The seda: component provides asynchronous SEDA behavior, so that messages are exchanged on a BlockingQueue and consumers are invoked in a separate thread from the producer.
Note that queues are only visible within a single
CamelContext. If you want to communicate across
CamelContext
instances (for example, communicating between Web
applications), see the VM component.
This component does not implement any kind of persistence or recovery, if the VM terminates while messages are yet to be processed. If you need persistence, reliability or distributed SEDA, try using either JMS or ActiveMQ.
Synchronous | |
---|---|
The Direct component provides synchronous invocation of any consumers when a producer sends a message exchange. |
seda:queueName[?options]
Where queueName
can be any string that uniquely identifies the endpoint
within the current CamelContext.
You can append query options to the URI in the following format,
?option=value&option=value&...
Note | |
---|---|
When matching consumer entpoints to producer endpoints, only the |
Name | Default | Description |
---|---|---|
size
|
Unbounded | The maximum size (= capacity of the number of messages it can max hold) of the SEDA
queue. The default value in Camel 2.2 or older is 1000 . From Camel 2.3
onwards the size is unbounded by default. |
concurrentConsumers
|
1
|
Fuse Mediation Router 1.6.1/2.0: Number of concurrent threads processing exchanges. |
waitForTaskToComplete
|
IfReplyExpected
|
Fuse Mediation Router 2.0: Option to specify whether the caller
should wait for the async task to complete or not before continuing. The following three
options are supported: Always , Never or
IfReplyExpected . The first two values are self-explanatory. The last
value, IfReplyExpected , will only wait if the message is Request Reply based. The default option is
IfReplyExpected . See more information about Async messaging. |
timeout
|
30000
|
Fuse Mediation Router 2.0: Timeout in millis a seda producer will at
most waiting for an async task to complete. See waitForTaskToComplete
and Async for more details. In Camel
2.2 you can now disable timeout by using 0 or a negative value. |
multipleConsumers
|
false
|
Camel 2.2: Specifies whether multiple consumers are allowed or not. If enabled, you can use SEDA for a publish/subscribe style of messaging. Send a message to a SEDA queue and have multiple consumers receive a copy of the message. |
limitConcurrentConsumers
|
true
|
Camel 2.3: Whether to limit the concurrentConsumers to maximum 500. If its configured with a higher number an exception will be thrown. You can disable this check by turning this option off. |
In Fuse Mediation Router 2.0 the Seda component supports using Request Reply, where the caller will wait for the Async route to complete. For instance:
from("mina:tcp://0.0.0.0:9876?textline=true&sync=true").to("seda:input"); from("seda:input").to("bean:processInput").to("bean:createResponse");
In the route above, we have a TCP listener on port 9876 that accepts incoming requests.
The request is routed to the seda:input
queue. As it is a Request Reply message, we wait for the response. When
the consumer on the seda:input
queue is complete, it copies the response to
the original message response.
Fuse Mediation Router 1.x does not have this feature implemented, the Seda queues in Fuse Mediation Router 1.x will never wait.
Camel 2.0 - 2.2: Works only with 2 endpoints | |
---|---|
Using Request Reply over SEDA or VM only works with 2 endpoints. You cannot chain endpoints by sending to A -> B -> C etc. Only between A -> B. The reason is the implementation logic is fairly simple. To support 3+ endpoints makes the logic much more complex to handle ordering and notification between the waiting threads properly. This has been improved in Camel 2.3 onwards, which allows you to chain as many endpoints as you like. |
By default, the SEDA endpoint uses a single consumer thread, but you can configure it to use concurrent consumer threads. So instead of thread pools you can use:
from("seda:stageName?concurrentConsumers=5").process(...)
The thread pool is a pool that can increase/shrink dynamically at runtime depending on load, whereas the concurrent consumers are always fixed.
Be aware that adding a thread pool to a SEDA endpoint by doing something like:
from("seda:stageName").thread(5).process(...)
Can wind up with two BlockQueues
: one from the SEDA endpoint, and one
from the workqueue of the thread pool, which may not be what you want. Instead, you might want
to consider configuring a Direct endpoint with a thread
pool, which can process messages both synchronously and asynchronously. For example:
from("direct:stageName").thread(5).process(...)
You can also directly configure number of threads that process messages on a SEDA endpoint
using the concurrentConsumers
option.
In the route below we use the SEDA queue to send the request to this async queue to be able to send a fire-and-forget message for further processing in another thread, and return a constant reply in this thread to the original caller.
public void configure() throws Exception { from("direct:start") // send it to the seda queue that is async .to("seda:next") // return a constant response .transform(constant("OK")); from("seda:next").to("mock:result"); }
Here we send a Hello World message and expect the reply to be OK.
Object out = template.requestBody("direct:start", "Hello World"); assertEquals("OK", out);
The "Hello World" message will be consumed from the SEDA queue from another thread for
further processing. Since this is from a unit test, it will be sent to a
mock
endpoint where we can do assertions in the unit test.
Available as of Camel 2.2
In this example we have defined two consumers and registered them as spring beans.
<!-- define the consumers as spring beans --> <bean id="consumer1" class="org.apache.camel.spring.example.FooEventConsumer"/> <bean id="consumer2" class="org.apache.camel.spring.example.AnotherFooEventConsumer"/> <camelContext xmlns="http://camel.apache.org/schema/spring"> <!-- define a shared endpoint which the consumers can refer to instead of using url --> <endpoint id="foo" uri="seda:foo?multipleConsumers=true"/> </camelContext>
Since we have specified multipleConsumers=true on the seda foo endpoint we can have those two consumers receive their own copy of the message as a kind of pub-sub style messaging.
As the beans are part of an unit test they simply send the message to a mock endpoint, but notice how we can use @Consume to consume from the seda queue.
public class FooEventConsumer { @EndpointInject(uri = "mock:result") private ProducerTemplate destination; @Consume(ref = "foo") public void doSomething(String body) { destination.sendBody("foo" + body); } }