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/*
 * Copyright 2017 The gRPC Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * API for the Stub layer.
 *
 * 

The gRPC Java API is split into two main parts: The stub layer and the call layer. The stub * layer is a wrapper around the call layer. * *

In the most common case of gRPC over Protocol Buffers, stub classes are automatically * generated from service definition .proto files by the Protobuf compiler. See gRPC Java Generated Code Guide * . * *

The server side stub classes are abstract classes with RPC methods for the server application * to implement/override. These classes internally use {@link io.grpc.stub.ServerCalls} to interact * with the call layer. The RPC methods consume a {@link io.grpc.stub.StreamObserver} object {@code * responseObserver} as one of its arguments. When users are implementing/override these * methods in the server application, they may call the {@link io.grpc.stub.StreamObserver#onNext * onNext()}, {@link io.grpc.stub.StreamObserver#onError onError()} and {@link * io.grpc.stub.StreamObserver#onCompleted onCompleted()} methods on the {@code responseObserver} * argument to send out a response message, error and completion notification respectively. If the * RPC is client-streaming or bidirectional-streaming, the abstract RPC method should return a * {@code requestObserver} which is also a {@link io.grpc.stub.StreamObserver} object. User should * typically implement the {@link io.grpc.stub.StreamObserver#onNext onNext()}, {@link * io.grpc.stub.StreamObserver#onError onError()} and {@link io.grpc.stub.StreamObserver#onCompleted * onCompleted()} callbacks of {@code requestObserver} to define how the server application would * react when receiving a message, error and completion notification respectively from the client * side. * *

The client side stub classes are implementations of {@link io.grpc.stub.AbstractStub} that * provide the RPC methods for the client application to call. The RPC methods in the client stubs * internally use {@link io.grpc.stub.ClientCalls} to interact with the call layer. For asynchronous * stubs, the RPC methods also consume a {@link io.grpc.stub.StreamObserver} object {@code * responseObserver} as one of its arguments, and moreover for client-streaming or * bidirectional-streaming, also return a {@code requestObserver} which is also a {@link * io.grpc.stub.StreamObserver} object. In contrast to the server side, users should implement the * {@link io.grpc.stub.StreamObserver#onNext onNext()}, {@link io.grpc.stub.StreamObserver#onError * onError()} and {@link io.grpc.stub.StreamObserver#onCompleted onCompleted()} callbacks of {@code * responseObserver} to define what the client application would do when receiving a response * message, error and completion notification respectively from the server side, and then pass the * {@code responseObserver} to the RPC method in the client stub. If the RPC method returns a {@code * requestObserver}, users should call the {@link io.grpc.stub.StreamObserver#onNext onNext()}, * {@link io.grpc.stub.StreamObserver#onError onError()} and {@link * io.grpc.stub.StreamObserver#onCompleted onCompleted()} methods on the {@code requestObserver} to * send out a request message, error and completion notification respectively. */ package io.grpc.stub;





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