利用HttpURLConnection发送post请求上传多个文件

本文要用java.net.HttpURLConnection来实现多个文件上传

1. 研究 form 表单到底封装了什么样的信息发送到servlet。

假如我参数写的内容是hello word,然后二个文件是二个简单的txt文件，form提交的信息为：

-----------------------------7da2e536604c8
Content-Disposition: form-data; name="username"  

hello word
-----------------------------7da2e536604c8
Content-Disposition: form-data; name="file1"; filename="D:/haha.txt"
Content-Type: text/plain  

haha
  hahaha
-----------------------------7da2e536604c8
Content-Disposition: form-data; name="file2"; filename="D:/huhu.txt"
Content-Type: text/plain  

messi
huhu
-----------------------------7da2e536604c8--  

研究下规律发现有如下几点特征

1.第一行是“ -----------------------------7d92221b604bc ”作为分隔符，然后是“ /r/n ” 回车换行符。 这个7d92221b604bc 分隔符浏览器是随机生成的。

2.第二行是Content-Disposition: form-data; name="file2"; filename="D:/huhu.txt";name=对应input的name值，filename对应要上传的文件名（包括路径在内），

3.第三行如果是文件就有Content-Type: text/plain；这里上传的是txt文件所以是text/plain,如果上穿的是jpg图片的话就是image/jpg了，可以自己试试看看。

然后就是回车换行符。

4.在下就是文件或参数的内容或值了。如：hello word。

5.最后一行是-----------------------------7da2e536604c8--,注意最后多了二个--;

有了这些就可以使用HttpURLConnection来实现上传文件功能了

        private void upload(String[] uploadFiles, String actionUrl) {
        String end = "/r/n";
        String twoHyphens = "--";
        String boundary = "*****";
        try {
            URL url = new URL(actionUrl);
            HttpURLConnection con = (HttpURLConnection) url.openConnection();
             // 发送POST请求必须设置如下两行
            con.setDoInput(true);
            con.setDoOutput(true);
            con.setUseCaches(false);
            con.setRequestMethod("POST");
            con.setRequestProperty("Connection", "Keep-Alive");
            con.setRequestProperty("Charset", "UTF-8");
            con.setRequestProperty("Content-Type",
                    "multipart/form-data;boundary=" + boundary);
            DataOutputStream ds =
                    new DataOutputStream(con.getOutputStream());
            for (int i = 0; i < uploadFiles.length; i++) {
                String uploadFile = uploadFiles[i];
                String filename = uploadFile.substring(uploadFile.lastIndexOf("//") + 1);
                ds.writeBytes(twoHyphens + boundary + end);
                ds.writeBytes("Content-Disposition: form-data; " +
                        "name=/"file" + i + "/";filename=/"" +
                        filename + "/"" + end);
                ds.writeBytes(end);
                FileInputStream fStream = new FileInputStream(uploadFile);
                int bufferSize = 1024;
                byte[] buffer = new byte[bufferSize];
                int length = -1;
                while ((length = fStream.read(buffer)) != -1) {
                    ds.write(buffer, 0, length);
                }
                ds.writeBytes(end);
                /* close streams */
                fStream.close();
            }
            ds.writeBytes(twoHyphens + boundary + twoHyphens + end);
            ds.flush();
            // 定义BufferedReader输入流来读取URL的响应
            InputStream is = con.getInputStream();
            int ch;
            StringBuffer b = new StringBuffer();
            while ((ch = is.read()) != -1) {
                b.append((char) ch);
            }
            String s = b.toString();
            if (s.contains("successfully")) {
                // for (int i = 1; i < 5; i++) {
                int beginIndex = s.indexOf("url =") + 5;
                int endIndex = s.indexOf("/n", beginIndex);
                String urlStr = s.substring(beginIndex, endIndex).trim();
                System.out.println(urlStr);
                // }
            }
            ds.close();
        } catch (Exception e) {
        }
    }