how to generate java interfaces instead of abstract classes for my service using protocol buffers compiler?

Question

How can I generate java interfaces instead of abstract classes for my service using protocol buffers compiler?

Right now I use a Gradle plugin which take .proto files and generates abstract classes for my services instead of interfaces. This can be problematic given that Java doesn't let you extend multiple classes.

I couldn't find a solution or a way so far after going through documentation so any help would be great.

My build.gradle looks like this

apply plugin: 'java'
apply plugin: 'com.google.protobuf'

buildscript {
  repositories {
    mavenCentral()
  }
  dependencies {
    // ASSUMES GRADLE 2.12 OR HIGHER. Use plugin version 0.7.5 with earlier
    // gradle versions
    classpath 'com.google.protobuf:protobuf-gradle-plugin:0.8.0'
  }
}

repositories {
  mavenCentral()
  mavenLocal()
}

// IMPORTANT: You probably want the non-SNAPSHOT version of gRPC. Make sure you
// are looking at a tagged version of the example and not "master"!

// Feel free to delete the comment at the next line. It is just for safely
// updating the version in our release process.
def grpcVersion = '1.0.0' // CURRENT_GRPC_VERSION

dependencies {
  compile "io.grpc:grpc-netty:${grpcVersion}"
  compile "io.grpc:grpc-protobuf:${grpcVersion}"
  compile "io.grpc:grpc-stub:${grpcVersion}"
}

protobuf {
  protoc {
    // The version of protoc must match protobuf-java. If you don't depend on
    // protobuf-java directly, you will be transitively depending on the
    // protobuf-java version that grpc depends on.
    artifact = 'com.google.protobuf:protoc:3.0.0'
  }
  plugins {
    grpc {
      artifact = "io.grpc:protoc-gen-grpc-java:${grpcVersion}"
    }
  }
  generateProtoTasks {
    all()*.plugins {
      grpc {
        // To generate deprecated interfaces and static bindService method,
        // turn the enable_deprecated option to true below:
        option 'enable_deprecated=false'
      }
    }
  }
}

// Inform IntelliJ projects about the generated code.
apply plugin: 'idea'

idea {
  module {
    // Not using generatedSourceDirs because of
    // https://discuss.gradle.org/t/support-for-intellij-2016/15294/8
    sourceDirs += file("${projectDir}/build/generated/source/proto/main/java");
    sourceDirs += file("${projectDir}/build/generated/source/proto/main/grpc");
  }

I found out the reason why it is not generating interfaces it looks like it has been deprecated so I am not sure what is the way to generate interface. if you look at my build.gradle option 'enable_deprecated=false' turning this on to true will generate interfaces however the annotations say it is deprecated so I am not sure what is the new way to generate interface. I want interface not abstract classes.

Answer 1

From an API perspective, Java interfaces must be immutable once created to prevent breaking consumers and implementors of the interface. Since adding new methods to an existing service needs to be API-compatible, grpc-java was forced to remove the interfaces.

Using default methods in Java 8 may be an option, but grpc-java can't require Java 8 any time soon, so it would probably be a new codegen flavor.