Spring Integration channel adapter code samples

pom.xml

@@ -89,6 +89,7 @@
         <module>pubsub/cloud-client</module>
         <module>spanner/cloud-client</module>
         <module>speech/cloud-client</module>
+        <module>spring/pubsub</module>
         <module>storage/cloud-client</module>
         <module>storage/json-api</module>
         <module>storage/storage-transfer</module>

spring/pubsub/README.md

@@ -0,0 +1,144 @@
+# Getting started with Spring Integration channel adapters for Google Cloud Pub/Sub
+
+This is a sample application that uses Spring Integration and Spring Boot to read and write messages
+to Google Cloud Pub/Sub.
+
+PubsubApplication is a typical Spring Boot application. We declare all the necessary beans for the
+application to work in the `PubsubApplication` class. The most important ones are the inbound and
+outbound channel adapters.
+
+## Channel adapters
+
+On Spring Integration, channel adapters are adapters that send or receive messages from external
+systems, convert them to/from an internal Spring message representation and read/write them to a
+Spring channel, which can then have other components attached to it, such as service activators.
+
+### Inbound channel adapter
+
+PubsubInboundChannelAdapter is Spring Cloud GCP Pub/Sub inbound channel adapter class. It's declared
+in the user app as follows:
+
+```
+@Bean
+public PubsubInboundChannelAdapter messageChannelAdapter(
+    @Qualifier("pubsubInputChannel") MessageChannel inputChannel,
+    SubscriberFactory subscriberFactory) {
+  PubsubInboundChannelAdapter adapter =
+      new PubsubInboundChannelAdapter(subscriberFactory, "messages");
+  adapter.setOutputChannel(inputChannel);
+  adapter.setAckMode(AckMode.MANUAL);
+
+  return adapter;
+}
+```
+
+In the example, we instantiate the `PubsubInboundChannelAdapter` object with a SubscriberFactory and
+a Google Cloud Pub/Sub subscription name, from where the adapter listens to messages, and then set
+its output channel and ack mode.
+
+In apps which use the Spring Cloud GCP Pubsub Boot starter, a SubscriberFactory is automatically
+provided. The subscription name (e.g., `"messages"`) is the name of a Google Cloud Pub/Sub
+subscription that must already exist when the channel adapter is created.
+
+The input channel is a channel in which messages get into Spring from an external system.
+In this example, we use a PublishSubscribeChannel, which broadcasts incoming messages to all its
+subscribers, including service activators.
+
+```
+@Bean
+public MessageChannel pubsubInputChannel() {
+  return new PublishSubscribeChannel();
+}
+```
+
+Setting the acknowledgement mode on the inbound channel adapter is optional. It is set to automatic
+by default. If set to manual, messages must be explicitly acknowledged through the
+`AckReplyConsumer` object from the Spring message header `GcpHeader.ACKNOWLEDGEMENT`.
+
+```
+AckReplyConsumer consumer =
+    (AckReplyConsumer) message.getHeaders().get(GcpHeaders.ACKNOWLEDGEMENT);
+consumer.ack();
+```
+
+A service activator is typically attached to a channel in order to process incoming messages. Here
+is an example of a service activator that logs and acknowledges the received message.
+
+```
+@Bean
+@ServiceActivator(inputChannel = "pubsubInputChannel")
+public MessageHandler messageReceiver1() {
+  return message -> {
+    LOGGER.info("Message arrived! Payload: "
+        + ((ByteString) message.getPayload()).toStringUtf8());
+    AckReplyConsumer consumer =
+        (AckReplyConsumer) message.getHeaders().get(GcpHeaders.ACKNOWLEDGEMENT);
+    consumer.ack();
+  };
+}
+```
+
+### Outbound channel adapter
+
+PubSubMessageHandler is Spring Cloud GCP's Pub/Sub outbound channel adapter. It converts Spring
+messages in a channel to an external representation and sends them to a Google Cloud Pub/Sub topic.
+
+```
+@Bean
+@ServiceActivator(inputChannel = "pubsubOutputChannel")
+public MessageHandler messageSender(PubsubTemplate pubsubTemplate) {
+  PubsubMessageHandler outboundAdapter = new PubsubMessageHandler(pubsubTemplate);
+  outboundAdapter.setTopic("test");
+  return outboundAdapter;
+}
+```
+
+`PubsubTemplate` is Spring Cloud GCP's abstraction to send messages to Google Cloud Pub/Sub. It
+contains the logic to create a Google Cloud Pub/Sub `Publisher`, convert Spring messages to Google
+Cloud Pub/Sub `PubsubMessage` and publish them to a topic.
+
+`PubsubMessageHandler` requires a `PubsubTemplate` to be instantiated. The Spring Cloud GCP Boot
+Pubsub starter provides a pre-configured `PubsubTemplate`, ready to use. `PubsubMessageHandler`
+also requires the name of a Google Cloud Pub/Sub topic, which must exist before any messages are
+sent.
+
+We use a messaging gateway to write to a Spring channel.
+
+```
+@MessagingGateway(defaultRequestChannel = "pubsubOutputChannel")
+public interface PubsubOutboundGateway {
+
+  void sendToPubsub(String text);
+}
+```
+
+Spring auto-generates the output channel, as well as the gateway code and injects it to the local
+variable in `WebAppController`.
+
+```
+@Autowired
+private PubsubOutboundGateway messagingGateway;
+```
+
+## Administration
+
+The Spring Cloud GCP Pubsub package provides a Google Cloud Pub/Sub administration utility,
+`PubsubAdmin`, to simplify the creation, listing and deletion of Google Cloud Pub/Sub topics and
+subscriptions. The Spring Cloud GCP Pubsub starter provides a pre-configured `PubsubAdmin`, based on
+an application's properties.
+
+```
+@Autowired
+private PubsubAdmin admin;
+```
+
+## Sample application
+
+This sample application uses Spring Boot and Spring Web to declare a REST controller. The front-end
+uses client-side scripting with Angular.
+
+It is exemplified how to:
+* Send messages to a Google Cloud Pub/Sub topic through an outbound channel adapter;
+* Receive and process messages from a Google Cloud Pub/Sub subscription through an inbound channel
+adapter;
+* Create new Google Cloud Pub/Sub topics and subscriptions through the Pub/Sub admin utility.

spring/pubsub/pom.xml

@@ -0,0 +1,120 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <parent>
+    <artifactId>doc-samples</artifactId>
+    <groupId>com.google.cloud</groupId>
+    <version>1.0.0</version>
+    <relativePath>../..</relativePath>
+  </parent>
+  <modelVersion>4.0.0</modelVersion>
+  <packaging>jar</packaging>
+
+  <artifactId>spring-integration-pubsub-samples</artifactId>
+
+  <properties>
+    <spring-cloud-gcp.version>1.0.0.BUILD-SNAPSHOT</spring-cloud-gcp.version>
+    <spring-boot.version>1.5.2.RELEASE</spring-boot.version>
+  </properties>
+
+  <dependencies>
+    <dependency>
+      <groupId>org.springframework.cloud</groupId>
+      <artifactId>spring-cloud-gcp-starter-pubsub</artifactId>
+      <version>${spring-cloud-gcp.version}</version>
+    </dependency>
+    <dependency>
+      <groupId>org.springframework.cloud</groupId>
+      <artifactId>spring-integration-gcp</artifactId>
+      <version>${spring-cloud-gcp.version}</version>
+    </dependency>
+    <dependency>
+      <groupId>org.springframework.boot</groupId>
+      <artifactId>spring-boot-starter-web</artifactId>
+      <version>${spring-boot.version}</version>
+    </dependency>
+  </dependencies>
+
+  <!-- Angular -->
+
+  <build>
+    <resources>
+      <resource>
+        <directory>src/main/resources</directory>
+      </resource>
+      <resource>
+        <directory>${project.build.directory}/generated-resources</directory>
+      </resource>
+    </resources>
+    <plugins>
+      <plugin>
+        <groupId>org.springframework.boot</groupId>
+        <artifactId>spring-boot-maven-plugin</artifactId>
+        <version>1.5.2.RELEASE</version>
+      </plugin>
+      <plugin>
+        <artifactId>maven-resources-plugin</artifactId>
+        <version>3.0.1</version>
+        <executions>
+          <execution>
+            <!-- Serves *only* to filter the wro.xml so it can get an absolute
+              path for the project -->
+            <id>copy-resources</id>
+            <phase>validate</phase>
+            <goals>
+              <goal>copy-resources</goal>
+            </goals>
+            <configuration>
+              <outputDirectory>${basedir}/target/wro</outputDirectory>
+              <resources>
+                <resource>
+                  <directory>src/main/wro</directory>
+                  <filtering>true</filtering>
+                </resource>
+              </resources>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+      <plugin>
+        <groupId>ro.isdc.wro4j</groupId>
+        <artifactId>wro4j-maven-plugin</artifactId>
+        <version>1.7.6</version>
+        <executions>
+          <execution>
+            <phase>generate-resources</phase>
+            <goals>
+              <goal>run</goal>
+            </goals>
+          </execution>
+        </executions>
+        <configuration>
+          <wroManagerFactory>ro.isdc.wro.maven.plugin.manager.factory.ConfigurableWroManagerFactory</wroManagerFactory>
+          <cssDestinationFolder>${project.build.directory}/generated-resources/static/css</cssDestinationFolder>
+          <jsDestinationFolder>${project.build.directory}/generated-resources/static/js</jsDestinationFolder>
+          <wroFile>${project.build.directory}/wro/wro.xml</wroFile>
+          <extraConfigFile>src/main/wro/wro.properties</extraConfigFile>
+          <contextFolder>${basedir}/src/main/wro</contextFolder>
+        </configuration>
+        <dependencies>
+          <dependency>
+            <groupId>org.webjars</groupId>
+            <artifactId>jquery</artifactId>
+            <version>2.1.1</version>
+          </dependency>
+          <dependency>
+            <groupId>org.webjars</groupId>
+            <artifactId>angularjs</artifactId>
+            <version>1.3.8</version>
+          </dependency>
+          <dependency>
+            <groupId>org.webjars</groupId>
+            <artifactId>bootstrap</artifactId>
+            <version>3.2.0</version>
+          </dependency>
+        </dependencies>
+      </plugin>
+    </plugins>
+  </build>
+</project>