New example for Dapr's Grpc invoke using Java.

README.md

@@ -19,10 +19,11 @@ Then head over to build the Maven project:
 mvn install
 ```
 
-### Running an example
-```sh
-dapr run --protocol grpc --grpc-port 50001 -- mvn exec:java -pl examples -Dexec.mainClass=io.dapr.examples.Example
-```
+### Running the examples
+Try the following examples to learn more about Dapr's Java SDK:
+* [Invoking a service via Grpc](./examples/src/main/java/io/dapr/examples/invoke/grpc)
+* [State management over Grpc](./examples/src/main/java/io/dapr/examples/state/grpc)
+* [State management over HTTP](./examples/src/main/java/io/dapr/examples/state/http)
 
 ### Creating and publishing the artifacts to Nexus Repository
 From the root directory:

examples/pom.xml

@@ -15,17 +15,91 @@
   <version>0.3.0-alpha</version>
   <name>dapr-sdk-examples</name>
 
+  <properties>
+    <protobuf.output.directory>${project.build.directory}/generated-sources</protobuf.output.directory>
+    <protobuf.input.directory>${project.parent.basedir}/proto</protobuf.input.directory>
+  </properties>
+
   <dependencies>
+    <dependency>
+      <groupId>commons-cli</groupId>
+      <artifactId>commons-cli</artifactId>
+      <version>1.4</version>
+    </dependency>
     <dependency>
       <groupId>org.json</groupId>
       <artifactId>json</artifactId>
       <version>20190722</version>
     </dependency>
+    <dependency>
+      <groupId>io.grpc</groupId>
+      <artifactId>grpc-protobuf</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>io.grpc</groupId>
+      <artifactId>grpc-stub</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>javax.annotation</groupId>
+      <artifactId>javax.annotation-api</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>io.grpc</groupId>
+      <artifactId>grpc-testing</artifactId>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>com.google.protobuf</groupId>
+      <artifactId>protobuf-java-util</artifactId>
+      <version>${protobuf.version}</version>
+    </dependency>
+    <dependency>
+      <groupId>com.github.os72</groupId>
+      <artifactId>protoc-jar-maven-plugin</artifactId>
+      <version>3.10.1</version>
+    </dependency>
     <dependency>
       <groupId>io.dapr</groupId>
       <artifactId>dapr-sdk</artifactId>
       <version>0.3.0-alpha</version>
     </dependency>
   </dependencies>
 
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>com.github.os72</groupId>
+        <artifactId>protoc-jar-maven-plugin</artifactId>
+        <version>3.10.1</version>
+        <executions>
+          <execution>
+            <phase>generate-sources</phase>
+            <goals>
+              <goal>run</goal>
+            </goals>
+            <configuration>
+              <protocVersion>${protobuf.version}</protocVersion>
+              <addProtoSources>inputs</addProtoSources>
+              <includeMavenTypes>direct</includeMavenTypes>
+              <includeStdTypes>true</includeStdTypes>
+              <inputDirectories>
+                <include>${protobuf.input.directory}/examples</include>
+              </inputDirectories>
+              <outputTargets>
+                <outputTarget>
+                  <type>java</type>
+                  <outputDirectory>${protobuf.output.directory}</outputDirectory>
+                </outputTarget>
+                <outputTarget>
+                  <type>grpc-java</type>
+                  <outputDirectory>${protobuf.output.directory}</outputDirectory>
+                  <pluginArtifact>io.grpc:protoc-gen-grpc-java:${grpc.version}</pluginArtifact>
+                </outputTarget>
+              </outputTargets>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
 </project>

examples/src/main/java/io/dapr/examples/invoke/grpc/HelloWorldClient.java

@@ -0,0 +1,127 @@
+package io.dapr.examples.invoke.grpc;
+
+import com.google.common.util.concurrent.ListenableFuture;
+import com.google.protobuf.Any;
+import com.google.protobuf.InvalidProtocolBufferException;
+import io.dapr.DaprGrpc;
+import io.dapr.DaprProtos.InvokeServiceEnvelope;
+import io.dapr.DaprProtos.InvokeServiceResponseEnvelope;
+import io.grpc.ManagedChannel;
+import io.grpc.ManagedChannelBuilder;
+import org.apache.commons.cli.CommandLine;
+import org.apache.commons.cli.CommandLineParser;
+import org.apache.commons.cli.DefaultParser;
+import org.apache.commons.cli.Options;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.TimeUnit;
+
+import static io.dapr.examples.DaprExamplesProtos.SayRequest;
+import static io.dapr.examples.DaprExamplesProtos.SayResponse;
+
+/**
+ * 1. Build and install jars:
+ *   mvn clean install
+ * 2. Send messages to the server:
+ *   dapr run --protocol grpc --grpc-port 50001 -- mvn exec:java -pl=examples -Dexec.mainClass=io.dapr.examples.invoke.grpc.HelloWorldClient -Dexec.args="-p 50001 'message one' 'message two'"
+ */
+public class HelloWorldClient {
+
+    /**
+     * Client mode: class representing a client-side logic for calling HelloWorld over Dapr.
+     */
+    private static class GrpcHelloWorldDaprClient {
+
+        /**
+         * Client communication channel: host, port and tls(on/off)
+         */
+        private final ManagedChannel channel;
+
+        /**
+         * Calls will be done asynchronously.
+         */
+        private final DaprGrpc.DaprFutureStub client;
+
+        /**
+         * Creates a Grpc client for the DaprGrpc service.
+         * @param host host for the remote service endpoint
+         * @param port port for the remote service endpoint
+         */
+        public GrpcHelloWorldDaprClient(String host, int port) {
+            this(ManagedChannelBuilder
+                    .forAddress("localhost", port)
+                    .usePlaintext()  // SSL/TLS is default, we turn it off just because this is a sample and not prod.
+                    .build());
+        }
+
+        /**
+         * Helper constructor to build client from channel.
+         * @param channel
+         */
+        private GrpcHelloWorldDaprClient(ManagedChannel channel) {
+            this.channel = channel;
+            this.client = DaprGrpc.newFutureStub(channel);
+        }
+
+        /**
+         * Client mode: sends messages, one per second.
+         * @param messages
+         */
+        private void sendMessages(String... messages) throws ExecutionException, InterruptedException, InvalidProtocolBufferException {
+            List<ListenableFuture<InvokeServiceResponseEnvelope>> futureResponses = new ArrayList<>();
+            for (String message : messages)
+            {
+                SayRequest request = SayRequest
+                        .newBuilder()
+                        .setMessage(message)
+                        .build();
+
+                // Now, wrap the request with Dapr's envelope.
+                InvokeServiceEnvelope requestEnvelope = InvokeServiceEnvelope
+                        .newBuilder()
+                        .setId("hellogrpc")  // Service's identifier.
+                        .setData(Any.pack(request))
+                        .setMethod("say")  // The service's method to be invoked by Dapr.
+                        .build();
+
+                futureResponses.add(client.invokeService(requestEnvelope));
+                System.out.println("Client: sent => " + message);
+                Thread.sleep(TimeUnit.SECONDS.toMillis(10));
+            }
+
+            for (ListenableFuture<InvokeServiceResponseEnvelope> future : futureResponses) {
+                Any data = future.get().getData();  // Blocks waiting for response.
+                // IMPORTANT: do not use Any.unpack(), use Type.ParseFrom() instead.
+                SayResponse response = SayResponse.parseFrom(data.getValue());
+                System.out.println("Client: got response => " + response.getTimestamp());
+            }
+        }
+
+        /**
+         * Client mode: gracefully shutdown client within 1 min, otherwise force it.
+         * @throws InterruptedException Propagated interrupted exception.
+         */
+        private void shutdown() throws InterruptedException {
+            this.channel.shutdown().awaitTermination(1, TimeUnit.MINUTES);
+            System.out.println("Client: Bye.");
+        }
+
+    }
+
+    public static void main(String[] args) throws Exception {
+        Options options = new Options();
+        options.addRequiredOption("p", "port", true, "Port to listen or send event to.");
+
+        CommandLineParser parser = new DefaultParser();
+        CommandLine cmd = parser.parse(options, args);
+
+        // If port string is not valid, it will throw an exception.
+        int port = Integer.parseInt(cmd.getOptionValue("port"));
+
+        GrpcHelloWorldDaprClient helloWorldClient = new GrpcHelloWorldDaprClient("localhost", port);
+        helloWorldClient.sendMessages(cmd.getArgs());
+        helloWorldClient.shutdown();
+    }
+}