一、 注意事项

1、responseType设置为：arraybuffer

2、Blob设置type，来源于后台封装的response.headers[‘content-type’]

3、使用encodeURIComponent()，避免符号影响文件名

function previewFile(file) {
    let newName = file.fileNewName
    let filePath = file.filePath
    let path = filePath+newName
    let encodedFileName =  encodeURIComponent(path)
    const lowerCaseFileName = newName.toLowerCase();
    const fileExtension = lowerCaseFileName.split('.').pop();
    const allowedExtensions = ['pdf', 'jpg', 'jpeg', 'png'];
    if (allowedExtensions.includes(fileExtension)) {
        let service = axios.create({
            baseURL: '/fjxz',
            responseType: 'arraybuffer',
            timeout: 60000,
            headers: {
                'Content-Type': 'application/octet-stream',
            },
            withCredentials: true,
        });
        service.get(`/system/fileupload/preview/file?filePath=${filePath + newName}`)
            .then((response) => {
                console.log(response)
                let contentType = response.headers['content-type'];
                let blob = new Blob([response.data], {
                    type: contentType
                });
                let link = document.createElement('a');
                link.href = window.URL.createObjectURL(blob);
                link.target = "_blank";
                link.click();
            })
            .catch((error) => { })
    } else {
        ElMessage({
            message: '只有PDF和图片才能预览！',
            type: 'warning',
        })
    }


}

二、java接口

@GetMapping("/preview/file")
public void filePreview(HttpServletResponse response, @RequestParam("filePath") String filePath){

    try {
        String extension = getFileExtension(filePath);
        String mimeType = getMimeType(extension);
        // 设置响应头
        response.setContentType(mimeType);

        String encodedFileName = URLEncoder.encode(getFileName(filePath), "UTF-8");
        response.setHeader("Content-Disposition", "attachment; filename=\"" + encodedFileName + "\"");

        FileInputStream fis = new FileInputStream(fileSavePath + filePath);
        ServletOutputStream os = response.getOutputStream();

        byte [] b = new byte[1024*8];
        while(fis.read(b)!=-1){
            os.write(b);
        }
        fis.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}