请看清楚你的微信支付是v2还是v3。在这里整理的是v3的，v2的同学请忽略！

前期准备须要用的是商户证书，用的是p12的。设置api密钥(在微信商户端中设置)，还须要在微信公众号中设置jsapi授权文件夹；

1.微信授权获取用户openid

<a href="https://open.weixin.qq.com/connect/oauth2/authorize?appid=你的微信公众号appid&redirect_uri=授权完回调你的url&response_type=code&scope=snsapi_userinfo&state=1#wechat_redirect">点击測试</a>

2.授权回调接口。在接口中解析获取用户openid，假设已经授权的过的。我是通过解析获取到code然后再请求微信得到openid

https://api.weixin.qq.com/sns/oauth2/access_token?

appid=你的微信公众号appid&secret="+appsecret+"&code="+code+"&grant_type=authorization_code

3.用户下单提交，分两步，第一步通过统一下单接口获取prepay_id，第二步提交微信支付

前端代码：依据获取的openid提交后端

function wxpayCommit(){        $.ajax({	    type : "POST",	    url : "/wxpayCommit",	    data :"openid=${openid}",	    dataType : "json",	    async : false,	    success : function(obj) {						    if(obj.prepay_id ==""){		  return;	    }	    WeixinJSBridge.invoke('getBrandWCPayRequest',{  		  "appId" : obj.appid,                    		  "timeStamp":obj.timeStamp,           		  "nonceStr" : obj.nonceStr,           		  "package" : "prepay_id="+obj.prepay_id,        		  "signType" : "MD5",        		  "paySign" : obj.paySign 	    },function(res){      		   alert(res.err_msg);  	           if(res.err_msg == "get_brand_wcpay_request:ok" ) {  		        window.location.href="/index";  		   }else{  		        alert("fail");  		        window.location.href="/wxpayCommit";     		                                      		   }  	    });  	},	error : function(msg) {                    alert("fail");  	}	});

//统一下单接口获取prepay_id

注意中间遇到签名错误，是你的sign有问题，最好办法在微信官网在线生成签名的比对一样。立即找到错误

SortedMap
     
       packageParams = new TreeMap
      
       ();packageParams.put("appid", TenpayConfig.appid);packageParams.put("mch_id", TenpayConfig.partner);packageParams.put("nonce_str", WXUtil.getNonceStr());packageParams.put("body", "測试");packageParams.put("out_trade_no", 你的唯一订单号);packageParams.put("total_fee","1"); 	  //银行币种packageParams.put("spbill_create_ip",  request.remoteAddress); //订单生成的机器IP，指用户浏览器端IPpackageParams.put("notify_url", 回调的url);packageParams.put("openid", openid); packageParams.put("trade_type", "JSAPI"); 			RequestHandler reqHandler = new RequestHandler(null, null);reqHandler.init(TenpayConfig.appid, TenpayConfig.appsecret, TenpayConfig.partnerkey);String sign = reqHandler.createSign(packageParams);packageParams.put("sign", sign);String xml = toXml(packageParams);String prepay_id = "";String createOrderURL = "https://api.mch.weixin.qq.com/pay/unifiedorder";//获取用户的prepay_id = new GetWxOrderno().getPayNo2(createOrderURL, xml);//生成paysignSortedMap
       
         payParams = new TreeMap
        
         ();String non = WXUtil.getNonceStr();String time = WXUtil.getTimeStamp();payParams.put("appId", TenpayConfig.appid);payParams.put("nonceStr", non);payParams.put("timeStamp", time);payParams.put("package", "prepay_id="+prepay_id);payParams.put("signType", "MD5");String paysign = reqHandler.createSign(payParams);
        
       
      
     

附上其它代码

public static String getNonceStr() {Random random = new Random();return MD5Util.MD5Encode(String.valueOf(random.nextInt(10000)),"GBK");}

public static String getTimeStamp() {return String.valueOf(System.currentTimeMillis() / 1000);}

public static String getMchBillno(Stringmchid) {SimpleDateFormat shortSdf =new SimpleDateFormat("yyyyMMdd");String result = mchid+shortSdf.format(new Date())+String.valueOf(System.currentTimeMillis() / 1000);returnresult;}

public String createSign(SortedMap
     
      packageParams) {StringBuffer sb =new StringBuffer();Set es = packageParams.entrySet();Iterator it = es.iterator();while (it.hasNext()) {Map.Entry entry = (Map.Entry)it.next();String k = (String)entry.getKey();String v = (String)entry.getValue();if (null !=v && !"".equals(v) && !"sign".equals(k)&& !"key".equals(k)) {sb.append(k +"=" +v +"&");}}sb.append("key=" +this.getKey());//api密钥String sign = MD5Util.MD5Encode(sb.toString(),this.charset).toUpperCase();returnsign;}
     

private static String toXml(SortedMap
     
      params){StringBuilder sb = new StringBuilder();sb.append("
      
       ");for (Map.Entry
       
        e :params.entrySet()){sb.append("<" +e.getKey() +">");sb.append(e.getValue());sb.append("
        ");}sb.append("
       
      ");returnsb.toString();}
     

public static String getPayNo2(Stringurl,StringxmlParam)throws Exception{  KeyStore keyStore  = KeyStore.getInstance("PKCS12");  String prepay_id = "";      FileInputStream instream = new FileInputStream(new File("p12的证书路径"));      try {          keyStore.load(instream, TenpayConfig.partner.toCharArray());      } finally {          instream.close();      }      // Trust own CA and all self-signed certs      SSLContext sslcontext = SSLContexts.custom()              .loadKeyMaterial(keyStore, TenpayConfig.partner.toCharArray())              .build();      // Allow TLSv1 protocol only      SSLConnectionSocketFactory sslsf = new SSLConnectionSocketFactory(              sslcontext,              new String[] { "TLSv1" },              null,              SSLConnectionSocketFactory.BROWSER_COMPATIBLE_HOSTNAME_VERIFIER);      CloseableHttpClient httpclient = HttpClients.custom()              .setSSLSocketFactory(sslsf)              .build();      try {      HttpPost httpost= HttpClientConnectionManager.getPostMethod(url);  httpost.setEntity(new StringEntity(xmlParam,"UTF-8"));      HttpResponse response = httpclient.execute(httpost);        String jsonStr = EntityUtils.toString(response.getEntity(),"UTF-8");        if(jsonStr.indexOf("FAIL")!=-1){      return "2";        }        Map map = doXMLParse(jsonStr);        prepay_id  = (String) map.get("prepay_id");      } finally {          httpclient.close();      }returnprepay_id;  }