Seda — provides an asynchronous connection to any consumer in the same camelContext
element
Seda endpoints provide asynchronous SEDA behavior, so that messages are exchanged on a BlockingQueue and consumers are invoked in a separate thread from the producer.
Queues are visible within a single
camelContext
element. If you want to communicate across camelContext
elements, use a VM endpoint.
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 the JMS or ActiveMQ component.
![]() | Note |
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Direct endpoints provide synchronous invocation of any consumers when a producer sends a message exchange. |
Example 9, “Seda URI format” shows the syntax for a Seda endpoint URI.
queueName
can be any string that uniquely identifies the
endpoint within the current camelContext
elements.
![]() | Note |
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When matching consumer endpoints to producer endpoints, only the
|
Table 32, “Seda component options” describes the Seda component's options.
Table 32. Seda component options
Name | Default | Description |
---|---|---|
size
| Unbounded | The maximum capacity of the SEDA queue (i.e., the number of messages it can hold). Notice: Mind if you use this option, then its the first endpoint being created with the queue name, that determines the size. To make sure all endpoints use same size, then configure the size option on all of them, or the first endpoint being created. From Camel 2.11 onwards, a validation is taken place to ensure if using mixed queue sizes for the same queue name, Camel would detect this and fail creating the endpoint. |
concurrent Consumers
|
1
| Apache Camel 1.6.1/2.0: Number of concurrent threads processing exchanges. |
waitForTaskTo Complete
|
IfReply Expected
| 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
| Apache Camel 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. |
multiple Consumers
|
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. |
limitConcurrent Consumers
|
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. |
blockWhenFull
|
false
| Camel 2.9: CamWhether a thread that sends messages to a full SEDA queue will block until the queue's capacity is no longer exhausted. By default, an exception will be thrown stating that the queue is full. By enabling this option, the calling thread will instead block and wait until the message can be accepted. |
queueSize
| None | Camel 2.9
Component only: The maximum default
size (capacity of the number of messages it can hold) of the SEDA queue.
This option is used if size is not in use. |
pollTimeout
| 1000 | Camel 2.9.3,Consumer onlySpecifies the timeout to use when polling. When a timeout occurs, the consumer can check whether it is allowed to continue running. Setting a lower value allows the consumer to react more quickly upon shutdown. |
purgeWhen Stopping
| false
| Camel 2.11.1:Specifies whether to purge the task queue when stopping the consumer/route. Doing so allows the route to stop faster, as any pending messages on the queue are discarded. |
queue
| null | Camel 2.12.0: Defines the queue instance which will be used by the seda endpoint. |
queueFactory
| null
| Camel2.12.0: Defines the
QueueFactory which can create the queue for
the seda endpoint. |
failIfNoConsumers
| false | Camel 2.12.0 Specifies whether the producer should fail by throwing an exception, when sending to a SEDA queue with no active consumers. |
Available as of Camel 2.12
By default, the SEDA component always intantiates LinkedBlockingQueue, but you can use different implementation, you can reference your own BlockingQueue implementation, in this case the size option is not used
<bean id="arrayQueue" class="java.util.ArrayBlockingQueue"> <constructor-arg index="0" value="10" ><!-- size --> <constructor-arg index="1" value="true" ><!-- fairness --> </bean> <!-- ... and later --> <from>seda:array?queue=#arrayQueue</from>
Or you can reference a BlockingQueueFactory implementation, 3 implementations are provided LinkedBlockingQueueFactory, ArrayBlockingQueueFactory and PriorityBlockingQueueFactory:
<bean id="priorityQueueFactory" class="org.apache.camel.component.seda.PriorityBlockingQueueFactory"> <property name="comparator"> <bean class="org.apache.camel.demo.MyExchangeComparator" /> </property> </bean> <!-- ... and later --> <from>seda:priority?queueFactory=#priorityQueueFactory&size=100</from>
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.
![]() | until 2.2: Works only with 2 endpoints |
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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); } }