BinancePayTool v0.1.0：币安支付个人收款网关（Go 核心 + 四语言 SDK）

- Go 服务端：唯一金额/备注码/回填订单编号三路匹配、托管收银页、HMAC 回调七级重试、SQLite 单二进制
- SDK：Go / Java / PHP / Python，共享签名测试向量（docs/test_vectors.json）
- 跨语言 e2e（真实二进制 × Python SDK × mock 币安）、GitHub Actions CI、Dockerfile
- 协议文档 docs/protocol.md、调研与实测结论 docs/research.md

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

examples/java/ExampleServer.java

@@ -0,0 +1,62 @@
+import com.bpaygate.sdk.BPayGateClient;
+import com.google.gson.JsonObject;
+import com.sun.net.httpserver.HttpServer;
+
+import java.io.ByteArrayOutputStream;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.net.InetSocketAddress;
+import java.nio.charset.StandardCharsets;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * 最小商户示例（Java 8+，无 Web 框架）。
+ * 编译运行后访问 http://127.0.0.1:9000/buy
+ */
+public class ExampleServer {
+    public static void main(String[] args) throws Exception {
+        String base = System.getenv().getOrDefault("BPG_BASE", "http://127.0.0.1:8080");
+        String secret = System.getenv().getOrDefault("BPG_SECRET", "");
+        BPayGateClient gw = new BPayGateClient(base, secret);
+
+        HttpServer srv = HttpServer.create(new InetSocketAddress("127.0.0.1", 9000), 0);
+        srv.createContext("/buy", ex -> {
+            JsonObject order = gw.createOrder("DEMO-" + System.currentTimeMillis(), "USDT", "1",
+                    "http://127.0.0.1:9000/notify", "http://127.0.0.1:9000/done", 0);
+            ex.getResponseHeaders().add("Location", order.get("pay_url").getAsString());
+            ex.sendResponseHeaders(302, -1);
+            ex.close();
+        });
+        srv.createContext("/notify", ex -> {
+            String body = readAll(ex.getRequestBody());
+            Map<String, String> headers = new HashMap<>();
+            ex.getRequestHeaders().forEach((k, v) -> headers.put(k, v.isEmpty() ? "" : v.get(0)));
+            try {
+                JsonObject payload = BPayGateClient.verifyCallback(headers, body, secret, 300000);
+                // TODO: 按 merchant_order_id 幂等发货
+                System.out.println("回调: " + payload.get("event") + " " + payload.get("merchant_order_id"));
+                ex.sendResponseHeaders(200, -1);
+            } catch (BPayGateClient.BPayGateException e) {
+                ex.sendResponseHeaders(401, -1);
+            }
+            ex.close();
+        });
+        srv.createContext("/done", ex -> {
+            byte[] b = "<h1>支付完成，感谢购买！</h1>".getBytes(StandardCharsets.UTF_8);
+            ex.getResponseHeaders().add("Content-Type", "text/html; charset=utf-8");
+            ex.sendResponseHeaders(200, b.length);
+            try (OutputStream os = ex.getResponseBody()) { os.write(b); }
+        });
+        System.out.println("商户示例: http://127.0.0.1:9000/buy");
+        srv.start();
+    }
+
+    private static String readAll(InputStream is) throws java.io.IOException {
+        ByteArrayOutputStream bos = new ByteArrayOutputStream();
+        byte[] buf = new byte[4096];
+        int n;
+        while ((n = is.read(buf)) > 0) bos.write(buf, 0, n);
+        return new String(bos.toByteArray(), StandardCharsets.UTF_8);
+    }
+}