duanlei4759
2017-05-22 12:08
浏览 272
已采纳

gRPC:如何使用Go服务器在Java客户端中获取多个返回值

I have a protocol buffer file:

syntax = "proto3";
package v1api;
option java_multiple_files = true;
option java_package = "myApp.v1";
option java_outer_classname = "V1";

service API {
    rpc Login(LoginRequest) returns (LoginResponse)
}

message LoginRequest {
    int pin = 1
}

message LoginResponse {
    string token = 1
}

I have my server written in Go (a language that can return multiple values), and my client being an Android application.

When I use this protoBuf to generate Go code for server, it is something like:

...
func (c *aPIClient) Login(ctx context.Context, in *LoginRequest, opts ...grpc.CallOption) (*LoginResponse, error) {
    out := new(LoginResponse)
    err := grpc.Invoke(ctx, "/v1api.API/Login", in, out, c.cc, opts...)
    if err != nil {
        return nil, err
    }
    return out, nil
}
...

Notice that there are two return values, (*LoginResponse, error).

Now, when I use this protoBuf to generate Java code for my Android side, I get something like:

public myApp.v1.LoginResponse login(myApp.v1.LoginRequest request) {
    return blockingUnaryCall(getChannel(), METHOD_LOGIN, getCallOptions(), request);
}

Notice that, here, there is just one return value like Java allows, myApp.v1.LoginResponse.

My question is, in case of an error returned by the server (something like: return nil, err), how will I get that second return value in my Android side.

图片转代码服务由CSDN问答提供 功能建议

我有一个协议缓冲区文件:

  syntax =“ proto3”; 
package v1api; 
option java_multiple_files = true; 
option java_package =“ myApp.v1”; 
option java_outer_classname =“ V1”; 
 
服务API {
 rpc Login(LoginRequest  )返回(LoginResponse)
} 
 
message LoginRequest {
 int销= 1 
} 
 
message LoginResponse {
字符串令牌= 1 
} 
   
  
 

我的服务器是用Go(可以返回多个值的语言)编写的,客户端是Android应用程序。

当我使用此protoBuf生成Go代码时, 对于服务器,它类似于:

  ... 
func(c * aPIClient)Login(ctx context.Context,在* LoginRequest中,选择... grpc.CallOption  )(* LoginResponse,错误){
 out:= new(LoginResponse)
 err:= grpc.Invoke(ctx,“ /v1api.API/Login”,in,out,c.cc,opts ...)  
 if err!= nil {
返回nil,err 
} 
返回nil 
} 
 ... 
   
 
  

请注意,有两个返回值(* LoginResponse,error)

现在,当我使用此protoBuf时 为我的Android端生成Java代码,我得到的内容如下:

  public myApp.v1.LoginResponse login(myApp.v1.LoginRequest request){
返回blockingUnaryCall(getChannel  (),METHOD_LOGIN,getCallOptions(),request); 
} 
   
 
 

请注意,这里的返回值只有一个 像Java允许的那样, myApp.v1.LoginResponse

我的问题是,如果服务器返回错误(例如: return nil ,err ),如何在Android端获取第二个返回值。

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2条回答 默认 最新

  • dongma2388 2017-05-22 19:57
    已采纳

    In Go, the error returned by your Login method will get converted into the wire format status code and message used by gRPC. In your case, if you return a status.Status, the Code and message will be sent and show up on the Java side as a StatusRuntimeException. If you return a non Status error, gRPC will convert it to the UNKNOWN code, but preserve the message.

    This is the reason there are two return values for Go, vs. just one for Java. Java can "return" a secondary value by throwing an exception in its place.

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  • dqwh0108 2017-05-22 12:37

    Since Java does not support multiple return values, when a protoBuf is generated into a java code, the errors are communicated by throwing exceptions. Make your gRPC call in a try-catch block and catch any StatusRuntimeException that the call may throw.

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