dubbo-java-interop-from-go

name	Dubbo Java interop from Go
description	Guides interoperability between dubbo-go v3 and dubbo-java — cross-language RPC calls using Triple+Protobuf or Dubbo+Hessian2. Use when user asks how to call a Java Dubbo service from Go, expose a Go service to Java clients, share a proto/interface across languages, or pick between Triple and Dubbo protocols for interop.

Dubbo Java ↔ Go Interop

Interop is one of dubbo-go's distinctive strengths: a single service definition can be served by Go and consumed by Java (or vice versa) without a gateway. Two viable paths:

Path	Wire format	Serialization	When to use
Triple + Protobuf (recommended)	HTTP/2	Protobuf	New services, polyglot teams, gRPC-compatible clients
Dubbo + Hessian2	TCP (dubbo)	Hessian2	Calling existing Java services that were originally defined with Java interfaces (no .proto)

Pick Triple unless you're integrating with an existing Hessian2-based Java codebase.

---

Path 1: Triple + Protobuf (recommended)

Shared .proto file drives both sides. Set both go_package and java_package:

syntax = "proto3";

package org.apache.dubbo.sample;

option go_package = "github.com/yourorg/yourapp/proto;greet";
option java_package = "org.apache.dubbo.sample";
option java_multiple_files = true;

service Greeter {
  rpc SayHello(HelloRequest) returns (HelloReply);
}

message HelloRequest  { string name = 1; }
message HelloReply    { string message = 1; }

Go server — nothing interop-specific, just plain Triple:

srv, _ := server.NewServer(
    server.WithServerProtocol(
        protocol.WithPort(20000),
        protocol.WithTriple(),
    ),
)
greet.RegisterGreeterHandler(srv, &impl{})
srv.Serve()

Testing interop without a client — Triple supports JSON over HTTP/1.1, so you can verify a Go Triple server from any HTTP tool:

curl -H "Content-Type: application/json" \
     -d '{"name":"Dubbo"}' \
     http://localhost:20000/org.apache.dubbo.sample.Greeter/sayHello

The path is /<java_package>.<service>/<method> — note the lowercase-first-letter method name (Java camelCase convention).

Java client calling the Go server uses standard dubbo-java APIs; no Go-specific code. See java_interop/protobuf-triple for the full working pair.

Rules of thumb for Triple interop

• Method name casing: Protobuf generators emit SayHello in Go and sayHello on the Java wire. The HTTP route uses the lowercase-first form.
• Package must match: The java_package in the proto is what Java's dubbo picks up as the interface FQN. Pick it deliberately — renaming later is a breaking change.
• Built-in reflection: Triple exposes gRPC reflection automatically, so Java clients using tools like grpcurl can list services without extra config.

---

Path 2: Dubbo protocol + Hessian2 (Java-defined services)

Use this when the service was defined by a Java interface (no .proto) and you need to add a Go side.

The Go side must mirror the Java POJO exactly, via Hessian2 registration. Each field name, type, and JavaClassName() must match the Java class.

package greet

import (
    dubbo_go_hessian2 "github.com/apache/dubbo-go-hessian2"
)

type GreetRequest struct {
    Name string
}

// Must match the Java class's fully-qualified name
func (x *GreetRequest) JavaClassName() string {
    return "org.apache.dubbo.hessian2.api.GreetRequest"
}

type GreetResponse struct {
    Greeting string
}

func (x *GreetResponse) JavaClassName() string {
    return "org.apache.dubbo.hessian2.api.GreetResponse"
}

func init() {
    dubbo_go_hessian2.RegisterPOJO(new(GreetRequest))
    dubbo_go_hessian2.RegisterPOJO(new(GreetResponse))
}

Go server:

srv, _ := server.NewServer(
    server.WithServerProtocol(
        protocol.WithPort(20000),
        protocol.WithDubbo(),   // NOT Triple
    ),
)
greet.RegisterGreetingsServiceHandler(srv, &impl{})
srv.Serve()

Generate the Go stub from the same proto that describes the Java interface with protoc-gen-go-dubbo (different plugin from protoc-gen-go-triple). That's what produces greet.dubbo.go and greet.hessian2.go.

See java_interop/non-protobuf-dubbo.

Hessian2 gotchas

• Field names are case-sensitive on the wire — Go's uppercase exports are serialized lowercase-first to match Java conventions. The hessian2 library handles this automatically, but custom struct tags can break it.
• Unsupported types: Go generics, channels, functions won't serialize. Stick to primitives, slices, maps, and other registered POJOs.
• Unregistered POJOs → hessian: failed to decode at runtime. Always RegisterPOJO in the package's init().
• Java enum maps to Go int (ordinal), not string — unless the Java side customized serialization.
• Time: Java Date ↔ Go time.Time generally works; java.time.* types need extra care.

---

Service discovery across languages

If both sides use the same registry (Nacos / ZooKeeper), they discover each other automatically — the registry entry is language-agnostic, just a URL with protocol + address.

dubbo.NewInstance(
    dubbo.WithName("polyglot-service"),   // same application name as Java side
    dubbo.WithRegistry(registry.WithNacos(), registry.WithAddress("127.0.0.1:8848")),
    dubbo.WithProtocol(protocol.WithTriple(), protocol.WithPort(20000)),
)

See java_interop/service_discovery.

---

Decision table

Scenario	Path
New service, Go + Java teams both need clients	Triple + Protobuf
Calling an existing Java Dubbo service defined by Java interface	Dubbo + Hessian2
Legacy Java service exports both Triple and Dubbo endpoints	Triple + Protobuf on Go side
Need gRPC-compatible wire	Triple + Protobuf
Can't touch Java side, and it's not Protobuf	Dubbo + Hessian2

---

Reference samples

• java_interop/protobuf-triple — both directions, Triple+Protobuf
• java_interop/non-protobuf-dubbo — Hessian2 POJO bridge
• java_interop/non-protobuf-triple — Triple without Protobuf (rare)
• java_interop/service_discovery — Nacos-based cross-language discovery

Official guide: Interoperability with Dubbo Java