前段时间在公司的开发了一个微信小程序的项目，今天来说一说微信小程序的支付，有很多优秀的文章都说了小程序支付的
开发流程步骤，这里我们推荐一个博主以前就是看他的开发小程序支付:https://github.com/1913045515/weixin
现在来说说我对小程序支付的理解，首先我们在开发文档中找到小程序支付流程，

上面的图是我们支付的流程图，下面是开发要调用接口的顺序,
首先第一步我们获取openid,因为在统一下单接口中的交易类型是JSAPI,是必须要填openid
第二步就是下单了，把我们要下单参数拼接成xml的形式去发送接口，这里主要是签名很重要
签名:
1.签名算法
签名生成的通用步骤如下：

第一步，设所有发送或者接收到的数据为集合M，将集合M内非空参数值的参数按照参数名ASCII码从小到大排序（字典序），使用URL键值对的格式（即key1=value1&key2=value2…）拼接成字符串stringA。

特别注意以下重要规则：

　◆　参数名ASCII码从小到大排序（字典序）；
◆　如果参数的值为空不参与签名；
◆　参数名区分大小写；
◆　验证调用返回或微信主动通知签名时，传送的sign参数不参与签名，将生成的签名与该sign值作校验。
◆　微信接口可能增加字段，验证签名时必须支持增加的扩展字段
第二步，在stringA最后拼接上key=(API密钥的值)得到stringSignTemp字符串，并对stringSignTemp进行MD5运算，再将得到的字符串所有字符转换为大写，得到sign值signValue。
假设传送的参数如下：

appid： wxd930ea5d5a258f4f

mch_id： 10000100

device_info： 1000

body： test

nonce_str： ibuaiVcKdpRxkhJA

第一步：对参数按照key=value的格式，并按照参数名ASCII字典序排序如下：

stringA=”appid=wxd930ea5d5a258f4f&body=test&device_info=1000&mch_id=10000100&nonce_str=ibuaiVcKdpRxkhJA”;

第二步：拼接API密钥：

stringSignTemp=”stringA&key=192006250b4c09247ec02edce69f6a2d”

sign=MD5(stringSignTemp).toUpperCase()=”9A0A8659F005D6984697E2CA0A9CF3B7”

网友的整理：

这样我们就得到了签名
我们下单成功后微信会给我们预支付交易会话标识 这个很主要，拿这个在进行一次签名加密，
因为我们调用支付的接口中需要一个签名,支付成功后就会调用我们下单时所传的回调地址，我们在回调方法中判断用户是否支付成功，进行业务处理

代码实例:
OrderController.java

    /*** 下单:* @param openid 用户openid* @param money 金额* @return map*/@RequestMapping("/createOrder")@ResponseBodypublic Map<String,String>createOrder(String openid,int money){logger.info("用户的openid:-------->"+openid+"下单的金额:-------------->"+money);String mch_id= WeChatTool.mch_id; //商户号String today = new SimpleDateFormat("yyyyMMddHHmmss").format(new Date());String WXPay= WXPayUtil.createCode(8);String out_trade_no=mch_id+today+WXPay;//生成订单号Map<String,String> result=new HashMap<String,String>();//去Service层中去生成签名,用户openid out_trade_no订单号  money支付的金额String formData=orderService.getopenid(openid,out_trade_no,money);//在servlet层中生成签名成功后，把下单所要的参数以xml的格式拼接，发送下单接口String httpResult = HttpUtils.httpXMLPost(WeChatTool.createOrderUrl,formData);try {//xml转换成Map对象或者值Map<String, String> resultMap = WXPayUtil.xmlToMap(httpResult);result.put("package", "prepay_id=" + resultMap.get("prepay_id")); //这里是拿下单成功的微信交易号去拼接，因为在下面的接口中必须要这个样子result.put("nonceStr",resultMap.get("nonce_str")); //随机字符串} catch (Exception e) {e.printStackTrace();}String times= WXPayUtil.getCurrentTimestamp()+""; //获取当前时间result.put("timeStamp",times); //当前时间戳//生成调用支付接口要的签名Map<String, String> packageParams = new HashMap<String ,String>();packageParams.put("appId", WeChatTool.wxspAppid);packageParams.put("signType", WeChatTool.sign_type);packageParams.put("nonceStr",result.get("nonceStr")+"");packageParams.put("timeStamp",times);packageParams.put("package", result.get("package")+"");//商户订单号String sign="";try {sign= WXPayUtil.generateSignature(packageParams, WeChatTool.sercet_key); //生成签名:} catch (Exception e) {e.printStackTrace();}result.put("paySign",sign);logger.info("签名成功----->"+result.get("paySign"));return result; //所有的参数放进map中保存发送到小程序页面中,去调用微信支付接口}

OrderServiceImpl.java:

/*** 统一下单* @param openid 用户标识* @param out_trade_no 订单号* @param total_fee 金额* @return String*/@Overridepublic String getopenid(String openid,String out_trade_no,int total_fee) {//下单的金额，因为在微信支付中默认是分所以要这样处理Integer total_fees=total_fee*100;微信下单的金额是String类型的所以要转换类型String money=total_fees.toString();String nonceStr=WXPayUtil.generateUUID(); //设置UUID作为随机字符串Map<String ,String> map = new HashMap<String ,String>();map.put("appid",WeChatTool.wxspAppid); //商户appidmap.put("mch_id", WeChatTool.mch_id);//商户号map.put("nonce_str",nonceStr); //随机数map.put("body","大米");//商户名称map.put("out_trade_no",out_trade_no);//商户订单号map.put("total_fee",money);//下单金额map.put("spbill_create_ip", "127.0.0.1");//终端IPmap.put("notify_url",https://xxxx/xxxxx/notify.do);//回调地址 这里的接口必须是在线上用户支付成功才能收到微信发送的信息map.put("trade_type","JSAPI");//交易类型map.put("openid",openid+"");//用户openidmap.put("sign_type","MD5");//加密类型String sign="";try {sign= WXPayUtil.generateSignature(map, WeChatTool.sercet_key); //生成sign签名WeChatTool.sercet_key是商户的支付秘钥} catch (Exception e) {e.printStackTrace();}//拼接成xml的格式，这里的参数必须要和上面的一致，并且每次下单的订单号不能一致String formData="<xml>";formData += "<appid>"+ WeChatTool.wxspAppid+"</appid>"; formData += "<mch_id>"+ WeChatTool.mch_id+"</mch_id>"; formData += "<nonce_str>"+nonceStr+"</nonce_str>";formData += "<body>"+WeChatTool.month+"</body>";formData += "<out_trade_no>"+out_trade_no +"</out_trade_no>"; formData += "<total_fee>"+money+"</total_fee>"; formData += "<spbill_create_ip>"+"127.0.0.1"+"</spbill_create_ip>"; formData += "<notify_url>"+WeChatTool.notify_url+"</notify_url>"; formData += "<trade_type>"+WeChatTool.trade_type+"</trade_type>";formData += "<openid>"+openid+"</openid>"; //appidformData += "<sign_type>"+WeChatTool.sign_type+"</sign_type>";formData += "<sign>"+sign+"</sign>"; //签名算法formData += "</xml>";return formData;}

工具类:
WXPayUtil.java:

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import com.youquan.utli.WXPayConstants.SignType;
import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import java.io.ByteArrayInputStream;
import java.io.InputStream;
import java.io.StringWriter;
import java.security.MessageDigest;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.*;
/*** <p>User: qrn* <p>Date: 14-1-28* <p>Version: 1.0* 描述: 工具类*/
public class WXPayUtil {/***  XML格式字符串转换为Map* @param strXML XML字符串* @return  Map XML数据转换后的Map* @see Exception*/public static Map<String, String> xmlToMap(String strXML) throws Exception {try {Map<String, String> data = new HashMap<String, String>();DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();DocumentBuilder documentBuilder = documentBuilderFactory.newDocumentBuilder();InputStream stream = new ByteArrayInputStream(strXML.getBytes("UTF-8"));org.w3c.dom.Document doc = documentBuilder.parse(stream);doc.getDocumentElement().normalize();NodeList nodeList = doc.getDocumentElement().getChildNodes();for (int idx = 0; idx < nodeList.getLength(); ++idx) {Node node = nodeList.item(idx);if (node.getNodeType() == Node.ELEMENT_NODE) {org.w3c.dom.Element element = (org.w3c.dom.Element) node;data.put(element.getNodeName(), element.getTextContent());}}try {stream.close();} catch (Exception ex) {// do nothing}return data;} catch (Exception ex) {WXPayUtil.getLogger().warn("Invalid XML, can not convert to map. Error message: {}. XML content: {}", ex.getMessage(), strXML);throw ex;}}/*** 将Map转换为XML格式的字符串* @param data Map类型数据* @return   XML格式的字符串* @see Exception*/public static String mapToXml(Map<String, String> data) throws Exception {DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();DocumentBuilder documentBuilder= documentBuilderFactory.newDocumentBuilder();org.w3c.dom.Document document = documentBuilder.newDocument();org.w3c.dom.Element root = document.createElement("xml");document.appendChild(root);for (String key: data.keySet()) {String value = data.get(key);if (value == null) {value = "";}value = value.trim();org.w3c.dom.Element filed = document.createElement(key);filed.appendChild(document.createTextNode(value));root.appendChild(filed);}TransformerFactory tf = TransformerFactory.newInstance();Transformer transformer = tf.newTransformer();DOMSource source = new DOMSource(document);transformer.setOutputProperty(OutputKeys.ENCODING, "UTF-8");transformer.setOutputProperty(OutputKeys.INDENT, "yes");StringWriter writer = new StringWriter();StreamResult result = new StreamResult(writer);transformer.transform(source, result);String output = writer.getBuffer().toString(); //.replaceAll("\n|\r", "");try {writer.close();}catch (Exception ex) {}return output;}/*** 生成6位或10位随机数 param codeLength(多少位)* @param codeLength 参数* @return  String*/public static String createCode(int codeLength) {String code = "";for (int i = 0; i < codeLength; i++) {code += (int) (Math.random() * 9);}return code;}/*** 生成带有 sign 的 XML 格式字符串* @param data Map类型数据* @param key API密钥* @see Exception* @return String 含有sign字段的XML*/public static String generateSignedXml(final Map<String, String> data, String key) throws Exception {return generateSignedXml(data, key, SignType.MD5);}/*** 生成带有 sign 的 XML 格式字符串** @param data Map类型数据* @param key API密钥* @param signType 签名类型* @see Exception* @return 含有sign字段的XML*/public static String generateSignedXml(final Map<String, String> data, String key, SignType signType) throws Exception {String sign = generateSignature(data, key, signType);data.put(WXPayConstants.FIELD_SIGN, sign);return mapToXml(data);}/*** 判断签名是否正确* @param xmlStr XML格式数据* @param key  API密钥* @return  boolean 签名是否正确* @see Exception*/public static boolean isSignatureValid(String xmlStr, String key) throws Exception {Map<String, String> data = xmlToMap(xmlStr);if (!data.containsKey(WXPayConstants.FIELD_SIGN) ) {return false;}String sign = data.get(WXPayConstants.FIELD_SIGN);return generateSignature(data, key).equals(sign);}/*** 判断签名是否正确，必须包含sign字段，否则返回false。使用MD5签名。* @param data Map类型数据* @param key API密钥* @return  boolean 签名是否正确* @see Exception*/public static boolean isSignatureValid(Map<String, String> data, String key) throws Exception {return isSignatureValid(data, key, SignType.MD5);}/*** 判断签名是否正确，必须包含sign字段，否则返回false。** @param data Map类型数据* @param key API密钥* @param signType 签名方式* @return boolean 签名是否正确* @exception Exception*/public static boolean isSignatureValid(Map<String, String> data, String key, SignType signType) throws Exception {if (!data.containsKey(WXPayConstants.FIELD_SIGN) ) {return false;}String sign = data.get(WXPayConstants.FIELD_SIGN);return generateSignature(data, key, signType).equals(sign);}/*** 生成签名* @param data  待签名数据* @param key  API密钥* @return String* @see Exception*/public static String generateSignature(final Map<String, String> data, String key) throws Exception {return generateSignature(data, key, SignType.MD5);}/*** 生成签名. 注意，若含有sign_type字段，必须和signType参数保持一致。** @param data 待签名数据* @param key API密钥* @param signType 签名方式* @return  String 签名* @see Exception*/public static String generateSignature(final Map<String, String> data, String key, SignType signType) throws Exception {Set<String> keySet = data.keySet();String[] keyArray = keySet.toArray(new String[keySet.size()]);Arrays.sort(keyArray);StringBuilder sb = new StringBuilder();for (String k : keyArray) {if (k.equals(WXPayConstants.FIELD_SIGN)) {continue;}if (data.get(k).trim().length() > 0) // 参数值为空，则不参与签名sb.append(k).append("=").append(data.get(k).trim()).append("&");}sb.append("key=").append(key);if (SignType.MD5.equals(signType)) {return MD5(sb.toString()).toUpperCase();}else if (SignType.HMACSHA256.equals(signType)) {return HMACSHA256(sb.toString(), key);}else {throw new Exception(String.format("Invalid sign_type: %s", signType));}}/*** 获取随机字符串 Nonce Str** @return String 随机字符串*/public static String generateNonceStr() {return UUID.randomUUID().toString().replaceAll("-", "").substring(0, 32);}/***** @param data 待处理数据* @return String MD5结果* @see Exception*/public static String MD5(String data) throws Exception {MessageDigest md = MessageDigest.getInstance("MD5");byte[] array = md.digest(data.getBytes("UTF-8"));StringBuilder sb = new StringBuilder();for (byte item : array) {sb.append(Integer.toHexString((item & 0xFF) | 0x100).substring(1, 3));}return sb.toString().toUpperCase();}/*** 生成 HMACSHA256* @param data 待处理数据* @param key 密钥* @return String 加密结果* @see  Exception*/public static String HMACSHA256(String data, String key) throws Exception {Mac sha256_HMAC = Mac.getInstance("HmacSHA256");SecretKeySpec secret_key = new SecretKeySpec(key.getBytes("UTF-8"), "HmacSHA256");sha256_HMAC.init(secret_key);byte[] array = sha256_HMAC.doFinal(data.getBytes("UTF-8"));StringBuilder sb = new StringBuilder();for (byte item : array) {sb.append(Integer.toHexString((item & 0xFF) | 0x100).substring(1, 3));}return sb.toString().toUpperCase();}/*** 日志* @return Logger*/public static Logger getLogger() {Logger logger = LoggerFactory.getLogger("wxpay java sdk");return logger;}/*** 获取当前时间戳，单位秒* @return long*/public static long getCurrentTimestamp() {return System.currentTimeMillis()/1000;}/*** 当前时间的下一个月:* @return String*/public static String getcuentime() {Calendar cal = Calendar.getInstance();cal.add(cal.MONTH, 1);SimpleDateFormat dft = new SimpleDateFormat("yyyy-MM-dd-HH-mm");String preMonth = dft.format(cal.getTime());System.out.println(preMonth);return preMonth;}/*** 给时间在加上一个月:* @param cur 时间参数* @return Date*/public Date getNewDate(Date cur) {  Calendar c = Calendar.getInstance();  c.setTime(cur);   //设置时间c.add(Calendar.MINUTE, 1); //日期分钟加1,Calendar.DATE(天),Calendar.HOUR(小时)  Date date = c.getTime(); //结果  return date;}/*** 获取当前时间戳，单位毫秒* @return long*/public static long getCurrentTimestampMs() {return System.currentTimeMillis();}/*** 生成 uuid， 即用来标识一笔单，也用做 nonce_str* @return String*/public static String generateUUID() {return UUID.randomUUID().toString().replaceAll("-", "").substring(0, 32);}/*** map 转换为* @param map* @return*/public  static String sunx(Map<String, String> map) {String  xmlResult="";StringBuffer sb = new StringBuffer();sb.append("<xml>");for (String key : map.keySet()) {sb.append("<" + key + ">" + map.get(key) + "</" + key + ">");System.out.println();}sb.append("</xml>");xmlResult = sb.toString();return xmlResult;}}

HttpUtils.java:

package com.youquan.utli;import com.alibaba.fastjson.JSONObject;
import org.apache.http.HttpResponse;
import org.apache.http.HttpStatus;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;import java.io.IOException;
import java.net.URLDecoder;
/*** <p>User: qrn* <p>Date: 14-1-28* <p>Version: 1.0* 描述: http请求的工具类*/
public class HttpUtils {private static Logger logger = LoggerFactory.getLogger(HttpUtils.class);    //日志记录/*** httpPost** @param url       路径* @param jsonParam 参数* @return JSONObject*/public static JSONObject httpPost(String url, String jsonParam) {return httpPost(url, jsonParam, false);}/*** post请求** @param url            url地址* @param param      参数* @param noNeedResponse 不需要返回结果* @return JSONObject*/public static JSONObject httpPost(String url, String param, boolean noNeedResponse) {//post请求返回结果HttpClient httpClient = HttpClients.createDefault();JSONObject jsonResult = null;HttpPost method = new HttpPost(url);try {if (null != param) {//解决中文乱码问题StringEntity entity = new StringEntity(param, "utf-8");entity.setContentEncoding("UTF-8");entity.setContentType("application/json");method.setEntity(entity);}HttpResponse result = httpClient.execute(method);url = URLDecoder.decode(url, "UTF-8");/**请求发送成功，并得到响应**/if (result.getStatusLine().getStatusCode() == 200) {String str = "";try {/**读取服务器返回过来的json字符串数据**/str = EntityUtils.toString(result.getEntity());System.out.println(str);if (noNeedResponse) {return null;}/**把json字符串转换成json对象**/jsonResult = JSONObject.parseObject(str);} catch (Exception e) {logger.error("post请求提交失败:" + url, e);}}} catch (IOException e) {logger.error("post请求提交失败:" + url, e);}return jsonResult;}/*** post请求** @param url            url地址* @param param      参数* @return String*/public static String httpXMLPost(String url, String param) {//post请求返回结果HttpClient httpClient = HttpClients.createDefault();String xmlResult = null;HttpPost method = new HttpPost(url);try {if (null != param) {//解决中文乱码问题StringEntity entity = new StringEntity(param, "utf-8");entity.setContentEncoding("utf-8");entity.setContentType("text/xml");method.setEntity(entity);}HttpResponse result = httpClient.execute(method);url = URLDecoder.decode(url, "utf-8");/**请求发送成功，并得到响应**/if (result.getStatusLine().getStatusCode() == 200) {try {/**读取服务器返回过来的json字符串数据**/xmlResult = EntityUtils.toString(result.getEntity(),"utf-8");} catch (Exception e) {logger.error("post请求提交失败:" + url, e);}}} catch (IOException e) {logger.error("post请求提交失败:" + url, e);}return xmlResult;}/*** 发送get请求* @param url    路径* @return  JSONObject*/public static JSONObject httpGet(String url){//get请求返回结果JSONObject jsonResult = null;try {HttpClient client = HttpClients.createDefault();//发送get请求HttpGet request = new HttpGet(url);HttpResponse response = client.execute(request);/**请求发送成功，并得到响应**/if (response.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {/**读取服务器返回过来的json字符串数据**/String strResult = EntityUtils.toString(response.getEntity());/**把json字符串转换成json对象**/jsonResult = JSONObject.parseObject(strResult);url = URLDecoder.decode(url, "UTF-8");} else {logger.error("get请求提交失败:" + url);}} catch (IOException e) {logger.error("get请求提交失败:" + url, e);}return jsonResult;}}

好了支付的代码就到这里了，拿到参数在前端使用小程序

wx.requestPayment(
{
'timeStamp': '',
'nonceStr': '',
'package': '',
'signType': 'MD5',
'paySign': '',
'success':function(res){},
'fail':function(res){},
'complete':function(res){}
})

把上面的参数填充就可以调用支付了，如果没有问题那么支付就成功了