feat: Add Functions tips scopes (GoogleCloudPlatform#1586)

* feat: Add functions_tips_scopes

* Fix: Fix tests by debugging locally

* Update functions/snippets/src/main/java/Scopes.java

Co-Authored-By: Kurtis Van Gent <31518063+kurtisvg@users.noreply.github.com>

* fix: functions_tips_scopes add util methods

* Update Scopes.java

* Update Scopes.java

Author: grant

functions/snippets/src/main/java/Scopes.java

@@ -0,0 +1,53 @@
+/*
+ * 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]
+
+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 functions_tips_scopes]

functions/snippets/src/test/java/SnippetsTests.java

@@ -156,6 +156,13 @@ public void parseContentTypeTest_form() throws IOException {
     assertThat(responseOut.toString(), containsString("Hello John!"));
   }
 
+  @Test
+  public void scopesTest() throws IOException {
+    new Scopes().scopeDemo(request, response);
+
+    assertThat(responseOut.toString(), containsString("Instance:"));
+  }
+
   @Test
   public void retrieveLogsTest() throws IOException {
     new RetrieveLogs().retrieveLogs(request, response);