第一步：准备工作：准备小程序的APPID和SECRET
可登陆微信公众平台查看APPID和secret
第二部：获取token
微信提供了获取token的接口，访问此接口同时传入APPID和secret作为参数，就能获取token值。
接口地址为：tokenURL = https://api.weixin.qq.com/cgi-bin/token？grant_type=client_credential&appid=APPID&secret=SECRET
Java代码：
1 public static String getAccessToken() throws UnsupportedEncodingException, IOException{ 2 String tokenURL = https://api.weixin.qq.com/cgi-bin/token？grant_type=client_credential&appid=APPID&secret=SECRET 3 JSONObject jsonObject = null; 4 URL conn_url = new URL(tokenURL ); 5 HttpURLConnection conn = (HttpsURLConnection)conn_url.openConnection(); 6 conn.setRequestMethod("GET"); 7 conn.setReadTimeout(5000); 8 conn.setConnectTimeout(5000); 9 conn.connect();10 //output获取access_token是不会用到11 12 //正常返回代码为20013 if(conn.getResponseCode()==200){14 InputStream stream = conn.getInputStream();15 InputStreamReader inputStreamReader = new InputStreamReader(stream, "utf-8");16 BufferedReader bufferedReader = new BufferedReader(inputStreamReader);17 String str = null;18 StringBuffer buffer = new StringBuffer();19 while ((str = bufferedReader.readLine()) != null) {20 buffer.append(str);21 }22 bufferedReader.close();23 inputStreamReader.close();24 stream.close();25 conn.disconnect();26 jsonObject = JSONObject.fromObject(buffer.toString());27 }28 29 String access_token = jsonObject.getString("access_token");30 return access_token;31 } 第三部：获取参数图片
微信官方提供了获取微信小程序二维码的接口，访问此接口，同时把第二步获取的token值作为参数传入，同时还需传入二维码内需要带的参数，和图片的一些设置参数，便可获取二维码图片的输入流。
接口地址：
https://api.weixin.qq.com/wxa/getwxacodeunlimit?access_token=access_token
基本的设置参数：
"scene", param --二维码内需要带的参数param
"path", "pages/ShouYe/ShouYe/ShouYe" --设置扫面二维码进入的页面 "width", width --设置二维码图片的大小 如果不设置，默认大小是430 "is_hyaline", true "auto_color", true
生成二维码代码：
1 public static String getQRImg(String param,String size, HttpServletRequest request) { 2 3 4 String p=request.getSession().getServletContext().getRealPath("/"); 5 String codeUrl = p+"image/codeImg/"+System.currentTimeMillis()+param + "Code.png"; 6 String twoCodeUrl="/image/codeImg/"+System.currentTimeMillis()+param + "Code.png"; 7 try 8 { 9 String access_token = token;10 URL url = new URL("https://api.weixin.qq.com/wxa/getwxacodeunlimit?access_token="+access_token);11 HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();12 httpURLConnection.setRequestMethod("POST");// 提交模式13 // conn.setConnectTimeout(10000);//连接超时 单位毫秒14 // conn.setReadTimeout(2000);//读取超时 单位毫秒15 // 发送POST请求必须设置如下两行16 httpURLConnection.setDoOutput(true);17 httpURLConnection.setDoInput(true);18 // 获取URLConnection对象对应的输出流19 PrintWriter printWriter = new PrintWriter(httpURLConnection.getOutputStream());20 // 发送请求参数21 JSONObject paramJson = new JSONObject();22 String width;23 if(size !=null && !size.trim().equals("")){24 if(size.trim().matches("^[1-9][0-9]*$")){25 width = size.trim();26 }else27 {28 width = "430";29 }30 }else{31 width = "430";32 }33 paramJson.put("scene", param);34 paramJson.put("path", "pages/ShouYe/ShouYe/ShouYe");35 paramJson.put("width", width);36 paramJson.put("is_hyaline", true);37 paramJson.put("auto_color", true);38 /**39 * line_color生效40 * paramJson.put("auto_color", false);41 * JSONObject lineColor = new JSONObject();42 * lineColor.put("r", 0);43 * lineColor.put("g", 0);44 * lineColor.put("b", 0);45 * paramJson.put("line_color", lineColor);46 * */47 48 printWriter.write(paramJson.toString());49 // flush输出流的缓冲50 printWriter.flush();51 //开始获取数据52 BufferedInputStream bis = new BufferedInputStream(httpURLConnection.getInputStream());53 OutputStream os = new FileOutputStream(new File(codeUrl));54 int len;55 byte[] arr = new byte[1024];56 while ((len = bis.read(arr)) != -1)57 {58 os.write(arr, 0, len);59 os.flush();60 }61 os.close();62 }63 catch (Exception e)64 {65 e.printStackTrace();66 }67 return twoCodeUrl;68 }