NATS Spring Support

• Using the Starter
• Using the NATS Modules
  • Multiple NATS Connections
• Using the Binder
  • Request-Reply
  • Partitions
• Configuration
  • Custom Listeners
• Samples
• Building This Project
• External Resources
• License

This repository contains two core packages:

• nats-spring an implementation of the autoconfigure pattern for a NATS connection using the core NATS Java Client
• nats-spring-cloud-stream-binder a spring cloud binder for NATS

A third package nats-samples is included to demonstrate how the other two modules can be used.

Version Notes

As of version 0.3.x the properties used to configure can be in YAML or properties if you pass in the NATS properties externally. If you want the application file to contain connection info it should be a properties file and not YAML. In other words:

spring.cloud.stream.bindings.input.destination=dataIn
spring.cloud.stream.bindings.input.binder=nats1
spring.cloud.stream.binders.nats1.type=nats
spring.cloud.stream.binders.nats1.environment.nats.spring.cloud.stream.binder.server=nats://localhost:4222

works while the YAML equivalent will not.

Snapshots are hosted on oss.sonatype.org, to access these within maven update your settings to include:

<profiles>
    <profile>
        <id>allow-snapshots</id>
        <activation>
            <activeByDefault>true</activeByDefault>
        </activation>
        <repositories>
            <repository>
                <id>snapshots-repo</id>
                <url>https://oss.sonatype.org/content/repositories/snapshots</url>
                <releases>
                    <enabled>false</enabled>
                </releases>
                <snapshots>
                    <enabled>true</enabled>
                </snapshots>
            </repository>
        </repositories>
    </profile>
</profiles>

The released version should be available at:

<repository>
    <id>oss-sonatype</id>
    <name>oss-sonatype</name>
    <url>https://oss.sonatype.org/content/repositories/</url>
</repository>

and ultimately at maven central.

Using the Starter

A spring boot starter is provided that will bring in the autoconfigure module.

To include the starter, add the following dependency to your pom.xml:

<dependency>
    <groupId>io.nats</groupId>
    <artifactId>nats-spring-boot-starter</artifactId>
    <version>0.5.6</version>
</dependency>

Using the NATS Modules

To depend on the autoconfigure module, simply add it as a dependency in your pom.xml:

<dependency>
    <groupId>io.nats</groupId>
    <artifactId>jnats</artifactId>
    <version>2.12.0</version>
</dependency>
<dependency>
<groupId>io.nats</groupId>
<artifactId>nats-spring</artifactId>
<version>0.5.6</version>
</dependency>

This module defines and exports an auto-configuration for NATS Connection objects.

Multiple NATS Connections

By default the autoconfigure modules will create a single NATS connection and the binders will create a second one.

An example multi-binder-sample demonstrates how to have multiple named binders.

Using the NATS Cloud Stream Binder

To use the binder, simply define a binding in your application.yml with the type nats:

spring:
    cloud:
        stream:
            bindings:
                input:
                    destination: dataIn
                    binder: nats
                output:
                    destination: dataOut
                    binder: nats

and include a dependency on the library:

<dependency>
    <groupId>io.nats</groupId>
    <artifactId>nats-spring-cloud-stream-binder</artifactId>
    <version>0.5.6</version>
</dependency>

See the Spring Cloud Stream Documentation for information about more complex configurations of the bindings.

The NATS binder leverages the autoconfigure module, or manual configuration to build a NATS connection. Standard properties are used to specify inputs and outputs. Inputs, specified with a destination and group name are mapped to subjects and queue names, with the destination becoming the subject, and the group becoming the queue. Outputs are specified with a destination name that becomes the subject.

Consumers are implemented with a dispatcher. Each consumer will create its own dispatcher in the core library, resulting in a thread per consumer.

Polled consumers are implemented with a subscription.

Currently the polling code will wait forever for a message and is not configurable.

Producers publish directly through the connection.

Request-Reply

The binder uses message header propagation to support NATS-style request-reply. The reply-to subject is passed as a header when a message is received. That reply to header is used as the outgoing subject if it is present when a message is sent. This system by-passes the configured producer destination.

Partitions

NATS does not use the concept of partitions. The binder supports the API for partitions as far as required, but no underlying messaging is associated with that change beyond the name of the destination.

Configuration

By default, properties are configured using the nats.spring prefix:

• nats.spring.server specifies the NATS server url or a list of urls in a comma separated list
• nats.spring.connection-name the connection name
• nats.spring.max-reconnect the maximum reconnects attempts on a single disconnect before the connection closes
• nats.spring.reconnect-wait the time, as a duration like 4s, to wait between trying to reconnect to the same server
• nats.spring.connection-timeout the time, as a duration like 4s, to wait before cancelling the connection
• nats.spring.ping-interval the time, as a duration like 4s, between pings to the server
• nats.spring.reconnect-buffer-size the size in bytes for the reconnect buffer
• nats.spring.inbox-prefix a custom inbox prefix
• nats.spring.no-echo turn off echo from the server
• nats.spring.utf8-support enable UTF-8 subject names (warning this is an experimental feature, not all language clients will support it)
• nats.spring.username, nats.spring.password the user name and password to authenticate with
• nats.spring.token an authentication token, takes precedence over the username/password
• nats.spring.credentials a path to a credentials file, takes precedence over the token and user/pass
• nats.spring.nkey a private key (seed) for NKey authentication, takes precedence over the credentials, token and user/pass

TLS can be configured several ways. Set up a default context using system properties like javax.net.ssl.keyStore, set a default SSLContext in the main method before running the spring application, or by setting several properties:

• nats.spring.trust-store-password the password for the trust store, defaults to ""

• nats.spring.trust-store-path the path to the trust store file

• nats.spring.trust-store-provider (optional) the format of the trust store, defaults to "SunX509". Common options are "SunX509", "PKIX".

• nats.spring.trust-store-type (optional) the format of the trust store, defaults to "PKCS12". Common options are "PKCS12", "JKS", "JCEKS", "DKS".

• nats.spring.key-store-password the password for the key store, defaults to ""

• nats.spring.key-store-path the path to the key store file

• nats.spring.key-store-provider (optional) the format of the key store, defaults to "SunX509". Common options are "SunX509", "PKIX".

• nats.spring.key-store-type (optional) the format of the key store, defaults to "PKCS12". Common options are "PKCS12", "JKS", "JCEKS", "DKS".

• nats.spring.tls-protocol (optional) the preferred protocol for TLS handshake. Common options: TLSv1.2 (default), TLSv1.3.

The key-store-path and trust-store-path must be non-empty to trigger the creation of an SSL context.

Custom Listeners

Custom ConnectionListener and ErrorListeners can be provided by a bean factory. For example, you can implement:

@Bean
public ConnectionListener createConnectionListener(){
        return new ConnectionListener(){
@Override
public void connectionEvent(Connection conn,Events type){
        System.out.println("## Custom status change "+type);
        }
        };
        }

to create a custom connection listener. The connect-error-sample has an example for both types of listener.

If no custom listeners are provided, a default one is used which will log errors and connection events.

Samples

This repo contains two types of samples. First there is a stand-alone demo that can be used as starter code, for a POM at least. Second there is a collection of samples showing the major use-cases implemented by the core code:

• autoconfigure-sample a simple command line runner with spring boot that uses the auto-configured nats connection from an application.properties file.

• listener-sample uses the binder to listen to a single subject and print messages it receives. The configuration in application.yml specifies a single subject dataIn.

• processor-sample creates a processor. The example listens to the subject dataIn and sends to the subject dataOut. If the message contains a UTF-8 string, it is converted to all CAPS before being sent.

• polling-sample is similar to the listener sample, but uses polling.

• source-sample generates messages on a timer and sends them to a NATS endpoint. In order to leverage this pattern you need to create a named source. See the application.yml for details.

• queue-sample listens on a subject and queue group, run multiple copies of the sample to see how messages are load balanced.

• multi-connect-sample copy of the processor-sample that uses 2 nats connections.

• connect-error-sample demonstrates how to set up a custom connection and error handler.

You can exercise the samples using the nats-sub and nats-pub executables for the client library. For example, to try out the listener:

% java -jar nats-samples/listener-sample/target/listener-sample-0.5.6.jar --nats.spring.server="nats://localhost:4222"
...
2019-06-24 15:36:43.690  INFO 36282 --- [         nats:3] o.s.cloud.stream.binder.nats.Listener    : received message hello

% nats-pub dataIn "hello"

For the multi-binder, try:

% java -jar nats-samples/processor-sample/target/processor-sample-0.5.6.jar --nats.spring.server="nats://localhost:4222"
...

% nats-pub dataIn "hello"

 % nats-sub ">"
Listening on [>]
...
[6] Received on [dataIn]: 'hello'
[7] Received on [dataOut]: 'HELLO'

Building This Project

This project is built with maven. The mvnw helper is included in the root folder and its implementation is included in the .mvn folder. You should be able to compile using ./mvnw clean compile, or package the jars with ./mvnw clean package.

Internally there are multiple pom files, one parent for the project, one parent for the samples, one for the autoconfigure code, one for the binder, and one each for the samples. When built, each will have its own artifacts.

Signing and deploying requires that you set up your settings.xml file for maven:

<settings>
    <servers>
        <server>
            <id>ossrh</id>
            <username>xxx</username>
            <password>xxxxx</password>
        </server>
    </servers>
    <profiles>
        <profile>
            <activation>
                <activeByDefault>true</activeByDefault>
            </activation>
            <properties>
                <gpg.keyid>xxx</gpg.keyid>
                <gpg.passphrase>xxxxx</gpg.passphrase>
                <gpg.secretkeyring>xxxxx</gpg.secretkeyring>
            </properties>
        </profile>
    </profiles>
</settings>

Sonatype will accept and close a non-staging repository, but you must manually release it.

Adding New Configuration Properties

All of the configuration properties are injected into the NatsProperties class in the autoconfigure module. This class provides a toOptions() method that spits out a valid options configuration from the NATS client library. To add new properties, simply add them to NatsProperties and update the toOptions() method appropriately.

External Resources

• NATS
• NATS server
• NATS Java Client
• Spring Cloud Stream

License

Unless otherwise noted, the nats-account-server source files are distributed under the Apache Version 2.0 license found in the LICENSE file.