How to transform nullvalues as java pojo fields with protobuffer?

[tangmin823]

Is this library supports null as default value, right? but google protobuffer dosen't, you know.

[sanjaypujare]

Sorry not clear about what the issue is. Can you give an example to clarify?

[tangmin823]

I have seen this, please open this link:Default Values
If I set the field as null, then it will set the default value.
I see Protocol Buffers dosen't support null? But I need null, how do I do? I use your help, thanks a lot.
@sanjaypujare

[sanjaypujare]

You will have to open the issue with protocol buffers. This is not a grpc-java issue.

[voidzcy]

I see Protocol Buffers dosen't support null? But I need null, how do I do? I use your help, thanks a lot.

Starting from protobuf 3.15, you can use optional keyword to preserve field presence for primitive types. The protobuf compiler will emit a hasXXX() method for fields with optional.

Effectively, this isn't something new. Wrapping a primitive type with oneof achieves the same thing.

Also, there are wrapper types. They are "useful for places needing to distinguish the absence of a primitive typed field and its default value".

[tangmin823]

@voidzcy Thank you very much, I will try it. I wish it'll dose.

@sanjaypujare Thank you too.

[ejona86]

To be a bit more clear, protobuf has always supported presence for messages. Only primitives (integer types, string, etc) lacked presence. No presence for integer types probably doesn't surprise Java programmers, but string probably does. I'll note that even with presence, Protobuf's API doesn't return null; you need to use the separate has*() methods.

Seems this issue is resolved, so closing. But if I missed something comment and we can reopen.

[tangmin823]

Using protoc below version3.12, When I compile the proto code below, This didn't work.

message CarBrandVO {
    optional string user_id;
    optional int64 id;
}

Explicit 'optional' labels are disallowed in the Proto3 syntax. To define 'optional' fields in Proto3, simply remove the 'optional' label, as fields are 'optional' by default.

But I use oneof instead optional, it's ok, like this:

message CarBrandVO {
    oneof oneof_user_id {
      string user_id;
   }
   oneof oneof_id {
      int64 id;
   }
}

In order to use optional, I upgrade the protoc plugin version to 3.12 ~ 3.13, the exception changed:

In the end, I go on to upgrade the protoc to newer version 3.15.8, and it still didn't work, the error info changed again.

@voidzcy @ejona86
I need your help, How can I use optional with proto3.0 which version is above 3.12 ?

[ejona86]

@tangmin823, this issue is unrelated to yours. Please open a separate issue instead. nm. I misread the flow through this issue.

[voidzcy]

@tangmin823

car.proto: is a proto3 file that contains optional fields, but code generator protoc-gen-grpc hasn't been updated to support optional fields int proto3.

Which gRPC-Java (its protoc plugin) version are you using? You need to use v1.31.0 or later, as this was added in #7054.

[tangmin823]

@tangmin823, this issue is unrelated to yours. Please open a separate issue instead. nm. I misread the flow through this issue.

Thanks for your response, it's ok!

[tangmin823]

@tangmin823

car.proto: is a proto3 file that contains optional fields, but code generator protoc-gen-grpc hasn't been updated to support optional fields int proto3.

Which gRPC-Java (its protoc plugin) version are you using? You need to use v1.31.0 or later, as this was added in #7054.

@voidzcy I used the older version io.grpc:protoc-gen-grpc-java:1.28.0.

then I upgraded it to v1.31.0, the .proto compilation did work, but I encounter another problem, maybe there're some incompatibilities existed.

2021-04-21 10:08:00.509 ERROR [tid=] [main] [SpringApplication] Application run failed
org.springframework.context.ApplicationContextException: Failed to start bean 'grpcServerLifecycle'; nested exception is java.lang.NoClassDefFoundError: io/grpc/InternalNotifyOnServerBuild
        at org.springframework.context.support.DefaultLifecycleProcessor.doStart(DefaultLifecycleProcessor.java:185)
        at org.springframework.context.support.DefaultLifecycleProcessor.access$200(DefaultLifecycleProcessor.java:53)
        at org.springframework.context.support.DefaultLifecycleProcessor$LifecycleGroup.start(DefaultLifecycleProcessor.java:360)
        at org.springframework.context.support.DefaultLifecycleProcessor.startBeans(DefaultLifecycleProcessor.java:158)
        at org.springframework.context.support.DefaultLifecycleProcessor.onRefresh(DefaultLifecycleProcessor.java:122)
        at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:894)
        at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.finishRefresh(ServletWebServerApplicationContext.java:162)
        at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:553)
        at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141)
        at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:747)
        at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:315)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226)
        at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215)
        at org.cango.mid.dictionary.CangoDictionaryApplication.main(CangoDictionaryApplication.java:20)
Caused by: java.lang.NoClassDefFoundError: io/grpc/InternalNotifyOnServerBuild
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:756)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:468)
        at java.net.URLClassLoader.access$100(URLClassLoader.java:74)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:369)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:363)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:362)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:355)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
        at org.cango.mid.grpc.server.autoconfig.server.GrpcServerConfiguration.configureServices(GrpcServerConfiguration.java:82)
        at org.cango.mid.grpc.server.autoconfig.server.GrpcServerConfiguration.configure(GrpcServerConfiguration.java:67)
        at org.cango.mid.grpc.server.autoconfig.server.GrpcServerConfiguration.createServer(GrpcServerConfiguration.java:48)
        at org.cango.mid.grpc.server.autoconfig.server.GrpcServerLifecycle.createAndStartGrpcServer(GrpcServerLifecycle.java:89)
        at org.cango.mid.grpc.server.autoconfig.server.GrpcServerLifecycle.start(GrpcServerLifecycle.java:49)
        at org.springframework.context.support.DefaultLifecycleProcessor.doStart(DefaultLifecycleProcessor.java:182)
        ... 14 common frames omitted
Caused by: java.lang.ClassNotFoundException: io.grpc.InternalNotifyOnServerBuild
        at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:355)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
        ... 32 common frames omitted

so I looked for the corresponding soution.incompatible with grpc 1.30.0 #370 the issue was the same as mine.
my grpc-services version was v1.27.2, I upgraded it to v1.31.0 too.

In the end, it was been solved, and it also supported nullvalue fields(fieldType: String, Number) transmission.
the client received the response message, there's fields that have null values.

Thank you very much!