How to deserialize protobuf to json?

[MPeli]

Hi,

I've successfully parsed a proto file and now have instances of ProtoFile and a protobuf. I would like to perform deserialization at runtime, as I do not know which proto files I will be dealing with before compilation. How can I deserialize a message using ProtoFile? I'm specifically interested in obtaining a JSON string as output.

Main

package org.example;

import java.nio.file.FileSystems;
import java.util.List;

import com.squareup.wire.schema.Field;
import com.squareup.wire.schema.Location;
import com.squareup.wire.schema.MessageType;
import com.squareup.wire.schema.ProtoFile;
import com.squareup.wire.schema.Schema;
import com.squareup.wire.schema.SchemaLoader;
import com.squareup.wire.schema.Type;

public class Main {
    public static void main(String[] args) {
        // Wire
        System.out.println("Wire");

        SchemaLoader loader = new SchemaLoader(FileSystems.getDefault());
        List<Location> sourcePath = List.of(Location.get("./src/main/proto"));
        List<Location> protoPath = List.of();
        loader.initRoots(sourcePath, protoPath);
        Schema schema = loader.loadSchema();
        List<ProtoFile> protoFiles = schema.getProtoFiles();
        for (ProtoFile protoFile : protoFiles) {
            System.out.println(protoFile);
        }

        Type type = schema.getType("Test.Tick");
        if (type instanceof MessageType) {
            MessageType messageType = (MessageType) type;
            for (Field f : messageType.getDeclaredFields()) {
                System.out.println(f);
            }
        }
    }
}

pom.xml

<dependencies>
    <!-- https://mvnrepository.com/artifact/com.squareup.wire/wire-runtime-jvm -->
    <dependency>
        <groupId>com.squareup.wire</groupId>
        <artifactId>wire-runtime-jvm</artifactId>
        <version>4.9.8</version>
        <scope>runtime</scope>
    </dependency>
    <!-- https://mvnrepository.com/artifact/com.squareup.wire/wire-schema-jvm -->
    <dependency>
        <groupId>com.squareup.wire</groupId>
        <artifactId>wire-schema-jvm</artifactId>
        <version>4.9.8</version>
    </dependency>
</dependencies>

Thank you.

[oldergod]

I would try to create a WireJsonAdapterFactory and pass it to Moshi.

[MPeli]

Thank you. I have made slight modifications to my code; I added wire-moshi-adapter to pom.xml. I used protoc to generate TickOuterClass, which will not be available during deserialization. It is included so that I can generate a serialized message.

I am uncertain about how to use Moshi to deserialize a protobuf to JSON. Specifically, I'm unsure about creating an adapter and whether it's necessary.

Thank you.

Main

package org.example;

import java.io.ByteArrayOutputStream;
import java.nio.file.FileSystems;
import java.util.List;

import com.squareup.moshi.Moshi;
import com.squareup.wire.schema.Field;
import com.squareup.wire.schema.Location;
import com.squareup.wire.schema.MessageType;
import com.squareup.wire.schema.ProtoFile;
import com.squareup.wire.schema.Schema;
import com.squareup.wire.schema.SchemaLoader;
import com.squareup.wire.schema.Type;
import com.squareup.wire.WireJsonAdapterFactory;

public class Main {
    public static void main(String[] args) {
        // Wire
        System.out.println("Wire");

        SchemaLoader loader = new SchemaLoader(FileSystems.getDefault());
        List<Location> sourcePath = List.of(Location.get("./src/main/proto"));
        List<Location> protoPath = List.of();
        loader.initRoots(sourcePath, protoPath);
        Schema schema = loader.loadSchema();
        List<ProtoFile> protoFiles = schema.getProtoFiles();
        for (ProtoFile protoFile : protoFiles) {
            System.out.println(protoFile);
        }

        Type type = schema.getType("org.example.Tick");
        if (type instanceof MessageType) {
            MessageType messageType = (MessageType) type;
            for (Field f : messageType.getDeclaredFields()) {
                System.out.println(f);
            }
        }

        // TickOuterClass will not be available
        // It is here just so that we can generate a serialized message
        TickOuterClass.Tick.Builder tickBuilder = TickOuterClass.Tick.newBuilder();
        tickBuilder.setAsk(1);
        tickBuilder.setBid(2);

        try {
            TickOuterClass.Tick tickToSerialize = tickBuilder.build();
            ByteArrayOutputStream output = new ByteArrayOutputStream();
            tickToSerialize.writeTo(output);

            TickOuterClass.Tick deserializedTick = TickOuterClass.Tick.parseFrom(output.toByteArray());
            System.out.println(deserializedTick);

            // Wire & Moshi
            Moshi moshi = new Moshi.Builder()
                    .add(new WireJsonAdapterFactory())
                    .build();

            // ToDo: use Moshi to deserialize a message to JSON
        }
        catch (Exception e) {
            System.out.println(e.getMessage());
        }
    }
}

pom.xml

<dependencies>
    <!-- https://mvnrepository.com/artifact/com.google.protobuf/protobuf-java -->
    <dependency>
        <groupId>com.google.protobuf</groupId>
        <artifactId>protobuf-java</artifactId>
        <version>4.26.0</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/com.google.inject/guice -->
    <dependency>
        <groupId>com.google.inject</groupId>
        <artifactId>guice</artifactId>
        <version>7.0.0</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/com.squareup.wire/wire-runtime-jvm -->
    <dependency>
        <groupId>com.squareup.wire</groupId>
        <artifactId>wire-runtime-jvm</artifactId>
        <version>4.9.8</version>
        <scope>runtime</scope>
    </dependency>
    <!-- https://mvnrepository.com/artifact/com.squareup.wire/wire-schema-jvm -->
    <dependency>
        <groupId>com.squareup.wire</groupId>
        <artifactId>wire-schema-jvm</artifactId>
        <version>4.9.8</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/com.squareup.wire/wire-moshi-adapter -->
    <dependency>
        <groupId>com.squareup.wire</groupId>
        <artifactId>wire-moshi-adapter</artifactId>
        <version>4.9.8</version>
    </dependency>
</dependencies>

Tick.proto

syntax = "proto3";
package org.example;

message Tick {
   double Ask = 1;
   double Bid = 2;
}