3. Processors

3. Processors
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3.1 Bridge Processor

A Processor module that returns messages that is passed by connecting just the input and output channels.

3.2 Filter Processor

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

3.2.1 Options

The filter processor has the following options:

expression: a SpEL expression used to transform messages (String, default: payload.toString())

3.3 Groovy Filter Processor

A Processor module that retains or discards messages according to a predicate, expressed as a Groovy script.

3.3.1 Options

The groovy-filter processor has the following options:

script: The script resource location (String, default: ``)
variables: Variable bindings as a comma delimited string of name-value pairs, e.g. 'foo=bar,baz=car' (String, default: ``)
variablesLocation: The location of a properties file containing custom script variable bindings (String, default: ``)

3.4 Groovy Transform Processor

A Processor module that transforms messages using a Groovy script.

3.4.1 Options

The groovy-transform processor has the following options:

script: The script resource location (String, default: ``)
variables: Variable bindings as a comma delimited string of name-value pairs, e.g. 'foo=bar,baz=car' (String, default: ``)
variablesLocation: The location of a properties file containing custom script variable bindings (String, default: ``)

3.5 Http Client Processor

A processor app that makes requests to an HTTP resource and emits the response body as a message payload. This processor can be combined, e.g., with a time source app to periodically poll results from a HTTP resource.

3.5.1 Options

The httpclient processor has the following options:

url: The URL to issue an http request to, as a static value.
urlExpression: A SpEL expression against incoming message to determine the URL to use.
httpMethod: The kind of http method to use.
body: The (static) body of the request to use.
bodyExpression: A SpEL expression against incoming message to derive the request body to use.
headersExpression: A SpEL expression used to derive the http headers map to use.
expectedResponseType: The type used to interpret the response.
replyExpression: A SpEL expression used to compute the final result, applied against the whole http response.

3.6 Scripable Transform Processor

A Spring Cloud Stream module that transforms messages using a script. The script body is supplied directly as a property value. The language of the script can be specified (groovy/javascript/ruby/python).

3.6.1 Options

The scriptable-transform processor has the following options:

script: The script text (String, default: ``)
lang: The script language (String, default: ``)
variables: Variable bindings as a comma delimited string of name-value pairs, e.g. 'foo=bar,baz=car' (String, default: ``)
variablesLocation: The location of a properties file containing custom script variable bindings (String, default: ``)

3.7 Splitter Processor

The splitter app builds upon the concept of the same name in Spring Integration and allows the splitting of a single message into several distinct messages.

3.7.1 Options

expression: a SpEL expression which would typically evaluate to an array or collection (String, default: null)
delimiters: A list of delimiters to tokenize a String payload ('expression' must be null) (String, default: null)
fileMarkers: Split File payloads, when true, START and END marker messages will be emitted, when false no markers are emitted (String, default: null)
charset: Split File payloads using this charset to convert bytes to String (String, default: null)
applySequence: Add correlation and sequence information to the message headers (String, default: true)

When no expression, fileMarkers, or charset is provided, a DefaultMessageSplitter is configured with (optional) delimiters. When fileMarkers or charset is provided, a FileSplitter is configured (you must provide either a fileMarkers or charset to split files, which must be text-based - they are split into lines). Otherwise, an ExpressionEvaluatingMessageSplitter is configured.

When splitting File payloads, the sequenceSize header is zero because the size cannot be determined at the beginning.

	Caution
	Ambiguous properties are not allowed.

3.7.2 JSON Example

As part of the SpEL expression you can make use of the pre-registered JSON Path function. The syntax is #jsonPath(payload, '<json path expression>').

For example, consider the following JSON:

{ "store": {
    "book": [
        {
            "category": "reference",
            "author": "Nigel Rees",
            "title": "Sayings of the Century",
            "price": 8.95
        },
        {
            "category": "fiction",
            "author": "Evelyn Waugh",
            "title": "Sword of Honour",
            "price": 12.99
        },
        {
            "category": "fiction",
            "author": "Herman Melville",
            "title": "Moby Dick",
            "isbn": "0-553-21311-3",
            "price": 8.99
        },
        {
            "category": "fiction",
            "author": "J. R. R. Tolkien",
            "title": "The Lord of the Rings",
            "isbn": "0-395-19395-8",
            "price": 22.99
        }
    ],
    "bicycle": {
        "color": "red",
        "price": 19.95
    }
}}

and an expression #jsonPath(payload, '$.store.book'); the result will be 4 messages, each with a Map payload containing the properties of a single book.

3.8 Splitter Processor

The splitter app builds upon the concept of the same name in Spring Integration and allows the splitting of a single message into several distinct messages.

3.8.1 Options

expression: a SpEL expression which would typically evaluate to an array or collection (String, default: null)
delimiters: A list of delimiters to tokenize a String payload ('expression' must be null) (String, default: null)
fileMarkers: Split File payloads, when true, START and END marker messages will be emitted, when false no markers are emitted (String, default: null)
charset: Split File payloads using this charset to convert bytes to String (String, default: null)
applySequence: Add correlation and sequence information to the message headers (String, default: true)

When splitting File payloads, the sequenceSize header is zero because the size cannot be determined at the beginning.

	Caution
	Ambiguous properties are not allowed.

3.8.2 JSON Example

As part of the SpEL expression you can make use of the pre-registered JSON Path function. The syntax is #jsonPath(payload, '<json path expression>').

For example, consider the following JSON:

{ "store": {
    "book": [
        {
            "category": "reference",
            "author": "Nigel Rees",
            "title": "Sayings of the Century",
            "price": 8.95
        },
        {
            "category": "fiction",
            "author": "Evelyn Waugh",
            "title": "Sword of Honour",
            "price": 12.99
        },
        {
            "category": "fiction",
            "author": "Herman Melville",
            "title": "Moby Dick",
            "isbn": "0-553-21311-3",
            "price": 8.99
        },
        {
            "category": "fiction",
            "author": "J. R. R. Tolkien",
            "title": "The Lord of the Rings",
            "isbn": "0-395-19395-8",
            "price": 22.99
        }
    ],
    "bicycle": {
        "color": "red",
        "price": 19.95
    }
}}

and an expression #jsonPath(payload, '$.store.book'); the result will be 4 messages, each with a Map payload containing the properties of a single book.

3.9 Transform Processor

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

The transform processor is used by passing a SpEL expression. The expression should return the modified message or payload. For example, --expression=payload.toUpperCase().

This transform will convert all message payloads to upper case.

As part of the SpEL expression you can make use of the pre-registered JSON Path function. The syntax is #jsonPath(payload,'<json path expression>')

3.9.1 Options

The transform processor has the following options:

expression: a SpEL expression used to transform messages (String, default: payload.toString())

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