---
title: Quick start
description: This guide gets you started with gRPC in Java with a simple working example.
weight: 10
---

### Prerequisites

- [JDK][] version 7 or higher

### Get the example code

The example code is part of the [grpc-java][] repo.

 1. [Download the repo as a zip file][download] and unzip it, or clone
    the repo:

    ```sh
    $ git clone -b {{< param grpc_vers.java >}} https://github.com/grpc/grpc-java
    ```

 2. Change to the examples directory:

    ```sh
    $ cd grpc-java/examples
    ```

### Run the example

From the `examples` directory:

 1. Compile the client and server

    ```sh
    $ ./gradlew installDist
    ```

 2. Run the server:

    ```sh
    $ ./build/install/examples/bin/hello-world-server
    INFO: Server started, listening on 50051
    ```

 3. From another terminal, run the client:

    ```sh
    $ ./build/install/examples/bin/hello-world-client
    INFO: Will try to greet world ...
    INFO: Greeting: Hello world
    ```

Congratulations! You've just run a client-server application with gRPC.

{{% alert title="Note" color="info" %}}
  We've omitted timestamps from the client and server trace output shown in this
  page.
{{% /alert %}}

### Update the gRPC service

In this section you'll update the application by adding an extra server method.
The gRPC service is defined using [protocol buffers][pb]. To learn more about
how to define a service in a `.proto` file see [Basics tutorial][]. For now, all
you need to know is that both the server and the client stub have a `SayHello()`
RPC method that takes a `HelloRequest` parameter from the client and returns a
`HelloReply` from the server, and that the method is defined like this:

```protobuf
// The greeting service definition.
service Greeter {
  // Sends a greeting
  rpc SayHello (HelloRequest) returns (HelloReply) {}
}

// The request message containing the user's name.
message HelloRequest {
  string name = 1;
}

// The response message containing the greetings
message HelloReply {
  string message = 1;
}
```

Open `src/main/proto/helloworld.proto` and add a new `SayHelloAgain()` method
with the same request and response types as `SayHello()`:

```protobuf
// The greeting service definition.
service Greeter {
  // Sends a greeting
  rpc SayHello (HelloRequest) returns (HelloReply) {}
  // Sends another greeting
  rpc SayHelloAgain (HelloRequest) returns (HelloReply) {}
}

// The request message containing the user's name.
message HelloRequest {
  string name = 1;
}

// The response message containing the greetings
message HelloReply {
  string message = 1;
}
```

Remember to save the file!

### Update the app

When you build the example, the build process regenerates `GreeterGrpc.java`,
which contains the generated gRPC client and server classes. This also
regenerates classes for populating, serializing, and retrieving our request and
response types.

However, you still need to implement and call the new method in the
hand-written parts of the example app.

#### Update the server

In the same directory, open
`src/main/java/io/grpc/examples/helloworld/HelloWorldServer.java`. Implement the
new method like this:

```java
private class GreeterImpl extends GreeterGrpc.GreeterImplBase {

  @Override
  public void sayHello(HelloRequest req, StreamObserver<HelloReply> responseObserver) {
    HelloReply reply = HelloReply.newBuilder().setMessage("Hello " + req.getName()).build();
    responseObserver.onNext(reply);
    responseObserver.onCompleted();
  }

  @Override
  public void sayHelloAgain(HelloRequest req, StreamObserver<HelloReply> responseObserver) {
    HelloReply reply = HelloReply.newBuilder().setMessage("Hello again " + req.getName()).build();
    responseObserver.onNext(reply);
    responseObserver.onCompleted();
  }
}
```

#### Update the client

In the same directory, open
`src/main/java/io/grpc/examples/helloworld/HelloWorldClient.java`. Call the new
method like this:

```java
public void greet(String name) {
  logger.info("Will try to greet " + name + " ...");
  HelloRequest request = HelloRequest.newBuilder().setName(name).build();
  HelloReply response;
  try {
    response = blockingStub.sayHello(request);
  } catch (StatusRuntimeException e) {
    logger.log(Level.WARNING, "RPC failed: {0}", e.getStatus());
    return;
  }
  logger.info("Greeting: " + response.getMessage());
  try {
    response = blockingStub.sayHelloAgain(request);
  } catch (StatusRuntimeException e) {
    logger.log(Level.WARNING, "RPC failed: {0}", e.getStatus());
    return;
  }
  logger.info("Greeting: " + response.getMessage());
}
```

### Run the updated app

Run the client and server like you did before. Execute the following commands
from the `examples` directory:

 1. Compile the client and server:

    ```sh
    $ ./gradlew installDist
    ```

 2. Run the server:

    ```sh
    $ ./build/install/examples/bin/hello-world-server
    INFO: Server started, listening on 50051
    ```

 3. From another terminal, run the client:

    ```sh
    $ ./build/install/examples/bin/hello-world-client
    INFO: Will try to greet world ...
    INFO: Greeting: Hello world
    INFO: Greeting: Hello again world
    ```

### What's next

- Learn how gRPC works in [Introduction to gRPC](/docs/what-is-grpc/introduction/)
  and [Core concepts](/docs/what-is-grpc/core-concepts/).
- Work through the [Basics tutorial][].
- Explore the [API reference](../api).

[Basics tutorial]: ../basics/
[download]: https://github.com/grpc/grpc-java/archive/{{< param grpc_vers.java >}}.zip
[grpc-java]: https://github.com/grpc/grpc-java
[JDK]: https://jdk.java.net
[pb]: https://developers.google.com/protocol-buffers
