feat(firestore): add firestore recursive delete sample

firestore/samples/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  Copyright 2026 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.
+-->
+<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xmlns="http://maven.apache.org/POM/4.0.0"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <groupId>com.example.firestore</groupId>
+  <artifactId>firestore-samples</artifactId>
+  <version>1.0-SNAPSHOT</version>
+
+  <!--
+   The parent pom defines common style checks and testing strategies for our samples.
+   Removing or replacing it should not affect the execution of the samples in anyway.
+  -->
+  <parent>
+    <artifactId>shared-configuration</artifactId>
+    <groupId>com.google.cloud.samples</groupId>
+    <version>1.2.2</version>
+  </parent>
+
+  <properties>
+    <maven.compiler.source>21</maven.compiler.source>
+    <maven.compiler.target>21</maven.compiler.target>
+  </properties>
+
+  <dependencyManagement>
+    <dependencies>
+      <dependency>
+        <artifactId>libraries-bom</artifactId>
+        <groupId>com.google.cloud</groupId>
+        <scope>import</scope>
+        <type>pom</type>
+        <version>26.80.0</version>
+      </dependency>
+    </dependencies>
+  </dependencyManagement>
+
+  <dependencies>
+    <dependency>
+      <groupId>com.google.cloud</groupId>
+      <artifactId>google-cloud-firestore</artifactId>
+    </dependency>
+
+    <!-- Test dependencies -->
+    <dependency>
+      <artifactId>truth</artifactId>
+      <groupId>com.google.truth</groupId>
+      <scope>test</scope>
+      <version>1.4.5</version>
+    </dependency>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter</artifactId>
+      <version>5.14.3</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>

firestore/samples/src/main/java/com/example/firestore/DeleteCollection.java

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+/*
+ * Copyright 2026 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.
+ */
+
+package com.example.firestore;
+
+// [START firestore_data_delete_collection]
+
+import com.google.api.core.ApiFuture;
+import com.google.cloud.firestore.CollectionReference;
+import com.google.cloud.firestore.Firestore;
+import com.google.cloud.firestore.FirestoreOptions;
+
+public class DeleteCollection {
+
+  /**
+   * Delete a collection and all its subcollections.
+   *
+   * @param projectId The Google Cloud project ID
+   * @param collectionName The name of the collection to delete
+   */
+  public static void deleteCollection(String projectId, String collectionName) throws Exception {
+    FirestoreOptions firestoreOptions =
+        FirestoreOptions.getDefaultInstance().toBuilder().setProjectId(projectId).build();
+    try (Firestore db = firestoreOptions.getService()) {
+      CollectionReference collection = db.collection(collectionName);
+
+      ApiFuture<Void> future = db.recursiveDelete(collection);
+
+      future.get();
+      System.out.println("Collection and all its subcollections deleted successfully.");
+    }
+  }
+
+  public static void main(String[] args) throws Exception {
+    String projectId = "example-project-id";
+    String collectionName = "example-collection-name";
+
+    deleteCollection(projectId, collectionName);
+  }
+}
+// [END firestore_data_delete_collection]

firestore/samples/src/test/java/com/example/firestore/DeleteCollectionIT.java

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+/*
+ * Copyright 2026 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.
+ */
+
+package com.example.firestore;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+public class DeleteCollectionIT {
+
+  private static ByteArrayOutputStream bout;
+  private static PrintStream prevPrintStream;
+  private static final String PROJECT_ID = System.getenv("GOOGLE_CLOUD_PROJECT");
+  private static final String COLLECTION_NAME = "usa-cities";
+  private static final String DOCUMENT_NAME = "LA";
+  private static final String NAME = "Los Angeles";
+
+  private static String getEnvVar(String varName) {
+    String value = System.getenv(varName);
+    assertNotNull(
+        String.format("Environment variable '%s' must be set to perform these tests.", varName),
+        value);
+    return value;
+  }
+
+  @BeforeAll
+  public static void setUp() throws Exception {
+    getEnvVar("GOOGLE_CLOUD_PROJECT");
+
+    // Create collection
+    Utils.createCollection(PROJECT_ID, COLLECTION_NAME, DOCUMENT_NAME, NAME);
+
+    prevPrintStream = System.out;
+    bout = new ByteArrayOutputStream();
+    System.setOut(new PrintStream(bout));
+  }
+
+  @AfterAll
+  public static void tearDown() {
+    System.setOut(prevPrintStream);
+  }
+
+  @Test
+  public void testDeleteCollection() throws Exception {
+    DeleteCollection.deleteCollection(PROJECT_ID, COLLECTION_NAME);
+
+    String output = bout.toString();
+    assertTrue(output.contains("Collection and all its subcollections deleted successfully."));
+  }
+}

firestore/samples/src/test/java/com/example/firestore/Utils.java

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+/*
+ * Copyright 2026 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.
+ */
+
+package com.example.firestore;
+
+import com.google.api.core.ApiFuture;
+import com.google.cloud.firestore.Firestore;
+import com.google.cloud.firestore.FirestoreOptions;
+import com.google.cloud.firestore.WriteResult;
+import java.util.HashMap;
+import java.util.Map;
+
+public class Utils {
+  public static void createCollection(
+      String projectId, String collectionName, String documentName, String name) throws Exception {
+    // Create collection and document to be deleted
+    FirestoreOptions firestoreOptions =
+        FirestoreOptions.getDefaultInstance().toBuilder().setProjectId(projectId).build();
+    try (Firestore db = firestoreOptions.getService()) {
+
+      Map<String, Object> docData = new HashMap<>();
+      docData.put("name", name);
+      ApiFuture<WriteResult> future =
+          db.collection(collectionName).document(documentName).set(docData);
+      future.get();
+    }
+  }
+}