多文件上传multipart/form-data

前言

在web开发中上传文件比较简单，一个普通的post表单再加上文件类型的标签就可以完成，上传的这些工作都是交给浏览器完成。但是在客户端上传文件时就需要自己写http上传相关的参数。

多文件上传

请求头

......
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryMHzissskK7K82uyt

• 多文件上传请求头的一个重要参数Content-Type，值必须为multipart/form-data; boundary=自定义的分隔符

请求体

------WebKitFormBoundaryMHzissskK7K82uyt
Content-Disposition: form-data; name="CLIENT_NO"

123344
------WebKitFormBoundaryMHzissskK7K82uyt
Content-Disposition: form-data; name="file"; filename="mdAndroid.json"
Content-Type: application/json


------WebKitFormBoundaryMHzissskK7K82uyt--

• 请求体必须是以上面这种方式进行拼接参数，而不是以键值对的方式进行传值
• web表单上传多文件时，浏览器会自动把表单的内容进行拼接，而移动客户端上传时，在不用框架的前提下，需要我们自己把上传参数拼接成上面这种形式

客户端上传

Android自带HttpURLConnection

private String prefix = "--";
private String boundary = CryptoUtil.genRandomKey();
private String endLine = "\r\n";

URL url = new URL(uploadUrl);
HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
httpURLConnection.setChunkedStreamingMode(128 * 1024); //128k
//允许输入输出流
httpURLConnection.setDoInput(true);
httpURLConnection.setDoOutput(true);
httpURLConnection.setUseCaches(false);
//设置请求头信息
httpURLConnection.setRequestMethod("POST");
httpURLConnection.setRequestProperty("Connection", "Keep-Alive");
httpURLConnection.setRequestProperty("Charset", "UTF-8");
httpURLConnection.setRequestProperty("Content-Type", "multipart/form-data;boundary=" + boundary);

DataOutputStream dos = new DataOutputStream(httpURLConnection.getOutputStream());
dos.writeBytes(prefix + boundary + endLine);
dos.writeBytes("Content-Disposition: form-data; name=\"CLIENT_NO\"" + endLine + endLine);
dos.writeBytes("8623732" + endLine);

dos.writeBytes(prefix + boundary + endLine);
dos.writeBytes("Content-Disposition: form-data; name=\"file\"; filename=\"mdAndroid.json\"" + endLine);
dos.writeBytes("Content-Type: application/json" + endLine + endLine);
dos.write(fileToByte("mdAndroid.json"));
dos.writeBytes(endLine);
dos.writeBytes(prefix + boundary + prefix + endLine);
dos.flush();

InputStream is = httpURLConnection.getInputStream();
InputStreamReader isr = new InputStreamReader(is, "utf-8");
BufferedReader br = new BufferedReader(isr);
String result = br.readLine();
dos.close();
is.close();

• 注意：1、请求体中的分隔符="--"+boundary+"\r\n"
• 2、参数值和上面的信息中间要空一行，所以会有两个"\r\n\r\n"

AsyncHttpClient上传

RequestParams params = new RequestParams();
params.put("CUSTOMER_NO", "8372721");
params.put("android", fileToStream("mdAndroid.json"), "mdAndroid.json");
AsyncHttpClient client = new AsyncHttpClient();
client.post(url, params, new APPResponseHandler() {
    @Override
    public void onSuccess(Object result) {
        Log.i("sfj", "result===="+result);
    }

    @Override
    public void onFailure(String errorCode, String errorMsg) {
        Log.i("sfj", errorCode + errorMsg);
    }
});

服务器端处理（java）

使用SpringMVC框架，全局spring-servlet.xml配置项

<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
        <!-- 默认编码 -->
        <property name="defaultEncoding" value="utf-8" />
        <!-- 文件大小最大值 -->
        <property name="maxUploadSize" value="10485760000" />
        <!-- 内存中的最大值 -->
        <property name="maxInMemorySize" value="40960" />
    </bean>

接收请求，文件保存操作，简化步骤：

1、转换请求为多文件请求，也可直接在方法参数里面直接接收MultipartHttpServletRequest参数

MultipartHttpServletRequest multiRequest = (MultipartHttpServletRequest) request

2、获取键值对参数：

request.getParameter("参数名")

3、获取文件数据集合：

request.getFileMap()

4、遍历集合，使用MultipartFile自带的方法进行文件保存

multiFile.transferTo(new File("文件保存路径"))