详解JAVA后端实现统一扫码支付：微信篇

最近做完了一个项目，正好没事做，产品经理就给我安排了一个任务。

做一个像收钱吧这样可以统一扫码收钱的功能。

一开始并不知道是怎么实现的，咨询了好几个朋友，才知道大概的业务流程：先是开一个网页用来判断支付平台，是微信还是支付宝，判断过后就好办了，直接照搬微信支付和支付宝的官方文档。不过微信的文档感觉有点坑，得多花点心思。

现在讲讲怎么实现微信支付网页支付，也就是公众号支付：

1.判断支付平台，在判断是微信平台时，必须使用window.location打开网页，使用其他方法在IOS版微信无法打开网页，至少现在的新版微信无法打开。对应的连接是请求获取code的链接。第2步会讲到。

<html>
<head>
 <title>判断客户平台</title>
 <basefont face="微软雅黑" size="2" />
 <meta http-equiv="Content-Type" content="text/html;charset=utf-8" />
 <meta name="exporter-version" content="Evernote Windows/303244 (zh-CN, DDL); Windows/6.1.7601 Service Pack 1 (Win64);"/>
<script type="text/javascript" src="jquery-3.1.1.min.js"></script>
 <style>
 body, td {
  font-family: 微软雅黑;
  font-size: 10pt;
 }
 </style>
</head>
<body>
<script type="text/javascript"> 

window.onload = function(){
 if(isWeiXin()){
 window.location='http://www.xxoo.com/InterfaceAPI/code';
 } else if(isZFB()){
 alert('支付宝即将开放....');
//var p = document.getElementsByTagName('p');
//p[0].innerHTML = window.navigator.userAgent;
 }else{
 alert('请使用微信或者支付宝App扫码');
 }
}
function isWeiXin(){
 var ua = window.navigator.userAgent.toLowerCase();
 if(ua.match(/MicroMessenger/i) == 'micromessenger'){
 return true;
 }else{
 return false;
 }
}
function isZFB(){
 var ua = window.navigator.userAgent.toLowerCase();
 if(ua.match(/AlipayClient/i) =='alipayclient'){
  return true;
 }else{
  return false;
  }
}
</script>
</body></html>

2.这里是获取code，回调地址必须使用URLEncoder的utf-8编码，这里最终只获取openid，需要获取UserInfo其他信息的自行测试，只需要修改一下 scope 的参数，

@RequestMapping({ "code" })
 public void getCode(HttpServletRequest request, HttpServletResponse response) {
  try {
   //回调地址
   String redirect_uri = URLEncoder.encode(
     "http://www.xxoo.com/InterfaceAPI/openid?codeID=7837283",
     "utf-8");
   String url = "https://open.weixin.qq.com/connect/oauth2/authorize?appid="
     + WechatConfig.APP_ID
     + "&redirect_uri="
     + redirect_uri
     + "&response_type=code&scope=snsapi_base&state=STATE#wechat_redirect";
   response.sendRedirect(url);
  } catch (Exception e) {
   e.printStackTrace();
  }
 }

3.里面有一个codeid的参数，不要在意这个，是用来测试用的。这里只需要openid,下面是使用get方法获取json返回结果，获取到openid后，重定向到支付页面。

@RequestMapping({ "openid" })
 public void getOpenid(String codeID, String code,
   HttpServletResponse response) {
  try {
   String requestUrl = "https://api.weixin.qq.com/sns/oauth2/access_token?appid="
     + WechatConfig.APP_ID
     + "&secret="
     + WechatConfig.APP_SECRET
     + "&code="
     + code
     + "&grant_type=authorization_code";
   if (code != null) {
    String json = WebUtils.get(requestUrl, null);
    WechatResult result = new Gson().fromJson(json,
      WechatResult.class);
    OPEN_ID = result.getOpenid();
    System.out.println("====OPEN_ID====" + OPEN_ID);
    response.sendRedirect("http://www.xxoo.com/InterfaceAPI/pay.html");
   }

  } catch (Exception e) {
   e.printStackTrace();
  }
 }

4.在前端支付页面输入要支付的金额，提交到后台

$.ajax({

    type: "POST",
    dataType: "html",
    url: "http://www.xxoo.com/InterfaceAPI/weixinPay",
    data: "value="+self.input.value,
    timeout:10000,
    cache: true,
    async: true,
    error: function(data){
      //alert(data+"---value-->"+self.input.value);
    }, },});

5.后端获取金额然后在后端统一下单，公众号支付有两个地方不一样，一是支付类型要改为 JSAPI，二是需要获取openid

 @RequestMapping({ "weixinPay" })
 public void weixinPay(HttpServletRequest request,
   HttpServletResponse response) {
  String value = request.getParameter("value");
  WechatTradeTest wechat = new WechatTradeTest();
  String json = wechat.testunifiedOrder(Integer.valueOf(value), OPEN_ID);
 //这里返回json到前端
  write(json, response);
 }

6.统一下单成功后返回的结果例子：

<xml>
 <return_code><![CDATA[SUCCESS]]></return_code>
 <return_msg><![CDATA[OK]]></return_msg>
 <appid><![CDATA[wx2421b1c4370ec43b]]></appid>
 <mch_id><![CDATA[10000100]]></mch_id>
 <nonce_str><![CDATA[IITRi8Iabbblz1Jc]]></nonce_str>
 <openid><![CDATA[oUpF8uMuAJO_M2pxb1Q9zNjWeS6o]]></openid>
 <sign><![CDATA[7921E432F65EB8ED0CE9755F0E86D72F]]></sign>
 <result_code><![CDATA[SUCCESS]]></result_code>
 <prepay_id><![CDATA[wx201411101639507cbf6ffd8b0779950874]]></prepay_id>
 <trade_type><![CDATA[JSAPI]]></trade_type>
</xml>

7.返回的参数需要重新签名并返回到前端，签名方法与统一下单时的签名是一样的！签名时必须要带上微信商户返回是以Json格式返回到前端。

public String testunifiedOrder(int fee,String openid) {
  WechatUnifiedOrder request = new WechatUnifiedOrder();
  request.setBody("测试商品");
  request.setDetail("一个好商品");
  request.setGoods_tag("测试");
  request.setOut_trade_no(System.currentTimeMillis() + "");
  request.setFee_type("CNY");
  request.setTotal_fee(1);
  request.setSpbill_create_ip("192.168.88.26");
  request.setTime_start(System.currentTimeMillis() + "");
  request.setOpenid(openid);
  //下单成功后返回
  WechatUnifiedOrder.Response response = WechatConfig.getInstance()
    .unifiedOrder(request);
  response.setTime_start(request.getTime_start());
  WeichatData data = new WeichatData();
  data.setAppId(response.getAppid());
  data.setTimeStamp(request.getTime_start());
  data.setNonceStr(response.getNonce_str());
  data.setPrepay_id(response.getPrepay_id());
  data.setSignType("MD5");
  TreeMap<String, String> requestMap = new TreeMap<String, String>();
  requestMap.put("appId", response.getAppid());
  requestMap.put("timeStamp", response.getTime_start());
  requestMap.put("nonceStr", response.getNonce_str());
  requestMap.put("package", "prepay_id="+response.getPrepay_id());
  requestMap.put("signType","MD5");
  data.setPaySign(sign(requestMap).toUpperCase());
  return new Gson().toJson(data);
 }

8.前端需要解析json，获取对应的值，唤醒微信支付

 success: function(data){
     if(data!=null){
      var obj=eval("("+data+")");
      appId = obj["appId"];
      //timeStamp = new Date().getTime();
      timeStamp = obj["timeStamp"];
      nonceStr = obj["nonceStr"];
      package = obj["prepay_id"];
      paySign = obj["paySign"];
     if (typeof WeixinJSBridge == "undefined"){
       if( document.addEventListener ){
        document.addEventListener('WeixinJSBridgeReady', onBridgeReady, false);
       }else if (document.attachEvent){
        document.attachEvent('WeixinJSBridgeReady', onBridgeReady);
       document.attachEvent('onWeixinJSBridgeReady', onBridgeReady);
       }
     }else{
       onBridgeReady();
     }
    }else{
     alert("支付失败");
    }
  },

  //微信回调
  function onBridgeReady(){
 WeixinJSBridge.invoke(
  'getBrandWCPayRequest', {
   "appId" :appId,
   "timeStamp":timeStamp,
   "nonceStr" :nonceStr,
   "package" :"prepay_id="+package,
   "signType" :"MD5",
   "paySign" : paySign
  },
  function(res){
   if(res.err_msg == "get_brand_wcpay_request：ok" ) {

   }else {

   }
  }
 );

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