java Paypal IPN 开发

Java Paypal IPN开发可以参照以下步骤进行：

1. 在Paypal账户中设置IPN（Instant Payment Notification），并将IPN URL设置为您的服务器上的Java Servlet。

2. 在Java代码中实现一个Servlet来接收Paypal发送的IPN信息，并解析该信息。

3. 验证Paypal发送的IPN信息的有效性。可以使用Paypal提供的IPN验证工具或者手动验证。

4. 对接收到的IPN信息进行处理，例如更新订单状态或发送电子邮件通知等。

以下是Java Paypal IPN开发的示例代码：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.net.URLEncoder;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.HashMap;
import java.util.Map;

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

public class IPNServlet extends HttpServlet {

  private static final String PAYPAL_URL = "https://www.paypal.com/cgi-bin/webscr";
  private static final String PAYPAL_SANDBOX_URL = "https://www.sandbox.paypal.com/cgi-bin/webscr";
  private static final String VERIFY_CMD = "_notify-validate";
  private static final String CHARSET = "UTF-8";
  private static final String TXN_TYPE = "txn_type";
  private static final String ITEM_NUMBER = "item_number";
  private static final String PAYMENT_STATUS = "payment_status";
  private static final String MC_GROSS = "mc_gross";
  private static final String MC_CURRENCY = "mc_currency";
  private static final String RECEIVER_EMAIL = "receiver_email";
  private static final String BUSINESS = "business";
  private static final String CUSTOM = "custom";

  private static final String PAYPAL_EMAIL = "YOUR_PAYPAL_EMAIL";
  private static final String PAYPAL_IDENTITY_TOKEN = "YOUR_PAYPAL_IDENTITY_TOKEN";

  @Override
  protected void doPost(HttpServletRequest req, HttpServletResponse resp)
      throws ServletException, IOException {
    String url = PAYPAL_URL;
    if (Boolean.parseBoolean(req.getParameter("test_ipn"))) {
      url = PAYPAL_SANDBOX_URL;
    }

    Map<String, String> params = new HashMap<String, String>();
    BufferedReader reader = new BufferedReader(new InputStreamReader(req.getInputStream()));
    String line = null;
    while ((line = reader.readLine()) != null) {
      params.putAll(parseQueryString(line));
    }
    reader.close();

    String txnType = params.get(TXN_TYPE);
    if (txnType == null) {
      resp.setStatus(HttpServletResponse.SC_BAD_REQUEST);
      return;
    }

    String itemNumber = params.get(ITEM_NUMBER);
    String paymentStatus = params.get(PAYMENT_STATUS);
    String mcGross = params.get(MC_GROSS);
    String mcCurrency = params.get(MC_CURRENCY);
    String receiverEmail = params.get(RECEIVER_EMAIL);
    String business = params.get(BUSINESS);
    String custom = params.get(CUSTOM);

    if (!PAYPAL_EMAIL.equals(receiverEmail) || !PAYPAL_IDENTITY_TOKEN.equals(custom)) {
      resp.setStatus(HttpServletResponse.SC_BAD_REQUEST);
      return;
    }

    String verifyUrl = url + "?" + VERIFY_CMD;
    for (String name : params.keySet()) {
      verifyUrl += "&" + name + "=" + URLEncoder.encode(params.get(name), CHARSET);
    }

    if (!verify(verifyUrl)) {
      resp.setStatus(HttpServletResponse.SC_BAD_REQUEST);
      return;
    }

    // Handle IPN message
  }

  private boolean verify(String url) throws IOException {
    HttpURLConnection conn = (HttpURLConnection) new URL(url).openConnection();
    conn.setRequestMethod("POST");
    conn.setDoOutput(true);
    conn.setDoInput(true);
    conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
    conn.setRequestProperty("User-Agent", "Java IPN Verification");
    conn.setRequestProperty("Host", "www.paypal.com");
    conn.setRequestProperty("Connection", "close");

    conn.getOutputStream().write(("cmd=" + VERIFY_CMD).getBytes());

    BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
    String line = null;
    while ((line = reader.readLine()) != null) {
      if ("VERIFIED".equals(line)) {
        return true;
      } else if ("INVALID".equals(line)) {
        return false;
      }
    }
    reader.close();

    return false;
  }

  private Map<String, String> parseQueryString(String queryString) throws UnsupportedEncodingException {
    Map<String, String> params = new HashMap<String, String>();
    for (String param : queryString.split("&")) {
      String pair[] = param.split("=");
      String name = URLDecoder.decode(pair[0], CHARSET);
      String value = "";
      if (pair.length > 1) {
        value = URLDecoder.decode(pair[1], CHARSET);
      }
      params.put(name, value);
    }
    return params;
  }

  private String md5(String string) {
    try {
      MessageDigest md5 = MessageDigest.getInstance("MD5");
      byte[] digest = md5.digest(string.getBytes());
      StringBuilder sb = new StringBuilder();
      for (byte b : digest) {
        sb.append(String.format("%02x", b & 0xff));
      }
      return sb.toString();
    } catch (NoSuchAlgorithmException e) {
      throw new RuntimeException(e);
    }
  }
}

以上代码中，IPNServlet类是一个Java Servlet，用于接收Paypal发送的IPN信息，验证IPN信息的有效性并进行处理。在该类中，PAYPAL_EMAIL和PAYPAL_IDENTITY_TOKEN分别为您Paypal账户的电子邮件地址和身份令牌，用于验证IPN信息是否来自Paypal。在实际的应用中，您需要替换这些值为您自己的Paypal账户信息。

在handle IPN message方法中，您可以根据接收到的IPN信息进行相应的处理，例如更新订单状态或发送电子邮件通知等。