main_resources], 在Springboot打包之后, 无法读取到jar包内的文件, 因此采取Resource来获取jar内相对路径地址的文件. **只有一个需要下载文件的时候没有问题, 然后在指定文件夹下新增一个文件后本地下载正常, 打包后下载出现问题: 下载该文件时, 后端抛出异常, 异常如下**

class path resource [static/xxx模板.xlsx] cannot be resolved to absolute file path because it does not reside in the file system: jar:file:/mis-project-java-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/static/%e5%b7%a5%e8%b5%84%e8%a1%a8%e6%a8%a1%e6%9d%bf.xlsx

--------------------

## 原因分析： ##

需要下载文件存放的地址:

![image-20221207140843161][]

修改前代码:

@Override
        @SneakyThrows(IOException.class)
        public HttpServletResponse downloadFile(HttpServletRequest request, HttpServletResponse response) {
        
            //设置文件路径
            org.springframework.core.io.Resource resource = new ClassPathResource("static/" + "xxx模板.xlsx");
            if (resource.exists()) {
        
                //异常在下一行抛出
                File file = resource.getFile();
                response.setCharacterEncoding("UTF-8");
                response.setContentType("application/vnd.ms-excel");
                String fileName = resource.getURI().toString().substring(resource.getURI().toString().lastIndexOf("/") + 1);
                response.setHeader("content-disposition", "attachment;filename=" + fileName);
                response.flushBuffer();
                BufferedInputStream bis = new BufferedInputStream(new FileInputStream(file));
                OutputStream os = response.getOutputStream();
                byte[] buffer = new byte[1024];
                int i = bis.read(buffer);
                while (i != -1) {
        
                    os.write(buffer, 0, i);
                    i = bis.read(buffer);
                }
                if (bis != null) {
        
                    bis.close();
                }
                return response;
            }
            return null;
        }

### 对问题部分本地断点调试 ###

**本地断点调试:**

1.  可以看到, 调用的是 AbstractFileResolvingResource下的getFIle 方法. 然后该方法会调用 ResourceUtils下的getFile() 方法  
    ![image-20221207174240268][]
2.  可以看到在ResourceUtils下的getFile() 方法中, 因为 resourceUrl.getProtocol() 为File, 说明该url 地址对应的资源是文件, 所以直接返回这个文件  
    ![image-20221207174553027][]
3.  后续源码如何返回这个文件可以自己继续深入

### **对问题部分远程断点调试:** ###

1.  依旧是进入 resource.getFile(); 的方法内. 因为当前 url的protocol 属性时 jar, 不是vfs, 依旧走的是ResourceUtils下的getFile() 方法  
    ![image-20221207175235179][]
2.  在ResourceUtils下的getFile() 方法中, 因为 resourceUrl.getProtocol() 为jar, 因此会抛出异常  
    ![image-20221207175509676][]
3.  异常抛出后被全局捕获, 然后在前端显示  
    ![image-20221207175641017][]

--------------------

## 解决方案： ##

> 通过上面的调试我们可以看到, org.springframework.core.io.Resource 这个类的getFile()方法,  
> 会自动获取构建resource对象带参构造中的url, 然后根据这个url确定该文件的类型.  
> 因为在本地时调试时, 通过resource.getFile()获取的url类型的 protocol 属性为File, 所以可以自动生成文件;  
> 然而在将项目打包成jar部署在服务器上时, 因为该文件是在jar里面的. 因此通过resource.getFile()获取的url类型的 protocol 属性为jar. 所以抛出该异常 `cannot be resolved to absolute file path because it does not reside in the file system: 文件url`.

**因此, 方法有两种:  
一种是直接将该文件放入服务器其他目录下而不是在jar包中. 另一种就是通过流来获取jar里面的文件.  
而本人采取第二种方式, 通过输入流来读取jar内的文件, 然后通过输出流将其输出.**

--------------------

**修改后的代码**

@Override
    @SneakyThrows(IOException.class)
    public HttpServletResponse downloadFile(HttpServletRequest request, HttpServletResponse response) {
        
        //设置文件路径
        org.springframework.core.io.Resource resource = new ClassPathResource("static/" + "xxx模板.xlsx");
        if (resource.exists()) {
        
            response.setCharacterEncoding("UTF-8");
            response.setContentType("application/vnd.ms-excel");
            String fileName = resource.getURI().toString().substring(resource.getURI().toString().lastIndexOf("/") + 1);
            response.setHeader("content-disposition", "attachment;filename=" + fileName);
            response.flushBuffer();
            //放弃使用直接获取文件的方式, 改成使用流的方式
            BufferedInputStream bis = new BufferedInputStream(resource.getInputStream());
            OutputStream os = response.getOutputStream();
            byte[] buffer = new byte[1024];
            int i = bis.read(buffer);
            while (i != -1) {
        
                os.write(buffer, 0, i);
                i = bis.read(buffer);
            }
            if (bis != null) {
        
                bis.close();
            }
            return response;
        }
        return null;
    }

[jar _src_main_resources]: https://timepause.blog.csdn.net/article/details/123803340
[image-20221207140843161]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/31/b118d6bfe2304ae19da961310123b6a4.png
[image-20221207174240268]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/31/2e46444f96c041e1945abaa30ea99f6d.png
[image-20221207174553027]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/31/705f5f9dbce242de907e6e0b0ac0653a.png
[image-20221207175235179]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/31/17b2892610a24f1480395d992e89cc5f.png
[image-20221207175509676]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/31/c46c05c24ee4486a953d126d56ed6fec.png
[image-20221207175641017]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/31/98f87dba91e841f287137e534e2f9725.png

cannot be resolved to absolute file path because it does not reside in the file system 问题解决

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