Android Java 快速使用 gRPC

更新时间: 2019-07-05 12:52

This guide gets you started with gRPC in Android Java with a simple working example.

Before you begin

Prerequisites

Note: gRPC Java does not support running a server on an Android device. For this quickstart, the Android client app will connect to a server running on your local (non-Android) computer.

Download the example

You’ll need a local copy of the example code to work through this quickstart. Download the example code from our GitHub repository (the following command clones the entire repository, but you just need the examples for this quickstart and other tutorials):

$ # Clone the repository at the latest release to get the example code:
$ git clone -b v1.21.0 https://github.com/grpc/grpc-java
$ # Navigate to the Java examples:
$ cd grpc-java/examples

Run a gRPC application

  1. Compile the server
   $ ./gradlew installDist
  1. Run the server
   $ ./build/install/examples/bin/hello-world-server
  1. In another terminal, compile and run the client
   $ cd android/helloworld
   $ ../../gradlew installDebug

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

Update a gRPC service

Now let’s look at how to update the application with an extra method on the server for the client to call. Our gRPC service is defined using protocol buffers; you can find out lots more about how to define a service in a .proto file in gRPC Basics: Android Java. 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 HelloResponse from the server, and that this method is defined like this:

// 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;
}

Let’s update this so that the Greeter service has two methods. Edit src/main/proto/helloworld.proto and update it with a new SayHelloAgain method, with the same request and response types:

// 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;
}

(Don’t forget to save the file!)

Update and run the application

When we recompile the example, normal compilation will regenerate GreeterGrpc.java, which contains our generated gRPC client and server classes. This also regenerates classes for populating, serializing, and retrieving our request and response types.

However, we still need to implement and call the new method in the human-written parts of our example application.

Update the server

Check out the Java quickstart here.

Update the client

In the same directory, open app/src/main/java/io/grpc/helloworldexample/HelloworldActivity.java. Call the new method like this:

    try {
        HelloRequest message = HelloRequest.newBuilder().setName(mMessage).build();
        HelloReply reply = stub.sayHello(message);
        reply = stub.sayHelloAgain(message);
    } catch (Exception e) {
        StringWriter sw = new StringWriter();
        PrintWriter pw = new PrintWriter(sw);
        e.printStackTrace(pw);
        pw.flush();
        return "Failed... : " + System.lineSeparator() + sw;
    }

Run!

Just like we did before, from the examples directory:

  1. Compile the server
   $ ./gradlew installDist
  1. Run the server
   $ ./build/install/examples/bin/hello-world-server
  1. In another terminal, compile and install the client to your device
   $ cd android/helloworld
   $ ../../gradlew installDebug

Connecting to the Hello World server via USB

To run the application on a physical device via USB debugging, you must configure USB port forwarding to allow the device to communicate with the server running on your computer. This is done via the adb command line tool as follows:

adb reverse tcp:8080 tcp:50051

This sets up port forwarding from port 8080 on the device to port 50051 on the connected computer, which is the port that the Hello World server is listening on.

Now you can run the Android Hello World app on your device, using localhost and 8080 as the Host and Port.

Connecting to the Hello World server from an Android Virtual Device

To run the Hello World app on an Android Virtual Device, you don’t need to enable port forwarding. Instead, the emulator can use the IP address 10.0.2.2 to refer to the host machine. Inside the Android Hello World app, enter 10.0.2.2 and 50051 as the Host and Port.

What’s next

计算机程序设计艺术(第1卷)

计算机程序设计艺术(第1卷)

[美] Donald E. Knuth / 清华大学出版社 / 2002-9 / 80.00元

第1卷首先介绍编程的基本概念和技术,然后详细讲解信息结构方面的内容,包括信息在计算机内部的表示方法、数据元素之间的结构关系,以及有效的信息处理方法。此外,书中还描述了编程在模拟、数值方法、符号计算、软件与系统设计等方面的初级应用。此第3版增加了数十项简单但重要的算法和技术,并根据当前研究发展趋势在数学预备知识方面做了大量修改。一起来看看 《计算机程序设计艺术(第1卷)》 这本书的介绍吧!

HTML 编码/解码

HTML 编码/解码

HTML 编码/解码

Base64 编码/解码

Base64 编码/解码

Base64 编码/解码

RGB HSV 转换

RGB HSV 转换

RGB HSV 互转工具