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Some editing/rewriting of example, fixed links, etc.
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LisaFC 10 years ago
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      README.md

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@ -118,10 +118,11 @@ familiar with protocol buffers, you can find out more in the [Protocol Buffers
Developer Guide](https://developers.google.com/protocol-buffers/docs/overview).
Here's our example service definition, defined using protocol buffers IDL in
[helloworld.proto](java/src/main/proto/helloworld.proto) _should we link to the version in the Java subdirectory or the one in the common protos directory?_. The `Greeting` service
[helloworld.proto](java/src/main/proto/helloworld.proto). The `Greeting` service
has one method, `hello`, that lets the server receive a single `HelloRequest`
message from the remote client containing the user's name, then send back
a greeting in a `HelloReply`.
a greeting in a single `HelloReply`. This is the simplest type of RPC you
can specify in gRPC - we'll look at some other types later in this document.
```
syntax = "proto3";
@ -167,7 +168,8 @@ this up in "what is gRPC"?]
the example, you can skip this step and move
onto the next one where we examine the generated code.)
As this is our first time using gRPC, we need to build the protobuf plugin that generates our RPC
As this is our first time using gRPC, we need to build the protobuf plugin
that generates our RPC
classes. By default `protoc` just generates code for reading and writing
protocol buffers, so you need to use plugins to add additional features
to generated code. As we're creating Java code, we use the gRPC Java plugin.
@ -190,77 +192,97 @@ $ protoc -I . helloworld.proto
--java_out=src/main/java
```
This generates the following classes, which contain all the generated code we need to create our example:
This generates the following classes, which contain all the generated code
we need to create our example:
- [`Helloworld.java`](java/src/main/java/ex/grpc/Helloworld.java), which has all the protocol buffer code to populate, serialize, and retrieve our `HelloRequest` and `HelloReply` message types
- [`GreetingsGrpc.java`](java/src/main/java/ex/grpc/GreetingsGrpc.java), which contains (along with some other useful code):
- [`Helloworld.java`](java/src/main/java/ex/grpc/Helloworld.java), which
has all the protocol buffer code to populate, serialize, and retrieve our
`HelloRequest` and `HelloReply` message types
- [`GreetingsGrpc.java`](java/src/main/java/ex/grpc/GreetingsGrpc.java),
which contains (along with some other useful code):
- an interface for `Greetings` servers to implement
```java
public static interface Greetings {
public void hello(ex.grpc.Helloworld.HelloRequest request,
com.google.net.stubby.stub.StreamObserver<ex.grpc.Helloworld.HelloReply> responseObserver);
com.google.net.stubby.stub.StreamObserver<ex.grpc.Helloworld.HelloReply>
responseObserver);
}
```
- _stub_ classes that clients can use to talk to a `Greetings` server.
- _stub_ classes that clients can use to talk to a `Greetings` server. As you can see, they also implement the `Greetings` interface.
```java
```java
public static class GreetingsStub extends
com.google.net.stubby.stub.AbstractStub<GreetingsStub, GreetingsServiceDescriptor>
com.google.net.stubby.stub.AbstractStub<GreetingsStub,
GreetingsServiceDescriptor>
implements Greetings {
...
}
```
```
<a name="server"></a>
### Writing a server
Now let's write some code! First we'll create a server application to implement our service. Note that we're not going to go into a lot of detail about how to create a server in this section More detailed information will be in the tutorial for your chosen language (coming soon).
Now let's write some code! First we'll create a server application to implement
our service. Note that we're not going to go into a lot of detail about how
to create a server in this section More detailed information will be in the
tutorial for your chosen language (coming soon).
Our server application has two classes:
- a simple service implementation [GreetingsImpl.java](java/src/main/java/ex/grpc/GreetingsImpl.java).
- a simple service implementation
[GreetingsImpl.java](java/src/main/java/ex/grpc/GreetingsImpl.java).
- a server that hosts the service implementation and allows access over the network: [GreetingsServer.java](src/main/java/ex/grpc/GreetingsServer.java).
- a server that hosts the service implementation and allows access over the
network: [GreetingsServer.java](java/src/main/java/ex/grpc/GreetingsServer.java).
#### Service implementation
[GreetingsImpl.java](java/src/main/java/ex/grpc/GreetingsImpl.java)
implements the behaviour we require of our GreetingService. There are a
number of important features of gRPC being used here:
actually implements our GreetingService's required behaviour.
As you can see, the class `GreetingsImpl` implements the interface
`GreetingsGrpc.Greetings` that we [generated](#generating) from our proto
[IDL](java/src/main/proto/helloworld.proto) by implementing the method `hello`:
```java
public void hello(Helloworld.HelloRequest req,
StreamObserver<Helloworld.HelloReply> responseObserver) {
Helloworld.HelloReply reply = Helloworld.HelloReply.newBuilder().setMessage(
Helloworld.HelloReply reply =
Helloworld.HelloReply.newBuilder().setMessage(
"Hello " + req.getName()).build();
responseObserver.onValue(reply);
responseObserver.onCompleted();
}
```
- it provides a class `GreetingsImpl` that implements a generated interface `GreetingsGrpc.Greetings`
- `GreetingsGrpc.Greetings` declares the method `hello` that was declared in the proto [IDL](src/main/proto/helloworld.proto)
- `hello's` signature is typesafe:
hello(Helloworld.HelloRequest req, StreamObserver<Helloworld.HelloReply> responseObserver)
`hello(Helloworld.HelloRequest req, StreamObserver<Helloworld.HelloReply>
responseObserver)`
- `hello` takes two parameters:
`Helloworld.HelloRequest`: the request
`StreamObserver<Helloworld.HelloReply>`: a response observer, an interface to be called with the response value
- to complete the call
- the return value is constructed
- the responseObserver.onValue() is called with the response
- responseObserver.onCompleted() is called to indicate that no more work will done on the RPC.
-`Helloworld.HelloRequest`: the request
-`StreamObserver<Helloworld.HelloReply>`: a response observer, which is
a special interface for the server to call with its response
To return our response to the client and complete the call:
1. We construct and populate a `HelloReply` response object with our exciting
message, as specified in our interface definition.
2. We call `responseObserver.onValue()` with the `HelloReply` that we want to send back to the client.
3. Finally, we call `responseObserver.onCompleted()` to indicate that we're
finished dealing with this RPC.
#### Server implementation
[GreetingsServer.java](src/main/java/ex/grpc/GreetingsServer.java) shows the
other main feature required to provde the gRPC service; how to allow a service
implementation to be accessed from the network.
[GreetingsServer.java](java/src/main/java/ex/grpc/GreetingsServer.java)
shows the other main feature required to provide a gRPC service; making the service
implementation available from the network.
```java
private ServerImpl server;
...
private void start() throws Exception {
server = NettyServerBuilder.forPort(port)
.addService(GreetingsGrpc.bindService(new GreetingsImpl()))
@ -271,9 +293,16 @@ implementation to be accessed from the network.
```
- it provides a class `GreetingsServer` that holds a `ServerImpl` that will run the server
- in the `start` method, `GreetingServer` binds the `GreetingsService` implementation to a port and begins running it
- there is also a `stop` method that takes care of shutting down the service and cleaning up when the program exits
The `GreetingsServer` class has a `ServerImpl` member that actually runs the
server. To create an appropriate `ServerImpl`, we use a special `ServerBuilder`
class (in this case a `NettyServerBuilder`) in the `GreetingsServer`'s `start`
method, binding the `GreetingsService` implementation that we created to a
port. Then we start the server running: the server is now ready to receive
requests from `Greetings` service clients on our specified port. We'll cover
how all this works in a bit more detail in our language-specific documentation.
`GreetingsServer` also has a `stop` method that takes care of shutting down
the service and cleaning up when the program exits.
#### Build it
@ -288,16 +317,22 @@ We'll look at using a client to access the server in the next section.
<a name="client"></a>
### Writing a client
Client-side gRPC is pretty simple. In this step, we'll use the generated code to write a simple client that can access the `Greetings` server we created in the previous section. You can see the complete client code in [GreetingsClient.java](src/main/java/ex/grpc/GreetingsClient.java).
Client-side gRPC is pretty simple. In this step, we'll use the generated code
to write a simple client that can access the `Greetings` server we created
in the [previous section](#server). You can see the complete client code in
[GreetingsClient.java](java/src/main/java/ex/grpc/GreetingsClient.java).
Again, we're not going to go into much detail about how to implement a client - we'll leave that for the tutorial.
Again, we're not going to go into much detail about how to implement a client
- we'll leave that for the tutorial.
#### Connecting to the service
. The internet address
is configured in the client constructor. gRPC Channel is the abstraction over
First let's look at how we connect to the `Greetings` server. The internet
address
is configured in the client constructor. gRPC `Channel` provides the
abstraction layer over
transport handling; its constructor accepts the host name and port of the
service. The channel in turn is used to construct the Stub.
service. The channel in turn is used to construct the stub instance.
```java
@ -313,20 +348,28 @@ service. The channel in turn is used to construct the Stub.
```
In this case, we create a blocking stub. This means that the RPC call waits
for the server to respond, and will either return a response or raise an
exception. gRPC Java has other kinds of stubs that make non-blocking calls
to the server, where the response is returned asynchronously.
#### Obtaining a greeting
The greet method uses the stub to contact the service and obtain a greeting.
It:
- constructs a request
- obtains a reply from the stub
- prints out the greeting
The `greet()` method uses the stub to contact the service and obtain
a greeting.
To do this:
1. We construct and fill in a `HelloRequest` to send to the stub.
2. We call the RPC with our request and get a `HelloReply` from the stub,
from which we can get our greeting.
```java
public void greet(String name) {
logger.debug("Will try to greet " + name + " ...");
try {
Helloworld.HelloRequest request = Helloworld.HelloRequest.newBuilder().setName(name).build();
Helloworld.HelloRequest request =
Helloworld.HelloRequest.newBuilder().setName(name).build();
Helloworld.HelloReply reply = blockingStub.hello(request);
logger.info("Greeting: " + reply.getMessage());
} catch (RuntimeException e) {
@ -355,22 +398,14 @@ line.
#### Build the client
This is the same as before: our client and server are part of the same maven
This is the same as building the server: our client and server are part of
the same maven
package so the same command builds both.
```
$ mvn package
```
#### Notes
- The client uses a blocking stub. This means that the RPC call waits for the
server to respond, and will either return a response or raise an exception.
- gRPC Java has other kinds of stubs that make non-blocking calls to the
server, where the response is returned asynchronously. Usage of these stubs
is a more advanced topic and will be described in later steps.
<a name="run"></a>
### Try it out!
@ -387,6 +422,10 @@ and in another terminal window confirm that it receives a message.
$ ./run_greetings_client.sh
```
### Adding another client
###TODO: Section on Go client for same server

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