feat(internal): DispatchHandler dispatches to registered HttpHandler by operationId

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: thced

src/main/java/com/retailsvc/http/MissingOperationHandlerException.java

@@ -0,0 +1,7 @@
+package com.retailsvc.http;
+
+public final class MissingOperationHandlerException extends RuntimeException {
+  public MissingOperationHandlerException(String operationId) {
+    super("no handler registered for operationId=" + operationId);
+  }
+}

src/main/java/com/retailsvc/http/internal/DispatchHandler.java

@@ -0,0 +1,26 @@
+package com.retailsvc.http.internal;
+
+import com.retailsvc.http.MissingOperationHandlerException;
+import com.retailsvc.http.Request;
+import com.sun.net.httpserver.HttpExchange;
+import com.sun.net.httpserver.HttpHandler;
+import java.io.IOException;
+import java.util.Map;
+
+public final class DispatchHandler implements HttpHandler {
+  private final Map<String, HttpHandler> handlers;
+
+  public DispatchHandler(Map<String, HttpHandler> handlers) {
+    this.handlers = Map.copyOf(handlers);
+  }
+
+  @Override
+  public void handle(HttpExchange exchange) throws IOException {
+    String opId = Request.operationId(exchange);
+    HttpHandler h = handlers.get(opId);
+    if (h == null) {
+      throw new MissingOperationHandlerException(opId);
+    }
+    h.handle(exchange);
+  }
+}

src/test/java/com/retailsvc/http/internal/DispatchHandlerTest.java

@@ -0,0 +1,36 @@
+package com.retailsvc.http.internal;
+
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+import com.retailsvc.http.MissingOperationHandlerException;
+import com.retailsvc.http.Request;
+import com.sun.net.httpserver.HttpExchange;
+import com.sun.net.httpserver.HttpHandler;
+import java.util.HashMap;
+import java.util.Map;
+import org.junit.jupiter.api.Test;
+import org.mockito.Mockito;
+
+class DispatchHandlerTest {
+  private final Map<String, Object> attrs = new HashMap<>();
+
+  private HttpExchange exchange(String operationId) {
+    HttpExchange ex = Mockito.mock(HttpExchange.class);
+    Mockito.when(ex.getAttribute(Request.OPERATION_ID)).thenReturn(operationId);
+    return ex;
+  }
+
+  @Test
+  void invokesRegisteredHandler() throws Exception {
+    HttpHandler handler = Mockito.mock(HttpHandler.class);
+    new DispatchHandler(Map.of("get-x", handler)).handle(exchange("get-x"));
+    Mockito.verify(handler).handle(Mockito.any());
+  }
+
+  @Test
+  void throwsWhenHandlerMissing() {
+    DispatchHandler d = new DispatchHandler(Map.of());
+    assertThatThrownBy(() -> d.handle(exchange("ghost")))
+        .isInstanceOf(MissingOperationHandlerException.class);
+  }
+}