jms 的基本概念
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一、Temporary Destinations
access temporary queues Or temporary topics :
jms:temp:queue:foo
jms:temp:topic:bar
This URL format enables multiple routes or processors or beans to refer to the same temporary destination
you can create three temporary destinations and use them in routes as inputs or outputs by referring to them by name.
二、JMS component reuses Spring 2's JmsTemplate
for sending messages
三、If you wish to use durable topic subscriptions, you need to specify both clientId
and durableSubscriptionName
. Note that the value of the clientId
.must be unique and
can only be used by a single JMS connection instance in your entire network.
You may prefer to use Virtual Topics
instead to avoid this limitation.
四、Options
You can configure many different properties on the JMS endpoint which map to properties on the JMSConfiguration POJO. Note: Many of these properties map to properties on Spring JMS, which Camel uses for sending and receiving messages. So you can get more information about these properties by consulting the relevant Spring documentation.
The options is divided into two tables, the first one with the most common options used. The latter contains the rest.
Most commonly used options
All the other options
Message Mapping between JMS and Camel
Camel automatically maps messages between javax.jms.Message and org.apache.camel.Message.
When sending a JMS message, Camel converts the message body to the following JMS message types:
When receiving a JMS message, Camel converts the JMS message to the following body type:
Disabling auto-mapping of JMS messages
Available as of Camel 1.6.2/2.0
You can use the mapJmsMessage option to disable the auto-mapping above. If disabled, Camel will not try to map the received JMS message, but instead uses it directly as the payload. This allows you to avoid the overhead of mapping and let Camel just pass through the JMS message. For instance, it even allows you to route javax.jms.ObjectMessage JMS messages with classes you do not have on the classpath.
Using a custom MessageConverter
Available as of Camel 1.6.2/2.0
You can use the messageConverter option to do the mapping yourself in a Spring org.springframework.jms.support.converter.MessageConverter class.
For example, in the route below we use a custom message converter when sending a message to the JMS order queue:
from("file://inbox/order"
).to("jms:queue:order?messageConverter=#myMessageConverter"
);
You can also use a custom message converter when consuming from a JMS destination.
Controlling the mapping strategy selected
Available as of Camel 2.0
You can use the jmsMessageType option on the endpoint URL to force a specific message type for all messages.
In the route below, we poll files from a folder and send them as javax.jms.TextMessage as we have forced the JMS producer endpoint to use text messages:
from("file://inbox/order"
).to("jms:queue:order?jmsMessageType=Text"
);
You can also specify the message type to use for each messabe by setting the header with the key CamelJmsMessageType. For example:
from("file://inbox/order"
).setHeader("CamelJmsMessageType"
, JmsMessageType.Text).to("jms:queue:order"
);
The possible values are defined in the enum class, org.apache.camel.jms.JmsMessageType.
Message format when sending
The exchange that is sent over the JMS wire must conform to the JMS Message spec.
For the exchange.in.header the following rules apply for the header keys:
- Keys starting with JMS or JMSX are reserved.
- exchange.in.headers keys must be literals and all be valid Java identifiers (do not use dots in the key name).
- From Camel 1.4 until Camel 1.6.x, Camel automatically replaces all dots with underscores in key names. This replacement is reversed when Camel consumes JMS messages.
- From Camel 2.0 onwards, Camel replaces dots & hyphens and the reverse when when consuming JMS messages:
. is replaced by _DOT_ and the reverse replacement when Camel consumes the message.
- is replaced by _HYPHEN_ and the reverse replacement when Camel consumes the message. - See also the option jmsKeyFormatStrategy introduced in Camel 2.0, which allows you to use your own custom strategy for formatting keys.
For the exchange.in.header, the following rules apply for the header values:
- The values must be primitives or their counter objects (such as Integer, Long, Character). The types, String, CharSequence, Date, BigDecimal and BigInteger are all converted to their toString() representation. All other types are dropped.
Camel will log with category org.apache.camel.component.jms.JmsBinding at DEBUG level if it drops a given header value. For example:
2008-07-09 06:43:04,046 [main ] DEBUG JmsBinding
- Ignoring non primitive header: order of class: org.apache.camel.component.jms.issues.DummyOrder with value: DummyOrder{orderId=333, itemId=4444, quantity=2}
Message format when receiving
Camel adds the following properties to the Exchange when it receives a message:
Camel adds the following JMS properties to the In message headers when it receives a JMS message:
As all the above information is standard JMS you can check the JMS documentation for further details.
About using Camel to send and receive messages and JMSReplyTo
The JMS component is complex and you have to pay close attention to how it works in some cases. So this is a short summary of some of the areas/pitfalls to look for.
When Camel sends a message using its JMSProducer, it checks the following conditions:
- The message exchange pattern,
- Whether a JMSReplyTo was set in the endpoint or in the message headers,
- Whether any of the following options have been set on the JMS endpoint: disableReplyTo, preserveMessageQos, explicitQosEnabled.
All this can be a tad complex to understand and configure to support your use case.
JmsProducer
The JmsProducer behaves as follows, depending on configuration:
JmsConsumer
The JmsConsumer behaves as follows, depending on configuration:
So pay attention to the message exchange pattern set on your exchanges.
If you send a message to a JMS destination in the middle of your route you can specify the exchange pattern to use, see more at Request Reply.
This is useful if you want to send an InOnly message to a JMS topic:
from("activemq:queue:in"
)
.to("bean:validateOrder"
)
.to(ExchangePattern.InOnly, "activemq:topic:order"
)
.to("bean:handleOrder"
);
Reuse endpoint and send to different destinations computed at runtime
Available as of Camel 1.6.2/2.0
If you need to send messages to a lot of different JMS destinations, it makes sense to reuse a JMS endpoint and specify the real destination in a message header. This allows Camel to reuse the same endpoint, but send to different destinations. This greatly reduces the number of endpoints created and economizes on memory and thread resources.
You can specify the destination in the following headers:
For example, the following route shows how you can compute a destination at run time and use it to override the destination appearing in the JMS URL:
from("file://inbox"
)
.to("bean:computeDestination"
)
.to("activemq:queue:dummy"
);
The queue name, dummy, is just a placeholder. It must be provided as part of the JMS endpoint URL, but it will be ignored in this example.
In the computeDestination bean, specify the real destination by setting the CamelJmsDestinationName header as follows:
public
void setJmsHeader(Exchange exchange) {
String
id = ....
exchange.getIn().setHeader("CamelJmsDestinationName"
, "order:"
+ id");
}
Then Camel will read this header and use it as the destination instead of the one configured on the endpoint. So, in this example Camel sends the message to activemq:queue:order:2, assuming the id value was 2.
If both the CamelJmsDestination and the CamelJmsDestinationName headers are set, CamelJmsDestination takes priority.
Configuring different JMS providers
You can configure your JMS provider in Spring XML as follows:
<camelContext id="camel"
xmlns="http://camel.apache.org/schema/spring"
>
<jmxAgent id="agent"
disabled="true"
/>
</camelContext>
<bean id="activemq"
class="org.apache.activemq.camel.component.ActiveMQComponent"
>
<property name="connectionFactory"
>
<bean class="org.apache.activemq.ActiveMQConnectionFactory"
>
<property name="brokerURL"
value="vm://localhost?broker.persistent=false&broker.useJmx=false"
/>
</bean>
</property>
</bean>
Basically, you can configure as many JMS component instances as you wish and give them a unique name using the id attribute. The preceding example configures an activemq component. You could do the same to configure MQSeries, TibCo, BEA, Sonic and so on.
Once you have a named JMS component, you can then refer to endpoints within that component using URIs. For example for the component name, activemq, you can then refer to destinations using the URI format, activemq:[queue:|topic:]destinationName. You can use the same approach for all other JMS providers.
This works by the SpringCamelContext lazily fetching components from the spring context for the scheme name you use for Endpoint URIs and having the Component resolve the endpoint URIs.
Using JNDI to find the ConnectionFactory
If you are using a J2EE container, you might need to look up JNDI to find the JMS ConnectionFactory rather than use the usual <bean> mechanism in Spring. You can do this using Spring's factory bean or the new Spring XML namespace. For example:
<bean id="weblogic"
class="org.apache.camel.component.jms.JmsComponent"
>
<property name="connectionFactory"
ref="myConnectionFactory"
/>
</bean>
<jee:jndi-lookup id="myConnectionFactory"
jndi-name="jms/connectionFactory"
/>
See The jee schema in the Spring reference documentation for more details about JNDI lookup.
Using JNDI to lookup the physical queues
You need to use the destinationResolver option to use the Spring JNDI resolver that can lookup in the JNDI, or use your own custom implementation.
See this nabble post for more details:http://www.nabble.com/JMS-queue---JNDI-instead-of-physical-name-td24484994.html
Using WebSphere MQ
See this link at nabble for details of how a Camel user configured JMS to connect to remote WebSphere MQ brokers.
Concurrent Consuming
A common requirement with JMS is to consume messages concurrently in multiple threads in order to make an application more responsive. You can set the concurrentConsumers option to specify the number of threads servicing the JMS endpoint, as follows:
from("jms:SomeQueue?concurrentConsumers=20"
).
bean(MyClass.class);
You can configure this option in one of the following ways:
- On the JmsComponent,
- On the endpoint URI or,
- By invoking setConcurrentConsumers() directly on the JmsEndpoint.
Request-reply over JMS
Camel supports request-reply over JMS. In essence the MEP of the Exchange should be InOut when you send a message to a JMS queue.
The JmsProducer detects the InOut and provides a JMSReplyTo header with the reply destination to be used. By default Camel uses a temporary queue, but you can use the replyTo option on the endpoint to specify a fixed reply queue.
Camel will automatic setup a consumer which listen on the reply queue, so you should not do anything.
This consumer is a Spring DefaultMessageListenerContainer which listen for replies. However it's fixed to 1 concurrent consumer.
That means replies will be processed in sequence as there are only 1 thread to process the replies. If you want to process replies faster, then we need to use concurrency. But not using the concurrentConsumer option. We should use the threads from the Camel DSL instead, as shown in the route below:
from(xxx)
.inOut().to("activemq:queue:foo"
)
.threads(5)
.to(yyy)
.to(zzz);
In this route we instruct Camel to route replies asynchronously using a thread pool with 5 threads.
Enabling Transacted Consumption
A common requirement is to consume from a queue in a transaction and then process the message using the Camel route. To do this, just ensure that you set the following properties on the component/endpoint:
- transacted = true
- transactionManager = a Transsaction Manager - typically the JmsTransactionManager
See also the Transactional Client EIP pattern for further details.
Transaction and Request Reply over JMSNote that when using Request Reply over JMS you cannot use a single transaction; as JMS will not send any messages until a commit is performed, the server side won't receive anything at all until the transaction commits. So, with request/response you must commit a transaction after sending the first request and then use a separate transaction for receiving the response.
This is why the transacted property applies only to the InOnly message Exchange Pattern (MEP). If you want to use transactions for the InOut MEP as well, you must set transactedInOut=true.
To recap: if you have transacted=true, transactedInOut=false and are sending an InOut, the Exchange will not use transactions.
Using JMSReplyTo for late replies
Avaiable as of Camel 2.0
When using Camel as a JMS listener, it sets an Exchange property with the value of the ReplyTo javax.jms.Destination object, having the key ReplyTo. You can obtain this Destination as follows:
Destination replyDestination = exchange.getIn().getHeader(JmsConstants.JMS_REPLY_DESTINATION, Destination.class);
And then later use it to send a reply using regular JMS or Camel.
// we need to pass in the JMS component, and in this
sample we use ActiveMQ
JmsEndpoint endpoint = JmsEndpoint.newInstance(replyDestination, activeMQComponent);
// now we have the endpoint we can use regular Camel API to send a message to it
template.sendBody(endpoint, "Here is the late reply."
);
A different solution to sending a reply is to provide the replyDestination object in the same Exchange property when sending. Camel will then pick up this property and use it for the real destination. The endpoint URI must include a dummy destination, however. For example:
// we pretend to send it to some non existing dummy queue
template.send("activemq:queue:dummy, new
Processor() {
public
void process(Exchange exchange) throws
Exception {
// and here we override the destination with the ReplyTo destination object so the message is sent to there instead of dummy
exchange.getIn().setHeader(JmsConstants.JMS_DESTINATION, replyDestination);
exchange.getIn().setBody("Here is the late reply."
);
}
}
Using a request timeout
In the sample below we send a Request Reply style message Exchange (we use the requestBody method = InOut) to the slow queue for further processing in Camel and we wait for a return reply:
// send a in-out with a timeout for
5 sec
Object
out = template.requestBody("activemq:queue:slow?requestTimeout=5000"
, "Hello World"
);
Samples
JMS is used in many examples for other components as well. But we provide a few samples below to get started.
Receiving from JMS
In the following sample we configure a route that receives JMS messages and routes the message to a POJO:
from("jms:queue:foo"
).
to("bean:myBusinessLogic"
);
You can of course use any of the EIP patterns so the route can be context based. For example, here's how to filter an order topic for the big spenders:
from("jms:topic:OrdersTopic"
).
filter().method("myBean"
, "isGoldCustomer"
).
to("jms:queue:BigSpendersQueue"
);
Sending to a JMS
In the sample below we poll a file folder and send the file content to a JMS topic. As we want the content of the file as a TextMessage instead of a BytesMessage, we need to convert the body to a String:
from("file://orders"
).
convertBodyTo(String
.class).
to("jms:topic:OrdersTopic"
);
Using Annotations
Camel also has annotations so you can use POJO Consuming and POJO Producing.
Spring DSL sample
The preceding examples use the Java DSL. Camel also supports Spring XML DSL. Here is the big spender sample using Spring DSL:
<route>
<from uri="jms:topic:OrdersTopic"
/>
<filter>
<method bean="myBean"
method="isGoldCustomer"
/>
<to uri="jms:queue:BigSpendersQueue"
/>
</filter>
</route>
Other samples
JMS appears in many of the examples for other components and EIP patterns, as well in this Camel documentation. So feel free to browse the documentation. If you have time, check out the this tutorial that uses JMS but focuses on how well Spring Remoting and Camel works together Tutorial-JmsRemoting.
Using JMS as a Dead Letter Queue storing Exchange
Available as of Camel 2.0
Normally, when using JMS as the transport, it only transfers the body and headers as the payload. If you want to use JMS with a Dead Letter Channel, using a JMS queue as the Dead Letter Queue, then normally the caused Exception is not stored in the JMS message. You can, however, use the transferExchange option on the JMS dead letter queue to instruct Camel to store the entire Exchange in the queue as a javax.jms.ObjectMessage that holds a org.apache.camel.impl.DefaultExchangeHolder. This allows you to consume from the Dead Letter Queue and retrieve the caused exception from the Exchange property with the key Exchange.EXCEPTION_CAUGHT. The demo below illustrates this:
// setup error handler to use JMS as queue and store the entire Exchange
errorHandler(deadLetterChannel("jms:queue:dead?transferExchange=true
"
));
Then you can consume from the JMS queue and analyze the problem:
from("jms:queue:dead"
).to("bean:myErrorAnalyzer"
);
// and in our bean
String
body = exchange.getIn().getBody();
Exception cause = exchange.getProperty(Exchange.EXCEPTION_CAUGHT, Exception.class);
// the cause message is
String
problem = cause.getMessage();
Using JMS as a Dead Letter Channel storing error only
You can use JMS to store the cause error message or to store a custom body, which you can initialize yourself. The following example uses the Message Translator EIP to do a transformation on the failed exchange before it is moved to the JMS dead letter queue:
// we sent it to a seda dead queue first
errorHandler(deadLetterChannel("seda:dead"
));
// and on the seda dead queue we can do
the custom transformation before its sent to the JMS queue
from("seda:dead"
).transform(exceptionMessage()).to("jms:queue:dead"
);
Here we only store the original cause error message in the transform. You can, however, use any Expression to send whatever you like. For example, you can invoke a method on a Bean or use a custom processor.
Sending an InOnly message and keeping the JMSReplyTo header
When sending to a JMS destination using camel-jms the producer will use the MEP to detect if its InOnly or InOut messaging. However there can be times where you want to send an InOnly message but keeping the JMSReplyTo header. To do so you have to instruct Camel to keep it, otherwise the JMSReplyTo header will be dropped.
For example to send an InOnly message to the foo queue, but with a JMSReplyTo with bar queue you can do as follows:
template.send("activemq:queue:foo?preserveMessageQos=true
"
, new
Processor() {
public
void process(Exchange exchange) throws
Exception {
exchange.getIn().setBody("World"
);
exchange.getIn().setHeader("JMSReplyTo"
, "bar"
);
}
});
Notice we use preserveMessageQos=true to instruct Camel to keep the JMSReplyTo header.
InOut
For example when using JMS with InOut the component will by default perform these actions
- create by default a temporary inbound queue
- set the JMSReplyTo destination on the request message
- set the JMSCorrelationID on the request message
- send the request message
- consume the response and associate the inbound message to the request using the JMSCorrelationID (as you may be performing many concurrent request/responses).
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