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.sessionqueue;
  
  import static java.util.Collections.singletonMap;
  import static org.openqa.selenium.remote.tracing.HttpTracing.newSpanAsChildOf;
  import static org.openqa.selenium.remote.tracing.Tags.HTTP_REQUEST;
  import static org.openqa.selenium.remote.tracing.Tags.HTTP_RESPONSE;
  
  import java.io.UncheckedIOException;
  import java.lang.reflect.Type;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import org.openqa.selenium.Capabilities;
  import org.openqa.selenium.grid.data.SessionRequest;
  import org.openqa.selenium.internal.Require;
  import org.openqa.selenium.json.Json;
  import org.openqa.selenium.json.TypeToken;
  import org.openqa.selenium.remote.http.Contents;
  import org.openqa.selenium.remote.http.HttpHandler;
  import org.openqa.selenium.remote.http.HttpRequest;
  import org.openqa.selenium.remote.http.HttpResponse;
  import org.openqa.selenium.remote.tracing.Span;
  import org.openqa.selenium.remote.tracing.Tracer;
  
  class GetNextMatchingRequest implements HttpHandler {
    private static final Type MAP_OF_CAPABILITIES = new TypeToken<Map<String, Long>>() {}.getType();
    private static final Json JSON = new Json();
  
    private final Tracer tracer;
    private final NewSessionQueue queue;
  
    public GetNextMatchingRequest(Tracer tracer, NewSessionQueue queue) {
      this.tracer = Require.nonNull("Tracer", tracer);
      this.queue = Require.nonNull("New session queue", queue);
    }
  
    @Override
    public HttpResponse execute(HttpRequest req) throws UncheckedIOException {
      try (Span span = newSpanAsChildOf(tracer, req, "sessionqueue.getrequest")) {
        HTTP_REQUEST.accept(span, req);
        Map<String, Long> stereotypesJson = Contents.fromJson(req, MAP_OF_CAPABILITIES);
  
        Map<Capabilities, Long> stereotypes = new HashMap<>();
  
        stereotypesJson.forEach(
            (k, v) -> {
              Capabilities caps = JSON.toType(k, Capabilities.class);
              stereotypes.put(caps, v);
            });
  
        List<SessionRequest> sessionRequestList = queue.getNextAvailable(stereotypes);
  
        HttpResponse response =
            new HttpResponse().setContent(Contents.asJson(singletonMap("value", sessionRequestList)));
  
        HTTP_RESPONSE.accept(span, response);
  
        return response;
      }
    }
  }
  