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Java从数据库中读取Blob文件访问文件上传接口

背景:

     最近在做数据对接方面的工作,其中有一个需求是将我们公司以 blob 形式存储在数据库中的文件读出来访问要对接公司的文件上传接口,将这些文件对接到对方公司,记录一下 Java 发送文件上传请求的代码。先贴出要访问的接口代码:

@RequestMapping(method = RequestMethod.POST, value = "/upload")
    @ApiOperation(value = "表单文件上传")
    @ApiImplicitParam(name = "file", value = "file", required = true, dataType = "MultipartFile", paramType = "form")
    public ResponseResult upload(@RequestParam("file") @NotNull(message = "上传文件不能为空") MultipartFile file) {
        String fileId = fileService.uploadFile(file);
        return ResponseResult.success(fileId);
    }
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     从这个接口可以看到我们要模拟 form 表单文件上传。下面是 java 代码模拟发送这个文件上传请求。

代码:

public String fileUploadPost(byte[] fileContent, String fileName) {
        String end = "\r\n";
        String twoHyphens = "--";
        String boundary = "*****";

        String result = "";
        try {
            URL url = new URL("http://192.168.10.75:16002/api/upload");
            HttpURLConnection con = (HttpURLConnection) url.openConnection();
            /* 允许Input、Output,不使用Cache */
            con.setDoInput(true);
            con.setDoOutput(true);
            con.setUseCaches(false);
            /* 设置传送的method=POST */
            con.setRequestMethod("POST");
            /* setRequestProperty */
            con.setRequestProperty("Connection", "Keep-Alive");
            con.setRequestProperty("Charset", "UTF-8");
            con.setRequestProperty("Content-Type",
                    "multipart/form-data;boundary=" + boundary);
            /* 设置DataOutputStream */
            DataOutputStream ds = new DataOutputStream(con.getOutputStream());
            ds.writeBytes(twoHyphens + boundary + end);
            ds.writeBytes("Content-Disposition: form-data; "
                    + "name=\"file\";filename=\"" + fileName + "\"" + end);
            ds.writeBytes(end);
            // byte 转 file

            /* 取得文件的FileInputStream */
            DataInputStream in = new DataInputStream(new ByteArrayInputStream(fileContent));
            /* 设置每次写入1024bytes */
            int bufferSize = 1024;
            byte[] buffer = new byte[bufferSize];
            int length = -1;
            /* 从文件读取数据至缓冲区 */
            while ((length = in.read(buffer)) != -1) {
                /* 将资料写入DataOutputStream中 */
                ds.write(buffer, 0, length);
            }
            ds.writeBytes(end);
            ds.writeBytes(twoHyphens + boundary + twoHyphens + end);
            /* close streams */
            in.close();
            ds.flush();

            int resultCode = con.getResponseCode();
            if (resultCode == HttpURLConnection.HTTP_OK) {
                InputStream is = con.getInputStream();
                BufferedReader reader = new BufferedReader(new InputStreamReader(is));
                String line;
                StringBuilder sb = new StringBuilder();
                while ((line = reader.readLine()) != null) {
                    sb.append(line);
                }
                reader.close();
                is.close();
                result = sb.toString();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return result;
    }
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  这个 fileContent 参数就是一个 byte[] 类型的,是使用 JDBCTemplate 这样从数据库中读出来的:

String sql = "select file_content from filecontent where file_content_id= ?";
Object[] params = {fileId};
Blob blob = jdbcTemplate.queryForObject(sql, params, Blob.class);
int length = (int) blob.length();
return blob.getBytes(1, length);
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