后台代码：

public Map<String,String> wxPayMoney(HttpServletRequest request, String payinfoid, String paymoney,String userip,String openId) throws Exception {

System.out.println("微信支付后台开始");

WxpayParam wxpayParam = new WxpayParam();

        wxpayParam.setTotalFee(paymoney);

        WxPayConfig ourWxPayConfig = new WxPayConfig();

        System.out.println("支付时openId:======="+openId);

        //获取请求ip地址

        String out_trade_no =getTradeNo();

        System.out.println("out_trade_no:"+out_trade_no);

        String ip = request.getHeader("x-forwarded-for");

        String notifyUrl ="https://www.12333333.com.cn";  //我这里的回调地址是随便写的，到时候需要换成处理业务的回调接口

        WXPay wxPay = new WXPay(ourWxPayConfig);

        //根据微信支付api来设置

        TreeMap<String,String> paramMap  = new TreeMap();

        TreeMap<String,String> dataMap  = new TreeMap();

        paramMap.put("appid",ourWxPayConfig.getAppID());

        paramMap.put("body",wxpayParam.getBody());

        paramMap.put("fee_type","CNY");

        paramMap.put("mch_id",ourWxPayConfig.getMchID()); 

        paramMap.put("nonce_str",WXPayUtil.generateNonceStr());

        paramMap.put("notify_url",notifyUrl);

        paramMap.put("openid",openId);  

        paramMap.put("out_trade_no",out_trade_no);    //交易号

        paramMap.put("spbill_create_ip",userip); 

        paramMap.put("total_fee",wxpayParam.getTotalFee()); 

        paramMap.put("trade_type","JSAPI"); 

        dataMap.put("appid",ourWxPayConfig.getAppID());

        dataMap.put("nonceStr",WXPayUtil.generateNonceStr());

        String sign = WXPayUtil.generateSignature(paramMap, ourWxPayConfig.getKey());  //第一次签名

        paramMap.put("sign",sign);   

        String xml = WXPayUtil.mapToXml(paramMap);//将所有参数(map)转xml格式

        System.out.println("发送的xml:"+xml);

        String unifiedorder_url = "https://api.mch.weixin.qq.com/pay/unifiedorder";

        //String xmlStr = HttpRequest.sendPost(unifiedorder_url, xml);//发送post请求"统一下单接口"返回预支付id:prepay_id

        String xmlStr = HttpUtil.sendPostXml(unifiedorder_url, xml, null);

        System.out.println("xmlStr:======="+xmlStr);

        String prepay_id = "";//预支付id

        if (xmlStr.indexOf("SUCCESS") != -1) {

            Map<String, String> map = WXPayUtil.xmlToMap(xmlStr);

            prepay_id = (String) map.get("prepay_id");

            dataMap.put("package","prepay_id="+prepay_id);

        }

        dataMap.put("signType",WXPayConstants.SignType.MD5.toString());

        dataMap.put("timeStamp",String.valueOf(System.currentTimeMillis()/1000));

        String secSign = WXPayUtil.generateSignature(paramMap, ourWxPayConfig.getKey());  //第二次签名

        /** wxPay.unifiedOrder 这个方法中调用微信统一下单接口 */

        Map<String, String> respData = wxPay.unifiedOrder(paramMap);

        respData.put("out_trade_no",payinfoid);    //交易号

        if (respData.get("return_code").equals("SUCCESS")){

        System.out.println("微信统一下单");

            //返回给APP端的参数，APP端再调起支付接口

            respData.put("appId",ourWxPayConfig.getAppID());

            respData.put("mchid",ourWxPayConfig.getMchID());

            respData.put("paySign",secSign);

            respData.put("signType", "MD5");

            respData.put("total_fee",paymoney);

            respData.put("timeStamp",dataMap.get("timeStamp"));

            respData.put("nonceStr", dataMap.get("nonceStr"));

            respData.put("package", "prepay_id=" + prepay_id);

            respData.put("prepay_id",prepay_id);

            System.out.println("respData:"+respData);

            return respData;

        }

        System.out.println("微信支付后台结束");

        throw new Exception(respData.get("return_msg"));

}

前台代码：

function pay_weixin(){

$.ajax({

type: "get",

url: http+'pay/wxPayMoney',

data: {payinfoid : payinfoid,paymoney:paymoney,userip:userip,openId:openid},

dataType: "json",

success: function(payConfig) {

var datamap={

"appId": payConfig.appid,

"nonceStr":payConfig.nonceStr,

"package": payConfig.package,

"paySign": payConfig.paySign,

"signType": "MD5",

"timeStamp": payConfig.timeStamp

};

alert("paySign"+datamap.paySign);

WeixinJSBridge.invoke(

   'getBrandWCPayRequest', datamap,

   function(res){

   if(res.err_msg == "get_brand_wcpay_request:ok" ){

   // 使用以上方式判断前端返回,微信团队郑重提示：

         //res.err_msg将在用户支付成功后返回ok，但并不保证它绝对可靠。

   } 

}); 

}

})

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();

}

}