Basic docs

docs/src/modules/java/pages/grpc-endpoints.adoc

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+= Designing gRPC Endpoints
+
+include::ROOT:partial$include.adoc[]
+
+gRPC Endpoint components make it possible to conveniently define public APIs accepting and responding in protobuf,
+a binary, typed protocol which is designed to handle evolution of a service over time.
+
+== Basics ==
+To define a gRPC Endpoint component, you start by defining a `.proto` file that defines the service and its messages
+in `src/main/proto` of the project.
+
+[source,protobuf]
+.{sample-base-url}/doc-snippets/src/main/proto/com/example/example_grpc_endpoint.proto
+----
+include::example$doc-snippets/src/main/proto/com/example/example_grpc_endpoint.proto[]
+----
+
+When compiling the project a Java interface for the service is generated `com.example.proto.ExampleGrpcEndpoint`. Define a class implementing this interface in the `api` package of your project
+and annotate the class with `@GrpcEndpoint`:
+
+[source,java]
+.{sample-base-url}/doc-snippets/src/main/java/
+----
+include::example$doc-snippets/src/main/java/com/example/api/ExampleGrpcEndpointImpl.java[]
+----
+
+