Java怎样实现支付宝电脑支付基于servlet版本

package cn.taosir.demo;

public class AlipayConfig {
  // 页面跳转同步通知页面路径 需http://格式的完整路径，不能加?id=123这类自定义参数
  public static String return_url = "http://localhost:8080/success.jsp";
  // 服务器异步通知页面路径 需http://格式的完整路径，不能加?id=123这类自定义参数，必须外网可以正常访问
  public static String notify_url = "http://localhost:8080/notify";
  // 应用ID,您的APPID，收款账号既是您的APPID对应支付宝账号
  public static String app_id = "";
  // 支付宝公钥,查看地址：https://openhome.alipay.com/platform/keyManage.htm 对应APPID下的支付宝公钥。
  public static String alipay_public_key = "";
  // 商户私钥，您的PKCS8格式RSA2私钥
  public static String merchant_private_key = "";
  // 签名方式
  public static String sign_type = "RSA2";
  // 字符编码格式
  public static String charset = "utf-8";
  // 支付宝网关
  public static String gatewayUrl = "https://openapi.alipaydev.com/gateway.do";
}

package cn.taosir.demo;

import java.io.IOException;
import java.util.Map;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/notify")
public class NotifyServlet extends HttpServlet{
  @Override
  protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    System.out.println("接收到支付宝的异步通知请求——");
    Map<String,String[]> parameterMap=request.getParameterMap();
    System.out.println(parameterMap);
    //成功处理后返回success
    response.getWriter().write("success");
  }
}

package cn.taosir.demo;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Calendar;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.alipay.api.AlipayApiException;
import com.alipay.api.AlipayClient;
import com.alipay.api.DefaultAlipayClient;
import com.alipay.api.request.AlipayTradePagePayRequest;
import com.alipay.api.response.AlipayTradePagePayResponse;

@WebServlet("/order/confirm")
public class OrderServlet extends HttpServlet{
  @Override
  protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    System.out.println("开始处理OrderServlet的服务");
    String title = "涛先森";
    String total = "666666";
    String message = "如有什么建议欢迎留言评论";
    //生成订单号
    SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyyMMddHHmmss");
    String orderSn = simpleDateFormat.format(Calendar.getInstance().getTime());
    //向支付宝发送请求
    //获得初始化的AlipayClient
    AlipayClient alipayClient = new DefaultAlipayClient(AlipayConfig.gatewayUrl, AlipayConfig.app_id,
        AlipayConfig.merchant_private_key, "json", AlipayConfig.charset, AlipayConfig.alipay_public_key,
        AlipayConfig.sign_type);
    //设置请求参数
    AlipayTradePagePayRequest alipayRequest = new AlipayTradePagePayRequest();
    alipayRequest.setReturnUrl(AlipayConfig.return_url);
    alipayRequest.setNotifyUrl(AlipayConfig.notify_url);
    //商户订单号，商户网站订单系统中唯一订单号，必填
    String out_trade_no = orderSn;
    //付款金额，必填
    String total_amount = total;
    //订单名称，必填
    String subject = title;
    //商品描述，可空
    String body = message;
    alipayRequest.setBizContent("{\"out_trade_no\":\"" + out_trade_no + "\"," + "\"total_amount\":\""
        + total_amount + "\"," + "\"subject\":\"" + subject + "\"," + "\"body\":\"" + body + "\","
        + "\"product_code\":\"FAST_INSTANT_TRADE_PAY\"}");
    //若想给BizContent增加其他可选请求参数，以增加自定义超时时间参数timeout_express来举例说明
    //alipayRequest.setBizContent("{\"out_trade_no\":\""+ out_trade_no +"\"," 
    //    + "\"total_amount\":\""+ total_amount +"\"," 
    //    + "\"subject\":\""+ subject +"\"," 
    //    + "\"body\":\""+ body +"\"," 
    //    + "\"timeout_express\":\"10m\"," 
    //    + "\"product_code\":\"FAST_INSTANT_TRADE_PAY\"}");
    //请求参数可查阅【电脑网站支付的API文档-alipay.trade.page.pay-请求参数】章节
    AlipayTradePagePayResponse alipayResponse = null;
    try {
      alipayResponse=alipayClient.pageExecute(alipayRequest);
      System.out.println(alipayResponse.getBody());
       System.out.println(alipayResponse.getMsg());
    } catch (AlipayApiException e) {
      e.printStackTrace();
    }
    response.setContentType("text/html;charset=UTF-8");
    response.getWriter().write(alipayResponse.getBody());
  }
}