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<String, String> packageParams = new TreeMap<String, String>();
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IP
packageParams.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paysign
SortedMap<String, String> payParams = new TreeMap<String, String>();
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<String, String>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<String, String>params)
{
StringBuilder sb = new StringBuilder();
sb.append("<xml>");

for (Map.Entry<String, String>e :params.entrySet())
{
sb.append("<" +e.getKey() +">");
sb.append(e.getValue());
sb.append("</" +e.getKey() +">");
}
sb.append("</xml>");
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;
  }