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commit 435f3bc192bd381fda66107579be470abb997e26
Author: Claus Ibsen <claus.ib...@gmail.com>
AuthorDate: Thu Oct 14 20:04:51 2021 +0200
CAMEL-16861: Cleanup and update EIP docs
---
.../docs/modules/eips/pages/scatter-gather.adoc | 91 +++++++++++++---------
1 file changed, 53 insertions(+), 38 deletions(-)
diff --git
a/core/camel-core-engine/src/main/docs/modules/eips/pages/scatter-gather.adoc
b/core/camel-core-engine/src/main/docs/modules/eips/pages/scatter-gather.adoc
index 859b814..ae1214f 100644
---
a/core/camel-core-engine/src/main/docs/modules/eips/pages/scatter-gather.adoc
+++
b/core/camel-core-engine/src/main/docs/modules/eips/pages/scatter-gather.adoc
@@ -10,17 +10,28 @@ specified recipients and re-aggregate the responses back
into a single message.
image::eip/BroadcastAggregate.gif[image]
With Camel this pattern is implemented by using the
xref:recipientList-eip.adoc[Recipient List]
-and the xref:aggregate-eip.adoc[Aggregate] patterns.
+which comes with aggregation built-in. This is often the simplest solution.
However, there can
+be some complex use-cases where you would need not use the built-in
aggregator, and instead
+use the more powerful xref:aggregate-eip.adoc[Aggregate] EIP for aggregation.
-== Sample
+== Using only Recipient List
-In this example we want to get the best quote for beer from several different
vendors.
-We use a dynamic Recipient List to get the request for a quote to all vendors
and an Aggregator
-to pick the best quote out of all the responses. The routes for this are
defined as:
+TODO: Simple example
+
+
+== Using both Recipient List and Aggregator EIP
+
+In this example we want to get the best quote for beer from several vendors.
+
+We use xref:recipientList-eip.adoc[Recipient List] to get the request for a
quote to all vendors
+and an xref:aggregate-eip.adoc[Aggregate] to pick the best quote out of all
the responses.
+
+The routes for this are defined as:
[source,xml]
----
-<camelContext xmlns="http://camel.apache.org/schema/spring";>
+<routes>
+
<route>
<from uri="direct:start"/>
<recipientList>
@@ -30,24 +41,26 @@ to pick the best quote out of all the responses. The routes
for this are defined
<route>
<from uri="seda:quoteAggregator"/>
- <aggregate strategyRef="aggregatorStrategy" completionTimeout="1000">
+ <aggregate strategyRef="beerAggregator" completionTimeout="1000">
<correlationExpression>
<header>quoteRequestId</header>
</correlationExpression>
<to uri="mock:result"/>
</aggregate>
</route>
-</camelContext>
+
+</routes>
----
-So in the first route you see that the Recipient List is looking at the
listOfVendors header
-for the list of recipients. So, we need to send a message like
+So in the first route you see that the xref:recipientList-eip.adoc[Recipient
List] is looking at the
+listOfVendors header for the list of recipients. So, we need to send a message
like:
[source,java]
----
Map<String, Object> headers = new HashMap<>();
headers.put("listOfVendors", "bean:vendor1, bean:vendor2, bean:vendor3");
headers.put("quoteRequestId", "quoteRequest-1");
+
template.sendBodyAndHeaders("direct:start", "<quote_request item=\"beer\"/>",
headers);
----
@@ -68,7 +81,7 @@ public class MyVendor {
public void quote(@XPath("/quote_request/@item") String item, Exchange
exchange) {
if ("beer".equals(item)) {
- exchange.getIn().setBody(beerPrice);
+ exchange.getMessage().setBody(beerPrice);
quoteAggregator.send(exchange);
} else {
// ignore no quote
@@ -77,54 +90,56 @@ public class MyVendor {
}
----
-And are loaded up in Spring XML like:
+And are loaded up in XML like:
[source,xml]
----
-<bean id="aggregatorStrategy"
class="org.apache.camel.spring.processor.scattergather.LowestQuoteAggregationStrategy"/>
-
-<bean id="vendor1"
class="org.apache.camel.spring.processor.scattergather.MyVendor">
- <constructor-arg>
- <value>1</value>
- </constructor-arg>
-</bean>
-
-<bean id="vendor2"
class="org.apache.camel.spring.processor.scattergather.MyVendor">
- <constructor-arg>
- <value>2</value>
- </constructor-arg>
-</bean>
-
-<bean id="vendor3"
class="org.apache.camel.spring.processor.scattergather.MyVendor">
- <constructor-arg>
- <value>3</value>
- </constructor-arg>
-</bean>
+<camelContext>
+
+ <bean id="aggregatorStrategy"
class="org.apache.camel.spring.processor.scattergather.LowestQuoteAggregationStrategy"/>
+
+ <bean id="vendor1"
class="org.apache.camel.spring.processor.scattergather.MyVendor">
+ <constructor-arg><value>1</value></constructor-arg>
+ </bean>
+
+ <bean id="vendor2"
class="org.apache.camel.spring.processor.scattergather.MyVendor">
+ <constructor-arg><value>2</value></constructor-arg>
+ </bean>
+
+ <bean id="vendor3"
class="org.apache.camel.spring.processor.scattergather.MyVendor">
+ <constructor-arg><value>3</value></constructor-arg>
+ </bean>
+
+</camelContext>
----
Each bean is loaded with a different price for beer. When the message is sent
to each bean endpoint,
it will arrive at the `MyVendor.quote` method. This method does a simple check
whether this quote
request is for beer and then sets the price of beer on the exchange for
retrieval at a later step.
-The message is forwarded on to the next step using POJO Producing (see the
`@Produce` annotation).
+The message is forwarded on to the next step using
xref:latest@manual:ROOT:pojo-producing.adoc[POJO Producing]
+(see the `@Produce` annotation).
At the next step we want to take the beer quotes from all vendors and find out
which one was the best
-(i.e. the lowest!). To do this we use an Aggregator with a custom aggregation
strategy.
-The Aggregator needs to be able to compare only the messages from this
particular quote;
-this is easily done by specifying a correlationExpression equal to the value
of the quoteRequestId header.
+(i.e. the lowest!). To do this we use the xref:aggregate-eip.adoc[Aggregate]
EIP with a custom
+`AggregationStrategy`.
+
+The xref:aggregate-eip.adoc[Aggregate] needs to be able to compare only the
messages from this particular quote;
+this is easily done by specifying a correlation expression equal to the value
of the quoteRequestId header.
As shown above in the message sending snippet, we set this header to
quoteRequest-1.
-This correlation value should be unique or you may include responses that are
not part of this quote.
-To pick the lowest quote out of the set, we use a custom aggregation strategy
like
+This correlation value must be unique, or you may include responses that are
not part of this quote.
+To pick the lowest quote out of the set, we use a custom `AggregationStrategy`
like:
[source,java]
----
public class LowestQuoteAggregationStrategy implements AggregationStrategy {
+
public Exchange aggregate(Exchange oldExchange, Exchange newExchange) {
// the first time we only have the new exchange
if (oldExchange == null) {
return newExchange;
}
- if (oldExchange.getIn().getBody(int.class) <
newExchange.getIn().getBody(int.class)) {
+ if (oldExchange.getMessage().getBody(int.class) <
newExchange.getMessage().getBody(int.class)) {
return oldExchange;
} else {
return newExchange;
