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Processors

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Eric Bottard edited this page Jun 17, 2013 · 7 revisions

Introduction

This section will cover the processors available out-of-the-box with Spring XD. As a prerequisite, start the XD Container as instructed in the Getting Started page.

The Processors covered are

See the section Creating a Processor Module for information on how to create custom processor modules.

Filter

Use the filter module in a stream to determine whether a Message should be passed to the output channel.

Filter with SpEL expression

The simplest way to use the filter processor is to pass a SpEL expression when creating the stream. The expression should evaluate the message and return true or false. For example:

$ curl -d "http | filter --expression=payload=='good' | log" http://localhost:8080/streams/filtertest

This filter will only pass Messages to the log sink if the payload is the word "good". Try sending "good" to the HTTP endpoint and you should see it in the XD log:

$ curl -d "good" http://localhost:9000

Alternatively, if you send the word "bad" (or anything else), you shouldn’t see the log entry.

Filter with Groovy Script

For more complex filtering, you can pass the location of a Groovy script using the script attribute. If you want to pass variable values to your script, you can optionally pass the path to a properties file using the properties-location attribute. All properties in the file will be made available to the script as variables.

$ curl -d "http --port=9001 | filter --script=custom-filter.groovy --properties-location=custom-filter.properties | log" http://localhost:8080/streams/groovyfiltertest

By default, Spring XD will search the classpath for custom-filter.groovy and custom-filter.properties. You can place the script in ${xd.home}/modules/processor/scripts and the properties file in ${xd.home}/config to make them available on the classpath. Alternatively, you can prefix the script and properties-location values with file: to load from the file system.

JSON Field Value Filter

Use this filter to only pass messages to the output channel if they contain a specific JSON field matching a specific value.

$ curl -d "http --port=9002 | json-field-value-filter --fieldName=firstName --fieldValue=John | log" http://localhost:8080/streams/jsonfiltertest

This filter will only pass Messages to the log sink if the JSON payload contains the firstName "John". Try sending this payload to the HTTP endpoint and you should see it in the XD log:

$ curl -d "{\"firstName\":\"John\", \"lastName\":\"Smith\"}" http://localhost:9002

Alternatively, if you send a different firstName, you shouldn’t see the log entry.

Transform

Use the transform module in a stream to convert a Message’s content or structure.

Transform with SpEL expression

The simplest way to use the transform processor is to pass a SpEL expression when creating the stream. The expression should return the modified message or payload. For example:

$ curl -d "http --port=9003 | transform --expression='FOO' | log" http://localhost:8080/streams/transformtest

This transform will convert all message payloads to the word "FOO". Try sending something to the HTTP endpoint and you should see "FOO" in the XD log:

$ curl -d "some message" http://localhost:9003
Transform with Groovy Script

For more complex transformations, you can pass the location of a Groovy script using the script attribute. If you want to pass variable values to your script, you can optionally pass the path to a properties file using the properties-location attribute. All properties in the file will be made available to the script as variables.

$ curl -d "http --port=9004 | transform --script=custom-transform.groovy --properties-location=custom-transform.properties | log" http://localhost:8080/streams/groovytransformtest

By default, Spring XD will search the classpath for custom-transform.groovy and custom-transform.properties. You can place the script in ${xd.home}/modules/processor/scripts and the properties file in ${xd.home}/config to make them available on the classpath. Alternatively, you can prefix the script and properties-location values with file: to load from the file system.

JSON Field Extractor

This processor converts a JSON message payload to the value of a specific JSON field.

$ curl -d "http --port=9005 | json-field-extractor --fieldName=firstName | log" http://localhost:8080/streams/jsontransformtest

Try sending this payload to the HTTP endpoint and you should see just the value "John" in the XD log:

$ curl -d "{\"firstName\":\"John\", \"lastName\":\"Smith\"}" http://localhost:9005

Script

The script processor contains a Service Activator that invokes a specified Groovy script. This is a slightly more generic way to accomplish processing logic, as the provided script may simply terminate the stream as well as transform or filter Messages.

To use the module, pass the location of a Groovy script using the location attribute. If you want to pass variable values to your script, you can optionally pass the path to a properties file using the properties-location attribute. All properties in the file will be made available to the script as variables.

$ curl -d "http --port=9006 | script --location=custom-processor.groovy --properties-location=custom-processor.properties | log" http://localhost:8080/streams/groovyprocessortest

By default, Spring XD will search the classpath for custom-processor.groovy and custom-processor.properties. You can place the script in ${xd.home}/modules/processor/scripts and the properties file in ${xd.home}/config to make them available on the classpath. Alternatively, you can prefix the location and properties-location values with file: to load from the file system.

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