生成java对接web端微信支付的demo

我可以提供一个参考实现：

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

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONObject;

public class WeChatPayDemo {

    public static void main(String[] args) throws IOException {
        // 微信支付接口地址
        String url = "https://api.mch.weixin.qq.com/pay/unifiedorder";
        // 组装请求参数
        Map<String, String> params = getParams();
        // 发起请求
        String result = sendPost(url, params);
        // 解析响应结果
        JSONObject jsonObject = JSON.parseObject(result);
        String return_code = jsonObject.getString("return_code");
        String return_msg = jsonObject.getString("return_msg");
        if (return_code.equals("SUCCESS")) {
            String result_code = jsonObject.getString("result_code");
            if (result_code.equals("SUCCESS")) {
                // 微信支付订单号
                String prepay_id = jsonObject.getString("prepay_id");
                // 构建微信支付参数
                Map<String, String> payParams = buildPayParams(prepay_id);
                // 调起微信支付
                invokeWeChatPay(payParams);
            }
        }
    }

    /**
     * 发送post请求
     * 
     * @param url
     *            请求地址
     * @param params
     *            请求参数
     * @return
     * @throws IOException
     */
    public static String sendPost(String url, Map<String, String> params) throws IOException {
        PrintWriter out = null;
        BufferedReader in = null;
        StringBuilder result = new StringBuilder();
        try {
            URL realUrl = new URL(url);
            URLConnection conn = realUrl.openConnection();
            conn.setRequestProperty("accept", "*/*");
            conn.setRequestProperty("connection", "Keep-Alive");
            conn.setRequestProperty("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1;SV1)");
            conn.setDoOutput(true);
            conn.setDoInput(true);
            out = new PrintWriter(conn.getOutputStream());
            String param = buildParams(params);
            out.print(param);
            out.flush();
            in = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            String line;
            while ((line = in.readLine()) != null) {
                result.append(line);
            }
        } finally {
            try {
                if (out != null) {
                    out.close();
                }
                if (in != null) {
                    in.close();
                }
            } catch (IOException ex) {
                ex.printStackTrace();
            }
        }
        return result.toString();
    }

    /**
     * 组装请求参数
     * 
     * @return
     */
    public static Map<String, String> getParams() {
        // TODO 组装请求参数
        return null;
    }

    /**
     * 构建请求参数字符串
     * 
     * @param params
     *            请求参数
     * @return
     */
    public static String buildParams(Map<String, String> params) {
        StringBuilder sb = new StringBuilder();
        for (Map.Entry<String, String> entry : params.entrySet()) {
            sb.append(entry.getKey()).append("=").append(entry.getValue()).append("&");
        }
        return sb.substring(0, sb.length() - 1);
    }

    /**
     * 构建微信支付参数
     * 
     * @param prepay_id
     *            预支付订单号
     * @return
     */
    public static Map<String, String> buildPayParams(String prepay_id) {
        // TODO 构建微信支付参数
        return null;
    }

    /**
     * 调起微信支付
     * 
     * @param payParams
     *            微信支付参数
     */
    public static void invokeWeChatPay(Map<String, String> payParams) {
        // TODO 调起微信支付
    }
}