Nats

Since Camel 2.17

Both producer and consumer are supported

NATS is a fast and reliable messaging platform.

Maven users will need to add the following dependency to their pom.xml for this component.

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-nats</artifactId>
    <!-- use the same version as your Camel core version -->
    <version>x.y.z</version>
</dependency>

URI format

nats:topic[?options]

Where topic is the topic name

Configuring Options

Camel components are configured on two separate levels:

  • component level

  • endpoint level

Configuring Component Options

The component level is the highest level which holds general and common configurations that are inherited by the endpoints. For example a component may have security settings, credentials for authentication, urls for network connection and so forth.

Some components only have a few options, and others may have many. Because components typically have pre configured defaults that are commonly used, then you may often only need to configure a few options on a component; or none at all.

Configuring components can be done with the Component DSL, in a configuration file (application.properties|yaml), or directly with Java code.

Configuring Endpoint Options

Where you find yourself configuring the most is on endpoints, as endpoints often have many options, which allows you to configure what you need the endpoint to do. The options are also categorized into whether the endpoint is used as consumer (from) or as a producer (to), or used for both.

Configuring endpoints is most often done directly in the endpoint URI as path and query parameters. You can also use the Endpoint DSL and DataFormat DSL as a type safe way of configuring endpoints and data formats in Java.

A good practice when configuring options is to use Property Placeholders, which allows to not hardcode urls, port numbers, sensitive information, and other settings. In other words placeholders allows to externalize the configuration from your code, and gives more flexibility and reuse.

The following two sections lists all the options, firstly for the component followed by the endpoint.

Component Options

The Nats component supports 7 options, which are listed below.

Name Description Default Type

servers (common)

URLs to one or more NAT servers. Use comma to separate URLs when specifying multiple servers.

String

verbose (common)

Whether or not running in verbose mode.

false

boolean

bridgeErrorHandler (consumer)

Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions (if possible) occurred while the Camel consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. Important: This is only possible if the 3rd party component allows Camel to be alerted if an exception was thrown. Some components handle this internally only, and therefore bridgeErrorHandler is not possible. In other situations we may improve the Camel component to hook into the 3rd party component and make this possible for future releases. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored.

false

boolean

lazyStartProducer (producer)

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

false

boolean

autowiredEnabled (advanced)

Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc.

true

boolean

headerFilterStrategy (filter)

To use a custom org.apache.camel.spi.HeaderFilterStrategy to filter header to and from Camel message.

HeaderFilterStrategy

useGlobalSslContextParameters (security)

Enable usage of global SSL context parameters.

false

boolean

Endpoint Options

The Nats endpoint is configured using URI syntax:

nats:topic

with the following path and query parameters:

Path Parameters (1 parameters)

Name Description Default Type

topic (common)

Required The name of topic we want to use.

String

Query Parameters (29 parameters)

Name Description Default Type

connectionTimeout (common)

Timeout for connection attempts. (in milliseconds).

2000

int

flushConnection (common)

Define if we want to flush connection when stopping or not.

true

boolean

flushTimeout (common)

Set the flush timeout (in milliseconds).

1000

int

maxPingsOut (common)

maximum number of pings have not received a response allowed by the client.

2

int

maxReconnectAttempts (common)

Max reconnection attempts.

60

int

noEcho (common)

Turn off echo. If supported by the gnatsd version you are connecting to this flag will prevent the server from echoing messages back to the connection if it has subscriptions on the subject being published to.

false

boolean

noRandomizeServers (common)

Whether or not randomizing the order of servers for the connection attempts.

false

boolean

pedantic (common)

Whether or not running in pedantic mode (this affects performance).

false

boolean

pingInterval (common)

Ping interval to be aware if connection is still alive (in milliseconds).

120000

int

reconnect (common)

Whether or not using reconnection feature.

true

boolean

reconnectTimeWait (common)

Waiting time before attempts reconnection (in milliseconds).

2000

int

requestCleanupInterval (common)

Interval to clean up cancelled/timed out requests.

5000

int

servers (common)

URLs to one or more NAT servers. Use comma to separate URLs when specifying multiple servers.

String

verbose (common)

Whether or not running in verbose mode.

false

boolean

maxMessages (consumer)

Stop receiving messages from a topic we are subscribing to after maxMessages.

String

poolSize (consumer)

Consumer thread pool size (default is 10).

10

int

queueName (consumer)

The Queue name if we are using nats for a queue configuration.

String

replyToDisabled (consumer)

Can be used to turn off sending back reply message in the consumer.

false

boolean

bridgeErrorHandler (consumer (advanced))

Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions (if possible) occurred while the Camel consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. Important: This is only possible if the 3rd party component allows Camel to be alerted if an exception was thrown. Some components handle this internally only, and therefore bridgeErrorHandler is not possible. In other situations we may improve the Camel component to hook into the 3rd party component and make this possible for future releases. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored.

false

boolean

exceptionHandler (consumer (advanced))

To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this option is not in use. By default the consumer will deal with exceptions, that will be logged at WARN or ERROR level and ignored.

ExceptionHandler

exchangePattern (consumer (advanced))

Sets the exchange pattern when the consumer creates an exchange.

Enum values:

  • InOnly

  • InOut

ExchangePattern

replySubject (producer)

the subject to which subscribers should send response.

String

requestTimeout (producer)

Request timeout in milliseconds.

20000

long

lazyStartProducer (producer (advanced))

Whether the producer should be started lazy (on the first message). By starting lazy you can use this to allow CamelContext and routes to startup in situations where a producer may otherwise fail during starting and cause the route to fail being started. By deferring this startup to be lazy then the startup failure can be handled during routing messages via Camel’s routing error handlers. Beware that when the first message is processed then creating and starting the producer may take a little time and prolong the total processing time of the processing.

false

boolean

connection (advanced)

Reference an already instantiated connection to Nats server.

Connection

headerFilterStrategy (advanced)

Define the header filtering strategy.

HeaderFilterStrategy

traceConnection (advanced)

Whether or not connection trace messages should be printed to standard out for fine grained debugging of connection issues.

false

boolean

secure (security)

Set secure option indicating TLS is required.

false

boolean

sslContextParameters (security)

To configure security using SSLContextParameters.

SSLContextParameters

Message Headers

The Nats component supports 5 message header(s), which is/are listed below:

Name Description Default Type

CamelNatsMessageTimestamp (common)

Constant: NATS_MESSAGE_TIMESTAMP

The timestamp of a consumed message.

long

CamelNatsSID (common)

Constant: NATS_SID

The SID of a consumed message.

String

CamelNatsReplyTo (common)

Constant: NATS_REPLY_TO

The ReplyTo of a consumed message (may be null).

String

CamelNatsSubject (common)

Constant: NATS_SUBJECT

The Subject of a consumed message.

String

CamelNatsQueueName (common)

Constant: NATS_QUEUE_NAME

The Queue name of a consumed message (may be null).

String

Configuring servers

You configure the NATS servers on either the component or the endpoint.

For example to configure this once on the component you can do:

NatsComponent nats = context.getComponent("nats", NatsComponent.class);
nats.setServers("someserver:4222,someotherserver:42222");

Notice how you can specify multiple servers separated by comma.

Or you can specify the servers in the endpoint URI

from("direct:send").to("nats:test?servers=localhost:4222");

The endpoint configuration will override any server configuration on the component level.

Configuring username and password or token

You can specify username and password for the servers in the server URLs, where its username:password@url, or token@url etc:

NatsComponent nats = context.getComponent("nats", NatsComponent.class);
nats.setServers("scott:tiger@someserver:4222,superman:123@someotherserver:42222");

If you are using Camel Main or Spring Boot you can configure the server urls in the application.properties file

camel.component.nats.servers=scott:tiger@someserver:4222,superman:123@someotherserver:42222

Request/Reply support

The producer supports request/reply where it can wait for an expected reply message.

The consumer will when routing the message is complete, send back the message as reply-message if required.

Examples

Producer example:

from("direct:send")
  .to("nats:mytopic");

In case of using Authorization you can directly specify your credentials in the server URL

from("direct:send")
  .to("nats:mytopic?servers=username:password@localhost:4222");

or your token

from("direct:send")
  .to("nats:mytopic?servers=token@localhost:4222);

Consumer example:

from("nats:mytopic?maxMessages=5&queueName=myqueue")
  .to("mock:result");