Scopes.java

/*
 * Copyright 2019 Google LLC
 *
 * Licensed 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.
 */

// [START functions_tips_scopes]
// [START run_tips_global_scope]

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Arrays;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class Scopes {
  // Global (instance-wide) scope
  // This computation runs at instance cold-start.
  // Warning: Class variables used in Servlet classes must be thread-safe,
  // or else might introduce race conditions in your code.
  private static final int InstanceVar = heavyComputation();

  public void scopeDemo(HttpServletRequest request, HttpServletResponse response)
      throws IOException {
    // Per-function scope
    // This computation runs every time this function is called
    int functionVar = lightComputation();

    PrintWriter writer = response.getWriter();
    writer.write(String.format("Instance: %s; function: %s", InstanceVar, functionVar));
  }

  private static int lightComputation() {
    int[] numbers = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
    return Arrays.stream(numbers).sum();
  }

  private static int heavyComputation() {
    int[] numbers = new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
    return Arrays.stream(numbers).reduce((t, x) -> t * x).getAsInt();
  }
}
// [END run_tips_global_scope]
// [END functions_tips_scopes]