All messages/responses received via a Receiver are passed to a
Correlator which notifies the correct SenderTask. The
Correlator component can extract a correlation ID from
both the requesnt and the response. It can also have an active role and actually create a
correlation ID and store it in the request message.
Correlator is always bound to a Receiver and does not make any
sense without it.
Example 4.27. An example of a correlator configuration
1 <receiver class="..." threads="..."> 2 <correlator class="..."> 3 ... 4 correlator properties 5 ... 6 </correlator> 7 <source>...</source> 8 ... 9 receiver properties 10 ... 11 </receiver>
When specifying the correlator class, unless you enter a fully classified class name,
the default package org.perfcake.message.correlator is assumed.
In the following sections you can find a complete description of all correlators that can be used by PerfCake including all of their properties.
GenerateHeaderCorrelator creates a new UUID style correlation
ID and stores it in a request message header and in message attributes. It then
searches for the same value in the response message headers. The header name used for storing
the UUID is perfcake.correlation.id.
GenerateHeaderCorrelator does not have any configurable properties.
Example 4.28. An example of GenerateHeaderCorrelator usage
1 <receiver class="HttpReceiver" threads="10"> 2 <correlator class="GenerateHeaderCorrelator" /> 3 <source>localhost:8080</source> 4 </receiver>
PrefixCorrelator
uses a message prefix - a string from the beginning of the message to a prefix boundary (: by default) - as a correlation ID.
The prefix boundary can be configured via prefixBoundary property of the correlator.
Following table shows the properties of the PrefixCorrelator:
| Property name | Description | Required | Default value |
|---|---|---|---|
| prefixBoundary | A character or a string specifying the prefix boundary. | No | : |
Table 4.25. PrefixCorrelator properties
Example 4.29. An example of PrefixCorrelator usage
1 <receiver class="HttpReceiver" threads="10"> 2 <correlator class="PrefixCorrelator"> 3 <property name="prefixBoundary" value=":"/> 4 </correlator> 5 <source>localhost:8080</source> 6 </receiver>
In the example, when a message prefix-01:What is the meaning of life? is sent through a sender,
the correlator extract the prefix prefix-01 according to the prefix boundary
:
and uses it as a correlation ID. The receiver then listens on HTTP address
http://localhost:8080
and waits for a response message with the same prefix
(e.g. prefix-01:I don't know, the computers are down.).