code: // Licensed to the Software Freedom Conservancy (SFC) under one
  // or more contributor license agreements.  See the NOTICE file
  // distributed with this work for additional information
  // regarding copyright ownership.  The SFC licenses this file
  // to you under the Apache License, Version 2.0 (the
  // "License"); you may not use this file except in compliance
  // with the License.  You may obtain a copy of the License at
  //
  //   http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing,
  // software distributed under the License is distributed on an
  // "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  // KIND, either express or implied.  See the License for the
  // specific language governing permissions and limitations
  // under the License.
  
  package org.openqa.selenium.grid.web;
  
  import static com.google.common.net.MediaType.JSON_UTF_8;
  import static java.net.HttpURLConnection.HTTP_NOT_FOUND;
  import static java.nio.charset.StandardCharsets.UTF_8;
  import static org.openqa.selenium.remote.ErrorCodes.UNKNOWN_COMMAND;
  import static org.openqa.selenium.remote.http.Contents.bytes;
  
  import com.google.common.collect.ImmutableMap;
  import java.io.UncheckedIOException;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.Map;
  import org.openqa.selenium.internal.Require;
  import org.openqa.selenium.json.Json;
  import org.openqa.selenium.remote.http.HttpHandler;
  import org.openqa.selenium.remote.http.HttpRequest;
  import org.openqa.selenium.remote.http.HttpResponse;
  
  public class NoHandler implements HttpHandler {
  
    private final Json json;
  
    public NoHandler(Json json) {
      this.json = Require.nonNull("Json converter", json);
    }
  
    @Override
    public HttpResponse execute(HttpRequest req) throws UncheckedIOException {
      // We're not using ImmutableMap for the outer map because it disallows null values.
      Map<String, Object> responseMap = new HashMap<>();
      responseMap.put("sessionId", null);
      responseMap.put("status", UNKNOWN_COMMAND);
      responseMap.put(
          "value",
          ImmutableMap.of(
              "error", "unknown command",
              "message",
                  String.format(
                      "Unable to find command matching %s to %s", req.getMethod(), req.getUri()),
              "stacktrace", ""));
      responseMap = Collections.unmodifiableMap(responseMap);
  
      byte[] payload = json.toJson(responseMap).getBytes(UTF_8);
  
      return new HttpResponse()
          .setStatus(HTTP_NOT_FOUND)
          .setHeader("Content-Type", JSON_UTF_8.toString())
          .setHeader("Content-Length", String.valueOf(payload.length))
          .setContent(bytes(payload));
    }
  }
  