1.封裝工具類：

　　包括的方法實現：

　　　　xml轉Map，Map轉xml，生成微信支付簽名sign，簽名的校驗，把Map轉為SortMap(有序)

package net.xdclass.xdvideo.controller;

import net.xdclass.xdvideo.config.WeChatConfig;
import net.xdclass.xdvideo.domain.JsonData;
import net.xdclass.xdvideo.domain.User;
import net.xdclass.xdvideo.domain.VideoOrder;
 
import net.xdclass.xdvideo.service.UserService;
import net.xdclass.xdvideo.service.VideoOrderService;
import net.xdclass.xdvideo.utils.CommonUtils;
import net.xdclass.xdvideo.utils.JwtUtils;
import net.xdclass.xdvideo.utils.WXPayUtil;
import org.springframework.beans.factory.annotation.Autowired;
 
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;
import
 
 org.w3c.dom.Node;
import org.w3c.dom.NodeList;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
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.*;
import java.net.URLEncoder;
import java.util.*;

@Controller
@RequestMapping("/api/v1/wechat")
public class WechatController {

    @Autowired
    private WeChatConfig weChatConfig;

    @Autowired
    private UserService userService;


    @Autowired
    private VideoOrderService videoOrderService;

    /**
     * 拼裝微信掃一掃登錄url
     * @return
     */
    @GetMapping("login_url")
    @ResponseBody
    public JsonData loginUrl(@RequestParam(value = "access_page",required = true)String accessPage) throws UnsupportedEncodingException {

        String redirectUrl = weChatConfig.getOpenRedirectUrl(); //獲取開放平臺重定向地址

        String callbackUrl = URLEncoder.encode(redirectUrl,"GBK"); //進行編碼

        String qrcodeUrl = String.format(weChatConfig.getOpenQrcodeUrl(),weChatConfig.getOpenAppid(),callbackUrl,accessPage);

        return JsonData.buildSuccess(qrcodeUrl);
    }


    /**
     * 微信掃碼登錄，回調地址
     * @param code
     * @param state
     * @param response
     * @throws IOException
     */
    @GetMapping("/user/callback")
    public void wechatUserCallback(@RequestParam(value = "code",required = true) String code,
                                   String state, HttpServletResponse response) throws IOException {


        User user = userService.saveWeChatUser(code);
        if(user != null){
            //生成jwt
            String token = JwtUtils.geneJsonWebToken(user);
            // state 當前用戶的頁面地址，需要拼接 http://  這樣才不會站內跳轉

            response.sendRedirect(state+"?token="+token+"&head_img="+user.getHeadImg()+"&name="+URLEncoder.encode(user.getName(),"UTF-8"));
        }


    }


    package net.xdclass.xdvideo.utils;

import org.w3c.dom.Entity;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

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.util.*;

    /**
     * 微信支付工具類，xml轉map,map轉xml，生成簽名
     */
    public class WXPayUtil {

        /**
         * XML格式字符串轉換為Map
         *
         * @param strXML XML字符串
         * @return XML數據轉換後的Map
         * @throws 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) {
                throw ex;
            }

        }

        /**
         * 將Map轉換為XML格式的字符串
         *
         * @param data Map類型數據
         * @return XML格式的字符串
         * @throws 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;
        }


        /**
         * 生成微信支付sign
         * @return
         */
        public static String createSign(SortedMap<String, String> params, String key){
            StringBuilder sb = new StringBuilder();
            Set<Map.Entry<String, String>> es =  params.entrySet();
            Iterator<Map.Entry<String,String>> it =  es.iterator();

            //生成 stringA="appid=wxd930ea5d5a258f4f&body=test&device_info=1000&mch_id=10000100&nonce_str=ibuaiVcKdpRxkhJA";
            while (it.hasNext()){
                Map.Entry<String,String> entry = (Map.Entry<String,String>)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=").append(key);
            String sign = CommonUtils.MD5(sb.toString()).toUpperCase();
            return sign;
        }


        /**
         * 校驗簽名
         * @param params
         * @param key
         * @return
         */
        public static boolean isCorrectSign(SortedMap<String, String> params, String key){
            String sign = createSign(params,key);

            String weixinPaySign = params.get("sign").toUpperCase();

            return weixinPaySign.equals(sign);
        }


        /**
         * 獲取有序map
         * @param map
         * @return
         */
        public static SortedMap<String,String> getSortedMap(Map<String,String> map){

            SortedMap<String, String> sortedMap = new TreeMap<>();
            Iterator<String> it =  map.keySet().iterator();
            while (it.hasNext()){
                String key  = (String)it.next();
                String value = map.get(key);
                String temp = "";
                if( null != value){
                    temp = value.trim();
                }
                sortedMap.put(key,temp);
            }
            return sortedMap;
        }

    }


}

2.根據配置的回調url開發controller：

　　掃碼後返回給回調url的結果是個xml字符串：

package net.xdclass.xdvideo.controller;

import net.xdclass.xdvideo.config.WeChatConfig;
import net.xdclass.xdvideo.domain.JsonData;
import net.xdclass.xdvideo.domain.User;
import net.xdclass.xdvideo.domain.VideoOrder;
import net.xdclass.xdvideo.service.UserService;
import net.xdclass.xdvideo.service.VideoOrderService;
import net.xdclass.xdvideo.utils.JwtUtils;
import net.xdclass.xdvideo.utils.WXPayUtil;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.*;
import java.net.URLEncoder;
import java.util.Date;
import java.util.Map;
import java.util.SortedMap;

@Controller
@RequestMapping("/api/v1/wechat")
public class WechatController {

    @Autowired
    private WeChatConfig weChatConfig;

    @Autowired
    private UserService userService;


    @Autowired
    private VideoOrderService videoOrderService;

    /**
     * 拼裝微信掃一掃登錄url
     * @return
     */
    @GetMapping("login_url")
    @ResponseBody
    public JsonData loginUrl(@RequestParam(value = "access_page",required = true)String accessPage) throws UnsupportedEncodingException {

        String redirectUrl = weChatConfig.getOpenRedirectUrl(); //獲取開放平臺重定向地址

        String callbackUrl = URLEncoder.encode(redirectUrl,"GBK"); //進行編碼

        String qrcodeUrl = String.format(weChatConfig.getOpenQrcodeUrl(),weChatConfig.getOpenAppid(),callbackUrl,accessPage);

        return JsonData.buildSuccess(qrcodeUrl);
    }


    /**
     * 微信掃碼登錄，回調地址
     * @param code
     * @param state
     * @param response
     * @throws IOException
     */
    @GetMapping("/user/callback")
    public void wechatUserCallback(@RequestParam(value = "code",required = true) String code,
                                   String state, HttpServletResponse response) throws IOException {


        User user = userService.saveWeChatUser(code);
        if(user != null){
            //生成jwt
            String token = JwtUtils.geneJsonWebToken(user);
            // state 當前用戶的頁面地址，需要拼接 http://  這樣才不會站內跳轉

            response.sendRedirect(state+"?token="+token+"&head_img="+user.getHeadImg()+"&name="+URLEncoder.encode(user.getName(),"UTF-8"));
        }


    }


    /**
     * 微信支付回調
     */
    @RequestMapping("/order/callback")
    public void orderCallback(HttpServletRequest request,HttpServletResponse response) throws Exception {

        InputStream inputStream =  request.getInputStream();

        //BufferedReader是包裝設計模式，性能更搞
        BufferedReader in =  new BufferedReader(new InputStreamReader(inputStream,"UTF-8"));
        StringBuffer sb = new StringBuffer();
        String line ;
        while ((line = in.readLine()) != null){
            sb.append(line);
        }
        in.close();
        inputStream.close();
        Map<String,String> callbackMap = WXPayUtil.xmlToMap(sb.toString());
        System.out.println(callbackMap.toString());

        SortedMap<String,String> sortedMap = WXPayUtil.getSortedMap(callbackMap);

        //判斷簽名是否正確
        if(WXPayUtil.isCorrectSign(sortedMap,weChatConfig.getKey())){

            if("SUCCESS".equals(sortedMap.get("result_code"))){
                //獲取訂單流水號
                String outTradeNo = sortedMap.get("out_trade_no");
                //根據訂單流水號獲取訂單信息
                VideoOrder dbVideoOrder = videoOrderService.findByOutTradeNo(outTradeNo);
                //判斷邏輯看業務場景，狀態是否為未支付0，是的話更新訂單信息
                if(dbVideoOrder != null && dbVideoOrder.getState()==0){
                    VideoOrder videoOrder = new VideoOrder();
                    videoOrder.setOpenid(sortedMap.get("openid"));
                    videoOrder.setOutTradeNo(outTradeNo);
                    videoOrder.setNotifyTime(new Date());
                    videoOrder.setState(1);
                    int rows = videoOrderService.updateVideoOderByOutTradeNo(videoOrder);
                    if(rows == 1){ //通知微信訂單處理成功
                        response.setContentType("text/xml");
                        response.getWriter().println("success");
                        return;
                    }
                }
            }
        }
        //都處理失敗
        response.setContentType("text/xml");
        response.getWriter().println("fail");

    }
}

文檔參考：https://pay.weixin.qq.com/wiki/doc/api/app/app.php?chapter=9_7&index=3

微信支付：回調處理