springboot接收from-data参数为空解决办法。

有时候我们传的参数很大，比如图片转成的base64字符，如果普通传参肯定会报错，可以把这种参数放在from-data的body里面，我们JAVA后台需要接收from-data的参数。

public ReturnModel fromDateTest(HttpServletRequest request){
        ReturnModel returnModel = new ReturnModel();
        JSONObject jsonObject = new JSONObject();
        DiskFileItemFactory factory = new DiskFileItemFactory();
        ServletFileUpload upload = new ServletFileUpload(factory);
        List<FileItem> items = null;
        try {
            items = upload.parseRequest(new ServletRequestContext(request));
        } catch (FileUploadException e) {
            returnModel.setCode(1);
            returnModel.setMessage("上传失败");
            e.printStackTrace();
        }
        for(int i=0;i<items.size();i++)
        {
            String fileName = items.get(i).getFieldName();
            String fileValue =  items.get(i).getString();
            jsonObject.put(fileName, fileValue);
        }
        
        returnModel.setCode(0);
        returnModel.setMessage("上传成功");
        returnModel.setBody("");
        return returnModel;
    }

正常这样子是可以接收到的。
但是实际情况是这样子的。


很明显，request里面是有值的，但是为什么我们获取不到呢？
后来查看了一些资料才知道使用Apache Commons FileUpload组件上传文件时总是返回null，调试发现ServletFileUpload对象为空，在Spring Boot中有默认的文件上传组件，在使用ServletFileUpload时需要关闭Spring Boot的默认配置 ，禁用MultipartResolverSpring提供的默认值，在配置文件中加入

spring.http.multipart.enabled=false

然后试了一下

就可以获取到了。
下面在贴一下发送from-data请求的代码：

@SuppressWarnings("rawtypes")
    public static String formUpload(String urlStr, Map<String, String> textMap) {
        String res = "";
        HttpURLConnection conn = null;
        textMap.put("keyId","111");
        textMap.put("photo","222");
        // boundary就是request头和上传文件内容的分隔符
        String BOUNDARY = "---------------------------123821742118716";
        try {
            URL url = new URL(urlStr);
            conn = (HttpURLConnection) url.openConnection();
            conn.setConnectTimeout(5000);
            conn.setReadTimeout(30000);
            conn.setDoOutput(true);
            conn.setDoInput(true);
            conn.setUseCaches(false);
            conn.setRequestMethod("POST");
            conn.setRequestProperty("Connection", "Keep-Alive");
            // conn.setRequestProperty("User-Agent","Mozilla/5.0 (Windows; U; Windows NT 6.1; zh-CN; rv:1.9.2.6)");
            conn.setRequestProperty("Content-Type","multipart/form-data; boundary=" + BOUNDARY);
            OutputStream out = new DataOutputStream(conn.getOutputStream());
            // text
            if (textMap != null) {
                StringBuffer strBuf = new StringBuffer();
                Iterator iter = textMap.entrySet().iterator();
                while (iter.hasNext()) {
                    Map.Entry entry = (Map.Entry) iter.next();
                    String inputName = (String) entry.getKey();
                    String inputValue = (String) entry.getValue();
                    if (inputValue == null) {
                        continue;
                    }
                    strBuf.append("\r\n").append("--").append(BOUNDARY).append("\r\n");
                    strBuf.append("Content-Disposition: form-data; name=\"" + inputName + "\"\r\n\r\n");
                    strBuf.append(inputValue);
                }
                out.write(strBuf.toString().getBytes());
            }
            byte[] endData = ("\r\n--" + BOUNDARY + "--\r\n").getBytes();
            out.write(endData);
            out.flush();
            out.close();
            // 读取返回数据
            StringBuffer strBuf = new StringBuffer();
            BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            String line = null;
            while ((line = reader.readLine()) != null) {
                strBuf.append(line).append("\n");
            }
            res = strBuf.toString();
            reader.close();
            reader = null;
        } catch (Exception e) {
            System.out.println("发送POST请求出错。" + urlStr);
            e.printStackTrace();
        } finally {
            if (conn != null) {
                conn.disconnect();
                conn = null;
            }
        }
        return res;
    }