gRPC Examples

The examples require grpc-java to already be built. You are strongly encouraged to check out a git release tag, since there will already be a build of gRPC available. Otherwise you must follow COMPILING.

You may want to read through the Quick Start before trying out the examples.

Basic examples

Hello world
Route guide
Metadata
Error handling
Compression
Flow control
Wait For Ready
Json serialization
Hedging

The hedging example demonstrates that enabling hedging can reduce tail latency. (Users should note that enabling hedging may introduce other overhead; and in some scenarios, such as when some server resource gets exhausted for a period of time and almost every RPC during that time has high latency or fails, hedging may make things worse. Setting a throttle in the service config is recommended to protect the server from too many inappropriate retry or hedging requests.)

The server and the client in the example are basically the same as those in the hello world example, except that the server mimics a long tail of latency, and the client sends 2000 requests and can turn on and off hedging.

To mimic the latency, the server randomly delays the RPC handling by 2 seconds at 10% chance, 5 seconds at 5% chance, and 10 seconds at 1% chance.

When running the client enabling the following hedging policy
```
      "hedgingPolicy": {
        "maxAttempts": 3,
        "hedgingDelay": "1s"
      }
```
Then the latency summary in the client log is like the following
```
Total RPCs sent: 2,000. Total RPCs failed: 0
[Hedging enabled]
========================
50% latency: 0ms
90% latency: 6ms
95% latency: 1,003ms
99% latency: 2,002ms
99.9% latency: 2,011ms
Max latency: 5,272ms
========================
```
See the section below for how to build and run the example. The executables for the server and the client are hedging-hello-world-server and hedging-hello-world-client.

To disable hedging, set environment variable DISABLE_HEDGING_IN_HEDGING_EXAMPLE=true before running the client. That produces a latency summary in the client log like the following
```
Total RPCs sent: 2,000. Total RPCs failed: 0
[Hedging disabled]
========================
50% latency: 0ms
90% latency: 2,002ms
95% latency: 5,002ms
99% latency: 10,004ms
99.9% latency: 10,007ms
Max latency: 10,007ms
========================
```

Retrying

The retrying example provides a HelloWorld gRPC client & server which demos the effect of client retry policy configured on the ManagedChannel via gRPC ServiceConfig. Retry policy implementation & configuration details are outlined in the proposal.

This retrying example is very similar to the hedging example in its setup. The RetryingHelloWorldServer responds with a status UNAVAILABLE error response to a specified percentage of requests to simulate server resource exhaustion and general flakiness. The RetryingHelloWorldClient makes a number of sequential requests to the server, several of which will be retried depending on the configured policy in retrying_service_config.json. Although the requests are blocking unary calls for simplicity, these could easily be changed to future unary calls in order to test the result of request concurrency with retry policy enabled.

One can experiment with the RetryingHelloWorldServer failure conditions to simulate server throttling, as well as alter policy values in the retrying_service_config.json to see their effects. To disable retrying entirely, set environment variable DISABLE_RETRYING_IN_RETRYING_EXAMPLE=true before running the client. Disabling the retry policy should produce many more failed gRPC calls as seen in the output log.

See the section below for how to build and run the example. The executables for the server and the client are retrying-hello-world-server and retrying-hello-world-client.

Health Service

The health service example provides a HelloWorld gRPC server that doesn't like short names along with a health service. It also provides a client application which makes HelloWorld calls and checks the health status.

The client application also shows how the round robin load balancer can utilize the health status to avoid making calls to a service that is not actively serving.

Keep Alive

To build the examples

$ ./gradlew installDist

This creates the scripts hello-world-server, hello-world-client, route-guide-server, route-guide-client, etc. in the build/install/examples/bin/ directory that run the examples. Each example requires the server to be running before starting the client.

For example, to try the hello world example first run:

$ ./build/install/examples/bin/hello-world-server

And in a different terminal window run:

$ ./build/install/examples/bin/hello-world-client

That's it!

For more information, refer to gRPC Java's README and tutorial.

Maven

If you prefer to use Maven:

Install gRPC Java library SNAPSHOT locally, including code generation plugin (Only need this step for non-released versions, e.g. master HEAD).
Run in this directory:

$ mvn verify
$ # Run the server
$ mvn exec:java -Dexec.mainClass=io.grpc.examples.helloworld.HelloWorldServer
$ # In another terminal run the client
$ mvn exec:java -Dexec.mainClass=io.grpc.examples.helloworld.HelloWorldClient

Bazel

If you prefer to use Bazel:

$ bazel build :hello-world-server :hello-world-client
$ # Run the server
$ bazel-bin/hello-world-server
$ # In another terminal run the client
$ bazel-bin/hello-world-client

Other examples

Android examples
Secure channel examples
- TLS examples
- ALTS examples
Google Authentication
JWT-based Authentication
OAuth2-based Authentication
Pre-serialized messages

Unit test examples

Examples for unit testing gRPC clients and servers are located in examples/src/test.

In general, we DO NOT allow overriding the client stub and we DO NOT support mocking final methods in gRPC-Java library. Users should be cautious that using tools like PowerMock or mockito-inline can easily break this rule of thumb. We encourage users to leverage InProcessTransport as demonstrated in the examples to write unit tests. InProcessTransport is light-weight and runs the server and client in the same process without any socket/TCP connection.

Mocking the client stub provides a false sense of security when writing tests. Mocking stubs and responses allows for tests that don't map to reality, causing the tests to pass, but the system-under-test to fail. The gRPC client library is complicated, and accurately reproducing that complexity with mocks is very hard. You will be better off and write less code by using InProcessTransport instead.

Example bugs not caught by mocked stub tests include:

Calling the stub with a null message
Not calling close()
Sending invalid headers
Ignoring deadlines
Ignoring cancellation

For testing a gRPC client, create the client with a real stub using an InProcessChannel, and test it against an InProcessServer with a mock/fake service implementation.

For testing a gRPC server, create the server as an InProcessServer, and test it against a real client stub with an InProcessChannel.

The gRPC-java library also provides a JUnit rule, GrpcCleanupRule, to do the graceful shutdown boilerplate for you.

Even more examples

A wide variety of third-party examples can be found here.