作者：苏雄伟，来自原文地址

第一步

进入小程序，下单，请求下单支付，调用小程序登录API来获取Openid（https://mp.weixin.qq.com/debug/wxadoc/dev/api/api-login.html#wxloginobject）,生成商户订单，这些都是在小程序端完成的业务。

小程序端代码

// pages/pay/pay.js
var app = getApp();
Page({
    data: {},
    onLoad: function (options) {
        // 页面初始化 options为页面跳转所带来的参数
    },
    /* 微信支付 */
    wxpay: function () {
        var that = this
        //登陆获取code
        wx.login({
            success: function (res) {
                console.log(res.code)
                //获取openid
                that.getOpenId(res.code)
            }
        });
    },
    getOpenId: function (code) {
        var that = this;
        wx.request({
            url: "https://api.weixin.qq.com/sns/jscode2session?appid=wxa142513e524e496c&secret=5d6a7d86048884e7c60f84f7aa85253c&js_code=" + code + "&grant_type=authorization_code",
            data: {},
            method: 'GET',
            success: function (res) {
                console.log('返回openId')
                console.log(res.data)
                that.generateOrder(res.data.openid)
            },
            fail: function () {
                // fail
            },
            complete: function () {
                // complete
            }
        })
    },
    /**生成商户订单 */
    generateOrder: function (openid) {
        var that = this
        //统一支付
        wx.request({
            url: 'http://localhost:8070/RMS/pay_pay.action',
            method: 'GET',
            data: {
                total_fee: '5',
                body: '支付测试',
                attach:'真假酒水'
            },
            success: function (res) {
                console.log(res)
                var pay = res.data
                //发起支付
                var timeStamp = pay[0].timeStamp;
                console.log("timeStamp:"+timeStamp)
                var packages = pay[0].package;
                console.log("package:"+packages)
                var paySign = pay[0].paySign;
                console.log("paySign:"+paySign)
                var nonceStr = pay[0].nonceStr;
                 console.log("nonceStr:"+nonceStr)
                var param = { "timeStamp": timeStamp, "package": packages, "paySign": paySign, "signType": "MD5", "nonceStr": nonceStr };
                that.pay(param)
            },
        })
    },
    /* 支付   */
    pay: function (param) {
        console.log("支付")
        console.log(param)
        wx.requestPayment({
            timeStamp: param.timeStamp,
            nonceStr: param.nonceStr,
            package: param.package,
            signType: param.signType,
            paySign: param.paySign,
            success: function (res) {
                // success
                console.log("支付")
                console.log(res)
                wx.navigateBack({
                    delta: 1, // 回退前 delta(默认为1) 页面
                    success: function (res) {
                        wx.showToast({
                            title: '支付成功',
                            icon: 'success',
                            duration: 2000
                        })
                    },
                    fail: function () {
                        // fail
                    },
                    complete: function () {
                        // complete
                    }
                })
            },
            fail: function (res) {
                // fail
                console.log("支付失败")
                console.log(res)
            },
            complete: function () {
                // complete
                console.log("pay complete")
            }
        })
    }
})

第二步

调用支付统一下单API来获取prepay_id，并将小程序调起支付数据需要签名的字段appId，timeStamp，nonceStr，package再次签名（https://pay.weixin.qq.com/wiki/doc/api/wxa/wxa_api.php?chapter=7_7&index=3）

后台代码

package cn.it.shop.action;
import java.io.ByteArrayInputStream;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import cn.it.shop.util.MessageUtil;
import cn.it.shop.util.PayUtil;
import cn.it.shop.util.PaymentPo;
import cn.it.shop.util.UUIDHexGenerator;
import net.sf.json.JSONArray;
import net.sf.json.JSONObject;
/** 
* @author 
* @version 创建时间：2017年1月21日 下午4:59:03 
* 小程序端请求的后台action，返回签名后的数据传到前台
*/
public class PayAction {
    private String total_fee;//总金额
    private String body;//商品描述
    private String detail;//商品详情    
    private String attach;//附加数据
    private String time_start;//交易起始时间
    private String time_expire;//交易结束时间 
    private String openid;//用户标识
    private JSONArray jsonArray=new JSONArray();
    public String pay() throws UnsupportedEncodingException, DocumentException{
         body = new String(body.getBytes("UTF-8"),"ISO-8859-1");  
        String appid = "替换为自己的小程序ID";//小程序ID
        String mch_id = "替换为自己的商户号";//商户号
        String nonce_str = UUIDHexGenerator.generate();//随机字符串
        String today = new SimpleDateFormat("yyyyMMddHHmmss").format(new Date());
        String code = PayUtil.createCode(8);
        String out_trade_no = mch_id+today+code;//商户订单号
        String spbill_create_ip = "替换为自己的终端IP";//终端IP
        String notify_url = "http://www.weixin.qq.com/wxpay/pay.php";//通知地址
        String trade_type = "JSAPI";//交易类型  
        String openid="替换为用户的openid";//用户标识
        /**/
        PaymentPo paymentPo = new PaymentPo();
        paymentPo.setAppid(appid);
        paymentPo.setMch_id(mch_id);
        paymentPo.setNonce_str(nonce_str);
        String newbody=new String(body.getBytes("ISO-8859-1"),"UTF-8");//以utf-8编码放入paymentPo，微信支付要求字符编码统一采用UTF-8字符编码
        paymentPo.setBody(newbody);
        paymentPo.setOut_trade_no(out_trade_no);
        paymentPo.setTotal_fee(total_fee);
        paymentPo.setSpbill_create_ip(spbill_create_ip);
        paymentPo.setNotify_url(notify_url);
        paymentPo.setTrade_type(trade_type);
        paymentPo.setOpenid(openid);
        // 把请求参数打包成数组
        Map<String, String> sParaTemp = new HashMap<String, String>();
        sParaTemp.put("appid", paymentPo.getAppid());
        sParaTemp.put("mch_id", paymentPo.getMch_id());
        sParaTemp.put("nonce_str", paymentPo.getNonce_str());
        sParaTemp.put("body",  paymentPo.getBody());
        sParaTemp.put("out_trade_no", paymentPo.getOut_trade_no());
        sParaTemp.put("total_fee",paymentPo.getTotal_fee());
        sParaTemp.put("spbill_create_ip", paymentPo.getSpbill_create_ip());
        sParaTemp.put("notify_url",paymentPo.getNotify_url());
        sParaTemp.put("trade_type", paymentPo.getTrade_type());
        sParaTemp.put("openid", paymentPo.getOpenid());
        // 除去数组中的空值和签名参数
        Map<String, String> sPara = PayUtil.paraFilter(sParaTemp);
        String prestr = PayUtil.createLinkString(sPara); // 把数组所有元素，按照“参数=参数值”的模式用“&”字符拼接成字符串
        String key = "&key=替换为商户支付密钥"; // 商户支付密钥
        //MD5运算生成签名
        String mysign = PayUtil.sign(prestr, key, "utf-8").toUpperCase();
        paymentPo.setSign(mysign);
        //打包要发送的xml
        String respXml = MessageUtil.messageToXML(paymentPo);
        // 打印respXml发现，得到的xml中有“__”不对，应该替换成“_”
        respXml = respXml.replace("__", "_");
        String url = "https://api.mch.weixin.qq.com/pay/unifiedorder";//统一下单API接口链接
        String param = respXml;
        //String result = SendRequestForUrl.sendRequest(url, param);//发起请求
        String result =PayUtil.httpRequest(url, "POST", param);
        // 将解析结果存储在HashMap中
        Map<String, String> map = new HashMap<String, String>();
         InputStream in=new ByteArrayInputStream(result.getBytes());  
        // 读取输入流
        SAXReader reader = new SAXReader();
        Document document = reader.read(in);
        // 得到xml根元素
        Element root = document.getRootElement();
        // 得到根元素的所有子节点
        @SuppressWarnings("unchecked")
        List<Element> elementList = root.elements();
        for (Element element : elementList) {
            map.put(element.getName(), element.getText());
        }
        // 返回信息
        String return_code = map.get("return_code");//返回状态码
        String return_msg = map.get("return_msg");//返回信息
        System.out.println("return_msg"+return_msg);
        JSONObject JsonObject=new JSONObject() ;
        if(return_code=="SUCCESS"||return_code.equals(return_code)){
            // 业务结果
            String prepay_id = map.get("prepay_id");//返回的预付单信息
            String nonceStr=UUIDHexGenerator.generate();
            JsonObject.put("nonceStr", nonceStr);
            JsonObject.put("package", "prepay_id="+prepay_id);
            Long timeStamp= System.currentTimeMillis()/1000;
            JsonObject.put("timeStamp", timeStamp+"");
            String stringSignTemp = "appId="+appid+"&nonceStr=" + nonceStr + "&package=prepay_id=" + prepay_id+ "&signType=MD5&timeStamp=" + timeStamp;
            //再次签名
            String paySign=PayUtil.sign(stringSignTemp, "&key=替换为自己的密钥", "utf-8").toUpperCase();
            JsonObject.put("paySign", paySign);
            jsonArray.add(JsonObject);
        }
        return "pay";
    }
    public String getTotal_fee() {
        return total_fee;
    }
    public void setTotal_fee(String total_fee) {
        this.total_fee = total_fee;
    }
    public String getBody() {
        return body;
    }
    public void setBody(String body) {
        this.body = body;
    }
    public JSONArray getJsonArray() {
        return jsonArray;
    }
    public void setJsonArray(JSONArray jsonArray) {
        this.jsonArray = jsonArray;
    }
    public String getDetail() {
        return detail;
    }
    public void setDetail(String detail) {
        this.detail = detail;
    }
    public String getAttach() {
        return attach;
    }
    public void setAttach(String attach) {
        this.attach = attach;
    }
    public String getTime_start() {
        return time_start;
    }
    public void setTime_start(String time_start) {
        this.time_start = time_start;
    }
    public String getTime_expire() {
        return time_expire;
    }
    public void setTime_expire(String time_expire) {
        this.time_expire = time_expire;
    }
    public String getOpenid() {
        return openid;
    }
    public void setOpenid(String openid) {
        this.openid = openid;
    }
}

后台业务逻辑涉及到的工具类及参数封装类

MessageUtil 
package cn.it.shop.util;
import java.io.IOException;
import java.io.Writer;
import java.util.HashMap;
import java.util.List;
import javax.servlet.http.HttpServletRequest;
import org.dom4j.Document;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import com.thoughtworks.xstream.XStream;
import com.thoughtworks.xstream.core.util.QuickWriter;
import com.thoughtworks.xstream.io.HierarchicalStreamWriter;
import com.thoughtworks.xstream.io.xml.PrettyPrintWriter;
import com.thoughtworks.xstream.io.xml.XppDriver;
public class MessageUtil {
    public static HashMap<String,String> parseXML(HttpServletRequest request) throws Exception, IOException{
        HashMap<String,String> map=new HashMap<String,String>();
        // 通过IO获得Document
        SAXReader reader = new SAXReader();
        Document doc = reader.read(request.getInputStream());
        //得到xml的根节点
        Element root=doc.getRootElement();
        recursiveParseXML(root,map);
        return map;
    }
    private static void recursiveParseXML(Element root,HashMap<String,String> map){
        //得到根节点的子节点列表
        List<Element> elementList=root.elements();
        //判断有没有子元素列表
        if(elementList.size()==0){
            map.put(root.getName(), root.getTextTrim());
        }
        else{
            //遍历
            for(Element e:elementList){
                recursiveParseXML(e,map);
            }
        }
    }
    private static XStream xstream = new XStream(new XppDriver() {
        public HierarchicalStreamWriter createWriter(Writer out) {
            return new PrettyPrintWriter(out) {
                // 对所有xml节点都增加CDATA标记
                boolean cdata = true;
                public void startNode(String name, Class clazz) {
                    super.startNode(name, clazz);
                }
                protected void writeText(QuickWriter writer, String text) {
                    if (cdata) {
                        writer.write("<![CDATA[");
                        writer.write(text);
                        writer.write("]]>");
                    } else {
                        writer.write(text);
                    }
                }
            };
        }
    });
    public static String messageToXML(PaymentPo paymentPo){
        xstream.alias("xml",PaymentPo.class);
        return xstream.toXML(paymentPo);
    }
}
PaymentPo//封装支付参数实体
package cn.it.shop.util;
/** 
* @author 
* @version 创建时间：2017年1月21日 下午4:20:52 
* 类说明 
*/
public class PaymentPo {
    private String appid;//小程序ID
    private String mch_id;//商户号
    private String device_info;//设备号
    private String nonce_str;//随机字符串
    private String sign;//签名
    private String body;//商品描述  
    private String detail;//商品详情    
    private String attach;//附加数据
    private String out_trade_no;//商户订单号
    private String fee_type;//货币类型
    private String spbill_create_ip;//终端IP
    private String time_start;//交易起始时间
    private String time_expire;//交易结束时间 
    private String goods_tag;//商品标记
    private String total_fee;//总金额
    private String notify_url;//通知地址    
    private String trade_type;//交易类型    
    private String limit_pay;//指定支付方式
    private String openid;//用户标识
    public String getAppid() {
        return appid;
    }
    public void setAppid(String appid) {
        this.appid = appid;
    }
    public String getMch_id() {
        return mch_id;
    }
    public void setMch_id(String mch_id) {
        this.mch_id = mch_id;
    }
    public String getNonce_str() {
        return nonce_str;
    }
    public void setNonce_str(String nonce_str) {
        this.nonce_str = nonce_str;
    }
    public String getSign() {
        return sign;
    }
    public void setSign(String sign) {
        this.sign = sign;
    }
    public String getBody() {
        return body;
    }
    public void setBody(String body) {
        this.body = body;
    }
    public String getOut_trade_no() {
        return out_trade_no;
    }
    public void setOut_trade_no(String out_trade_no) {
        this.out_trade_no = out_trade_no;
    }
    public String getTotal_fee() {
        return total_fee;
    }
    public void setTotal_fee(String total_fee) {
        this.total_fee = total_fee;
    }
    public String getNotify_url() {
        return notify_url;
    }
    public void setNotify_url(String notify_url) {
        this.notify_url = notify_url;
    }
    public String getTrade_type() {
        return trade_type;
    }
    public void setTrade_type(String trade_type) {
        this.trade_type = trade_type;
    }
    public String getOpenid() {
        return openid;
    }
    public void setOpenid(String openid) {
        this.openid = openid;
    }
    public String getSpbill_create_ip() {
        return spbill_create_ip;
    }
    public void setSpbill_create_ip(String spbill_create_ip) {
        this.spbill_create_ip = spbill_create_ip;
    }
    public String getDevice_info() {
        return device_info;
    }
    public void setDevice_info(String device_info) {
        this.device_info = device_info;
    }
    public String getDetail() {
        return detail;
    }
    public void setDetail(String detail) {
        this.detail = detail;
    }
    public String getAttach() {
        return attach;
    }
    public void setAttach(String attach) {
        this.attach = attach;
    }
    public String getFee_type() {
        return fee_type;
    }
    public void setFee_type(String fee_type) {
        this.fee_type = fee_type;
    }
    public String getTime_start() {
        return time_start;
    }
    public void setTime_start(String time_start) {
        this.time_start = time_start;
    }
    public String getTime_expire() {
        return time_expire;
    }
    public void setTime_expire(String time_expire) {
        this.time_expire = time_expire;
    }
    public String getGoods_tag() {
        return goods_tag;
    }
    public void setGoods_tag(String goods_tag) {
        this.goods_tag = goods_tag;
    }
    public String getLimit_pay() {
        return limit_pay;
    }
    public void setLimit_pay(String limit_pay) {
        this.limit_pay = limit_pay;
    }
}
PayUtil
package cn.it.shop.util;
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.apache.commons.codec.digest.DigestUtils;
/**
 * @author 
 * @version 创建时间：2017年1月17日 下午7:46:29 类说明
 */
public class PayUtil {
    /**
     * 签名字符串
     * @param text需要签名的字符串
     * @param key 密钥
     * @param input_charset编码格式
     * @return 签名结果
     */
    public static String sign(String text, String key, String input_charset) {
        text = text + key;
        return DigestUtils.md5Hex(getContentBytes(text, input_charset));
    }
    /**
     * 签名字符串
     *  @param text需要签名的字符串
     * @param sign 签名结果
     * @param key密钥
     * @param input_charset 编码格式
     * @return 签名结果
     */
    public static boolean verify(String text, String sign, String key, String input_charset) {
        text = text + key;
        String mysign = DigestUtils.md5Hex(getContentBytes(text, input_charset));
        if (mysign.equals(sign)) {
            return true;
        } else {
            return false;
        }
    }
    /**
     * @param content
     * @param charset
     * @return
     * @throws SignatureException
     * @throws UnsupportedEncodingException
     */
    public static byte[] getContentBytes(String content, String charset) {
        if (charset == null || "".equals(charset)) {
            return content.getBytes();
        }
        try {
            return content.getBytes(charset);
        } catch (UnsupportedEncodingException e) {
            throw new RuntimeException("MD5签名过程中出现错误,指定的编码集不对,您目前指定的编码集是:" + charset);
        }
    }
    /**
     * 生成6位或10位随机数 param codeLength(多少位)
     * @return
     */
    public static String createCode(int codeLength) {
        String code = "";
        for (int i = 0; i < codeLength; i++) {
            code += (int) (Math.random() * 9);
        }
        return code;
    }
    private static boolean isValidChar(char ch) {
        if ((ch >= '0' && ch <= '9') || (ch >= 'A' && ch <= 'Z') || (ch >= 'a' && ch <= 'z'))
            return true;
        if ((ch >= 0x4e00 && ch <= 0x7fff) || (ch >= 0x8000 && ch <= 0x952f))
            return true;// 简体中文汉字编码
        return false;
    }
    /**
     * 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;
    }
    /**
     * 
     * @param requestUrl请求地址
     * @param requestMethod请求方法
     * @param outputStr参数
     */
    public static String httpRequest(String requestUrl,String requestMethod,String outputStr){
        // 创建SSLContext
        StringBuffer buffer=null;
        try{
        URL url = new URL(requestUrl);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod(requestMethod);
        conn.setDoOutput(true);
        conn.setDoInput(true);
        conn.connect();
        //往服务器端写内容
        if(null !=outputStr){
            OutputStream os=conn.getOutputStream();
            os.write(outputStr.getBytes("utf-8"));
            os.close();
        }
        // 读取服务器端返回的内容
        InputStream is = conn.getInputStream();
        InputStreamReader isr = new InputStreamReader(is, "utf-8");
        BufferedReader br = new BufferedReader(isr);
        buffer = new StringBuffer();
        String line = null;
        while ((line = br.readLine()) != null) {
                      buffer.append(line);
        }
        }catch(Exception e){
            e.printStackTrace();
        }
        return buffer.toString();
        }   
    public static String urlEncodeUTF8(String source){
        String result=source;
        try {
            result=java.net.URLEncoder.encode(source, "UTF-8");
        } catch (UnsupportedEncodingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return result;
    }
}
UUIDHexGenerator
package cn.it.shop.util;
import java.net.InetAddress;
/**
 * @author 
 * @version 创建时间：2017年1月17日 下午7:45:06 类说明
 */
public class UUIDHexGenerator {
    private static String sep = "";
    private static final int IP;
    private static short counter = (short) 0;
    private static final int JVM = (int) (System.currentTimeMillis() >>> 8);
    private static UUIDHexGenerator uuidgen = new UUIDHexGenerator();
    static {
        int ipadd;
        try {
            ipadd = toInt(InetAddress.getLocalHost().getAddress());
        } catch (Exception e) {
            ipadd = 0;
        }
        IP = ipadd;
    }
    public static UUIDHexGenerator getInstance() {
        return uuidgen;
    }
    public static int toInt(byte[] bytes) {
        int result = 0;
        for (int i = 0; i < 4; i++) {
            result = (result << 8) - Byte.MIN_VALUE + (int) bytes[i];
        }
        return result;
    }
    protected static String format(int intval) {
        String formatted = Integer.toHexString(intval);
        StringBuffer buf = new StringBuffer("00000000");
        buf.replace(8 - formatted.length(), 8, formatted);
        return buf.toString();
    }
    protected static String format(short shortval) {
        String formatted = Integer.toHexString(shortval);
        StringBuffer buf = new StringBuffer("0000");
        buf.replace(4 - formatted.length(), 4, formatted);
        return buf.toString();
    }
    protected static int getJVM() {
        return JVM;
    }
    protected synchronized static short getCount() {
        if (counter < 0) {
            counter = 0;
        }
        return counter++;
    }
    protected static int getIP() {
        return IP;
    }
    protected static short getHiTime() {
        return (short) (System.currentTimeMillis() >>> 32);
    }
    protected static int getLoTime() {
        return (int) System.currentTimeMillis();
    }
    public static String generate() {
        return new StringBuffer(36).append(format(getIP())).append(sep).append(format(getJVM())).append(sep)
                .append(format(getHiTime())).append(sep).append(format(getLoTime())).append(sep)
                .append(format(getCount())).toString();
    }
    /**
     * @param args
     */
    public static void main(String[] args) {
        String id="";
        UUIDHexGenerator uuid = UUIDHexGenerator.getInstance();
        /*
        for (int i = 0; i < 100; i++) {
            id = uuid.generate();
        }*/
        id = uuid.generate();
        System.out.println(id);
    }
}

第一次写，写的不是太完整，希望同大家多多交流，一起进步。

安卓系统源代码是什么语言