java后台post请求上传图片

直接上代码：
1.actionUrl-----请求地址
2. file-----文件,如果是文件地址的话需要 File file =new File(“文件地址”)

public static String getQrCodePost(String actionUrl, File file) {
        String result = "";
        String BOUNDARY = java.util.UUID.randomUUID().toString();
        String PREFIX = "--", LINEND = "\r\n";
        String MULTIPART_FROM_DATA = "multipart/form-data";
        String CHARSET = "UTF-8";
        try {
            URL url = new URL(actionUrl);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setReadTimeout(10 * 1000);
            conn.setDoInput(true);// 允许输入
            conn.setDoOutput(true);// 允许输出
            conn.setUseCaches(false);
            conn.setRequestMethod("POST"); // Post方式
            conn.setRequestProperty("connection", "keep-alive");
            conn.setRequestProperty("Charsert", "UTF-8");
            conn.setRequestProperty("Content-Type", MULTIPART_FROM_DATA
                    + ";boundary=" + BOUNDARY);
            DataOutputStream outStream = new DataOutputStream(
                    conn.getOutputStream());
            // 发送文件数据
            if (file != null) {
                StringBuilder sb1 = new StringBuilder();
                sb1.append(PREFIX);
                sb1.append(BOUNDARY);
                sb1.append(LINEND);
                sb1.append("Content-Disposition: form-data; name=\"file\"; filename=\""
                        + file.getName() + "\"" + LINEND);
                sb1.append("Content-Type: application/octet-stream; charset="
                        + CHARSET + LINEND);
                sb1.append(LINEND);
                outStream.write(sb1.toString().getBytes());
                InputStream is = new FileInputStream(file);
                byte[] buffer = new byte[1024];
                int len = 0;
                while ((len = is.read(buffer)) != -1) {
                    outStream.write(buffer, 0, len);
                }

                is.close();
                outStream.write(LINEND.getBytes());
            }
            // 请求结束标志
            byte[] end_data = (PREFIX + BOUNDARY + PREFIX + LINEND).getBytes();
            outStream.write(end_data);
            outStream.flush();

            // 得到响应码
            int res = conn.getResponseCode();
            if (res == 200) {
                InputStream in = conn.getInputStream();
                InputStreamReader isReader = new InputStreamReader(in);
                BufferedReader bufReader = new BufferedReader(isReader);
                String line = "";
                while ((line = bufReader.readLine()) != null) {
                    result += line;
                }
                outStream.close();
                conn.disconnect();
                return result;
            }
            outStream.close();
            conn.disconnect();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return result;
    }