methanol-protobuf

Adapters for Google's Protocol Buffers.

Encoding & Decoding

Any subtype of MessageLite is supported by encoders & decoders. Decoders can optionally have an ExtensionRegistryLite or an ExtensionRegistry to enable message extensions.

Installation

Gradle

implementation 'com.github.mizosoft.methanol:methanol-protobuf:1.7.0'

Maven

<dependency>
  <groupId>com.github.mizosoft.methanol</groupId>
   <artifactId>methanol-protobuf</artifactId>
   <version>1.7.0</version>
</dependency>

The adapters need to be registered as service providers so Methanol knows they're there. The way this is done depends on your project setup.

Module Path

Follow these steps if your project uses the Java module system.

1. Add this class to your module:

   public class ProtobufProviders {   
     public static class EncoderProvider {
       public static BodyAdapter.Encoder provider() {
         return ProtobufAdapterFactory.createEncoder();
       }
     }
   
     public static class DecoderProvider {
       public static BodyAdapter.Decoder provider() {
         return ProtobufAdapterFactory.createDecoder();
       }
     }
   }
   

2. Add the corresponding provider declarations in your module-info.java file.

   requires methanol.adapter.protobuf;
   
   provides BodyAdapter.Encoder with ProtobufProviders.EncoderProvider;
   provides BodyAdapter.Decoder with ProtobufProviders.DecoderProvider;
   

Classpath

Registering adapters from the classpath requires declaring the implementation classes in provider-configuration files that are bundled with your JAR. You'll first need to implement delegating Encoder & Decoder that forward to the instances created by ProtobufAdapterFactory. Extending from ForwardingEncoder & ForwardingDecoder makes this easier.

You can use Google's AutoService to generate the provider-configuration files automatically, so you won't bother writing them.

Using AutoService

First, install AutoService.

Gradle

implementation "com.google.auto.service:auto-service-annotations:$autoServiceVersion"
annotationProcessor "com.google.auto.service:auto-service:$autoServiceVersion"

Maven

<dependency>
  <groupId>com.google.auto.service</groupId>
  <artifactId>auto-service-annotations</artifactId>
  <version>${autoServiceVersion}</version>
</dependency>

Configure the annotation processor with the compiler plugin.

<plugin>
  <artifactId>maven-compiler-plugin</artifactId>
  <configuration>
    <annotationProcessorPaths>
      <path>
        <groupId>com.google.auto.service</groupId>
        <artifactId>auto-service</artifactId>
        <version>${autoServiceVersion}</version>
      </path>
    </annotationProcessorPaths>
  </configuration>
</plugin>

Next, add this class to your project:

public class ProtobufAdapters {  
  @AutoService(BodyAdapter.Encoder.class)
  public static class Encoder extends ForwardingEncoder {
    public Encoder() {
      super(ProtobufAdapterFactory.createEncoder());
    }
  }

  @AutoService(BodyAdapter.Decoder.class)
  public static class Decoder extends ForwardingDecoder {
    public Decoder() {
      super(ProtobufAdapterFactory.createDecoder());
    }
  }
}

Manual Configuration

You can also write the configuration files manually. First, add this class to your project:

public class ProtobufAdapters {
  public static class Decoder extends ForwardingDecoder {
    public Decoder() {
      super(ProtobufAdapterFactory.createDecoder());
    }
  }

  public static class Encoder extends ForwardingEncoder {
    public Encoder() {
      super(ProtobufAdapterFactory.createEncoder());
    }
  }
}

Next, create two provider-configuration files in the resource directory: META-INF/services, one for the encoder and the other for the decoder. Each file must contain the fully qualified name of the implementation class.

Let's say the above class is in a package named com.example. You'll want to have one file for the encoder named:

META-INF/services/com.github.mizosoft.methanol.BodyAdapter$Encoder

and contains the following line:

com.example.ProtobufAdapters$Encoder

Similarly, the decoder's file is named:

META-INF/services/com.github.mizosoft.methanol.BodyAdapter$Decoder

and contains:

com.example.ProtobufAdapters$Decoder