在开发微信小程序支付的功能前，我们先熟悉下微信小程序支付的业务流程图：

不熟悉流程的建议还是仔细阅读微信官方的开发者文档。

一，准备工作

事先需要申请企业版小程序，并开通“微信支付”（即商户功能）。并获取一下参数：

appid=******** //小程序appid
mchid=******** //小程序绑定商户id
key=***************** //商户后台设置的key
并在商户后天设置开发者选项，主要是设置回调域名。

二，Java后台代码编写

Controller层代码：

@RestController
@RequestMapping(value = "/payment/")
public class PaymentController {

private static Logger logger = LoggerFactory.getLogger(PaymentController.class);
@Value("${hcc.wx.domain}")
private String orderDomain;

@Autowired
private PaymentService paymentService;

/**
* <p>统一下单入口</p>
*
* @param request
* @param response
* @throws Exception
*/
@ResponseBody
@RequestMapping(value="toPay", method=RequestMethod.POST,
produces ={"application/json;charset=UTF-8"})
public JSONObject toPay(HttpServletRequest request) throws Exception {
String requestStr = RequestStr.getRequestStr(request);
if (StringUtils.isEmpty(requestStr)) {
throw new ParamException();
}
JSONObject jsonObj = JSONObject.parseObject(requestStr);
if(StringUtils.isEmpty(jsonObj.getString("orderNo")) || StringUtils.isEmpty(jsonObj.getString("openId"))){
throw new ParamException();
}
OrderInfo orderInfo = .....//此处写获取订单信息方法
if(orderInfo == null){
return AjaxUtil.renderFailMsg("订单不存在！");
}else if(orderInfo.getPayAmount() == null || orderInfo.getPayAmount() <= 0){
return AjaxUtil.renderFailMsg("订单有误，请确认！");
}else if(orderInfo.getOrderStatus() != 1){//1待付款
String msg = orderInfo.getOrderStatus() >1 ?"此订单已支付！":"订单未提交，请确认！";
return AjaxUtil.renderFailMsg(msg);
}else{
logger.info("【小程序支付服务】请求订单编号:["+orderInfo.getOrderNo()+"]");
Map<String, String> resMap = paymentService.xcxPayment(+orderInfo.getOrderNo(),orderInfo.getPayAmount(),jsonObj.getString("openId"));
if("SUCCESS".equals(resMap.get("returnCode")) && "OK".equals(resMap.get("returnMsg"))){
//统一下单成功
resMap.remove("returnCode");
resMap.remove("returnMsg");
logger.info("【小程序支付服务】支付下单成功！");
return AjaxUtil.renderSuccessMsg(resMap);
}else{
logger.info("【小程序支付服务】支付下单失败！原因:"+resMap.get("returnMsg"));
return AjaxUtil.renderFailMsg(resMap.get("returnMsg"));
}
}

}
/**
* <p>回调Api</p>
*
* @param request
* @param response
* @throws Exception
*/
@RequestMapping(value="xcxNotify")
public void xcxNotify(HttpServletRequest request,HttpServletResponse response) throws Exception {
InputStream inputStream = request.getInputStream();
//获取请求输入流
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
byte[] buffer = new byte[1024];
int len = 0;
while ((len=inputStream.read(buffer))!=-1){
outputStream.write(buffer,0,len);
}
outputStream.close();
inputStream.close();
Map<String,Object> map = BeanToMap.getMapFromXML(new String(outputStream.toByteArray(),"utf-8"));
logger.info("【小程序支付回调】 回调数据： \n"+map);
String resXml = "";
String returnCode = (String) map.get("return_code");
if ("SUCCESS".equalsIgnoreCase(returnCode)) {
String returnmsg = (String) map.get("result_code");
if("SUCCESS".equals(returnmsg)){
//更新数据
int result = paymentService.xcxNotify(map);
if(result > 0){
//支付成功
resXml = "<xml>" + "<return_code><![CDATA[SUCCESS]]></return_code>"
+ "<return_msg><![CDATA[OK]]></return_msg>"+"</xml>";
}
}else{
resXml = "<xml>" + "<return_code><![CDATA[FAIL]]></return_code>"
+ "<return_msg><![CDATA[报文为空]></return_msg>" + "</xml>";
logger.info("支付失败:"+resXml);
}
}else{
resXml = "<xml>" + "<return_code><![CDATA[FAIL]]></return_code>"
+ "<return_msg><![CDATA[报文为空]></return_msg>" + "</xml>";
logger.info("【订单支付失败】");
}

logger.info("【小程序支付回调响应】 响应内容：\n"+resXml);
response.getWriter().print(resXml);
}
}
Service接口层代码（部分代码）：

/**
* <p>支付接口层</p>
*
* @author att
* @date 2018年5月27日
* @since jdk1.8
* @version 1.0
*/
public interface PaymentService {

Map<String,String> xcxPayment(String orderNo, double money,String openId) throws Exception;

int xcxNotify(Map<String,Object> map) throws Exception;
}
Service接口实现（部分代码）：

@Service(value = "paymentService")
public class PaymentServiceImpl implements PaymentService{
private static Logger LOGGER = LoggerFactory.getLogger(PaymentServiceImpl.class);

@Value("${spring.profiles.active}")
private String PROJECT_ENV;

@Value("${hcc.wx.domain}")
private String orderDomain;

@Autowired
private PaymentRecordMapper paymentRecordMapper;
@Autowired
private PaymentNotifyMapper paymentNotifyMapper;

@Override
public Map<String, String> xcxPayment(String orderNum, double money,String openId) throws Exception {
LOGGER.info("【小程序支付】 统一下单开始, 订单编号="+orderNum);
SortedMap<String, String> resultMap = new TreeMap<String, String>();
//生成支付金额，开发环境处理支付金额数到0.01、0.02、0.03元
double payAmount = PayUtil.getPayAmountByEnv(PROJECT_ENV, money);
//添加或更新支付记录(参数跟进自己业务需求添加)
int flag = this.addOrUpdatePaymentRecord(orderNum, payAmount,.....);
if(flag < 0){
resultMap.put("returnCode", "FAIL");
resultMap.put("returnMsg", "此订单已支付！");
LOGGER.info("【小程序支付】 此订单已支付！");
}else if(flag == 0){
resultMap.put("returnCode", "FAIL");
resultMap.put("returnMsg", "支付记录生成或更新失败！");
LOGGER.info("【小程序支付】 支付记录生成或更新失败！");
}else{
Map<String,String> resMap = this.xcxUnifieldOrder(orderNum, PayConfig.TRADE_TYPE_JSAPI, payAmount,openId);
if(PayConstant.SUCCESS.equals(resMap.get("return_code")) && PayConstant.SUCCESS.equals(resMap.get("result_code"))){
resultMap.put("appId", PayConfig.XCX_APP_ID);
resultMap.put("timeStamp", PayUtil.getCurrentTimeStamp());
resultMap.put("nonceStr", PayUtil.makeUUID(32));
resultMap.put("package", "prepay_id="+resMap.get("prepay_id"));
resultMap.put("signType", "MD5");
resultMap.put("sign", PayUtil.createSign(resultMap,PayConfig.XCX_KEY));
resultMap.put("returnCode", "SUCCESS");
resultMap.put("returnMsg", "OK");
LOGGER.info("【小程序支付】统一下单成功，返回参数:"+resultMap);
}else{
resultMap.put("returnCode", resMap.get("return_code"));
resultMap.put("returnMsg", resMap.get("return_msg"));
LOGGER.info("【小程序支付】统一下单失败，失败原因:"+resMap.get("return_msg"));
}
}
return resultMap;
}

/**
* 小程序支付统一下单
*/
private Map<String,String> xcxUnifieldOrder(String orderNum,String tradeType, double payAmount,String openid) throws Exception{
//封装参数
SortedMap<String,String> paramMap = new TreeMap<String,String>();
paramMap.put("appid", PayConfig.XCX_APP_ID);
paramMap.put("mch_id", PayConfig.XCX_MCH_ID);
paramMap.put("nonce_str", PayUtil.makeUUID(32));
paramMap.put("body", BaseConstants.PLATFORM_COMPANY_NAME);
paramMap.put("out_trade_no", orderNum);
paramMap.put("total_fee", PayUtil.moneyToIntegerStr(payAmount));
paramMap.put("spbill_create_ip", PayUtil.getLocalIp());
paramMap.put("notify_url", this.getNotifyUrl());
paramMap.put("trade_type", tradeType);
paramMap.put("openid",openid);
paramMap.put("sign", PayUtil.createSign(paramMap,PayConfig.XCX_KEY));
//转换为xml
String xmlData = PayUtil.mapToXml(paramMap);
//请求微信后台，获取预支付ID
String resXml = HttpUtils.postData(PayConfig.WX_PAY_UNIFIED_ORDER, xmlData);
LOGGER.info("【小程序支付】 统一下单响应：\n"+resXml);
return PayUtil.xmlStrToMap(resXml);
}

private String getNotifyUrl(){
//服务域名
return PayConfig.PRO_SERVER_DOMAIN + "/wxapp/payment/xcxNotify";
}

/**
* 添加或更新支付记录
*/
@Override
public int addOrUpdatePaymentRecord(String orderNo, double payAmount,......) throws Exception{
//写自己的添加或更新支付记录的业务代码
return 0;
}

@Override
@Transactional(readOnly=false,rollbackFor={Exception.class})
public int xcxNotify(Map<String,Object> map) throws Exception{
int flag = 0;
//支付订单编号
String orderNo = (String)map.get("out_trade_no");
//检验是否需要再次回调刷新数据
//TODO 微信后台回调，刷新订单支付状态等相关业务

return flag;
}
PayUtil工具类：

/**
* Function: 支付工具类 <br/>
* date: 2018-01-18 <br/>
*
* @author att
* @version 1.0
* @since JDK1.8
* @see
*/
public class PayUtil {

static Logger log = LogManager.getLogger(PayUtil.class.getName());
/**
* 获取当前机器的ip
*
* @return String
*/
public static String getLocalIp(){
InetAddress ia=null;
String localip = null;
try {
ia=ia.getLocalHost();
localip=ia.getHostAddress();
} catch (Exception e) {
e.printStackTrace();
}
return localip;

}

/**
* Map转换为 Xml
*
* @param data
* @return Xml
* @throws Exception
*/
public static String mapToXml(SortedMap<String, String> map) throws Exception {
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
//防止XXE攻击
documentBuilderFactory.setXIncludeAware(false);
documentBuilderFactory.setExpandEntityReferences(false);
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: map.keySet()) {
String value = map.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();
try {
writer.close();
}
catch (Exception ex) {
}
return output;
}

/**
* 创建签名Sign
*
* @param key
* @param parameters
* @return
*/
public static String createSign(SortedMap<String,String> parameters,String key){
StringBuffer sb = new StringBuffer();
Set es = parameters.entrySet();
Iterator<?> it = es.iterator();
while(it.hasNext()) {
Map.Entry entry = (Map.Entry)it.next();
String k = (String)entry.getKey();
if(entry.getValue() != null || !"".equals(entry.getValue())) {
String v = String.valueOf(entry.getValue());
if (null != v && !"".equals(v) && !"sign".equals(k) && !"key".equals(k)) {
sb.append(k + "=" + v + "&");
}
}
}
sb.append("key=" + key);
String sign = MD5Util.MD5Encode(sb.toString(), "UTF-8").toUpperCase();
return sign;
}


/**
* XML转换为Map
*
* @param strXML
* @return Map
* @throws Exception
*/
public static Map<String, Object> getMapFromXML(String strXML) throws Exception {
try {
Map<String, Object> data = new HashMap<String, Object>();
DocumentBuilderFactory documentBuilderFactory = DocumentBuilderFactory.newInstance();
//防止XXE攻击
documentBuilderFactory.setXIncludeAware(false);
documentBuilderFactory.setExpandEntityReferences(false);
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) {
ex.printStackTrace();
}
return data;
} catch (Exception ex) {
throw ex;
}
}

/**
* 生成随机数
*
* @return
*/
public static String makeUUID(int len) {
return UUID.randomUUID().toString().replaceAll("-", "").substring(0, len);
}

/**
* 获取当前的Timestamp
*
* @return
*/
public static String getCurrentTimeStamp() {
return Long.toString(System.currentTimeMillis()/1000);
}

/**
* 获取当前的时间
* @return
*/
public static long getCurrentTimestampMs() {
return System.currentTimeMillis();
}

/**
* 生成订单号
*
* @return
*/
public static String generateOrderNo() {
SimpleDateFormat sdf = new SimpleDateFormat("yyMMdd");
return sdf.format(new Date())+makeUUID(16);
}

/**
* 获取当前工程url
*
* @param request
* @return
*/
public static String getCurrentUrl(HttpServletRequest request){
return request.getScheme() +"://" + request.getServerName() + ":" +request.getServerPort() +request.getContextPath();
}

/**
* Xml字符串转换为Map
*
* @param xmlStr
* @return
*/
public static Map<String,String> xmlStrToMap(String xmlStr){
Map<String,String> map = new HashMap<String,String>();
Document doc;
try {
doc = DocumentHelper.parseText(xmlStr);
Element root = doc.getRootElement();
List children = root.elements();
if(children != null && children.size() > 0) {
for(int i = 0; i < children.size(); i++) {
Element child = (Element)children.get(i);
map.put(child.getName(), child.getTextTrim());
}
}
} catch (DocumentException e) {
e.printStackTrace();
}
return map;
}

public static String getSceneInfo(String wapUrl,String name){
Map<String,Map<String,String>> map = new HashMap<String, Map<String,String>>();
if(!StringUtils.isEmpty(wapUrl) && !StringUtils.isEmpty(name)){
/*{"h5_info": {"type":"Wap","wap_url": "https://pay.qq.com","wap_name": "腾讯充值"}}*/
Map<String,String> childmap = new TreeMap<String, String>();
childmap.put("type", "Wap");
childmap.put("wap_url",wapUrl);
childmap.put("wap_name", name);
map.put("h5_info", childmap);
return JSON.toJSONString(map);
}
return null;
}

/**
* 转换金额型到整型
* @param money
* @return
*/
public static String moneyToIntegerStr(Double money){
BigDecimal decimal = new BigDecimal(money);
int amount = decimal.multiply(new BigDecimal(100))
.setScale(0, BigDecimal.ROUND_HALF_UP).intValue();
return String.valueOf(amount);
}

/**
* 除去数组中的空值和签名参数
* @param sArray 签名参数组
* @return 去掉空值与签名参数后的新签名参数组
*/
public static Map<String, String> paraFilter(Map<String, String> sArray) {

Map<String, String> result = new HashMap<String, String>();

if (sArray == null || sArray.size() <= 0) {
return result;
}

for (String key : sArray.keySet()) {
String value = sArray.get(key);
if (value == null || value.equals("") || key.equalsIgnoreCase("sign")
|| key.equalsIgnoreCase("sign_type")) {
continue;
}
result.put(key, value);
}

return result;
}

/**
* 把数组所有元素排序，并按照“参数=参数值”的模式用“&”字符拼接成字符串
* @param params 需要排序并参与字符拼接的参数组
* @return 拼接后字符串
*/
public static String createLinkString(Map<String, String> params) {
List<String> keys = new ArrayList<String>(params.keySet());
Collections.sort(keys);
String prestr = "";
for (int i = 0; i < keys.size(); i++) {
String key = keys.get(i);
String value = params.get(key);
if (i == keys.size() - 1) {//拼接时，不包括最后一个&字符
prestr = prestr + key + "=" + value;
} else {
prestr = prestr + key + "=" + value + "&";
}
}
return prestr;
}

/**
* 根据不同环境生成支付金额
*
* @param env
* @param money
* @param payType
* @return
*/
public static double getPayAmountByEnv(String env,Double money){
double pay_money = 0.01;
//测试环境
if(BaseConstants.PLATFORM_ENV_DEV.equals(env)){
if(money>10000){
pay_money = 0.03;
}else if(money>1000){
pay_money = 0.02;
}else{
pay_money = 0.01;
}
return pay_money;
}else{
//生成环境
return money;
}
}
}
支付配置类：

/**
* Function: 支付配置 <br/>
* date: 2018-01-18 <br/>
*
* @author att
* @version 1.0
* @since JDK1.8
*/
public class PayConfig {

//微信支付类型
//NATIVE--原生支付
//JSAPI--公众号支付-小程序支付
//MWEB--H5支付
//APP -- app支付
public static final String TRADE_TYPE_NATIVE = "NATIVE";
public static final String TRADE_TYPE_JSAPI = "JSAPI";
public static final String TRADE_TYPE_MWEB = "MWEB";
public static final String TRADE_TYPE_APP = "APP";

//小程序支付参数
public static String XCX_APP_ID;
public static String XCX_MCH_ID;
public static String XCX_KEY;

//微信支付API
public static final String WX_PAY_UNIFIED_ORDER = "https://api.mch.weixin.qq.com/pay/unifiedorder";

//参数
static{
Properties properties = new Properties();
try {
properties.load(PayConstant.class.getClassLoader().getResourceAsStream("payment_config.properties"));
//xcx
XCX_APP_ID=(String) properties.get("xcx.pay.appid");
XCX_MCH_ID=(String) properties.get("xcx.pay.mchid");
XCX_KEY=(String) properties.get("xcx.pay.key");
} catch (Exception e) {
e.printStackTrace();
}
}
}
Properties配置：

##config
xcx.pay.appid=wx**********
xcx.pay.mchid=*****
xcx.pay.key=**********
三，小程序端（获取统一下单返回参数发起支付）

在小程序端，发起支付请求到，Java后台的统一下单接口返回prepay_id等参数，然后封装调起微信的js方法：wx.requestPayment(OBJECT)，具体参考文档：官方文档

测试一把：

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---------------------
作者：键盘客
来源：CSDN
原文：https://blog.csdn.net/u011134780/article/details/90609548
版权声明：本文为博主原创文章，转载请附上博文链接！