Before following this tutorial, make sure you’ve installed

You will need a private-public key pair to register your service in SNET. Generate them in Metamask before you start this tutorial.

Run this tutorial from a bash terminal.

We’ll use Java gRPC, for more details see

In this tutorial we’ll create a Java service and publish it in SingularityNET.

Step 1

Setup a ubuntu:18.04 docker container (with current SNET Daemon version) using provided Dockerfile.

docker build \
    --build-arg language=java \
    -t snet_java_service

docker run -p 7000:7000 -v $ETCD_HOST:$ETCD_CONTAINER -ti snet_java_service bash

From this point we follow the tutorial in the Docker container’s prompt.

cd dev-portal/tutorials/java

Step 2

Create the skeleton structure for your service’s project


PROJECT_NAME is a short tag for your project. It will be used to name project’s directory and as a namespace tag in the .proto file.

ORGANIZATION_ID is the id of an organization that you are a member or owner.

SERVICE_ID is the id of your service.

SERVICE_PORT is the port number (in localhost) the service will listen to. will create a directory named PROJECT_NAME with a basic empty implementation of the service.

In this tutorial we’ll implement a service with two methods:

  • int div(int a, int b)
  • string check(int a)

So we’ll use this command line to create project’s skeleton

./ tutorial my-org math-operations 7070
cd tutorial

Step 3

Now we’ll customize the skeleton code to actually implement our basic service. We need to edit ../howToWriteJavaService/tutorial/src/main/java/service_spec/tutorial.proto and define

  • the data structures used to carry input and output of the methods, and
  • the RPC API of the service.

Take a look at to understand everything you can do in the .proto file.

Edit the proto file:

nano src/main/java/service_spec/tutorial.proto

In this tutorial our proto file should be like this:

syntax = "proto3";

option java_generic_services = true;
option java_multiple_files = true;

message IntPair {
    int32 a = 1;
    int32 b = 2;

message SingleInt {
    int32 v = 1;

message SingleString {
    string s = 1;

service ServiceDefinition {
    rpc div(IntPair) returns (SingleInt) {}
    rpc check(SingleInt) returns (SingleString) {}

Each message statement define a data structure used either as input or output in the API. The service statement defines the RPC API itself.

Step 4

In order to actually implement our API we need to edit the file.

Look for SERVICE_API and replace doSomething() by our actual API methods:

public void div(IntPair request, StreamObserver<SingleInt> responseObserver) {
    int result = request.getA() / request.getB();
    SingleInt reply = SingleInt.newBuilder().setV(result).build();

Step 5

Now we’ll write a client to test our server locally (without using the Blockchain). Edit

Look for TEST_CODE and replace doSomething() implementation by our testing code:

public void div(int a, int b) {"Trying to divide "+a+" by "+ b);
    IntPair request = IntPair.newBuilder().setA(a).setB(b).build();
    SingleInt response;
    try {
        response = blockingStub.div(request);
        logger.log(Level.INFO, "Result: " + response.getV());
    } catch (StatusRuntimeException e) {
        logger.log(Level.WARNING, "RPC failed: {0}", e.getStatus());

Step 6

To compile the protobuf and generate server and client jar:

Note 1: protobuf compile is embedded in the commands below. For more details, please edit

Note 2: On you project name, used in the previous command ./

To generate a server application:

sh tutorial server

To generate a client application:

sh tutorial client

Step 7

To test our server locally (without using the Blockchain)

java -jar ./bin/JavaServer.jar &

In a new terminal instance

java -jar ./bin/JavaClient.jar 12 4

You should have something like the following output:

java -jar ./bin/JavaServer.jar &

# [1] 1627
# Nov 18, 2018 5:27:16 AM JavaServer start
# INFO: Server listening on 7070

java -jar ./bin/JavaClient.jar 12 4

# Client connected on port: 7070
# Nov 18, 2018 5:30:13 AM JavaClient div
# INFO: Trying to div 12 by 4
# Nov 18, 2018 5:30:13 AM JavaClient div

At this point you have successfully built a gRPC Java service. The executables can be used from anywhere inside the container (they don’t need anything from the installation directory) or outside the container.

The next steps in this tutorial will publish the service in SingularityNET.

Step 8

Now you must follow the publish tutorial to publish this service or use our script (next step).

You’ll also need a SNET CLI identity (check step 3 from publish tutorial).

Step 9

First, make sure you killed the server process started in Step 7.

Then publish and start your service:


Replace PAYMENT_ADDRESS by your public key (wallet).


./ 0x501e8c58E6C16081c0AbCf80Ce2ABb6b3f91E717

This will start the SNET Daemon and your service. If everything goes well you will see the Blockchain transaction logs and then the following messages (respectively from: your service and SNET Daemon):

# [Blockchain log]
# INFO: Server listening on 7070
# [daemon initial log]
# INFO[0002] Blockchain is enabled: instantiate payment validation interceptor 
# INFO[0002]                                               PaymentChannelStorageClient="&{ConnectionTimeout:5s RequestTimeout:3s Endpoints:[]}"
# INFO[0002] Default payment handler registered            defaultPaymentType=escrow
# DEBU[0002] starting daemon                              

You can double check if it has been properly published using

snet organization list-services my-org

Optionally you can un-publish the service

snet service delete my-org math-operations

Actually, since this is just a tutorial, you are expected to un-publish your service as soon as you finish the tests.

Other snet commands and options (as well as their documentation) can be found here.

Step 10

You can test your service making requests in command line:

The script will open and initialize a new payment channel, it’ll output the new channel id (that will be used by


# [Blockchain log]
# #channel_id
# 10

In this example the channel id is 10.

Now you can run VALUE_A VALUE_B:

./ 12 4

# [Blockchain log]
#   response:
#       v: 3

That’s it. Remember to delete your service as explained in Step 9.

snet service delete my-org math-operations

Last modified on : 24-Jan-24

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