methanol-jackson-flux

Adapters for JSON & Reactive Streams using Jackson & Reactor.

Decoding

This adapter converts response bodies into publisher-based sources. Supported types are Mono, Flux, org.reactivestreams.Publisher and java.util.concurrent.Flow.Publisher. For all these types except Mono, the response body is expected to be a JSON array. The array is tokenized into its individual elements, each mapped to the publisher's element type.

Note that an HttpResponse handled with this adapter is completed immediately after the response headers are received. Body completion is handled by the returned publisher source. Additionally, the decoder always uses Jackson's non-blocking parser. This makes MoreBodyHandlers::ofDeferredObject redundant with this decoder.

Encoding

With the exception of Mono, any subtype of org.reactivestreams.Publisher or java.util.concurrent.Flow.Publisher is encoded to a JSON array containing zero or more elements, each mapped from each published object. Mono sources are encoded to a single JSON object (if completed with any).

Installation

Gradle

implementation 'com.github.mizosoft.methanol:methanol-jackson-flux:1.7.0'

Maven

<dependency>
  <groupId>com.github.mizosoft.methanol</groupId>
   <artifactId>methanol-jackson-flux</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 JacksonFluxProviders {
     private static final ObjectMapper mapper = new ObjectMapper();
   
     public static class EncoderProvider {
       public static BodyAdapter.Encoder provider() {
         return JacksonFluxAdapterFactory.createEncoder(mapper);
       }
     }
   
     public static class DecoderProvider {
       public static BodyAdapter.Decoder provider() {
         return JacksonFluxAdapterFactory.createDecoder(mapper);
       }
     }
   }
   

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

   requires methanol.adapter.jackson.flux;
   
   provides BodyAdapter.Encoder with JacksonFluxProviders.EncoderProvider;
   provides BodyAdapter.Decoder with JacksonFluxProviders.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 JacksonAdapterFactory. 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 JacksonFluxAdapters {
  private static final ObjectMapper mapper = new ObjectMapper();

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

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

Manual Configuration

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

public class JacksonFluxAdapters {
  private static final ObjectMapper mapper = new ObjectMapper();

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

  public static class Decoder extends ForwardingDecoder {
    public Decoder() {
      super(JacksonFluxAdapterFactory.createDecoder(mapper));
    }
  }
}

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.JacksonFluxAdapters$Encoder

Similarly, the decoder's file is named:

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

and contains:

com.example.JacksonFluxAdapters$Decoder