java开发微信公众号支付（JSAPI）

https://www.cnblogs.com/gopark/p/9394951.html，这篇文章写的已经很详细了。

下面写一下自己的思路:

1.首先下载demo，地址：https://pay.weixin.qq.com/wiki/doc/api/jsapi.php?chapter=11_1

2.demo中很多方法对于公众号支付用不到，不需要全都看

3.主要是获取11个参数，放到Map中，用demo里提供WXPayUtil.mapToXml方法转为XML格式，通过post方法请求微信端的统一下单接口，后台收到微信传过来的XML字符串，通过WXPayUtil.xmlToMap方法转为Map，根据key值，获取prepay_id(预支付ID)，再把需要的6个参数放到Map中，发送给前台，前台根据prepay_id，唤起微信支付，完成付款。

4.11个参数跟6个参数在controller里面都有写，重点的是:openid

5.查看订单，取消订单等其他功能，后续接触到再进行更新

下面放上自己写的controller

package com.github.wxpay.controller;

import com.github.wxpay.sdk.WXPayConstants;
import com.github.wxpay.sdk.WXPayUtil;
import com.github.wxpay.util.Constant;
import com.github.wxpay.util.HttpRequestUtil;
import com.github.wxpay.util.OrderUtil;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import java.util.HashMap;
import java.util.Map;
import org.springframework.web.bind.annotation.RequestMapping;
import com.github.wxpay.sdk.WXPayConstants.SignType;

public class WxPayController {

    /**
     *
     * @Description 微信浏览器内微信支付/公众号支付(JSAPI)
     */
    @RequestMapping(value = "/orders",method = RequestMethod.GET)
    @ResponseBody
    public Map orders(HttpServletRequest request){
        try {
            Map<String, String> paramMap = new HashMap<String, String>();
            HttpSession session = request.getSession();
            String wxopenid = session.getAttribute("openid") == null ? null : session.getAttribute("openid").toString();
            //在商户平台的账户中心下:需要用户自行下载证书及安装
            String key = Constant.signCustomerKey;
            String ip = request.getHeader("x-forwarded-for");

            if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
                ip = request.getHeader("Proxy-Client-IP");
            }
            if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
                ip = request.getHeader("WL-Proxy-Client-IP");
            }
            if (ip == null || ip.length() == 0 || "unknown".equalsIgnoreCase(ip)) {
                ip = request.getRemoteAddr();
            }
            if (ip.indexOf(",") != -1) {
                String[] ips = ip.split(",");
                ip = ips[0].trim();
            }
            paramMap.put("appid", Constant.APPIDS[0]);
            paramMap.put("mch_id", "");
            paramMap.put("nonce_str", WXPayUtil.generateNonceStr());
            paramMap.put("body", "测试订单XX矿泉水");
            paramMap.put("openid", wxopenid);
            paramMap.put("out_trade_no", OrderUtil.orderNumber());
            paramMap.put("spbill_create_ip", ip);
            paramMap.put("total_fee", "0.01");
            paramMap.put("notify_url", "http://127.0.0.1:8080/alipay.trade.page.pay-JAVA-UTF-8/notify_url.jsp");// 此路径是微信服务器调用支付结果通知路径
            paramMap.put("trade_type", "JSAPI");
            String sign = WXPayUtil.generateSignature(paramMap,key,SignType.MD5);
            paramMap.put("sign", sign);

            // 将所有参数(map)转xml格式
            String mapToXml = WXPayUtil.mapToXml(paramMap);
            System.out.println(mapToXml);
            // 统一下单 https://api.mch.weixin.qq.com/pay/unifiedorder
            String unifiedorder_url = "https://api.mch.weixin.qq.com/pay/unifiedorder";
            // 发送post请求"统一下单接口"返回预支付id:prepay_id
            String xmlStr = HttpRequestUtil.sendPost(unifiedorder_url,mapToXml);

            Map<String,String> XmlToMap = WXPayUtil.xmlToMap(xmlStr);
            // 以下内容是返回前端页面的json数据
            String prepay_id = ""; // 预支付ID
            if (xmlStr.indexOf("SUCCESS") != -1) {
                Map<String, String> map = WXPayUtil.xmlToMap(xmlStr);
                prepay_id =  map.get("prepay_id");
            }
            Map<String, String> payMap = new HashMap<String, String>();
            XmlToMap.put("appId", Constant.APPIDS[0]);
            XmlToMap.put("timeStamp", WXPayUtil.getCurrentTimestamp()+"");
            XmlToMap.put("nonceStr", WXPayUtil.generateNonceStr());
            XmlToMap.put("signType", "MD5");
            XmlToMap.put("package", "prepay_id=" + prepay_id);
            String paySign = WXPayUtil.generateSignature(payMap, key);
            payMap.put("paySign", paySign);
            return XmlToMap;
        }catch (Exception e){
            e.printStackTrace();
        }
        return null;
    }
}
    

httpRequest工具：

package com.github.wxpay.util;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.URLConnection;
import java.util.List;
import java.net.URL;
import java.util.Map;

public class HttpRequestUtil {
    /**
     * 向指定URL发送GET方法的请求
     *
     * @param url
     *            发送请求的URL
     * @param param
     *            请求参数，请求参数应该是 name1=value1&name2=value2 的形式。
     * @return URL 所代表远程资源的响应结果
     */
    public static String sendGet(String url, String param) {
        String result = "";
        BufferedReader in = null;
        try {
            String urlNameString = url + "?" + param;
            URL realUrl = new URL(urlNameString);
            // 打开和URL之间的连接
            URLConnection connection = realUrl.openConnection();
            // 设置通用的请求属性
            connection.setRequestProperty("accept", "*/*");
            connection.setRequestProperty("connection", "Keep-Alive");
            connection.setRequestProperty("user-agent",
                    "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
            // 建立实际的连接
            connection.connect();
            // 获取所有响应头字段
            Map<String, List<String>> map = connection.getHeaderFields();
            // 遍历所有的响应头字段
            for (String key : map.keySet()) {
                System.out.println(key + "--->" + map.get(key));
            }
            // 定义 BufferedReader输入流来读取URL的响应
            in = new BufferedReader(new InputStreamReader(
                    connection.getInputStream()));
            String line;
            while ((line = in.readLine()) != null) {
                result += line;
            }
        } catch (Exception e) {
            System.out.println("发送GET请求出现异常！" + e);
            e.printStackTrace();
        }
        // 使用finally块来关闭输入流
        finally {
            try {
                if (in != null) {
                    in.close();
                }
            } catch (Exception e2) {
                e2.printStackTrace();
            }
        }
        return result;
    }

    /**
     * 向指定 URL 发送POST方法的请求
     *
     * @param url
     *            发送请求的 URL
     * @param param
     *            请求参数，请求参数应该是 name1=value1&name2=value2 的形式。
     * @return 所代表远程资源的响应结果
     */
    public static String sendPost(String url, String param) {
        PrintWriter out = null;
        BufferedReader in = null;
        String result = "";
        try {
            URL realUrl = new URL(url);
            // 打开和URL之间的连接
            URLConnection conn = realUrl.openConnection();
            // 设置通用的请求属性
            conn.setRequestProperty("accept", "*/*");
            conn.setRequestProperty("connection", "Keep-Alive");
            conn.setRequestProperty("user-agent",
                    "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
            // 发送POST请求必须设置如下两行
            conn.setDoOutput(true);
            conn.setDoInput(true);
            // 获取URLConnection对象对应的输出流
            out = new PrintWriter(conn.getOutputStream());
            // 发送请求参数
            out.print(param);
            // flush输出流的缓冲
            out.flush();
            // 定义BufferedReader输入流来读取URL的响应
            in = new BufferedReader(
                    new InputStreamReader(conn.getInputStream()));
            String line;
            while ((line = in.readLine()) != null) {
                result += line;
            }
        } catch (Exception e) {
            System.out.println("发送 POST 请求出现异常！"+e);
            e.printStackTrace();
        }
        //使用finally块来关闭输出流、输入流
        finally{
            try{
                if(out!=null){
                    out.close();
                }
                if(in!=null){
                    in.close();
                }
            }
            catch(IOException ex){
                ex.printStackTrace();
            }
        }
        return result;
    }
}

随机数工具：

package com.github.wxpay.util;


import com.github.wxpay.sdk.WXPayUtil;

public class OrderUtil {

    public static String orderNumber(){
        int r1 = (int)(Math.random()*10);
        int r2 = (int)(Math.random()*10);
        long now = WXPayUtil.getCurrentTimestampMs();
        String paymentID = String.valueOf(r1)+String.valueOf(r2)+String.valueOf(now);
        return paymentID;
    }
}